ESTRO 2021 Abstract Book

S1331

ESTRO 2021

PO-1610 Proton and carbon range verification for anatomy-like objects with the use of animal tissue samples J. Gora 1 , M. Bolsa-Ferruz 1 , S. Vatnitsky 2 , G. Kragl 3 , A. Carlino 2 , A. Elia 2 , M. Stock 2 1 MedAustron Ion Therapy Center, Medical Department, Wiener Neustadt, Austria; 2 MedAustron Ion Therapy Center, Medical Department , Wiener Neustadt, Austria; 3 Ordensklinikum Linz GmbH, Barmherzige Schwestern, Strahlentherapie, Linz, Austria Purpose or Objective Proton and carbon dose calculation in the treatment planning system(TPS) is based on the relationship between CT numbers(HU) and the relative stopping powers(RSP). Previously*), validation of RSP for various animal tissues in the proton field has been performed. As a next step of HU-to-RSP conversion validation, the irradiation of a box-like plan in presence of different tissue interfaces was performed and dose calculation accuracy with proton Monte Carlo (MCv4.2) and carbon pencil beam (PBv3.0) was evaluated. Materials and Methods Three different tissue samples (fig.1), were placed in the PMMA phantom, scanned in the CT scanner, acquired images were imported into the RayStation v8BSP1 (RaySearch Laboratories) and 3d dose distribution for 4x4x4cm3 targets were generated for protons and carbons, with and without range shifter (Rashi). Subsequently, the phantom was attached to the MP3 water phantom, each plan was irradiated and measured with a set of 24 pinpoint chambers (PTW, Freiburg), in multiple positions (1-3mm spacing). The differences between measured and computed ranges were evaluated. Results Independently on the algorithm, particle type and anatomy setup, ranges at R80 were within 1mm(Fig2). Larger deviations were observed in the fragmentation tail for the carbon plans. With the increased anatomy complexity (air/bone/tissue interfaces), especially for carbon Rashi beam, the PB algorithm struggled to model the tail of dose distribution, which was not the case for the proton MC algorithm, or in general for homogeneous anatomy. Conclusion This deficiency of PB algorithm in calculating the dose behind the target (even 8mm) needs to be taken into the account in the treatment planning process.