ESTRO 2023 - Abstract Book

S381

Sunday 14 May 2023

ESTRO 2023

Conclusion In this cohort of stage I-III NSCLC patients treated with curative intent radiotherapy +/- sequential chemotherapy there is little evidence of any association between comorbidity burden and an increase in treatment duration that could signify treatment interruption. These data suggest that comorbidities do not have a significant impact on radiotherapy interruption.

Mini-Oral: Advanced treatment planning with photons and particles

MO-0475 Late toxicity-associated patient-specific subregions in plan optimization for prostate cancer L. Alborghetti 1 , R. Castriconi 1 , C. Sosa Marrero 2 , A. Tudda 1 , M.G. Ubeira-Gabellini 1 , S. Broggi 1 , J. Pascau 3 , L. Cubero 3 , C. Cozzarini 4 , R. De Crevoisier 2 , T. Rancati 5 , O. Acosta 2 , C. Fiorino 1 1 IRCCS San Raffaele Scientific Institute, Medical Physics, Milano, Italy; 2 CLCC Eugène Marquis, INSERM, LTSI—UMR1099, F 35000, Univ Rennes, Rennes, France; 3 Universidad Carlos III de Madrid, Bioengineering Department, Madrid, Spain; 4 IRCCS San Raffaele Scientific Institute, Radiotherapy, Milano, Italy; 5 Fondazione IRCCS Istituto Nazionale dei Tumori (INT), Progetto Prostata, Milano, Italy Purpose or Objective An association between the dose received by local subregions of bladder/rectum and toxicity in prostate cancer radiotherapy has been recently evidenced by voxel-wise analyses. An exploratory study was performed to assess if a knowledge based (KB) plan prediction model can be further optimized using multi-criteria optimization (MCO), reducing the dose to symptom-related subregions (SRS) without any detriment of the dose distribution in targets and OARs. Materials and Methods Forty-five high-risk prostate cancer patients previously treated in Institute A to 74.2Gy/28fr were selected. Using deformable registration, according to previous studies, contours of SRS were generated in institute B and returned to institute A for planning. Five patients were selected to reasonably represent the different anatomy (i.e. the location of SRS in relation to PTVs). A KB RapidPlan (Varian, Inch.) model was used to obtain clinically suitable plans using VMAT with four complete arcs (KB plan). Then, keeping the same beam ballistic, plans were further optimized using MCO (Trade-Off Exploration, Varian Eclipse v. 16.1) to reduce the dose to the four SRS shown in Fig.1. Three are vesical regions linked to specific late symptoms, namely dysuria (DYS_LAT), hematuria (HEM_LAT) and retention (RET_LAT). The last in the rectum relates to rectal bleeding (SRR). First, a set of clinical goals was established: for low (pelvic nodes), intermediate (seminal vesicles) and high dose (prostate) PTV, the minimum value of V95% was set to 95%. Moreover, objectives for MCO were chosen. Compared to the KB plan: a) dose homogeneity for PTVs should be unchanged; b) DVHs of the whole rectum/bladder and other OARs cannot be worsened; c) mean dose of SRS should decrease as much as possible while respecting the previous criteria. Finally, a database of optimal plans was generated and navigated to find the best compromised plan, giving the same importance to all SRS.

Results DVH variations from KB to KB+MCO plan and differences in dose parameters were evaluated. Mean dose difference ranges between -2,4 and -1,5 Gy for DYS_LAT, -2,1 and -1,2 Gy for HEM_LAT, -4,0 and -1.9 Gy for RET_LAT, -2,3 and -0,5 Gy for SRR. Dose to 1% of the volume (D1%) also decreased in most cases: the ranges were between -1,3 and -0,1 Gy for DYS_LAT, -6,4 and -1,9 Gy for HEM_LAT, -5,4 and -1,7 Gy for RET_LAT, -2,3 and 0,2 Gy for SRR. The better sparing of SRS was clearly visible on DVH; at the same time, PTVs and OARs DVH not only was not worsened, but in some cases even improved (Fig.2).