ESTRO 2020 Abstract Book

S795 ESTRO 2020

Results D98 was larger than 95% prescription dose for all patients. Fig.2 shows OAR DVHs parameters time evolution between RT techniques. Heart D mean decreased over time due to the increased concern about cardiotoxicity and the consequent change in dose constrains (from 10 to 6Gy for left breast and 3 for right breast). The impact of the IMRT planning learning curve can be seen in the first year. IMRT increased D mean to heart and to CtlBreast compared with 3DCRT. VMAT significantly increased doses received by liver and CtlBreast (p<0.05). DBHI decreased doses to heart significantly with respect to non DBHI(p<2.2e-16).There was no correlation between DVHs parameters and the physician in charge. No correlation between PTV volumes and DVHs parameters was found.

Purpose or Objective Survival in breast cancer has been increasing and therefore it is mandatory to decrease secondary toxicity of breast cancer treatment. Changes in position of the patient from supine to prone have allowed to separate glandular tissue from chest wall, moving away the organs at risk (OAR) and reducing the side effects while maintaining local tumor control accordingly. The objective of this study is to analyze the differences in toxicity and local tumor control observed between patients with breast cancer treated in supine position and in prone position. Material and Methods All patients with early stage breast cancer have been treated with adjuvant radiotherapy after conservative surgery. The treatments were performed hypofractionated, 2,67Gy/fraction in breast and 0,3Gy/fraction in the concomitant boost. 72 patients have been analyzed, 75% have been treated in prone position with a Bionix prone breast system 6025-03 (Bionix, Toledo, OH, USA) and 25% have been treated in supine position. Dose parameters in lung, V4, V8 and V16 have also been evaluated. A retrospective analysis has been performed in terms of side effects, dosimetry and local tumor control. Results Acute skin toxicity has been the unique adverse effect observed. No Grade 4 radiodermatitis was observed. Grade 1 was found in 52% patients, grade 2 in 19 % patients and grade 3 in 11% patients. Around 80% of the patients treated in supine position presented radiodermatitis Grade 1. No patient presented anymore acute skin toxicity in supine position (figure1). Skin toxicity was observed in 85% patients situated in prone position. Grade 1 was observed in 44% patients, grade 2 in 26% patients and grade 3 was observed in 15% prone patients (figure1). Bionix prone breast system multi- layered variable density foam pad set has allowed patients to be comfortable, but also it is not completely rigid in the opening breast bridge and a small bolus effect has been observed. Doses in lung have decreased significantly in patients situated in prone position compared to supine. Volume of lung which has received more than 4 Gy (V4) was 2,95% in prone position and 20,22 % in supine position (table1). Both positions have presented local tumor control for all patients.

Conclusion The first patients treated with IMRT showed high doses in OAR. This shows the importance of training and external peer review when a new technique is used. Systematic collection of DVH parameters on a database allows to monitor doses to OAR helping to identify any special causes that could represent relevant changes both regarding equipment, change of practice o new personnel. For instance, VMAT significantly increases doses to OARs away from PTV, and should be used with care on breast cancer patients. As European guidelines had been always followed, the analysis made can provide useful information to other institutions that are going through technological changes. Acknowledges: This work was financed by the Spanish Association Against Cancer (AECC) PO-1480 Position in breast cancer radiotherapy: dosimetry and toxicity D. Hernandez 1 , M.S. Talaya 2 , C. Anson 1 , P. Castro 1 , M. Roch 1 , P. García 1 , S. Martín 2 , A. Valiente 2 , A. Viñals 1 , R. Capilla_Fayos 1 , M.T. Murillo 2 1 H.U.La Princesa, Medical Physics, Madrid, Spain ; 2 H.U.La Princesa, Radiation Oncology, Madrid, Spain