ESTRO 2020 Abstract book

S817 ESTRO 2020

The results of our method were analysed in the light of results obtained by using the commercial method implemented in Varian TPS. Material and Methods Study was carried out on data of one patient with prostate- restricted cancer. The workflow of the procedure developed focused on three executive elements: (1) in-house script for movement simulation of the CTV, (2) the Velocity software for the calculations of the deformation matrixes and (3) the Eclipse treatment planning system for the dose re- calculations and analysis.

The contours from original plan are used by in-house script to create a set of artificial CT images (aCT). In the next step, the in-house script simulates all possible positions of the CTV and generates the group of aCT sets that differ in the position of the CTV. All of the aCT sets are uploaded to the Velocity software where they are used to generate the deformation matrixes and then to generate deformed CT sets (dCT). The dCT sets are moved to the Eclipse software where they are linked with the original plan geometry. For each dCT set, the dose is re-calculated. There are two possible scenarios of the dose recalculation: (1) first when the re-calculation is done for the original geometry - simulates image guidance based on the bone anatomy, (2) second when the isocentre from original plan geometry is moved according to the movement of the CTV. The dose distributions for both scenarios were analysed on DVHs in the light of the results obtained from Varian method. Results Initial results are promising and suggest that soft tissue deformations significantly affect the simulations of dose distribution. They shall allow it to be noted respectively: (1) In general - the DVHs from our methods are more informative than the DVH from method implemented in Eclipse TPS. (2) For the 1 st method: (a) the highest impact on dose uncertainty has boundary positions of CTV in relation to CTV-PTV margin, (b) relocation of CTV causes changes of OARs volumes that receive high doses. (2) For the 2 nd method: (a) the highest impact on dose uncertainty has relation to CTV position to the whole body, (b) relocation of iso causes changes in the general dose distribution (visible for OARs volume receiving low and intermediate doses).

Conclusion The novel FAST segmentation algorithm allows for efficient generation of clinically deliverable treatment plans for robotic radiotherapy. The total runtime can be further reduced by using parallel segment dose calculations. PO-1442 New methods of robust plan analysis incorporating the deformation of soft tissues T. Piotrowski 1 , A. Ryczkowski 1 1 Greater Poland Cancer Centre, Medical Physics, Poznan, Poland Purpose or Objective The aim of this study is to develop an effective tool for robust plan analysis, which include the effects of the soft tissue deformations on the simulated dose distributions.