Abstract
To determine delivered dose to the spinal cord, a technique has been developed to propagate manual contours from kilovoltage computed-tomography (kVCT) scans for treatment planning to megavoltage computed-tomography (MVCT) guidance scans. The technique uses the Elastix software to perform intensity-based deformable image registration of each kVCT scan to the associated MVCT scans. The registration transform is then applied to contours of the spinal cord drawn manually on the kVCT scan, to obtain contour positions on the MVCT scans. Different registration strategies have been investigated, with performance evaluated by comparing the resulting auto-contours with manual contours, drawn by oncologists. The comparison metrics include the conformity index (CI), and the distance between centres (DBC). With optimised registration, auto-contours generally agree well with manual contours. Considering all 30 MVCT scans for each of three patients, the median CI is , and the median DBC is () mm. An intra-observer comparison for the same scans gives a median CI of and a DBC of () mm. Good levels of conformity are also obtained when auto-contours are compared with manual contours from one observer for a single MVCT scan for each of 30 patients, and when they are compared with manual contours from six observers for two MVCT scans for each of three patients. Using the auto-contours to estimate organ position at treatment time, a preliminary study of 33 patients who underwent radiotherapy for head-and-neck cancers indicates good agreement between planned and delivered dose to the spinal cord.
Highlights
Introduction pte an usPatients undergoing radical radiotherapy for head-and-neck cancers (HNC) frequently experience weight loss during the course of treatment [1]
Changes in patient anatomy over a course of treatment may lead to differences between planned dose and delivered dose [8]
We have calculated planned and delivered doses from kilovoltage computed-tomography (kVCT) and megavoltage computed-tomography (MVCT) scans, using our own software, CheckTomo [17], which takes into account couch shifts between an MVCT scan and treatment delivery
Summary
Introduction pte an usPatients undergoing radical radiotherapy for head-and-neck cancers (HNC) frequently experience weight loss during the course of treatment [1]. Cumulative radiation doses to these structures can differ from those expected from the initial planning process [3]. Understanding these differences, and developing strategies to manage the problems that can ensue, are objectives of adaptive radiotherapy, which is the subject of much current research [4]. The VoxTox research programme aims to investigate differences between planned and delivered dose to millimetre-scale volume elements (voxels) of the organs at risk, and to correlate delivered dose with toxicity. Changes in patient anatomy over a course of treatment may lead to differences between planned dose and delivered dose [8]. If the delivered dose is lower than planned, there is potential for dose escalation to the tumour
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