The MammoSite balloon brachytherapy catheter for accelerated partial breast irradiation.

Whole-breast irradiation after lumpectomy for early-stage breast cancer appears to prevent relapse only at the site of initial involvement, and therefore it is likely that radiation can safely be limited to tissues immediately surrounding the excision cavity. Accelerated partial-breast irradiation (APBI) with the MammoSite catheter (Proxima Therapeutics, Alpharetta, GA) has been proposed as a means through which APBI can be offered to a wide range of patients. Although sufficient follow-up is not yet available regarding local control, survival, late toxicity, and long-term cosmetic results, early results are promising. This article reviews the current literature reflecting treatment, dose optimization, outcomes, and toxicity of APBI with the MammoSite brachytherapy catheter.

MammoSite and interstitial brachytherapy for accelerated partial breast irradiation: factors that affect toxicity and cosmesis.

BACKGROUND: In interstitial brachytherapy (IB), cosmesis and toxicity correlate with volume of tissue irradiated, dose homogeneity index (DHI), and adjuvant doxorubicin/cyclophosphamide based chemotherapy (ACCT). MammoSite brachytherapy (MSB) irradiates smaller volumes than IB, and lower dose homogeneity does not appear to affect toxicity. However, clinical experience suggests that other factors may also play an important role in cosmesis and toxicity with MSB. We reviewed our prospectively maintained data base of women who underwent accelerated partial breast irradiation (APBI) to assess this issue. METHODS: Beginning in September 1995, 115 women were enrolled in a trial evaluating APBI as monotherapy after lumpectomy. The first 75 eligible patients received IB, and the most recent 28 eligible patients received MSB. All patients received 34 gray (Gy) in 10 twice-daily fractions through high-dose rate iridium-192 brachytherapy; 19% of patients in the IB group and 0% of patients in the MSB group received ACCT. RESULTS: At 1 year after treatment, MSB caused significantly less Grade 2-4 subcutaneous fibrosis (as graded by a radiation oncologist according to the Radiation Therapy Oncology Group/Eastern Cooperative Oncology Group system) compared with IB (10.7% vs. 32%; P = 0.04). However, when only ACCT-naïve patients in the IB group were compared with patients in the MSB group, this finding became nonsignificant. Among the patients who received MSB, significantly smaller volumes were irradiated, and the DHI was lower. CONCLUSIONS: Current studies suggest an improved toxicity profile with MSB compared with IB that is attributed to lower irradiated volumes with MSB. When only chemotherapy-naïve patients were compared, however, toxicity and cosmesis were found to be similar between MSB and IB, suggesting a more complex interplay between irradiated volumes, DHI, and chemotherapy. The relation of ACCT to toxicity in this scenario is intriguing and warrants further investigation.