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Quantification of Dose Uncertainties in DIR-Based Accumulated Dose Estimation On Prostate Passive-Scattering Proton Therapy

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Y Abe

Y Abe1,2*, N Kadoya2 , K Arai1,2 , Y Takayama2 , T Kato1 , K Kimura1 , T Ono1 , T Nakamura1 , H Wada1 , Y Kikuchi1 , K Jingu2 , (1) Southern Tohoku Proton Therapy Center, Koriyama, Fukushima, (2) Tohoku University Graduate School of Medicine, Sendai


TU-C3-GePD-J(B)-1 (Tuesday, August 1, 2017) 10:30 AM - 11:00 AM Room: Joint Imaging-Therapy ePoster Lounge - B

Purpose: Deformable image registration (DIR) plays an important role in dose accumulation, but the impact of uncertainties associated with DIR algorithms in proton therapy is not clear. The purpose of this study was to quantify the effect of DIR uncertainty on prostate passive-scattering proton therapy (PSPT) dose accumulation.

Methods: Ten patients with an intermediate risk for prostate cancer who were treated by PSPT (PTV D95=78GyE) were studied. Dose distributions from all verification CT images (acquired every two weeks) were warped and accumulated in the planning CT geometry with DIR. The dose-volume histogram (DVH) parameters Dmean, V40 and V70 for rectum and bladder were calculated. We used two different commercially available DIR software packages: Velocity AI (Varian Medical Systems) and RayStation (RaySearch Laboratories). The dice similarity coefficient (DSC) and surface distance (based on Hausdorff distance) were calculated for quantitative DIR validation. The relationship between the dose parameter and DIR uncertainty was investigated.

Results: The DSC was on average increased by 0.14 using RayStation compared to Velocity. The surface distance on average decreased 6.4 mm RayStation compared to Velocity. For the Dmean, V40 and V70 to the rectum, the average dose difference between Raystation and Velocity were 3.9 GyE (9.6 GyE maximum), 5.5 % (14.4 % maximum) and 3.2 % (8.1 % maximum). For the bladder, these were 5.2 GyE (15.6 GyE maximum), 5.8 % (22.8 % maximum) and 5.4 % (19.6 % maximum).

Conclusion: The maximum differences in V40 between RayStation and Velocity were 14.4 % and 22.8 % for rectum and bladder, respectively when average DSC and surface distance differences more than were 0.14 and 6.2 mm, respectively. Our results suggest that DIR uncertainties might have a significant impact on prostate PSPT dose accumulation.

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