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We have yet to meet a clinical therapy physicist who does not readily acknowledge the great desirability for more comprehensive and efficient dosimetry tools, including 3D dosimetry systems, for the verification of modern radiation treatments. The innovations and progress toward this goal are remarkably captured in the proceedings of nine prior conferences, the last five of which are freely available in the Journal of Physics: Conference Series.

This 10^th IC3DDose meeting was the first to be held in China and was exciting to see the meeting expand and new researchers and ideas enter the field. The scientific program was carefully crafted to try to meet the objectives listed below and we were fortunate that many leading speakers shared their experience and perspectives to achieve them.

List of Conference Objectives, Co-Chairs, Duke Kunshan University Local Organizing Committee and International Scientific Committee are available in this pdf.

List of Welcome Message, Conference Objectives, Program at a glance, Co-Chairs, Local Organizing Committee, International Scientific Committee, Invited Speaker Listing, 10th IC3DDose Conference Program, Sept. 2018, SPONSORS are available in this pdf.

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

Modern radiation therapy (RT) includes conformal therapy, intensity modulated radiation therapy, proton therapy, image-guided radiation therapy, adaptive radiation therapy (ART), and recently magnetic-resonance guided radiation therapy and, upcoming, 4π radiation therapy. These techniques show the continual increase in complexity of radiation therapy techniques which, coupled with a stagnant medical physics workforce, means that the amount and complexity of work per physicist has increased and is likely to increase in the foreseeable future. Three distinct challenges can be identified that need to be addressed. First, is the recent commercial development of automated multi-metastases stereotactic radiosurgery (SRS) techniques. These techniques plan and irradiate a number (up to approximately 20) brain lesions in one treatment session, typically employing one isocenter. The spatial accuracy specifications for SRS imply that attention to the angular accuracy is more critical for these treatments than conventional SRS or other treatment methods. In parallel, our and other groups are developing 4π techniques, which is a proposed method for optimizing both beam angles and intensity fluence to provide x-ray based dose distributions with unparalleled compactness and conformality. One cost to deliver these dose distributions is the added requirement to not only rotate the couch but also shift the couch to increase the number of available beam angles. These two techniques will require efficient and quantitative dose distribution measurements of relatively large volumes for, at least, end to end testing of multi-metastases and 4π treatments. Finally, magnetic resonance guided radiation therapy has led to a resurgence in the development of on-table ART, which requires that the medical physicist compare two calculated treatment plans and efficiently and effectively determine if differences between those treatment plans are clinically significant. Modifying and improving existing tools will be critical to the safe and effective on-table ART.

Deformable 3D dosimetry represents a robust method of verifying the accuracy of clinical deformable dose accumulation algorithms used to monitor interfraction anatomical changes during radiotherapy treatments. For this study, a deformable abdominal phantom was developed incorporating a deformable nPAG gel dosimeter for the dose verification of Adaptivo™, a commercial software program with a deformable dose accumulation algorithm. A comparison was made for three single fraction irradiations of gel dosimeters, each with a different deformation state. Additionally, a comparison was made for the cumulative dose over a three-fraction treatment of a single gel dosimeter with individual fraction deformations matching those of the single fraction measurements. The single fraction irradiations resulted in target contour dose volume histograms (DVH) created by Adaptivo™ that were in close agreement with those determined by gel dosimeter measurements for doses similar to and higher than the planned target dose, with two of the three cases matching to within 5%. Discrepancies are attributed to a deformed contour compression during analysis in the cases where the phantom was deformed. The three-fraction treatment resulted in very close agreement between the DVHs determined through the gel dosimeter measurements and Adaptivo™ calculations across the full range of doses, with an average absolute discrepancy of 2.0% and a maximum absolute discrepancy of 6.3%.

This paper describes the investigation of lung tumour peripheral doses for 6MV, 6MV FFF, 10MV FFF and 15MV conformal arc therapy (CAT) beams calculated in the Monaco® TPS and delivered using a flattening filter free capable Elekta® Agility^TM linac. Two independent high resolution dosimetry techniques were used for investigations. Measurements were performed using the normoxic PAG polymer gel dosimeter and GAFchromic^TM EBT3 film and compared against the calculated dose plane from the Monaco treatment planning system. Both measurement methodologies indicate that Monaco is overestimating the lung tumour peripheral dose for the beams investigated in this study. It is shown that when using 10MV FFF in lung for arc deliveries, there is a dosimetric compromise compared with 6MV and 6MV FFF.

We investigated the feasibility of using N-isopropylacrylamide (NIPAM) dosimeters with x-ray CT to verify radiosurgery dose. Dosimeters were prepared at one facility and shipped to a second facility for irradiation. A simulation CT was acquired and plans prepared for a 4 field box, and a 4 arc VMAT radiosurgery plan to 6 targets with 1cm diameter. Each dosimeter was aligned via CBCT and irradiated, followed by 5 diagnostic CTs acquired after >24 hours, which were averaged for analysis. Absolute dose calibration was applied and dose evaluated for both plans. Hounsfield Units were proportional to dose above 10-12Gy. For the 4-field box, mean difference between measured and predicted dose >10Gy was -0.13Gy ±1.69Gy and gamma index was <1 for 72% and 65% of voxels using a 5% / 1mm and 3% / 2mm criteria, respectively (threshold = 15Gy, global dose criteria). For the multifocal SRS case, mean dose within each target was within -0.14Gy± 0.55Gy of the expected value, and gamma index was < 1 for 94.0% and 99.5% of voxels, respectively (threshold = 15Gy). NIPAM based 3D dosimetry with x-ray CT is well suited for validating radiosurgery spatial alignment, as well as dose distributions when dose is above 10-12Gy.

The accuracy of Eclipse^TM-calculated head and neck VMAT plan dose delivery was assessed in the situation when there is a gap between placed bolus on a head and neck thermoplastic mask and the body surface. GafchromicEBT3 film dosimetry was used for dose delivery validation. The results from 3%, 3 mm 2D gamma comparison indicate better than 95% agreement between measured film dose and calculated plan dose for gap widths up to 25 mm between placed bolus and body surface.

The combination of MRI and radiotherapy on a single platform has the potential to revolutionise image-guided delivery of radiation doses. However, in order to realise these ambitions, good dosimetry must be available. The electron return effect gives rise to significant perturbations of dose at interfaces between tissue and air within the body, and this might lead to difficulties in dose compensation if air cavities move during treatment. In this article, I review briefly the ways in which the available methods of dosimetry are affected by the presence of magnetic fields and discuss the contribution that three-dimensional measurements can make to studies in this area. The methods of MRI and optical computed tomography have well known issues in imaging close to interfaces. These are described together with progress so far in providing solutions.

As magnetic resonance-guided radiotherapy (MRgRT) is becoming increasingly important in clinical applications, the development of new quality assurance (QA) methods is needed. One important aspect is the alignment of the radiation and imaging isocenter. MR-visible polymer gels offer a way to perform such measurements online and additionally may allow for 3-dimensional (3D) evaluation. We present a star shot measurement irradiated and scanned with a 0.35 T MR-LINAC device evaluating the polyacrylamide gelatin (PAGAT) gel dosimeter immediately and 48 h after irradiation. The gel was additionally scanned at a 3 T MR device 5 h and 52 h after irradiation. The evaluation revealed an isocircle radius of 0.5 mm for both imaging devices and all image resolutions and time points after irradiation. The distance between radiation and imaging isocenter varied between 0.25 mm and 1.30 mm depending on the applied image resolution. This demonstrates that evaluation of a star shot measurement in a 0.35 T MR-LINAC is feasible, even immediately after irradiation.

Polymer gels formulated with methacrylic acid as the main monomer source have been investigated for several decades. However, there is some discrepancy in the literature regarding their dose rate and fractionation dependence. This study investigated whether the read-out technique, optical versus MRI, affected the measured dependence for dose rate and fractionation.

Measurements near the edges of PRESAGE® 3D dosimeters will be important for validating the electron return effect (ERE) that can occur at tissue-air interfaces during radiotherapy treatment delivered with the Elekta MR-linac. We investigate and characterize the spatially non-uniform response of small samples of PRESAGE® to radiation in a conventional linac. We develop a correction to compensate for these non-uniformities and obtain dose values near the dosimeter edges. Five samples from the same batch were uniformly irradiated in a water tank with a broad beam. The non-uniform response of the samples to radiation was investigated and a radial dose-correction function was generated from each sample to obtain a correction image. We then applied these correction images to another sample from the same batch, irradiated with four beams in an inhomogeneous medium, and compared this with the relevant simulated data. Additionally, we irradiated samples after physically removed their edges (axially and top and bottom edges). Higher sensitivity to radiation was observed at the edges (~6mm) of the samples in comparison with the central region. Applying the dose correction function improved agreement between simulations and measurements, but only partial correction was possible. A uniform response was observed on the samples with the edges removed, which we propose as the best option to measure dose at the edges of PRESAGE® samples.

The pursuit of real-time image-guided radiotherapy has prompted the development of hybrid devices coupling MRI scanners with radiotherapy treatment units, usually linear accelerators (linacs). One of the challenges in MRI-linac technology is the magnetic field impact on the dose deposition. Dose deposition effects have to be considered in the radiation therapy chain as they alter the dose distribution in patients and influence the response of many commonly used radiation detectors. In this presentation specific issues of dosimetry for MRI-linacs will be reviewed and illustrated with examples from the Australian MRI-linac commissioning process.

A recent extension of image guidance in radiation therapy has been brought about by the introduction of the MR-linac; a hybrid system comprising an MR imager and a medical linear accelerator. The University of Texas MD Anderson Cancer Center is one of seven institutes around the world that have collaborated with the manufacturer to develop this system and bring it into clinical use. In the process, a great deal has been learned about the influence of the magnetic field on radiation dose deposition and upon dosimetry systems. A number of dosimetry systems have been evaluated and issues affecting their performance have been investigated. The potential value of three-dimensional dosimetry systems has been explored.

With recent advances in magnetic resonance image-guided radiation therapy (MR-IGRT), Fricke gel dosimetry has demonstrated value for its ability to measure three-dimensional dose distributions in the presence of a strong magnetic field. This strong magnetic field causes hot and cold spots in dose distributions at the interfaces of lung and normal tissue due to a phenomenon known as the electron return effect (ERE). In this paper, we report the development of lung-equivalent gel dosimeters to better measure dose to lung tissue caused by the ERE. Small polystyrene beads of variable sizes were mixed into Fricke xylenol orange gelatin (FXG) and ferrous oxide xylenol orange (FOX) gels. Lung-equivalence was confirmed by measuring the average CT number of each gel. The effects of gel type, bead size, and voxel size on uniformity and signal intensity were investigated. The smallest beads ( < 1 mm) exhibited the best uniformity, with values comparable to conventional gel with 2 mm voxels. Signal intensity followed an inverse relationship with uniformity, but FXG low-density dosimeters generated enough signal to produce acceptable quality images. The spin-lattice relaxation rate (R1 = 1/T1) increased with dose, which enabled us to measure dose to both soft tissue and lung due to the ERE using a phantom simulating the soft tissue-lung interface.

In an estimation of iPAGAT polymer gel dosimeters using a magnetic resonance imaging (MRI) system, the dosimetric characteristics were investigated with two echo sequences: a spin echo (SE) and a fast recovery fast spin echo (FRFSE) sequence. FRFSE can shorten total scan time compared to SE because of its short repetition time (TR) and long echo train length (ETL). Although the R2-dose response measured from FRFSE was decreased compared to SE, both responses were fitted quadratic curve with a high correlation coefficient. In addition, their calibrated dose distributions showed high conformity to the planned data in the three-dimensional (3D) gamma index, dose volume histogram (DVH) and surface rendering analyses; however, results of SE were a little superior to FRFSE. In conclusion, it is suggested that FRFSE can present the accurate characteristics of polymer gel dosimeters under the optimum parameters.

The integration of magnetic resonance (MR) imagers with radiotherapy units provided a new opportunity to demonstrate the value of polymer gels as volumetric dosimeters. The purpose of this work was to investigate the use of methacrylic-acid based polymer gels for quality assurance of patient-specific treatment plans delivered with these novel treatment machines. The characterization of the gel was performed while the gel was subjected to a strong magnetic field and in the absence of the magnetic field. Additionally, an end-to-end phantom study was conducted using an MR image-guided radiotherapy (MR-IGRT) unit. This data will be used to support the implementation of volumetric dosimeters in MR-IGRT.

A new method of time-resolved volumetric (4D) dosimetry combining transversal projected view scintillation imaging with the multi-leaf collimator (MLC) geometry information is presented and demonstrated in a magnetic resonance (MRI) guided linear accelerator (linac). The setup consisted of a time gated intensified camera and a cylindrical plastic scintillator phantom. Positioning the camera outside the 0.35 T magnetic field suppresses the interference between the MRI-linac and dosimeter camera. Transversal view images of the scintillation light were recorded at 20 Hz framerate and the light distribution along optical axis was decoded from the MLC data by Fourier algorithm. Considering scintillation light as dose surrogate, the dose volume was reconstructed with sub-millimeter resolution, and this was tested on an intensity modulated delivery of a TG119 C-shape plan. 3D gamma analysis of the recorded cumulative dose volume as compared to a Monte-Carlo simulation reported 95% pass rate at 3%/3mm criteria. By enabling the use of measurement-based 3D beam comparison metrics, the presented method may provide a comprehensive solution for volumetric end-to-end dosimetry and fast machine performance checks in this challenging environment of an MRI-linac.

Total Skin Electron Irradiation (TSEI) utilizes high-energy electrons to treat skin cancers, mostly mycosis fungoides. The otherwise invisible radiation beam can be visualized using the optical Cherenkov light emitted from interaction between incident electron beams and tissue during radiation therapy. Using a gated camera system with built-in intensifier, the Cherenkov emission can be used to evaluate the dose uniformity on the surface of the patient in real-time. Each patient was also monitored on the skin surface using in-vivo diode or OSLD dosimeters.

Measurement of the dose gradients from the entrance surface to depth is a standard task for characterizing an ionizing radiation beam. Most gel dosimeters provide spurious results near an air interface, limiting their value for this geometry. In this study, a 3D dosimeter system consisting of a low-diffusion, radiochromic hydrogel cast in a custom polyethylene terephthalate (PETE) vessel and imaged with a modified commercial optical cone-beam computed tomography (CBCT) scanner was employed. The cylindrical vessel wall and flat ends were constructed from a 0.025 cm thick PETE sheet. The optical CBCT scanner was modified to place the entire vessel in the centre of the field of view or to have the vessel base at the optical axis. Pre-irradiation and post-irradiation scans were acquired with the sample mounted in the standard and elevated positions. The sample was irradiated with a 2x2 cm square, 6 MV x-ray beam. Normalized attenuation coefficients from the central quarter of the reconstructed beam images were compared to a Monte Carlo depth dose calculation. Placing the vessel base at the optical axis allowed accurate dose measurements to within 0.2 cm of the entrance face and for the standard position to within 0.4 cm. These measurements validated the Monte Carlo calculation and provide an alternative to parallel plate ion chambers for dose measurement in the build-up region.

Dry scanners have been proposed as alternatives to scanners in which a refractive index matching fluid is used. Previous dry scanners either have a small field-of-view or employ a thick cast with a higher refractive index than the phantom. This may not always be feasible. A new design is proposed in this study where two aspherical meniscus lenses are employed to direct the laser beams in parallel lines through the phantom.

The present study investigates a cost effective and practical non-telecentric optical-CT scanner developed for 3D dosimetry, the Duke Integrated-Lens Optical-CT scanner (DIOS). The DIOS system includes an upgraded light-collimating tank (the LC-tank) made of solid polyurethane with precision curved ends (with lensing functionality) and a precision cylindrical central hollow for the dosimeter. The LC-tank thus collimates light from a small area light source (~2cm diameter) into parallel rays through the dosimeter, with refocusing of emergent light onto a CCD camera with a focusing lens with an aperture. The solid nature of the LC-Tank dramatically reduces the amount of required refractive matching fluid compared to earlier scanning systems. The aim of this work was to perform preliminary characterization studies of DIOS in comparison to earlier systems, particularly telecentric systems. The preliminary results indicate promising performance for the DIOS approach.

When a radiochromic micelle gel dosimeter is employed for optical computed tomography (CT) measurement, cupping (or dishing) artifacts appear at areas irradiated with a high dose. Anti-scatter polarizer correction is employed to remove scatter signals from optical CT data, but cupping remains. Here, measurement conditions for reducing cupping artifacts are investigated. A change in observation wavelength is found to suppress the cupping influence. Measurements involving aqueous dye solutions with varying jar sizes and dye concentrations reveal cupping artifact behavior under various conditions.

The pre- and post-irradiation scan strategy for optical-CT gel readout often turns out to be corrupted by angular mismatch between these two scans. In this study, we used computational simulations to investigate the influence of angular mismatch. Two phantoms are constructed: one cylindrical phantom with synthetic impurities and one elliptical phantom. The reconstructed results of angular mismatched pre- and post-data show that the dual-scan method is very sensitive to repositioning error, and positive-negative pair errors can be easily identified around impurities and phantom edges. From the simulation results, we believe that the angular mismatch should be less than 0.1 degree.

Since 1999 it has been convention at the IC3Ddose conferences to provide an opportunity for interested attendees to come together for an early morning session to review the basic properties of one family of 3D dosimeters: volumetric chemical dosimeters. Seasoned workers in the field benefit from a refreshed perspective, while those new to the field get an overview of this one modality for 3D dose measurement early in the conference. The intent of the session is to describe the basic science and characteristics of these true 3D systems, how they work and how they are read out. This provides some basic foundation to all attendees before the conference moves to the more detailed presentations directed to various specific issues and applications (e.g., looking at specific gel or plastic dosimeter, its readout and its clinical utilization). This talk is that session.

Preclinical in vivo studies have drastically improved over the past decade with the development of cone beam computed tomography (CBCT) image-guided small animal irradiation systems. Such systems produce 220 or 225 kV x-rays with square and circular field sizes ranging from 0.5 to 10 mm. The dosimetry of such equipment involving kilovoltage small-field dosimetry has not received as much attention as the megavoltage small-field dosimetry. The dosimetry of megavoltage small fields can be challenging due to lateral charged particle disequilibrium, detector volume averaging effect, and high dose gradients. Clinically there has been a rapid increase in the use of small fields in modern radiotherapy techniques such as stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SBRT). This study presents dosimetric properties of image-guided small animal irradiation systems. Both EBT Gafchromic films and 3-D PRESAGE measured beam data were presented and compared with the calculated dose distribution from a commissioned planning system. For megavoltage small-field dosimetry, EBT3 films and PRESAGE dosimeters were used to measure the dose distributions for MLC-delimited 6 x 6 to 20 x 20 mm² square fields, and for selected IMRT and VMAT plans with small field sizes or segments of 1-4 cm. A single-beam optical CT scanner was used as the readout mechanism of the radiation-induced 3-D information in the PRESAGE phantoms. Measured data sets were compared with calculated results from Eclipse Acuros XB. The results for kilovoltage small animal irradiator showed that PDD data measured from EBT films and PRESAGE dosimeters are in agreement within 3%; profiles and 2-D dose distributions measured from PRESAGE present a larger penumbra compared with those from EBT films. Discrepancies between measured beam data and treatment planning data were identified. For megavoltage small fields, the measured data percent depth dose, beam profiles, and dose distributions were found to agree within experimental uncertainties for EBT films and PRESAGE dosimeters. Beam profiles for MLC-delimited field sizes less than 10 mm reveal some discrepancies in the penumbra region between measured data and calculated results. Dose distributions from EBT film and PRESAGE measurements demonstrate that 3-D dosimetry measurement for small-field IMRT and VMAT QA may be necessary to ensure a complete verification of dose delivery and accuracy.

Stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) are among the most demanding of radiation therapy techniques in terms of requirements for high accuracy and conformality of treatment delivery. Compared to conventional treatments, they require specialized high-precision equipment (including high specification medical accelerators and alignment frames), extensive imaging (including multi-modal and motion management methods), specialized Quality Assurance protocols, and increased person-power effort. In addition, the high dose-per-fraction renders SRS/SBRT a high-stakes treatment setting, where small errors may cause significant treatment morbidity in normal healthy tissue. All of these issues combine to render SRS/SBRT one of the most opportunistically rich and clinically important areas for advanced dosimetry research. Some of the applications of advanced 3D dosimetry to SRS and SBRT and small field treatment verification are explored. Applications include base of skull IMRT, single-isocenter multi-lesion radiosurgery, pre-clinical precision treatments, interpreting the clinical significance of 3D QA data, remote dosimetry, dosimetry in magnetic fields, trigeminal neuralgia, rodent-morphic dosimetry, motion, and small field commissioning.

Image Guided Radiotherapy (IGRT) systems allow delivering high doses of radiation to a tumour with great precision and accuracy. In this work, we use patient-specific head MR-based gel dosimeters as an end-to-end test to commission IGRT delivery systems, for stereotactic cranial radiotherapy, and investigate possible sources of errors associated with practical aspects of the measurements. A CT scan of a patient is used to 3D print the shape of the cranial bones to create head phantoms with MR-based gel inside. Each phantom was used as a patient, following the radiotherapy workflow which includes: taking a CT scan of the phantom, calculating the dose distribution using a treatment planning system (TPS) and delivering the radiation calculated by the TPS (to target three different lesions: Big, Medium and Small). Each phantom was then scanned on an MR scanner to obtain a T2 map (linear with dose), which was then rigidly registered with the CT scan of the phantom based on the phantom structures. Good agreement was obtained between the normalized R2 (=1/T2) values and TPS simulations. The relationship between R2 values and dose was investigated based on 3D regions including each lesion. Good linearity was found, but different R2-dose values relationship was obtained depending on the selected regions. The impact of applying a registration based on each lesion (and not the phantom structures) was also tested. Results show that the registration has an impact on the relationship between R2 values and dose, and although absolute dose measurements are still not possible with these MR-based gel dosimeters, they provide very detailed geometrical 3D information to validate IGRT radiotherapy treatments with high level of accuracy.

Cone beam computed tomography (CBCT) imaging has been implemented on the Leksell Gamma Knife Icon^TM for repeated patient positioning in mask-based Gamma Knife radiosurgery. The purpose of this study was to evaluate the accuracy of the CBCT-based patient positioning on the Gamma Knife Icon^TM. Two Presage phantoms of 15 cm diameter and 10 cm height were irradiated with identical shot placements on an Acoustic Neuroma target with the same prescription dose following standard mask-based treatment workflow according to two different fraction schedules: a single fraction of 7.5 Gy and 5 fractions with 1.5 Gy fraction dose. On the top and the bottom portions of each phantom, 8 single 16 mm collimator shots were delivered with maximum doses from 2 Gy to 20 Gy for dose sensitivity calibration. The irradiated Presage phantoms were scanned and analyzed using an OCTOPOUS optical CT scanner. Both the absolute dose distributions and the relative dose distributions for the Acoustic target on each phantom were compared with those from the treatment planning system. The relative dose distribution from the single fraction irradiation agrees better with the planning system than the 5 fraction irradiation, indicating noticeable change in the dose distribution caused by the phantom positioning/repositioning process. No difference between the absolute dose distributions from the two phantoms could be identified because of the large uncertainty in the experiment data.

A dosimetric evaluation of a respiratory gated VMAT SABR technique was performed at two different beam energies. Dynamic ion chamber, EBT3 film and Fricke-xylenol orange-gelatin (FXG) gel measurements were acquired using a motion phantom with custom inserts for each dosimeter. Ion chamber and gel dosimeter measurements show good agreement between the measured and calculated plan dose within the planning target volume (PTV). Lower agreement than expected was observed between calculated plan dose and measured film dose, particularly for the 10 MV flattening filter free beam plan, a result that warrants further investigation.

Measuring radiation exposure has long been a priority in radiation therapy. Over the last 115 years numerous chemical-based dosimeters have been developed to measure radiation exposure. These dosimeters contain either metal complexes or leuco dyes. Among the factors which influence dose sensitivity and color stability in leuco dye based dosimeters are chemical structure and the solvent content in the formulation.

This invited technical review will discuss the numerous options available for making 3-D measurements of radiation dose, including both the physical principles underlying them and the potential sources of error involved.

Previous formulations of the FlexyDos3D dosimeter have shown significant changes in the dose-response over time. In this study, various formulations of the dosimeter were created and tested to see if this stability could be improved. A dosimeter that was stable over a three-day period was found. Rapid manufacture of this dosimeter for patient-specific validation of radiotherapy treatments is desirable. The use of 3D printing manufacturing techniques for thermosetting polymers require high temperatures to cure the polymer within a reasonable time. The effect of different curing temperatures and times were investigated for the FlexyDos3D radiation dosimeter for its effect on stability. No significant difference in the dose-response was found for dosimeters cured for different curing times beyond an hour. A significant dose-response offset was found between dosimeters cured at different temperatures, but the dose-response sensitivity was the same.

A novel radiochromic gel dosimeter based on a poly(vinyl alcohol)-iodide complex (PVA-I) has been developed with the aim of using it in optical computed tomography (CT). The PVA-I gel dosimeter exhibits excellent characteristics such as high sensitivity, dose rate independence, a wide dose range, and especially reusability. The standard PVA-I gel dosimeter is composed of poly(vinyl alcohol) (average degree of polymerization 1000 and degree of saponification 88 mol%), iodide (potassium iodide), reducing sugar (fructose), gelling agent (gellan gum), and water. In this study, the influence on dose response is investigated upon substitution of the components by PVAs with different degrees of polymerization (500, 1500, 3500) and saponification (80 mol%, 98 mol%), different iodide salts (LiI, NaI, NH₄I), and different reducing sugars (glucose, maltose, lactose). The results show that these substitutions have little effect on the dose rate dependence, while the iodide salt affects the sensitivity.

This work investigates a novel reusable radiochromic sheet developed as an economic film substitute or as a radiochromic bolus. The radiation-induced optical density (OD) change of the sheet is read-out with a commercial flat-bed optical scanner. An optimized readout procedure was developed including an optimal scan-time window. Fundamental radiochromic properties of the sheets were characterized including temporal decay of OD, dose sensitivity and consistency through repeated irradiations, and temperature sensitivity. The radiation induced OD change in the sheets was found to decay to baseline within ~24 hours, after which the sheet could be reused. The sensitivity of subsequent re-irradiations was found to be consistent within ±5% (coefficient of variation of 4.5%) for at least 6 irradiations and potentially many more. Importantly, the sheets were not observed to carry any detectable memory of previous irradiations within measurement uncertainty. In conclusion, the Presage sheets show promise as an economic multi-purpose alternative for film applications and potentially as a radiochromic bolus. Further work is required to test the sheet in diverse clinical applications, and to develop a softer material for bolus applications.

Benzothiazole-containing tetrazolium salts (Bt-TS) have been previously described but have never been tested for dosimetry applications. Considering that such salts may provide higher dose sensitivity than previously tested tetrazolium salts, we synthesized a library of Bt-TS, three of which are reported here. Dosimeters based on the salts BtPP, BtNP and BtNpP were prepared in gellan gum gels, and compared to a previously-described gel dosimeter, based on bisnitrotetrazolium chloride (BNC) in the same medium. All three Bt-TS showed a higher sensitivity at their respective wavelengths of maximum optical attenuation post-irradiation. Two of the new Bt-TS (BtNP and BtNpP) were identified for further studies in large-scale samples and other gel-forming materials.

A novel formula of crosslinked polyvinyl alcohol (PVA) with glutaraldehyde (GTA), a tri-iodide complex, and glucono-δ-lactone (GDL) acid for gel dosimetry was investigated in the present study. The objectives of this study were to evaluate the formula's dose response properties through spectrophotometry and possible reusability by reannealing. After production, the gel samples were irradiated from 1 to 70 Gy of gamma-rays from a Cs-137 source with a constant dose rate of 0.857 Gy/min. Spectrum data were obtained using a UV-Vis spectrophotometer and analyses were done for dose linearity, dose sensitivity versus GTA concentration, and absorbance profile versus time. The resulting unirradiated gel samples were colorless and transparent, while the irradiated samples turned to a reddish-brown hue with a peak absorbance response at 490 nm. Dose linearity results indicated R² values of 0.9, 0.986 and 0.8 for GTA concentrations of 7 mM, 15 mM and 30 mM, respectively. Moreover, dose sensitivity is higher for lower concentrations of GTA. Time progression results indicated that the absorbance decreases within one day after irradiation and increases subsequently. Through reannealing for 24 hours at 45°C in an oven, a colorless material with an absorbance value identical to the unirradiated samples was finally made for samples irradiated from 1 to 20 Gy, while the 70 Gy irradiated sample had a significant decrease in color and absorbance peak. This radiochromic gel dosimeter is promising and should be useful for 3D radiation dose assessments. Further investigation of the formula and preparation techniques are suggested for future experiments.

A co-polymer of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127, PEO-PPO-PEO) was proposed as a physical gel matrix, substituting gelatine for three-dimensional polymer gel dosimeters and as a matrix for the preparation of new radiochromic gel dosimeters. Two polymer gel dosimeters and seven radiochromic gel dosimeters were obtained with this new matrix. In this review we summarise the main advantages of using Pluronic F-127 for manufacturing radiation dosimeters and the best performing new Pluronic dosimeters.

Tetrazolium-based 3D gellan gum gel dosimeters have been reported previously and tested at several sites. They show no image diffusion and excellent stability; however, the dose sensitivity of the current commercial product, ClearView™, is relatively low for routine clinical applications. Here we report initial testing of a second generation product with increased sensitivity and retained non-diffusive properties. This formulation has a 25% increase in sensitivity relative to ClearView™. However, the sample has a higher initial attenuation and the background attenuation increases faster than ClearView™. The composition was tested in a 1-liter sealed container using a 2x2 cm, 6MV, x-ray beam, and show agreement between Monte Carlo simulation and measurements.

Several 3D dosimeters are commercially available. However, there are many circumstances that require a customized 3D dosimeter. Examples include feasibility tests of non-standard treatment modalities, inhomogeneous tissue configurations, unique shapes and sizes and teaching. In this session, general approaches for preparing radiochromic dosimeters, Fricke and polymer gel dosimeters, micelle gel and silicone dosimeters were presented. Advise will be given to developers of new 3D dosimeters. For optical readout, light absorption and scatter can limit the practical size of dosimeters. Specifically, increasing from 5 to 15 cm diameter dosimeters is optically challenging. Strategies to maximize initial optical transmission were presented. For MRI readout, the dose resolution is determined by both the dosimeter sensitivity and the pulse sequence parameters and the accuracy is determined by the sensitivity of the dosimeter to temperature and dose rate, next to imaging performance. For X-ray CT imaging, the dose resolution is determined by the sensitivity of the dosimeter which largely depends on the polymer density that can be achieved. The importance of characterizing the dosimeter in terms of dose sensitivity and stability, spatial integrity, dose rate and fractionation dependence, oxygen and ambient light sensitivity, temperature sensitivity and thermal history were emphasized. The dosimeter requirements also dictate the types of vessels and scanners appropriate for readout. For example, the preferred dosimeter formulation may include a compound that is incompatible with the preferred vessel.

We have been developing novel 3-dimensional (3D) detector systems using organic plastic and liquid scintillators to measure and image the dose distribution from proton therapy beams in near-real time. Proof-of-concept and initial feasibility studies using a single charge-coupled device camera have already been conducted. Our recent studies focused on the characterization of scanning proton beams used for patient treatments using a 3D liquid scintillator-based detector system with a set of scientific-complementary metal-oxide-semiconductor (sCMOS) cameras. The basic concept consists of using a large volume of a solid or liquid scintillator to measure or image the dose distributions from proton beams in 3D. We recently developed a large liquid scintillator-based detector system consisting of a 20 × 20 × 20cm transparent acrylic tank filled with a water-equivalent, commercially available liquid scintillator that generates scintillation light when irradiated with protons. To track rapid spatial and dose variations in spot-scanned proton beams, we used 3 high-speed sCMOS cameras to image the scintillation light signals from 3 orthogonal projections in cine mode. Furthermore, we developed a new image acquisition approach that synchronized camera imaging times with dynamic pencil-beam deliveries to efficiently capture the dose and therefore enable accurate dosimetric calculations. This system was fully developed and characterized at the Proton Therapy Center at The University of Texas MD Anderson Cancer Center. We show that such systems can provide fast and accurate measurements of the range, lateral profile, and lateral position of scanning proton beams with excellent spatial resolution (0.21 mm). We also demonstrate that such detectors can rapidly measure proton beam characteristics and intensities at multiple energies, which makes them an ideal tool for scanned proton-beam systems, beam quality assurance studies, and verification of patient treatment delivery.

A rapid development of the new radiation based cancer treatment technologies that are more individualized and patient oriented request precise 3D treatment dose verification methods in high dose gradient fields. Polymeric dose gels are excellent 3D dosemeters that allow analysis of spatial dose distribution in the irradiated target and also in the regions out of the target since the investigation of low dose induced secondary effects (secondary cancer, inflammations) stands on the priority list. Since the sensitivity of dose gel to different types of irradiation depends on radiation induced polymerization processes, in this work we present Raman analysis results related to advanced nMAG dose gels polymerization upon its irradiation with high energy photons and protons to doses ≤ 5 Gy.

We built a clear micelle gel dosimeter with nanoclay. Jordan et al. reported that Laponite RD clay nanoparticles when added to radiochromic leucomalachite green micelle gels eliminate diffusion and increase the dose sensitivity by roughly ten folds. However, owing to the cloudiness of the sample, there was a problem in reading the optical computed tomography (CT). In this study, we constructed a nanoclay-added micelle gel dosimeter by changing the type of gelatin. As a result, in addition to yielding a clear gel and making the optical CT readable, diffusion and temporal stability were improved more than the gel without using nanoclay, and the dosimeter showed the same level of sensitivity and diffusion as the one based on Laponite-added micelle gel reported by Jordan et al.

A novel radiochromic PRESAGE sheet (Heuris Inc.) with variable thickness of 1-3 mm has been developed to provide 2D dosimetry. It can also be used for patient surface dosimetry or as a tool for patient-specific QA (PSQA) in 3D dosimetry. Its softness and flexibility to conform with the patient's skin make this product advantageous for future clinical applications. This study presents a comprehensive investigation into the PRESAGE sheet's dosimetric accuracy at different scanning times and its potential use for clinical applications. For the characterization of the dosimeter, temporal stability of dose rate, energy dependence, dose linearity, beam profile, and dose distribution measurements were investigated by irradiating a single sheet of PRESAGE with different doses and energies while scanning the sheet with an Epson 11000XL high-resolution scanner at different time intervals following its irradiation. Additionally, two clinical applications, including PSQA and surface dose measurement, were conducted and were compared to dosimeters currently used for clinical applications. For QA measurement, a stack of PRESAGE sheets, with EBT3 films sandwiched in-between, was used to measure the dose distribution of a pancreas SBRT treatment plan at different depths. For surface dose measurement, PRESAGE sheets, EBT3 films, and OSLDs were placed on the surface of an anthropomorphic phantom to measure the skin dose of a modulated treatment fields. When the stack of PRESAGE sheets were scanned within a period of two hours following its irradiation, the dosimeter exhibits a stable linear response to dose with negligible dose rate and energy dependence. In addition to its temporal stability, the dosimeter can provide accurate relative dose measurements comparable to those exhibited by EBT3 films. In the application of PSQA, when compared with EBT3 films using gamma test with a 2%/2 mm criteria, PRESAGE sheets have a passing rate of 99.7% measured at the isocenter and 99.1% in application of surface dose measurements. This study demosntrates the dosimetric characteristics and the potential use of a novel dosimeter, PRESAGE sheets.

The basic characteristics of a VIPET-type polymer gel dosimeter were assessed using AQUAJOINT® as a hydrogel matrix. The dosimeter exhibited a good dose response. The threshold dose was 0.5–0.6 Gy and the linear section of the response curve, in the range of 1.7 – 2.7 Gy, had a minimum dose response of 0.05–0.06 Gy. The dose-rate dependence was determined by the delivery of 200 MU for dose rates between 100 and 600 MU/min; the resulting value of R2 was 3.222 ± 0.036 (mean ± 1SD). A slight change in the value of R2 in the integration of the divided doses was observed; the R2 value was 3.059 ± 0.015 (mean ± 1SD) for a total irradiation of 200 MU. Gel samples of different volumes were irradiated and compared with a PAGAT polymer gel. The change in sensitivity of the AQUAJOINT®-based VIPET was smaller than that of the PAGAT.

Dual-wavelength scanning is a technique eliminating the need of phantom repositioning for optical-CT gel readout. To further diminish artifacts caused by phantom impurities, we hereby propose a novel dual-wavelength imaging method based on phantom impurity recognition and correction. In this method, impurities in motion trajectories during phantom rotation are recognized at the reference wavelength via motion-tracking as a binary mask, which is then applied to correct impurity-contaminated pixels at the data wavelength. Compared with the existent dual-wavelength imaging method, the proposed method is demonstrated to be capable of reducing impurity-induced artifacts and improving imaging SNR and CNR in the same process.

Chloroform in the FlexyDos3D dosimeter acts as a radical initiator which brings about the colour change of the dosimeter when the radicals react with the leucomalachite green. However, the volatility of the chloroform likely results in a rapid loss of chloroform from the dosimeter. Gravimetric analysis and NMR diffusion-ordered coherence spectroscopy were used to measure the diffusion and evaporation rates of chloroform from the dosimeter and found that both rates were both significantly large resulting in a rapid loss of chloroform. Dose maps of irradiated phantoms aged for different times found a significant difference in the dose measurements of the dosimeter, likely a result of the different chloroform concentrations within the dosimeters.

Rhodamine 6G (R6G) and 7-diethylamino-4-methylcoumarin (7D4MC) were applied to a nanoclay gel dosimeter based on radiation-induced degradation. The radiological properties were evaluated under X-ray irradiation. The fluorescent dyes showed linear degradation with an increase in dose. In addition, the distribution of fluorescence induced by inhomogeneous irradiation was maintained for two months and a suppressed diffusion of the fluorescent dyes in the gel matrix was observed.

Recently bismuth-based nanoparticles as a promising radiosensitizer have drawn great attention in radiation therapy. To prove physical dose enhancement effect of the nanoparticles, gel dosimeters can be considered as an ideal method. This study aims to prove the applicability of bismuth ferrite nanoparticles as a magnetic localized dose enhancement agent by gel dosimetry method. Bismuth ferrite nanoparticle was synthesized by the conventional sol-gel method. Then we investigated dose enhancement property of the nanoparticles with gel dosimetry. MAGIC Polymer Gel dosimeters with nanoparticles were prepared and irradiated. According to gel dosimetry assay, for 0.5 mg/ml concentration of bismuth ferrite nanoparticles dose enhancement factor were obtained as 2 and 1.6 at 160 keV and average energy of 380 keV, respectively. Moreover, radiosensitiser effect of bismuth ferrite nanoparticles in presence of a low dose rate brachytherapy source (125-I) was investigated by Monte Carlo method. Whereas bismuth ferrite nanoparticles have magnetic property, we made a biodegradable spacer (fiducial) brachytherapy loaded with the nanoparticles for delivering nanoparticles and drug by applying an external magnetic field.

The performance of normoxic PAG (nPAG) gel dosimeter with respect to spatial integrity, temperature sensitivity and dose-rate dependency makes it more reliable than PAG gel dosimeter. As a 3D dose distribution measurement in dosimetry, nPAG gel dosimeter with THPC as anti-oxidant, named PAGAT was studied. 2.9% mass concentration of the formaldehyde solution was added into PAGAT to solidify the gel, named PAGAT-f. The melting point of PAGAT-f polymer gel was increased by adding formaldehyde and can be stored at room temperature after gel preparation without refrigeration. After irradiation with a 9 MV LINAC, magnetic resonance imaging (MRI) is employed as readout modality. It's found that by adding formaldehyde, R₂-dose response of PAGAT-f is similar to PAGAT but the dose response sensitivity of PAGAT-f is better than that of PAGAT at low doses. The results prove the feasibility and good temporal stability of PAGAT-f for dose distribution measurement.

The utility of gel dosimeters is sought to be improved upon in this study which proposes a target region of different X-ray CT contrast that is dose sensitive. The changes in the physico-chemical makeup of nPAG caused by the addition of the X-ray imaging Iodine based contrast agent Isovue are explored. The impact of this change on dose measurements is also discussed. The increase in HU as it correlates with increasing Isovue concentration is detailed, along with the dosimetric changes that occur, namely the steepness of the dose response curve and general shape of the percentage depth dose curve. It is noted that diffusion of Isovue from one gel region to another has significant dosimetric impact and the experimental method was constructed and conducted with this in mind. Further refinement and optimisation of the Isovue nPAG formulation will lead to a target region dosimeter that can be contoured on X-ray CT and used in the improvement of planning protocols, especially in cases that involve motion and deformation of target volumes.

Many novel modulated radiation treatment techniques are sensitive to patient motion which may degrade the dose distribution considerably. As there may be a simultaneous movement of the tumour and treatment machine, undesired heterogeneities in the dose distribution can be resulted. Methods to estimate the dosimetric effect of motion and treatment deliveries for both photons and protons are needed. We have recently studied Hodgkin's lymphoma, liver and left sided breast cancer cases and developed tools to be able to simulate simultaneous organ movement and treatment delivery. Furthermore, it is of great importance to validate potential simulations in a realistic quality control set-up, ideally including a complete dosimetry volume and movement/deformation (4D). Radiation sensitive deformable gels have the potential to meet this dosimetry challenge owing to the unique 3D characteristic to form both phantom and detector in one volume. Multi-array detectors together with a moving platform and a realistic object trajectory is an alternative to evaluate the clinical setting. The evaluation could then in principle be done on-line. Gel/plastic 3D dosimeters have the potential to also be irradiated during motion in a similar matter but have to be read-out post irradiation.

As part of a recent commissioning process for an ultrasound-guided prostate HDR technique at our centre, a representative dose delivery was validated using Gafchromic EBT3 film dosimetry. Agreement between Oncentra Prostate-calculated plan dose and measured film dose was within 5-10% over most of the 2D film dose planes, except in the regions within 5 mm of the catheter axes. Given the uncertainties associated with the measurement, this result was deemed to be clinically acceptable.

The cause and removal of streaking artifacts from catheters within radiochromic 3D dosimeters was investigated to allow the use of these dosimeters for high dose rate (HDR) brachytherapy applications. The OSC-TV iterative reconstruction algorithm's ability to remove the streaking artifacts from one or more catheters was validated using external beam irradiations and leuco crystal violet (LCV) micelle gels. One and two catheter HDR plans were then delivered to LCV gels. Dose volumes from the gels were reconstructed with the OSC-TV algorithm, calibrated, and registered to treatment planning system dose volumes, and were shown to be artifact free and in agreement with the expected values.

High-dose rate brachytherapy treatment has become more complicated with the use of three-dimensional image-guided brachytherapy (3D-IGBT) to prepare treatment plans using 3D images, such as those obtained from computed tomography (CT). In planning a 3D-IGBT, spatial measurement of dose distribution verification is recommended. In this study, the spatial dose distribution of intrauterine cavity irradiation by a Co-60 sealed brachytherapy source was acquired using an AQUAJOINT® polymer gel dosimeter. A CT/magnetic resonance imaging (MRI) compatible applicator was inserted into the gel in a bottle. It was irradiated and visualized using MRI. The image was converted to an R2 image using a DD-System (R-TECH INC, Japan), and dose distribution was evaluated using the dose–R2 response curve. The obtained dose distribution, dose profile of the radiotherapy treatment planning system, isodose curve, and gradient passing were calculated. In the dose profile, the dose difference was large near the applicator (high-dose region) and was less than ±2% in the middle-dose region. The isodose curves showed good agreement in the region of 2–6 Gy near the prescription point. The gamma analysis was 87.594% on the sagittal cross-section and 93.711% on the coronal cross-section based on the dose difference (DD)/distance to agreement (DTA) of 3%/3 mm.

An in-house developed program for real-time reconstruction of motion-induced dose errors, DoseTracker, was extended to handle rotational target motion in addition to the previously implemented translational motion, and applied offline for prostate VMAT treatments. For translational motion, the motion-induced errors of DoseTracker were in good agreement with ground truth dose reconstructions performed in a commercial treatment planning system. For rotational motion, no ground truth was available, but DoseTracker showed that the VMAT dose is highly robust against static interfractional rotations but quite sensitive to dynamic intrafraction rotations due to interplay effects between target motion and machine motion.

External radiotherapy largely proved its efficacy to treat cancer. However, this technique leads to unavoidable exposure of normal tissues that may results in adverse effects. One of the main concerns is the induction of second cancers that may appear at the periphery or even away from the treated area. Risk estimation models need accurate 3-D dosimetric data on healthy organs. To this aim, we developed an experimental tool based on radiochromic films measurements. In this work, we present a study performed with a heterogeneous phantom. EBT3 films were positioned in between the phantom slices and irradiated according to a VMAT plan. The dose was reconstructed in 3-D by interpolation thanks to an in-house Matlab tool. Two interpolation methods are studied and the reconstructed dose is compared to independent film measurements for validation. Finally, dosimetric data such as DVH are compared to the TPS evaluation. Continuous interpolation proves to better reconstruct the doses in high gradient areas whereas linear interpolation seems to be a better option to evaluate doses away from the field edge. Besides, TPS and 3-D measurements give comparable results for organs placed inside the beams (maximum 6.3% difference on organs mean doses). However, the TPS tends to underestimate doses to organs placed at least partially outside the fields (from 29 to 59% difference on mean doses). Optimization of the dose reconstruction tool by using a combination of the two interpolation methods is ongoing. Comparison with gel dosimetry will also be investigated.

To increase the clinical utility of deformable gel dosimeters an X-ray CT visible target region is introduced into the DEFGEL dosimeter, with the goal to enable the determination of the change in marginal doses around planned boundaries. The production of the dosimeter components is detailed and the requirements in making, deforming, irradiating and analysing the dosimeter are explored with several areas of required improvement identified. A single degree of motion is used to deform the dosimeter with the intent of identifying the volumetric dose changes caused by the deformation. The planned target volume dose structure was registered to the physical target region present in an optical CT data array and the dose volume histograms of the target volume while static and undergoing deformation are investigated and reported. The total dose to the target volume was shown to decrease by 9.4% due to a 1cm compression of the entire dosimeter volume. Further ways to improve the use of the target region are suggested with a view to improving the dose map information that can be obtained from target-in-gel dosimeters.

Brachytherapy plays an important role in the treatment of various cancers. The TG-43 formalism is widely used in dose calculation for brachytherapy, but it is not accurate as it assumes the patient as homogeneously constituted of water. Monte Carlo simulation can obtain accurate result, but computing time using traditional code is too long to be accepted in clinical application. This work developed a fast Monte Carlo code THUBrachy for high dose rate brachytherapy dose calculation. THUBrachy can simulate photon with energy up to 3MeV for heterogeneous materials and obtain dose, fluence and dose distribution. It applies several accelerators such as Graphics Processing Unit (GPU), Intel Xeon Phi to perform dose calculation with good accuracy and high speed. THUBrachy adopts several parallel programming models to transplant the code onto different hardware accelerators. Voxel geometry based on CT images is used to describe the tissues of patient. A linear track-length estimator is used for dose calculation. In the preliminary accuracy test, a cuboid water model and a heterogeneous-material model were selected as the phantoms. Dose and fluence distributions were calculated by both THUBrachy and FLUKA which is a well-benchmarked Monte Carlo code. A total of 5×108 photons were simulated to make the uncertainty in all area less than 5%. The maxium difference of the results in low dose area is less than 3% and in high dose area is less than 1%, indicating a good agreement. In the performance test, a phantom consisted by 24 types of human tissue materials was chosen to estimate the performance in practical application. Dose distributions with an uncertainty of 2% or less for the target volume were obtained in less than 1 min by simulating 5×107 photons with a GTX 1080Ti, while FLUKA taking several hours to simulate the same number of particles. There is great potential for clinical application in brachytherapy dose planning using this fast Monte Carlo code.

Interest in the application of Computer Simulation within Medical training continues to grow and the use of the VERT (Virtual Environment for Radiotherapy Training) system in radiotherapy training equally so. Herein we explore the use of the VERT system to understand, illustrate and experience the process required to calibrate an ion chamber and use it to obtain an accurate output measurement on a high energy Linac. The VERT system provides a detailed and accurate simulation of conventional Linacs and has a variety of physics activities that mirror the tasks medical physicists are required to become familiar with during their training. One such activity has been implemented to follow the steps defined by the IAEA TRS398 protocol. All activities on the virtual Linac can be undertaken with deliberate errors having been introduced to explore their consequences. The system was used to make the necessary 'measurements' to determine the various calibration factors required to correct the raw electrometer reading for ion recombination, polarity, temperature/pressure. Likewise, the Quality Index of the Linac's 6MV beam was determined to enable the correction of the Absorbed Dose to Water factor measured in the reference Quality. The VERT system provides a simulation environment for training and enhancing the trainees understanding of radiotherapy concepts and practices. Dosimetry practice can be experienced and explored in the classroom during standard working hours rather than waiting until a clinical Linac is available. Random and systematic errors can be introduced, however, the virtual machine can be used without risk of leaving it in a mis-calibrated or unsafe condition.

Teaching demonstrations of computerized tomography (CT) and Single-Photon Emission Tomography (SPECT) to biomedical engineering and medical physics students is hampered by a limited accessibility to clinical scanners, especially during day time. The use of ionizing radiation and radioactive sources in X-ray CT and SPECT further complicates the design of a teaching laboratory session. We here propose an inexpensive and safe educational demonstration of CT and SPECT on an anthropomorphic phantom whereby a visible light source serves as source and a CCD camera serves as detector. The equivalent of a SPECT radionuclide in optical CT scanning is a chemiluminescent material which can be obtained relatively inexpensive in the form of party glow sticks. The proposed teaching tool comprises several learning outcomes such as hands-on construction of the scanner, the acquisition of images and image reconstruction. Also, different imaging artefacts can be simulated and investigated.

Several kinds of chemical 3D radiation dosimeters have been fabricated to acquire the dose distribution in clinical radiotherapy. A legitimate concern with every new dosimeter is its dose rate dependent response because, the dose rate in each point of the phantom during a clinical treatment is unknown. Unfortunately, many 3D dosimeters have shown some degree of dose rate dependence. In practice, radiation dosimeters are mostly calibrated using a calibration curve that is obtained by irradiating calibration vials with different doses but using a fixed dose rate. Therefore, when applying a dose calibration to an experimentally obtained dose distribution, a deviation between the measured dose distribution and the actual dose distribution can be expected. In this computational study, the effect of a dose rate dependent dosimeter response on a theoretical dose distribution has been investigated. In order to compare the effect of dose rate, a gamma evaluation is performed between the predefined dose distribution and the dose distribution that is affected by a dose rate dependent radiation response. It is found that a dose rate difference of -10%, results in a gamma pass rate of 100% in the 3D dose distribution.

Purpose: To compare the physical and dosimetric aspects of radiation beam collimation systems that may affect the stereotactic radiosurgery and radiotherapy of small lesions. Methods: Gamma knife (GK) cones, Cyber-knife Iris/InCise collimators, popular Varian and Elekta multi-leaf collimators (MLCs) were theoretically analyzed. Leaf-edge effects (Inter- and intra-leaf leakages, field penumbras, and dosimetric leaf gap - DLG) and transmission through some collimators were measured with ion chambers and films in phantoms and electronic portal imagers in an extended distance. GK plans and IMRT/VMAT plans were generated for ten patients and conformity index (CI) and dose drop (DD) from target to 5-mm ring were compared. Results: New MLCs have improved field shaping conformity, reduced transmission but not field penumbra and DLG. The measured DLG changed with time of usage and varied across the field. GK plans had better CI and DD for small lesions of < 1 cm while MLC-based VMAT/IMRT plans improved CI for large lesions of > 2 cm. Conclusions: New thinner and taller MLCs have improved the field shaping conformity and transmission but not leaf edge effects. Cone-based irradiation is still the best to small lesions of < 1 cm while VMAT/IMRT using new MLCs provide more conformal dose to irregular target usually with size of > 2 cm.

In this paper I will summarize the various possibilities of EPIDs for their use as tools for QA of advanced treatments. After elucidating the choice of EPIDs for this purpose, I will review the use of EPIDs for pre-treatment and in vivo (transit) dosimetry applications. Several solutions became recently commercially available, allowing relative and/or absolute dose verification at points (0D), in 2D, or in 3D. Each of these solutions will be briefly discussed, indicating the differences in possibilities with respect to QA of advanced treatments. I will conclude with some general remarks about the current status of EPID-based QA of advanced treatments and revealing some future developments in 3D pre-treatment and in vivo dosimetry using EPIDs.

It has been suggested that modern radiation therapy could benefit from adopting the "End to End" (E2E) type of testing developed originally in computer science to determine whether applications and systems work as required under real-world scenarios. The motivation for adopting E2E techniques for image guided adaptive radiation therapy validation is to extend beyond current common testing using standard physics QA that inherently probes only select points or systems within the IGART schema. E2E methodologies extend the testing to evaluate complete IGART processes, including the complex interchanges that occur during and throughout a patient's treatment as clinical staff interpret and respond to information acquired during the treatment course.

While limited radiotherapy E2E QA may have been adopted periodically by clinics when implementing a new treatment technique, clinical E2E QA has been confined to date mainly to tests mediated by external auditing bodies such as IROC, the Imaging and Radiation Oncology Core in the United States. This testing often includes having the clinic in question irradiate a purpose-built phantom containing dosimeters to specific criteria under protocols set by the auditing body. The auditors then determine off site whether the clinic's treatment process was successful by comparing the dose measurements with the intended dose delivery.

The advance of three dimensional (3D) radiation dosimeters opens the possibility for in-house E2E testing. Approaches for in-house E2E testing have been proposed for over a decade, but such comprehensive internal E2E testing has not been widely adopted. In this presentation the barriers and challenges to the development of clinical in-house E2E QA will be reviewed primarily based on the experience in Kingston.

Conventional verification of linac performance is conducted by measuring percent depth dose (PDD) as well as beam profiles in a water tank, which is labor intensive and requires expensive beam scanning equipment. We present a novel method to benchmark the linac beam characteristics using pixel sensitivity map (PSM) corrected EPID images and to evaluate the feasibility of EPID-based beam benchmarking. A novel approach was developed to generate a two-dimensional (2D) PSM for EPIDs utilizing an alternating beam and dark-field image acquisition technique. The calculated PSM based on a recursive calculation algorithm was used to correct EPID pixel response. The acceptability of a benchmarked beam is based on its profiles being within predetermined tolerances. The PSM-corrected open field EPID images were compared for three photon energies (6 MV, 10 MV and 6FFF) between three TrueBeam and one Edge linacs with aS1200 imaging panels. The output factors were measured with EPID from 2×2 cm² to 40×40 cm². The differences in beam profiles and output factors from EPID were evaluated. The four dosimetrically similar linacs with less than 1% variation in PDD, profiles and output factors measured in water scans showed excellent agreement in the EPID profile measurements. The 1D Gamma of the PSM-corrected profiles between any two linacs showed 100% passing rate for 6 MV and 6 FFF and >97% for 10 MV with 1mm/1% criteria. The maximum difference of output factors was 0.18% among all the measurements except for 2×2 cm² with 0.6% difference. By preserving the beam dosimetry information, the PSM-corrected EPID images enable the possibility of validating the beam data of linac dosimetry and benchmarking linac performance with the common EPID detector.

The recently published AAPM TG100 has advocated streamline IMRT/VMAT QA procedure based on Failure Mode and Effects Analysis (FMEA) criteria, i.e., the product of incidence severity, occurrence probability, and detection probability. Transmission EPID has proven to be able to detect dose errors at a detection probability of 60% vs. those based on pre-treatment patient specific QA, at a detection probability of less than 5%. The objective of this study is to retrospectively evaluate the gamma index (3%, 3mm) using composite transmission EPID images for various treatment sites on a Halcyon Linac. Transmission EPID images are recorded during treatment and compared to first day EPID as reference. Over 1000 treatment fractions, the average gamma index and standard deviation of gamma for various treatment sites are 99.04±1.64, 99.95±0.093, 100±0 and 99.7±0.567 and 95.65±3.57 for head and neck, brain, prostate, pelvis and breast respectively. In conclusion: Our data show very high inter-treatment consistency for most treatment sites except breast. For breast cases, using second day treatment images as reference, the gamma index is much higher and standard deviation is lower than using day1 images as reference. Overall a threshold of gamma passing rate of 95% is a reasonable value.

A sliding-window (SW) methodology for VMAT dose calculation was developed. For any two adjacent VMAT control points (CPs) n and n+1, the dose distribution was approximated by a 2-CP SW IMRT beam with the starting MLC positions at CP n and ending MLC positions at CP n+1, with the gantry angle fixed in the middle of the two VMAT CPs. Therefore, for any VMAT beam with N CPs, the dose is calculated with N-1 SW beams. VMAT plans were generated for ten patients in Pinnacle using 4° gantry spacing. For each patient, the VMAT plan was converted to a SW IMRT plan and dose was re-calculated. Another VMAT plan, with 1° gantry spacing, was created by interpolating the original VMAT beam. The original plans were delivered on an Elekta Versa HD and measured with Mapcheck2 using an in-house developed subarc method. For both the isodose distribution and DVH, there were significant differences between the original VMAT plan and either the SW or the interpolated plan. However, they were indistinguishable between the SW and interpolated plans. The average passing rate between the original VMAT plan and measurements was 84%. For both the interpolated and SW plans, the average passing rate was 96%. We conclude that the proposed SW approach improves VMAT dose calculation accuracy without increase in dose calculation time.

Recent studies on the development and applications of Chinese reference phantoms are reported in this paper. The Chinese adult reference male (CRAM) and female (CRAF) phantoms had been developed in previous work. A Chinese male phantom library was constructed with 7 different heights ranging from 155 cm to 185 cm and 12 phantoms with different total body masses in each height. Chinese paediatric reference phantoms were constructed for 3 months, 1 year, 5 years, 10 years, and 15 years male and female respectively. Detailed organ models were developed, including a set of microscopic skeletal models, a set of detailed breast models, a detailed human respiratory tract model and a detailed eye model. The phantoms were applied in radiation protection, including dose estimation from external exposure and internal exposure, in normal situations and in accidental situations, and detailed dose distributions in radiation-sensitive organs. The phantoms were also applied in medical imaging field such as dose estimation in mammography, CT and X-ray radiology, and could be potentially used in the secondary cancer estimation induced by radiation therapy.

NVP-containing three-dimensional polymer gel dosimeters for radiotherapy dosimetry have been developed for more than 20 years. There have been 11 main modifications of the originally proposed VIPAR polymer gel dosimeter that altogether have amounted to 12 gel dosimeter formulae. This communication is to summarise the main chemical changes made to the VIPAR dosimeter over these years of research. The newest NVP-polymer gel dosimeters are also introduced.

With the increasing complexity of radiotherapy treatments typical 1D and 2D quality assurance (QA) detectors may fail to detect out-of-plane dose discrepancies, in particular in the presence of motion. In this work, small samples of the PRESAGE® 3D radiochromic dosimeter were used in combination with a motion phantom to measure real-time multileaf collimator (MLC)-tracked radiotherapy treatments. A different sample of PRESAGE® was irradiated for each of three different irradiation scenarios: (1) static: static sample, without tracking (2) motion: moving sample, without tracking and (3) tracking: moving sample, with tracking. Our in-house software DynaTrack dynamically moves the linac's MLC leafs based on the target position. The doses delivered to the samples were reconstructed based on the recorded positions of the MLC and phantom during the beam delivery. PRESAGE® samples were imaged with an in-house optical-CT scanner. Comparison between simulated and measured 3D dose showed good agreement for all three irradiation scenarios (static: 99.2%; motion: 99.7%; tracking: 99.3% with a 3%, 2 mm and a 10% threshold local gamma criterion), failing only at the edges of the PRESAGE® samples (~ 6 mm). Given that the dose distributions deposited using the DynaTrack system have been independently verified, this experiment demonstrates the ability of PRESAGE to measure 3D doses correctly in a tracking context. We conclude that this methodology could be used in the future to validate the delivery of dynamic MLC-tracked radiotherapy.

Many different chemical radiation dosimeters have been fabricated over the last 20 years. In the search for new dosimeters, next to being sensitive to clinical radiation doses, several other physicochemical characteristics need to be satisfied, such as stability of the dose response, spatial integrity, temperature independence, dose rate independence and tissue equivalence. The development of new dosimeters is often hindered by a limited access to radiation facilities to irradiate hundreds of test tubes or cuvettes to study these physicochemical properties. To facilitate this basic experimental research, we propose the use of an inexpensive UVC irradiator. While care is required in extrapolating the results obtained with UV radiation to high energetic X-rays, for several studies, a UV irradiator is a handy tool for first line investigation of new dosimeters. In this study, we calculated the dose distribution in a cylindrical test tube when being rotated during UV exposure. A quantitative analysis allows the optimization of the set-up to obtain dose rates in the sample in similar order of magnitude that are delivered at a clinical Linac. Regardless the usefulness of a UVC irradiator in the laboratory for preliminary testing, it should not be a complete replacement for measurements with high energetic X-rays.