ESTRO 2020 Abstract Book

S818 ESTRO 2020

plans, reoptimized clinical plans and seven out of ten original 10-arc plans. Wilcoxon signed-rank test was used to evaluate differences with the clinical plans, a p-value below 0.05 was considered significant. Results Dose statistics for the high-dose and low-dose PTV are shown in Table 1. V 100% and D 98% were significantly different between clinical and trajectory plans.

Conclusion Non-coplanar trajectory VMAT achieved similar plans compared to the clinical plans. The results indicate a potential patient-specific benefit of using dynamic couch rotations. In the future, the gantry/couch trajectories will be optimized automatically, which is expected to increase the performance of non-coplanar trajectory-based treatment planning. Moreover, treatment delivery efficiency will be evaluated in future studies. PO-1515 A tale of two image-based treatment workflows for prostate HDR: can dosimetry alone tell the story? L. Francis 1 , A. Urdaneta 1 , D. Todor 1 1 VCU Health System, Radiation Oncology, Richmond, USA Purpose or Objective This is a single institution comparative study between two different workflows for HDR prostate brachytherapy. Workflow A, CT-based, and Workflow B, US-based, were each associated with one physician and a different implantation and planning style. While one can imagine multiple perspectives in evaluating differences, this study is aiming to determine if dosimetry parameters alone are capable of completely and accurately describing two vastly different procedures. Material and Methods A total of consecutive 221 delivered patient plans, 74 from Workflow A and 147 from Workflow B, were analyzed. DICOM files containing plans, structures and dose matrices were exported from the treatment planning system (BrachyVision-Varian Medical Sytems, Inc) and analyzed by in-house developed software. In a CT based setting implants had a mean of 18±2.7 needles, while in US-based setting the mean was lower at 14±3.5 needles. In the CT based workflow, patients were implanted using free handed US, then transported under anesthesia to CT and back to the HDR treatment room. In the US based setting, both implantation and planning were done with stepper based acquired images routinely incorporating MRI-US fusions. Patient never moved. All treatments were created using inverse optimization with similar constraints, with physician in workflow A routinely using the graphical tool to ‘adjust’ the optimized plan.

Dose statistics to OARs are summarized in Figure 1. Overall, dose to the kidneys was not significantly different between the techniques. Increased kidney sparing could only be reproduced for two patients using the trajectory technique.