OAR dose constraints consensus in hypofractionated breast cancer radiotherapy is urgently needed!

Purpose or Objective: Hypofractionated radiotherapy is widely used and has even become a standard in several countries, but consensus on dose constraints for OARs still has not been established. Our aim was to verify the reproducibility of the dose constraints adopted by FAST-Forward trial investigators in the 40 Gy/15fr arm. Materials and Methods: We retrospectively analyzed dosimetric plans of 81 breast cancer patients, treated with 3D-hypofractionated monoisocentric radiotherapy from December 2017 to February 2020. The prescribed dose was 40.05 Gy in 15 fractions to the whole breast. Dose volume histograms (DVH) were evaluated and we recorded heart mean dose (MHD), cardiac volume receiving 2 Gy (V2Gy) and 10 Gy (V10Gy), Lung mean dose (MLD) and volume of ispsilateral lung receiving 12 Gy (V12Gy). These variables were compared to the dose constraints used in the Fast-Forward trial namely: volume of ipsilateral lung receiving 12 Gy less than 15%, volume of heart receiving 2 Gy less than 30% and that receiving 10 Gy less than 5% in their 40 Gy/15fr group. Results: The mean MHD, V2Gy and V10Gy were respectively 1.78 Gy, 16.14 % and 2.56 %. V2Gy was less than 30% in 86.4% of cases (n=70). V10Gy was less than 5 % in 75.3% of patients (n=61). The mean MLD and V12Gy were respectively 5.58 Gy and 36 %. V12Gy was less than 15% in 63% of patients (n=51) (table 1). (Table Presented) Conclusion: In our study, we only matched in 2 out of 3 cases to the dose constraints used in the Fast-Forward trial despite the very low mean doses obtained to the lung and heart (mean MHD=1.78Gy and mean MLD= 5.58Gy) which are the main consensual constraints used in conventional fractionation radiotherapy, but not adopted in the Fast-Forward trial. An international consensus adopting the most relevant dose constraints in hypofractionated radiotherapy is waited.