MammoSite® accelerated partial breast irradiation: A single-institution outcomes analysis with 2 years of followup

Abstract Purpose To provide longitudinal follow-up and assess the intermediate outcomes in breast cancer patients treated with the MammoSite ® radiation therapy system. Methods and Material Ninety-two patients with histologically proven stage 0-II breast cancer were treated with MammoSite ® accelerated partial breast irradiation after breast-conserving surgery. The catheter was placed at the time of surgery or postoperatively. Treatment prescription was 3.4 Gy b.i.d. for a period of five days using high-dose-rate afterloading. Clinical and dosimetric parameters including dose to 90% of PTV, volume of PTV receiving 100% of dose, volume of PTV receiving 150% of dose, edited PTV, and dose homogeneity index were analyzed as variables correlating with late effects. Results All patients received the prescribed treatment. Seventy-seven percent of patients had intraoperative catheter placement, which was associated with a higher rate of persistent seroma (79%). The presence of seroma did not affect cosmesis. Ten patients developed telangiectasia at a median of 20.5 months. Skin dose and balloon-to-skin distance had a significant correlation with the development of telangiectasia that significantly affected cosmetic grading. The telangiectasia incidence for maximum skin dose of >100% and >125% of the prescription dose were 28% and 63%, compared with 0% ( p  = 0.0001) and 4.2% ( p  = 0.0001) for doses of ≤100% and ≤125%, respectively. Overall, most patients had excellent cosmetic results, and local control of disease was excellent. Conclusions MammoSite ® radiation therapy system demonstrates excellent local control and cosmetic outcome with extended followup. The maximum skin dose should be kept below 100% to reduce late effects on skin and improve cosmetic outcome. The persistence of seroma is higher with intraoperative placement of the catheter, and therefore postoperative placement is preferred.