Long-term outcome and toxicity in a Phase I/II trial using high-dose-rate multicatheter interstitial brachytherapy for T1/T2 breast cancer.

PURPOSE: To present an updated analysis of survival, recurrence rate, and toxicity for a cohort of women with early-stage breast cancer treated with high-dose-rate interstitial brachytherapy for accelerated partial breast irradiation.

METHODS AND MATERIALS: From August 1997 to July 2001, a total of 32 women with 33 breast cancers were treated with interstitial high-dose-rate brachytherapy after breast-conserving surgery as part of a Phase I/II protocol. All patients had T1-2 tumors with < or b=3 axillary nodes positive, nonlobular histology, negative surgical margins, and no evidence of extracapsular lymph node extension. Multiple brachytherapy catheters were used and radiation was delivered with a high activity (3-10Ci) (192)Ir source placed via remote after loader. Dose was prescribed to the tumor bed plus a 2 cm margin. A total of 3400 cGy was delivered in 10 fractions of 340 cGy each given twice daily over 5 days. Toxicities (skin, subcutaneous tissue, pain, fat necrosis) were evaluated by Radiation Therapy Oncology Group criteria; cosmesis was assessed using a previously published scale. Toxicity scores were separated into four followup intervals: < or =6 months, >6 months and < or =2 years, >2 and < or =5 years, and >5 years.

RESULTS: The actuarial local recurrence rate was 6.1% at 5 years with the last measured event at 70.5 months. A total of three treatment failures were observed at 25.8, 39.9, and 70.5 months of followup. All three were elsewhere failures within the treated breast. One patient died after 90.0 months of followup secondary to a subsequently diagnosed small-cell lung cancer. For the purpose of analysis, toxicity scores were assigned to each of four followup intervals: < or =6 months, >6 but < or =24 months, >24 but < or =60 months, and >60 months. Fat necrosis was not seen in the first 6 months after treatment, then appeared in 27.3% of patients from 6 to 24 months, 28.1% from 24 to 60 months, and 17.9% beyond 60 months. Skin toxicity appeared to stabilize with longer followup: the percentage of patients showing any degree of skin toxicity was 69.7%, 33.3%, 40.6%, and 28.6% at each successive time interval. Subcutaneous toxicity increased beyond 60 months: moderate to severe subcutaneous toxicity was seen in 15.2%, 18.2%, 18.8%, and 35.7% of patients successively. The percentage of patients with less than excellent cosmetic outcome improved beyond 60 months (21.2%, 21.2%, 21.9%, and 11.1% successively). Only 1 patient experienced more than mild pain at any time. The percentage of patients experiencing any degree of pain improved over time (30.3%, 33.3%, 18.8%, 17.9%).

CONCLUSIONS: Our series showed a local recurrence rate of 6.1% at 5 years, which is comparable to that seen in conventional whole breast series. Fat necrosis was found in more than half the cohort. Fat necrosis, pain, and cosmesis appeared to improve with longer followup, whereas subcutaneous toxicity worsened and skin toxicity stabilized.