Dosimetric impact of post-operative seroma reduction during radiotherapy after breast-conserving surgery

Abstract Purpose Three boost radiotherapy (RT) techniques were compared to evaluate the dosimetric effect of seroma reduction during RT after breast-conserving surgery (BCS). Materials and methods Twenty-one patients who developed seroma after BCS were included. Each patient underwent three CT scans: one week before RT (CT−1 ), in the third (CT3 ) and fifth (CT5 ) week of RT. For each patient, three plans were generated. (1) SEQ: whole breast irradiation planned on CT−1, sequential boost planned on CT5 , (2) SIB: simultaneous integrated boost planned on CT−1 , (3) SIB adaptive radiation therapy (SIB-ART): planned on CT−1 and re-planned on CT3 . Irradiated volumes, mean lung (MLD) and maximum heart dose (HDmax ) were projected and compared on CT5. Results On average 62% seroma reduction during RT was observed. Volumes receiving ⩾107% of prescribed whole breast dose were significantly smaller with SIB-ART compared to SEQ and SIB. The undesired volume receiving ⩾95% of prescribed total dose was also significantly smaller with SIB-ART. For SEQ, SIB-ART and SIB, respectively, small but significant differences were found in MLD (4.2 vs. 4.6 vs. 4.7 Gy) and in HDmax for patients with left-sided breast cancer (39.9 vs. 35.8 vs. 36.9 Gy). Conclusions This study demonstrates a dosimetric advantage for patients with seroma when simultaneous integrated boost is used with re-planning halfway through treatment.