ESTRO 2022 - Abstract Book

S1286

Abstract book

ESTRO 2022

Conclusion Establishing a proper robust optimization and evaluation workflow is essential to realize the potential of proton therapy. Optimization using SSJP yielded significant OAR sparing in all recorded metrics with a target robustness within our clinical objectives, provided that a more statistically sound robustness evaluation method was used. This highlights the importance of using both advanced optimization and evaluation tools when we aim at ensuring a quantified level of robustness.

PO-1507 Dose comparison of clinical robust intensity modulated proton therapy plans for testicular seminoma

H.S. Rønde 1 , C. Kronborg 2 , M. Høyer 2 , A.B. Als 3 , M. Agerbæk 3 , J. Lauritsen 4 , P.M. Petersen 4 , L. Dysager 5 , J.F. Kallehauge 2

1 Aarhus Universitets Hospital, Danish Center for Particle Therapy, Århus N, Denmark; 2 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus N, Denmark; 3 Aarhus University Hospital, Department of Oncology, Aarhus N, Denmark; 4 Rigshospitalet, Department of Oncology, Copenhagen, Denmark; 5 Odense University Hospital, Department of Oncology, Odense, Denmark Purpose or Objective Seminoma patients with indication for radiotherapy have traditionally been treated with photons – opposing IMRT fields or VMAT. Due to the extent of the target there is a substantial dose bath to surrounding organs at risk (OAR). The patients are young with excellent prognosis so reducing the risk of secondary cancer is of utmost importance. A comparative dose planning study was done to determine if robust optimized intensity modulated proton therapy (IMPT) could reduce dose to OAR with the aim of clinical implementation of IMPT. Materials and Methods Six patients with seminoma, treated with photons ("dog-leg" 3 field IMRT, n=4 or 2 full arc VMAT, n=2) were used for comparative dose planning. CTV-E (Elective) extended from Th11/12 to top of acetabulum on the ipsilateral side. Prescribed dose ranged from 20–25 Gy RBE to CTV-E. Pathological lymph nodes were subsequently boosted to 10 Gy RBE (Table 1). The clinical photon treatment plan was used as comparator in the photon/proton comparison. Proton plans were made using 5 field-robust (5 mm setup error; 3.5% range uncertainty) IMPT planning (Multi field optimization, Eclipse v13.7) for the CTV-E (3 posterior supplemented by 2 anterior fields at the level of iliaca arteries). Three posterior robust IMPT fields were used for the paraaortic boost. Boost in the pelvis area had an individual field arrangement. Plan where recalculated to check for changes in bowel gas. Dose to OARs (body outline, bowel bag, bladder, spinal cord, duodenum, kidneys, pancreas, stomach) where compared for photon vs. proton plans. The risk of secondary cancer was calculated by the model described in Schneider et al., 2011 (Theor Biol Med Model 2011 Jul 26;8:27). Wilcoxon's signed rank test was used for comparison. A p-value<0.05 was considered statistically significant.