ESTRO 2023 - Abstract Book

S1778

Digital Posters

ESTRO 2023

Conclusion Based on growing experience in the literature, adding a high focal boost to the DIL, identified through a mpMRI, could improve oncological outcomes in localized PCa patients. In this setting, SBRT delivery technique is required to improve tumor control probability while respecting OARs dose constraints. This in-silico planning comparison proved that CK UH-SBRT plus a focal boost to the DIL for localized PCa appears to be feasible. These encouraging dosimetric results need to be confirmed in phase II/III clinical trial such as the upcoming mono- institution phase II “PRO-SPEED” IEO trial. E. Rosa 1 , L. Breschi 2 , B. Fionda 3 , V. Lancellotta 3 , G. Stimato 2 , G. Meffe 2 , P. Cornacchione 3 , L. Tagliaferri 3 , L. Indovina 2 , E. Placidi 2 1 Università Cattolica Del Sacro Cuore Roma, Istituto di Fisica, Rome, Italy; 2 Policlinico Universitario A. Gemelli, UOSD Fisica Medica e Radioprotezione, Fondazione Policlinico Universitario A. Gemelli, IRCCS, Rome, Italy; 3 Policlinico Universitario A. Gemelli, UOC Radioterapia Oncologica, Fondazione Policlinico Universitario A. Gemelli, IRCCS, Rome, Italy Purpose or Objective Interventional radiotherapy (IRT, brachytherapy) is a well established radiotherapy technique that is able to deliver very high doses to tumors sparing the organs at risk (OARs). In particular, skin IRT is an effective alternative to external beam radiotherapy (EBRT). Currently, the algorithm used and certified for IRT dose calculation is the TG43 (a). In the last few years new model-based dose calculation algorithms (MBDCA) have been released (b) but their clinical used is still to be developed. This work investigates three aspects of one of the MBDCA (advanced collapsed cone engine, ACE): first the dose distributions calculated with TG43 and ACE for skin tumors are compared. Secondly, we evaluated the differences between the algorithms regarding the calculation time and the CTV coverage, as a function of number of active dwell positions. The impact of the presence of a water bolus on the CTV coverage was also investigated for both algorithms. Materials and Methods Five treatment plans for high-dose-rate IRT were selected for analysis. All plans were calculated with TG43 formula and recalculated with the ACE algorithm on Oncentra Masterplan v 4.6 (Elekta) treatment planning system (TPS). One of the plans was also calculated with TG43 and ACE with five different bolus thicknesses. In order to evaluate the dose differences between the two algorithms, DVH parameters for each region of interest were compared: for the eye D2cc was computed, whilst for the CTV the D100, D95, D90, D50 were reported. The differences in CTV coverage were evaluated with V100, V95 and V90. The calculation time was also reported for the five treatment plans. Results Table 1 shows the mean dosimetric results for CTV and OAR calculated with algorithms, showing lower values for ACE compared to TG43, even if not statistically significant. A linear dependence was found for both the calculation time for the ACE algorithm as a function of active dwell positions and the CTV coverage (Fig 1). Table 1: ACE mean and st.dev TG43 mean and st.dev V100 (%) 92 ± 4 93 ± 4 V95 (%) 96 ± 2 97 ± 2 V90 (%) 99 ± 1 99 ± 1 D100 (%) 80 ± 8 81 ± 9 D95 (%) 85 ± 10 99 ± 4 D90 (%) 103 ± 3 104 ± 4 PO-2006 Evaluation of a Model Based Dose Calculation Algorithm for skin interventional radiation therapy