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. 2023 Apr;24(4):e13861.
doi: 10.1002/acm2.13861. Epub 2022 Dec 7.

Reducing PTV margins for prostate SBRT with motion compensation and gating techniques

Lee Goddard  1   2 , Kyoungkeun Jeong  1   2 , Justin Tang  1   2 , Madhur Garg  1   2 , Wolfgang A Tomé  1   2
Affiliations

Reducing PTV margins for prostate SBRT with motion compensation and gating techniques

Lee Goddard et al. J Appl Clin Med Phys. 2023 Apr.

Abstract

The purpose of this study is to investigate the dosimetric accuracy of prostate SBRT when motion is considered. To account for target movement, motion compensation and gating techniques were investigated with PTV margins reduced to 2 mm. To allow for dosimetric measurements a Delta4 phantom, Gafchromic film, and Hexamotion motion platform were utilized. Four motion files were utilized that represent a range of motions. Analysis of measured prostate motions for fifteen patients was performed to ensure detected motions were similar to those previously reported and motion files utilized were suitable. Five patient plans were utilized to allow for the effects of MLC and target motion interplay to be investigated. For both motion compensation and gating techniques, plans were delivered to the stationary phantom and for each of four motion types with/without compensation/gating enabled. Using a 3%, 2 mm and 80% threshold gamma criteria, film measurements had an average pass rate of 80.5% for uncorrected deliveries versus 96.0% for motion compensated deliveries. For gated techniques average pass rates increased from 89.9% for uncorrected to 94.8% with gating enabled. Measurements with the Delta4 arrays were analyzed with a 3%, 2 mm and 10% threshold dose. An average pass rate of 83.8% was measured for uncorrected motions versus 94.8% with motion compensation. For the gated technique an average pass rate of 87.2% was found for uncorrected motions versus 96.9% with gating enabled. These results show that very high gamma pass rates are achievable when motion compensation or gating techniques are applied. When target motion is not accounted for shifts up to 5 mm in planned versus delivered isodose distributions were found. However, when motion compensation, or gated techniques were applied, much smaller differences between planned and delivered isodose distributions were found. With these techniques dose delivery accuracy is greatly improved, allowing for PTV margins to be reduced.

Keywords: Prostate SBRT intrafraction motion.

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Conflict of interest statement

Montefiore Medical Center has ongoing collaboration agreements with Accuray Inc. Dr's Garg and Tomé have previously received research funding from Accuray Inc. and Varian Medical Systems not related to this work.

Figures

FIGURE 1
FIGURE 1
Prostate motion files utilized for phantom motion
FIGURE 2
FIGURE 2
Dose distributions and DVH for one example Truebeam plan showing the axial (a), coronal (b), and sagittal (c) film measurement planes
See this image and copyright information in PMC

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