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

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 3.4Gy 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 < or =100% and < or =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.