EP-1184: HDR boost decreases the risk of breast failure in invasive breast ca. with close or involved margins

Results: 12 patients had mastectomy and 1 patient had lumpectomy.7 patients had immediate reconstruction: 2 tissue expanders, 5 autologous deep inferior epigastric perforator flaps.All patients received systemic chemotherapy.Toxicity was evaluated once weekly.84 % (11/13) of patients had G1 skin toxicity, while 15 % had G2-G3 (2/13) toxicity.In one patient with G3 toxicity skin dose was intentionally increased with a bolus. 1 patient had G1 esophagitis and there was no acute lung toxicity.CTV coverage was within limitations for all patients (V93%PD > 99%).For evaluation PTV (target volume reduced by 5mm buildup region) the selected target dosimetric metrics were the following: for left-sided breast treatment V95%PD = 96.8%(standard deviation -SD 3.7%), V107%PD = 3.7% (SD 5.4%) and for right-sided breast treatment V95% = 96.3%(SD 4.7%), V107%PD = 1.0%(SD 0.7%).Dosimetric metrics for OARs for the whole group were: heart Dmean = 5.6 Gy (SD 3.2 Gy), V20 Gy = 4.9% (SD 6.4%), for both lungs Dmean = 9.6 Gy (SD 1.7 Gy), V20 Gy = 15.9% (SD 3.4%), for contralateral lung V5 Gy = 8.7% (SD 16.8%) and for contralateral breast Dmean = 1.7 Gy (SD 1.0 Gy).Dose to the OARs and restrictions are presented separately for left and right side in table 1. Conclusion Conclusion:IMRT of breast/chest wall and regional lymph nodes in patients with challenging anatomy is feasible with acceptable short term toxicity.We had some difficulties in balancing constraints for OARs and target coverage especially in left-sided breast treatment.Better results may be achieved with the introduction of deep inspiratory breath hold (DIBH) combined with IMRT or even VMAT technique.