ESTRO 2023 - Abstract Book

S1800

Digital Posters

ESTRO 2023

Results The electron dose distribution was most impacted by the resolution of the dose calculation grid (p<0.01), where the finest grid (0.15 cm) had higher similarity to the reference (stored) doses (see Figure 2(A)). In contrast, varying the CT calibration curve and the number of histories had a negligible influence on dose calculations. The absolute difference between the reconstructed and reference doses was less than 1 Gy for breast and tumour bed considered at D95%, D2%, and Dmean (Figure 2(A)). Results were comparable in the validation set, with > 90% gamma passing rate. However, differences were observed at the build-up region (within 1cm from the skin) and at tissue interface regions as shown in the DLH (Figure 2(B)).

Conclusion In this cohort, the electron dose distributions could be reconstructed retrospectively with satisfactory accuracy. However, caution is advised when assessing dose close to the skin. Further validation is needed to confirm accuracy outside of the REQUITE dataset. This study will be beneficial for large-scale efforts to recover electron dose distributions and increase the number of complete records for retrospective analysis, even in recent data cohorts.

PO-2026 Comprehensive Plan Quality assessment of FAST-Forward treatments: VMAT and DIBH Technique

M. Fusella 1 , M. Nicoletto 1 , M.C. Schifano 1 , E. Maffi 1 , C. Antonelli 1 , C. Gelmi 1 , L. Corti 1 , A. Testolin 1

1 Policilinico Abano Terme, Department of Radiation Oncology, Abano Terme, Padua, Italy

Purpose or Objective This study present a comprehensive Plan Quality [1] assessment of ultrahypofractionation of adjuvant radiation therapy (RT) following primary surgery in women affected by early breast cancer (EBC) [2], using Volumetric Arc Radiation Therapy (VMAT) and Deep Inspiration Breath Hold (DIBH). To evaluate the treatment plan quality we calculated Dose metrics, Robustness, Plan Complexity metrics and Delivery Time. Materials and Methods A total of 50 consecutive patients were selected to be treated with VMAT DIBH technique. All of them were able to comply with the requirement for DIBH, monitored by Varian Respiratory Gating System. ESTRO guidelines for the clinical target volume (CTV) delineation and FAST-FORWARD protocol for CTV to planning target volume (PTV) margin definition were followed. Total prescribed dose was 26 Gy in five fractions. Before plan approval, for each patient a comparison with tangential static field IMRT (SF) was carried out to assess feasibility and safety of VMAT plan. VMAT arc arrangement consist in two Arcs (6MV - FFF, maximum dose rate: 1400 MU/minute) completely blocked, apart the first and last 30° of rotation, collimators are rotated of ± 10–20°, and the dose distribution was computed with AcurosXB v.13.7. Relevant dose metrics for heart, left anterior descending (LAD) coronary artery, lungs, contra-lateral breast and PTV were analyzed. Plan complexity metrics for VMAT plans were extracted to track reference values for further and future comparison. [3]