ESTRO 2023 - Abstract Book

S1773

Digital Posters

ESTRO 2023

PO-2000 Dosimetric analyses of 3 radiation techniques used in the EORTC 22922/10925 breast cancer trial

O. Kaidar-Person 1 , M. Siman Tov 2 , A. Ostrovski 2 , L. Bogers 3 , A. Petoukhova 3 , S. Hol 4 , M. Mast 5 , H. Struikmans 6 , P. Poortmans 7

1 Sheba Medical Center, Breast Radiation Unit, Ramat Gan, Israel; 2 Sheba Medical Center, Radiation Oncology, Ramat Gan, Israel; 3 Haaglanden Medical Center, Department of Medical Physics, Leidschendam, The Netherlands; 4 Institute Verbeeten, Radiation Oncology, Tilburg, The Netherlands; 5 Haaglanden Medical Center, Research & Development, Leidschendam, The Netherlands; 6 Leiden University Medical Centre, Radiation Oncology, Leiden , The Netherlands; 7 Iridium Netwerk, Radiation Oncology, Wilrijk-Antwerp, Belgium Purpose or Objective EORTC 22922/10925 trial, conducted between 1996 and 2004, aimed to evaluate the effect of internal mammary and medial supraclavicular lymph nodes (IM-MS) irradiation (RT) in stage I-III breast cancer patients. The trial allowed for 3 RT- techniques for IM-MS RT: standard, standard-modified, individualised. In our previous analysis we showed that these techniques varied in disease related outcomes and toxicity. The aim of the current study is to assess and compare the dosimetry of these 3 techniques and to correlate them to clinical outcomes of the trial using the robust treatment planning system available nowadays for dose calculation. Materials and Methods Retrospective dosimetric analysis of anonymized data, therefore patient consent was waived. Ten cases of left breast/chest wall irradiation were randomly chosen for RT planning to a total dose of 50 Gy in 25 fractions. All cases were delineated by an expert radiation oncologist (HS). The treatment planning was done by a dosimetrist (AO) and a physicist (MS) according to the trial protocol and under close guidance of the EORTC 22922/10925 trial coordinators and members of EORTC radiation quality assurance team (RTQA). In short, the standard technique used a fixed set-up combining photon/electron beams to the IM and tangential fields to breast/chest wall; the standard-modified technique permitted minor adaptations for beam settings and the individualised technique allowed more freedom based on individual localisation of the IM. The full RT protocol and the outcomes are published before We present dosimetric parameters to the target volumes and organs at risk (OAR), mostly in % of the prescribed dose. Results Table 1 summarizes dosimetric parameters of 3 left breast cancer cases out of 10 that were planned according to the 3 RT techniques. Each colour represents one patient case. Target dose coverage differs between techniques for a single case and between patients. The dose to OARs varies per case and according to each technique. Mean heart dose was significantly higher in the standard and modified techniques (15-19 Gy) compared to individualised technique (6.5-13.3Gy), while the dose to the left anterior descending artery (LAD) was higher in the individualised technique. The differences in Dmax were up to 70% per case. Overall, the differences between the standard and modified standard techniques are relatively minor but significantly differ from the individualised technique (~30% differences in target coverage, ~70% in Dmax).

Conclusion The 3 RT techniques used in the EORTC 22922/10925 trial varied in target coverage and OARs dose per patient case. The full report will include a dosimetric analysis of 10 cases planned according to the 3 RT techniques in correlation with the clinical outcomes of the trial reported per technique.

PO-2001 Initial clinical experience with ITV-free Lung SABR using Synchrony tracking on Radixact Tomotherapy

F. Menegatti 1 , M. Cerrato 1 , C. Grossi 1 , E. Gallio 2 , I. Bonavero 1 , C. Casale 1 , P. Brossa 3 , S. Badellino 1 , F.R. Giglioli 2 , R. Parise 1 , M. Levis 1 , U. Ricardi 1 1 University of Turin, Department of Oncology, Turin, Italy; 2 A.O.U. Città della Salute e della Scienza, Medical Physics Unit, Turin, Italy; 3 A.O.U. Città della Salute e della Scienza, RTT Member, Turin, Italy Purpose or Objective In 2020 Synchrony® was installed on Radixact® tomotherapy at our department. The aim of this study is to report our clinical experience with the use of lung SABR treatments delivered with tomotherapy and Synchrony® respiratory tracking system.