ESTRO 2022 - Abstract Book

S396

Abstract book

ESTRO 2022

RayStation10B (RaySearch Laboratories, Sweden) (RS = RSpred-RSmim) and (3) a hybrid combination of both (HYB = IHpred- RSmim). Materials and Methods Our database consisted of 60 bilateral head and neck cancer (HNC) patients planned with robust intensity-modulated proton therapy (IMPT). Prediction models (RSpred and IHpred) used the same training (50), validation (5), and test (5) data sets. Both prediction models were based on U-Net architecture. Our IHmim used isodose contours generated from the predicted doses and minimum and maximum optimization objectives to replicate the predicted dose distribution in the planning-CT. RayStation mimicking strategy, RSmim, was an optimization method mixing voxel-wise optimization and composite loss function with weighted dose-volume objectives. For the 5 test patients, nominal and worst-case values for target coverage (D98% > 95%Prescription) and OAR clinical goals were reported from robustness evaluations of the automatically generated plans (IH, RS, HYB) and compared to the values from the clinical plan. Results Figure 1. shows the target coverage differences with respect to reference in two clinical target volumes (CTVs) with different prescriptions. For the three RS, HYB and IH automatic planning strategies, target coverage in low-dose and high- dose CTVs was replicated within [-0.65, 0.95] Gy and [-1.78, 0.88] Gy difference with respect to planning for nominal and worst-case, respectively. Higher differences were observed for the OARs, sparing of the spinal canal and the parotid differed between RS and IH while HYB found a compromise with median values closer to the clinical plan (Figure 2). Superior robustness level (i.e higher worst-case values), in low-dose target coverage was observed for HYB with respect to RS and IH.

Conclusion RSM, HYB and IH automatically generated plans obtained satisfactory mimicked nominal doses with results acceptably similar to the clinical reference dose. However, this study showed the importance of analysing the key step of robust dose mimicking in automatic planning to assess OAR toxicity and robustness of the chosen strategy.

OC-0452 The role of RBE and LET in treatment efficacy of carbon ion radiotherapy for sacral chordoma

S. molinelli 1 , G. Magro 2 , A. Mairani 3 , A. Allajbej 4 , A. Chalaszczyk 5 , A. Mirandola 2 , M. Ciocca 2 , M.R. Fiore 5 , E. Orlandi 5

1 Fondazione CNAO, Medical physics, pavia, Italy; 2 Fondazione CNAO, Medical Physics, pavia, Italy; 3 Heidelberg Ion Beam Therapy Center , Radiation Oncology, Heidelberg, Germany; 4 Istituto Nazionale dei Tumori, Radiation Oncology, Milano, Italy; 5 Fondazione CNAO, Clinical Department, pavia, Italy