ESTRO 2023 - Abstract Book

S1718

Digital Posters

ESTRO 2023

Conclusion PBS proton arc therapy has the potential to improve focal boosting to the intraprostatic GTV while reducing the dose to the urethra and rectum and could thereby enhance treatment outcome for selected PCa patients.

PO-1956 Normal Tissue Control Probability evaluation of photon versus proton therapy for left breast cancer

C. Giandini 1,2 , A. Cavallo 3 , A. Bazani 4 , S. Russo 4 , R.R. Colciago 5,6 , L.R. Eliana 5 , T. Rancati 7 , E. Pignoli 3 , T. Giandini 3 , A. Barcellini 8 , M. Ciocca 4 , L. Lozza 5 , R. Valdagni 5,2,7 , B.A. Jereczek-Fossa 2,9 , E. Orlandi 8 , M.C. De Santis 5 1 Fondazione IRCCS Istituto Nazionale Tumori, Radiation Oncology , Milano, Italy; 2 University of Milan, Oncology and Hemato-Oncology, Milano, Italy; 3 Fondazione IRCCS Istituto Nazionale Tumori, Medical Physics, Milano, Italy; 4 CNAO National Center for Oncological Hadrontherapy, Medical Physics, Pavia, Italy; 5 Fondazione IRCCS Istituto Nazionale Tumori, Radiation Oncology, Milano, Italy; 6 University of Milan-Bicocca, School of Medicine, Milano, Italy; 7 Fondazione IRCCS Istituto Nazionale Tumori, Prostate Cancer Program, Milano, Italy; 8 CNAO National Center for Oncological Hadrontherapy, Radiation Oncology , Pavia, Italy; 9 European Institute of Oncology IRCCS, Radiation Oncology, Milano, Italy Purpose or Objective To evaluate differences in dosimetry and to apply and compare Normal Tissue Control Probability (NTCP) models in rival photon Volumetric Modulated Arc Therapy (VMAT) and Pencil-Beam Scanning Intensity Modulated Proton Therapy (PBS IMPT) plans for left-sided breast cancer (LSBC) patients (pts). Materials and Methods A dosimetric analysis on VMAT and IMPT plans was performed. Both plans were generated on the simulation CT scans, acquired in Deep Inspiration Breath Hold (DIBH). Relevant dose metrics for organs at risk (OARs) and targets were retrieved from dose-volume histograms (DVHs). Target coverage was evaluated in terms of the volume receiving 95% of the prescription dose (V95 %). VMAT plans were optimized on PTV, elaborated on Eclipse treatment planning system (TPS) and calculated using the Analytical Anisotropic Algorithm. IMPT plans were optimized on CTV with Raystation TPS and calculated using Monte Carlo algorithm, applying robustness settings to the target to account for set-up and range uncertainties (5 mm isotropic and 3-5% range, respectively). Relative Biological Effectiveness (RBE) was assumed to be 1.1. Ten NTCP models for selected toxicities were then applied to both rival plans for all pts. Paired, 2-tailed Wilcoxon signed rank test was employed to evaluate median differences in OARs dosimetry and NTCP values in VMAT versus IMPT plans ( ∆ NTCP PH-PT). Results Twenty-two CT scans of LSBC pts were performed from April 2022 to July 2022. Target volume consisted of the breast gland in 13 patients (59%) and the chest wall, with or without reconstruction, in 9 patients (41%). Loco-regional irradiation was delivered in 9 patients (41%). Prescribed dose range was 40.05-42.4 Gy/15-16 fractions . Tumour bed boost was delivered in 7 patients, specifically a simultaneous boost (up to 48 Gy[RBE]) in 5 patients (71 %) and a sequential boost in 2 patients