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(Monday, 7/15/2019) 1:15 PM - 1:45 PM
Room: Exhibit Hall | Forum 3
Purpose: To investigate a new metric, the prostate walk, to characterize and classify intra-treatment motion during stereotactic body radiotherapy (SBRT) and evaluate its correlation to pre-treatment rectal and bladder volumes.
Methods: Intra-treatment motion was evaluated using simultaneous MV/kV imaging for 43 prostate cancer patients undergoing hypofractionated SBRT (205 treatment sessions). Bladder, rectum, and rectal gas volumes were determined from each patient’s planning scan as well as pre-treatment cone-beam CTs. MV/kV pairs were obtained at ~15 second intervals throughout two-arc VMAT and a trace was generated by registering gold seed fiducial positions on each pair to a planning reference. Position corrections applied during treatment delivery were retrospectively removed to generate the “natural motion” trace. The prostate walk in each direction was calculated as the cumulative motion over the treatment session after applying a Savitsky-Golay filter to minimize measurement uncertainty and/or clinically insignificant motion. Walk was compared to the average positional deviation from the daily reference position and the pre-treatment rectal, bladder and rectal gas volumes.
Results: Linear correlation coefficients between prostate walk and average positional deviations were moderate at 0.27, 0.36, 0.35 in the S/I, A/P, and 3D directions, respectively. Large prostate walks were not always associated with large average deviations. Statistically significant correlations were observed in the R/L (p=0.01) and A/P (p < 0.005) directions between walk and pre-treatment rectal volume but not bladder volume. Rectal gas volume was correlated with walk in the R/L direction only (p=0.011).
Conclusion: Pre-treatment rectal volumes correlated with prostate walk in the R/L and A/P directions while rectal gas volume correlated with prostate walk in the R/L direction only. No correlation between walk and pre-treatment bladder volume was observed. Additional study is required to determine if walk can serve as a robust metric to identify different types of intra-treatment motion and predict dosimetric impact.
Funding Support, Disclosures, and Conflict of Interest: MSKCC is the recipient of research funding from Varian Medical Systems and Philips Healthcare.
Keywords
Prostate Therapy, Image-guided Therapy, Treatment Verification
Taxonomy
TH- RT Interfraction motion management : General (most aspects)
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