ESTRO 2021 Abstract Book

S950

ESTRO 2021

Conclusion This preliminary analysis presents encouraging results, which are in line with our research hypotheses supporting that MANIV-DIBH could offer highly accurate left breast positioning over time while maximizing OARs protection. Further patient inclusion is ongoing to provide statistical analyses with sufficient power. PO-1142 Hypofractionated whole breast radiotherapy in large breast size: is it really a solved issue? R.R. Colcago 1 , A. Cavallo 2 , M.C. Magri 3 , E. La Rocca 4 , A. Vitullo 1 , P. Baili 5 , M. Sant 3 , E. Pignoli 2 , R. Valdagni 1 , L. Lozza 1 , M.C. De Santis 1 1 Fondazione IRCCS Istituto Nazionale dei Tumori, Radiation Oncology 1, Milan, Italy; 2 Fondazione IRCCS Istituto Nazionale dei Tumori, Medical Physics Unit, Milan, Italy; 3 Fondazione IRCCS Istituto Nazionale dei Tumori, Analytical Epidemiology and Health Impact Unit, Milan, Italy; 4 Fondazione IRCCS Istituto Nazionale dei Tumori, Radiation Oncology, Milan, Italy; 5 Fondazione IRCCS Istituto Nazionale dei Tumori, Analytical Epidemiology and Health Impact Unit, Milan, Italy Purpose or Objective Nowadays, Hypofractionated RadioTherapy (HRT) is considered the standard of care for the adjuvant treatment of breast cancer (BC). However, there are still a few concerns about late toxicity after HRT, especially in patients with large breast size. The purpose of this study was to evaluate the impact of breast size on acute and late side effects in BC patients treated with HRT. Materials and Methods In this study we analyzed pts over 60 years with a diagnosis of early BC, candidate to HRT (42.40 Gy in 16 daily fractions, 2.65 Gy per fraction) after conservative surgery. Boost to the tumor bed was admitted and was administered in patients with grade III breast cancer (10 Gy in 4 daily fractions, 2.5 Gy per fraction) or with