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ABSTRACT: Background and purpose
During radiotherapy, prostate motion changes over time. Quantifying and accounting for this motion is essential. This study aimed to assess intra-fraction prostate motion and derive duration-dependent planning margins for two treatment techniques.Material and methods
A four-dimension (4D) transperineal ultrasound Clarity® system was used to track prostate motion. We analysed 1913 fractions from 60 patients undergoing volumetric-modulated arc therapy (VMAT) to the prostate. The mean VMAT treatment duration was 3.4?min. Extended monitoring was conducted weekly to simulate motion during intensity-modulated radiation therapy (IMRT) treatment (an additional seven minutes). A motion-time trend analysis was conducted and the mean intra-fraction motion between VMAT and IMRT treatments compared. Duration-dependent margins were calculated and anisotropic margins for VMAT and IMRT treatments were derived.Results
There were statistically significant differences in the mean intra-fraction motion between VMAT and the simulated IMRT duration in the inferior (0.1?mm versus 0.3?mm) and posterior (-0.2 versus -0.4?mm) directions respectively (p???0.01). An intra-fraction motion trend inferiorly and posteriorly was observed. The recommended minimum anisotropic margins are 1.7?mm/2.7?mm (superior/inferior); 0.8?mm (left/right), 1.7?mm/2.9?mm (anterior/posterior) for VMAT treatments and 2.9?mm/4.3?mm (superior/inferior), 1.5?mm (left/right), 2.8?mm/4.8?mm (anterior/posterior) for IMRT treatments. Smaller anisotropic margins were required for VMAT compared to IMRT (differences ranging from 1.2 to 1.6?mm superiorly/inferiorly, 0.7?mm laterally and 1.1-1.9?mm anteriorly/posteriorly).Conclusions
VMAT treatment is preferred over IMRT as prostate motion increases with time. Larger margins should be employed in the inferior and posterior directions for both treatment durations. Duration-dependent margins should be applied in the presence of prolonged imaging and verification time.
SUBMITTER: Pang EPP
PROVIDER: S-EPMC7807728 | biostudies-literature | 2018 Jan
REPOSITORIES: biostudies-literature
Physics and imaging in radiation oncology 20180101
<h4>Background and purpose</h4>During radiotherapy, prostate motion changes over time. Quantifying and accounting for this motion is essential. This study aimed to assess intra-fraction prostate motion and derive duration-dependent planning margins for two treatment techniques.<h4>Material and methods</h4>A four-dimension (4D) transperineal ultrasound Clarity® system was used to track prostate motion. We analysed 1913 fractions from 60 patients undergoing volumetric-modulated arc therapy (VMAT) ...[more]