Abstract
PurposeThe aim of this study is to investigate the performance and limitations of a real-time transit electronic portal imaging device (EPID) dosimetry system for error detection during dynamic intensity modulated radiation therapy (IMRT) treatment delivery. Sites studied are prostate, head and neck (HN), and rectal cancer treatments.MethodsThe system compares measured cumulative transit EPID image frames with predicted cumulative image frames in real-time during treatment using a χ comparison with 4 %, 4 mm criteria. The treatment site-specific thresholds (prostate, HN and rectum IMRT) were determined using initial data collected from 137 patients (274 measured treatment fractions) and a statistical process control methodology. These thresholds were then applied to data from 15 selected patients including 5 prostate, 5 HN, and 5 rectum IMRT treatments for system evaluation and classification of error sources.ResultsClinical demonstration of real-time transit EPID dosimetry in IMRT was presented. For error simulation, the system could detect gross errors (i.e. wrong patient, wrong plan, wrong gantry angle) immediately after EPID stabilisation; 2 seconds after the start of treatment. The average rate of error detection was 7.0 % (prostate = 5.6 %, HN= 8.7 % and rectum = 6.7 %). The detected errors were classified as either clinical in origin (e.g. patient anatomical changes), or non-clinical in origin (e.g. detection system errors). Classified errors were 3.2 % clinical and 3.9 % non-clinical.ConclusionAn EPID-based real-time error detection method for treatment verification during dynamic IMRT has been developed and tested for its performance and limitations. The system is able to detect gross errors in real-time, however improvement in system robustness is required to reduce the non-clinical sources of error detection.
Highlights
In vivo dosimetry using an electronic portal imaging device (EPID) has been investigated and implemented clinically to improve the quality of treatment and safety during external beam radiotherapy (EBRT) [1,2,3]. This has been shown to be of particular benefit to modern dynamic delivery techniques such as intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) as well as for hypo-fractionated
The Netherlands Cancer Institute have fully replaced pre-treatment verification with 3D EPID-based in vivo dosimetry
We have developed the first system where transit EPID images frames are acquired and compared to predicted image frames in real-time during the delivery of dynamic EBRT [13, 14]
Summary
In vivo dosimetry using an electronic portal imaging device (EPID) has been investigated and implemented clinically to improve the quality of treatment and safety during external beam radiotherapy (EBRT) [1,2,3]. This has been shown to be of particular benefit to modern dynamic delivery techniques such as intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) as well as for hypo-fractionated. It has been shown that, using automation, this can potentially be less time consuming than traditional phantom-based pre-treatment QA
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