G J Price et al 2009 Phys. Med. Biol. 54 6515 doi:10.1088/0031-9155/54/21/005
G J Price1,5, P J Sharrock1, T E Marchant1, J M Parkhurst1, D Burton2, P Jain3, P Price4 and C J Moore1
Show affiliationsPatient motion is an important factor affecting the quality of external beam radiotherapy in breast patients. We analyse the motion of a dense set of surface points on breast patients throughout their treatment schedule to assess the magnitude and stability of motion, in particular, with respect to breast volume. We use an optical sensor to measure the surface motion of 13 breast cancer patients. Patients were divided into two cohorts dependent upon breast volume. Measurements were made during radiotherapy treatment beam delivery for an average of 12 fractions per patient (total 158 datasets). The motion of each surface point is parameterized in terms of its period, amplitude and relative phase. Inter-comparison of the motion parameters across treatment schedules and between patients is made through the creation of corresponding regions on the breast surfaces. The motion period is spatially uniform and is similar in both patient groups (mean 4 s), with the small volume cohort exhibiting greater inter-fraction period variability. The mean motion amplitude is also similar in both groups with a range between 2 mm and 4 mm and an inter-fraction variability generally less than 1 mm. There is a phase lag of up to 0.4 s across the breast, led by the sternum. Breast patient motion is reasonably stable between and during treatment fractions, with the large volume cohort exhibiting greater repeatability than the small volume one.
General scientific summary. The use of image guidance to monitor the position and motion of patients during external beam radiotherapy is fast becoming a part of clinical routine. In this paper we use an optical surface measurement system installed above a treatment linear accelerator to observe patients undergoing breast radiotherapy. The aim is to assess patient motion and determine if it is predictable, uniform and stable across the treatment site. Previously such measurements have often been restricted to isolated surface markers; here we simultaneously observe the motion of the entire treatment site. We calculate the periodicity and amplitude of the observed surface motion and also its relative phase, or how local regions of the surface move in relation to each other. As well as motion amplitudes and periods in agreement with previous studies, we report that in respiratory motion the patient's sternum leads the breast body by up to 1/10 of a breathing cycle.
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Issue 21 (7 November 2009)
Received 3 July 2009, in final form 21 September 2009
Published 14 October 2009
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