Abstract
Intrafraction motion during intensity‐modulated radiation therapy can cause differences between the planned and delivered patient dose. The magnitude of these differences is dependent on a number of variables, including the treatment modality. This study was designed to compare the relative susceptibility of plans generated with three different treatment modalities to intrafraction motion. The dosimetric effects of motion were calculated using computational algorithms for seven lung tumor patients. Three delivery techniques — MLC‐based step‐and‐shoot (SNS), beam attenuating compensators, and helical tomotherapy (HT) — were investigated. In total 840 motion‐encoded dose‐volume histograms (DVHs) were calculated for various combinations of CTV margins and sinusoidal CTV motion including CTV offsets. DVH‐based metrics (e.g., D95% and D05%) were used to score plan degradations. For all three modalities, dosimetric degradations were typically smaller than 3% if the CTV displacement was smaller than the CTV margin. For larger displacements, technique and direction‐specific sensitivities existed. While the HT plans show similar D95% degradations for motion in the SI and AP directions, SNS and compensator plans showed larger D95% degradations for motion in the SI direction than for motion in the AP direction. When averaged over all motion/margin combinations, compensator plans resulted in 0.9% and 0.6% smaller D95% reductions compared to SNS and HT plans, respectively. These differences were statistically significant. No statistically significant differences in D95% degradations were found between SNS and HT for data averaged over all margin and motion track combinations. For CTV motion that is larger than the CTV margin, the dosimetric impact on the CTV varies with treatment technique and the motion direction. For the cases presented here, the effect of motion on CTV dosimetry was statistically smaller for compensator deliveries than SNS and HT, likely due to the absence of the interplay effect which is present for the more dynamic treatment deliveries. The differences between modalities were, however, small and might not be clinically significant. As expected, margins that envelop the CTV motion provide dosimetric protection against motion for all three modalities.PACS numbers: 87.53.Jw, 87.55.dk, 87.55.de
Highlights
122 Waghorn et al.: Multimodality intensity-modulated radiation therapy (IMRT) motion the dosimetric impact of motion among different treatment techniques.[1,2,3] Often a choice of treatment techniques exists, so it is of practical interest to explore the relative susceptibilities of different treatment techniques to intrafraction motion
For all three delivery techniques, it can be observed that if the CTV moves within the margins (A-M ≤ 0 mm), D95% degradations are typically less than 3%
Dosimetric degradations larger than about 3% were only observed if the CTV displacement due to sinusoidal motion was larger than the CTV margin
Summary
122 Waghorn et al.: Multimodality IMRT motion the dosimetric impact of motion among different treatment techniques.[1,2,3] Often a choice of treatment techniques exists, so it is of practical interest to explore the relative susceptibilities of different treatment techniques to intrafraction motion. The dosimetric penumbra itself can be a function of the delivery technique and this can cause the effect of dose blurring to depend indirectly on the delivery technique. A second effect is caused by the interplay of a moving target with the treatment dynamics. This effect causes a variation of the delivered dose around the expected dose in individual fractions, and the size of this variation depends on the treatment technique.[4] the variation from the expected value after the delivery of multiple fractions is characterized by a Gaussian distribution whose width is inversely proportional to the square root of the number of fractions.[5]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
