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Sci‐Fri PM: Radiation Therapy, Planning, Imaging, and Special Techniques ‐ 04: Assessment of intra‐fraction motion during lung SABR VMAT using a custom abdominal compression device
Author(s) -
Hyde Derek,
Robinson Mark,
Araujo Cynthia,
Teke Tony,
Halperin Ross,
Petrik David,
Mou Benjamin,
Mohamed Islam
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4961847
Subject(s) - sabr volatility model , medicine , nuclear medicine , margin (machine learning) , radiation therapy , image guided radiation therapy , radiology , mathematics , computer science , volatility (finance) , stochastic volatility , machine learning , econometrics
Purpose: Lung SABR patients are treated using Volumetrically Modulated Arc Therapy (VMAT), utilizing 2 arcs with Conebeam CT (CBCT) image‐guidance prior to each arc. Intra‐fraction imaging can prolong treatment time (up to 20%), and the aim of this study is to determine if it is necessary. Methods: We utilize an in‐house abdominal compression device to minimize respiratory motion, 4DCT to define the ITV, a 5 mm PTV margin and a 2–3 mm PRV margin. We treated 23 patients with VMAT, fifteen were treated to 48 Gy in 4 fractions, while eight were treated with up to 60 Gy in 8 fractions. Intrafraction motion was assessed by the translational errors recorded for the second CBCT. Results: There was no significant difference (t‐test, p=0.93) in the intra‐fraction motion between the patients treated with 4 and 8 fractions, or between the absolute translations in each direction (ANOVA, p=0.17). All 124 intra‐fraction CBCT images were analysed and 95% remained localized within the 5 mm PTV margin The mean magnitude of the vector displacement was 1.8 mm. Conclusions: For patients localized with an abdominal compression device, the intrafraction CBCT image may not be necessary, if it is only the tumor coverage that is of concern, as the patients are typically well within the 5 mm PTV margin. On the other hand, if there is a structure with a smaller PRV margin, an intrafraction CBCT is recommended to ensure that the dose limit for the organ at risk is not exceeded.