Abstract
This study presents beam characteristics of five recently available x-ray beams produced by an on-board imager (OBI 1.4) for acquiring kilovoltage cone-beam computed tomography (kV-CBCT) and investigates suitable methods for the beam radiation output determination resulting from an image acquisition. Both are essential for commissioning an x-ray beam in a radiotherapy treatment planning system. The BEAM/DOSXYZnrc Monte Carlo codes were used in the investigation. The simulated beam data were benchmarked against measurements. Three different commercially available plastic phantom materials are investigated as liquid water substitutes in the beam radiation output determination. Ionization chambers are used for the measurements. Five kV-CBCT beam characteristics including photon fluence, average beam energy and photon spectra are generated from Monte Carlo simulations. The Monte Carlo calculated dose profiles are validated by measurements. The fluence of kV-CBCT beams is strongly dependent on the geometry of added filters as well as X and Y beam collimations. The potential errors of determining the beam output of a kV-CBCT beam in Solid Water and PMMA phantoms may approach 8% and 20%, respectively, for use in a conventional treatment planning system, whereas using the Plastic Water low-energy range (PW-LR) phantom results in errors within 2%. The Monte Carlo simulation is essential in providing the parameters of an x-ray beam which are needed for the commissioning of a kV-CBCT beam in a radiotherapy treatment planning system. The PW-LR phantom is a suitable liquid water substitute in the beam output determination resulting from a kV-CBCT acquisition.
Export citation and abstract BibTeX RIS
General scientific summary. Image-guided radiation therapy (IGRT) has dramatically improved the accuracy of radiotherapy and has emerged as the new paradigm in radiotherapy. The additional radiation exposure resulting from the repeated x-ray imaging procedures during the course of radiation treatment may entail a biological risk to patients. There is growing interest to determine and to manage the additional x-ray image dose to radiotherapy patients. In order to include the additional radiation dose resulting from imaging guidance procedures in the management of the total radiation dose to a patient's treatment targets and radiosensitive organs, an x-ray source used in the imaging guidance has to be configured and commissioned in a radiotherapy treatment planning system. Commissioning an x-ray source requires x-ray parameters including the output of the beam. This study is to provide a method to obtain beam parameters and to determine the beam output of an x-ray source.