Dose–volume analysis of radiotherapy for T1N0 invasive breast cancer treated by local excision and partial breast irradiation by low-dose-rate interstitial implant

Abstract Purpose To evaluate the toxicity of partial breast irradiation (RT) using escalating doses of low-dose-rate interstitial implant as the sole adjuvant local therapy for selected T1N0 breast cancer patients treated by wide local excision. The results of a European Organization for Research and Treatment of Cancer study have demonstrated a significant local control benefit using external beam RT to 65 Gy compared with 50 Gy. Thus, the tolerance of escalating doses of partial breast RT should be determined, because this approach may become a standard treatment for patients with early-stage breast cancer. Methods and materials Between 1997 and 2001, 48 patients with T1N0M0 breast cancer were enrolled into an institutional review board–approved Phase I/II protocol using low-dose-rate brachytherapy implants after wide local excision and lymph node staging surgery. Brachytherapy was started 3–4 days after surgery at a dose rate of 50 cGy/h, using 192 Ir sources evenly spaced to cover 3 cm around the resection margins. Typically, 2–3 planes were used, with a median of 14 catheters (range 10–16). The total dose was escalated in three groups: 50 Gy ( n = 19), 55 Gy ( n = 16), and 60 Gy ( n = 13). The implant volume was calculated and used to classify patients into quartiles: 76–127 cm 3 ( n = 12), 128–164 cm 3 ( n = 12), 165–204 cm 3 ( n = 12), and >204 cm 3 ( n = 12). Cosmesis, patient satisfaction, treatment-related complications, mammographic abnormalities, rebiopsies, and disease status were recorded at each scheduled patient visit. Results The median follow-up for all patients was 23.1 months (range 2–43). Very good to excellent cosmetic results were observed in 91.8% of patients. Ninety-two percent of patients were satisfied with their cosmetic outcome and said they would choose brachytherapy again over the standard course of external beam RT. Six perioperative complications occurred: two developed bleeding at the time of catheter removal, two had abscesses, one developed a hematoma, and one had a nonhealing sinus tract requiring surgical intervention. Significant fibrosis (moderate-to-severe scarring and thickening of the skin and breast) was noted in only 4 patients; 1 had received 55 Gy and 3 had received 60 Gy. Abnormal posttreatment mammograms were seen in 19 patients. Eight patients underwent rebiopsy for abnormalities found either by mammography or on physical examination; all proved to be fat necrosis or post-RT changes. The rebiopsy rates appeared to correlate with doses ≥55 Gy (6 [75%] of 8 compared with 29 [60%]of 48 overall) and implant volumes ≥128 cm 3 (7 [87.5%] of 8 compared with 36 [75%] of 48 overall). To date, no local, regional, or distant recurrences have been observed. Conclusion Low-dose-rate implants up to 60 Gy were well-tolerated overall. With an implant dose of 60 Gy, the incidence of posttreatment fibrosis (25%) appeared to be increased. Only the long-term follow-up of this and other implant studies will allow an understanding of the total radiation dose necessary for tumor control and the volume of breast that requires treatment.