Program Information
Dose Reconstruction for Prostate SBRT by Use of Cone-Beam CT and a Log File During FFF-VMAT Delivery
T Imae*, A Haga , Y Watanabe , S Takenaka , K Nawa , W Takahashi , H Yamashita , Y Takeuchi , K Yano , K Nakagawa , O Abe , The University of Tokyo Hospital, Tokyo, Japan
Presentations
SU-I-GPD-J-14 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: Stereotactic body radiotherapy (SBRT) with volumetric modulated arc therapy (VMAT) is an effective strategy for prostate cancer. Flattening-filter-free (FFF) beam can quickly deliver with very high dose rate. The purpose of this study was to reconstruct in-treatment dose distribution for prostate SBRT by use of cone-beam CT (CBCT) and a log file during FFF-VMAT delivery.
Methods: Actual dose distribution for three SBRT prostate patients was reconstructed. A D95 dose of 36.25 Gy in five fractions was prescribed to each planning target volume (PTV) on each treatment planning CT (pCT). The patients were treated by FFF-VMAT while acquiring projection images for in-treatment CBCT (in-CBCT) imaging and a log file. Deformed pCT (dCT) was obtained from the in-CBCT using a hybrid deformable image registration (DIR) algorithm provided by a commercial treatment planning system, RayStation (RaySearch Laboratories). Dose distributions on the dCT were calculated in Pinnacle3 v9.10 (Philips), by converting the log file data to Pinnacle data format using in-house software. Dose warping was carried out by referring to deformation vector fields calculated from pCT (as reference images) and the dCT (as target images). The reconstructed dose distribution was compared with that of the original plan.
Results: The dose differences between the reconstructed and the original distributions at the isocenter and D95% of each PTV agreed within 2.0%. The difference in organs at risk (OARs) varied significantly depending on the shape, the volume and the position of the OARs. The dose differences in the OAR regions were relatively large compared to that of PTV presumably because the OARs were more deformed than the PTV.
Conclusion: The present method successfully reconstructed dose distributions using in-CBCT and a log file during FFF-VMAT treatment. The proposed method may provide the actual dose distribution for a FFF-VMAT SBRT delivery to prostate cancer.
Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by a Grant-in-Aid from JSPS (Japan Society for the Promotion of Science) KAKENHI JP Scientific Research (C) Grant Number 15K08692.
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