Ongoing clinical experience utilizing 3D conformal external beam radiotherapy to deliver partial-breast irradiation in patients with early-stage breast cancer treated with breast-conserving therapy.

PURPOSE: We present our ongoing clinical experience utilizing 3D conformal radiation therapy (3D-CRT) to deliver partial-breast irradiation (PBI) in patients with early-stage breast cancer treated with breast-conserving therapy.
MATERIALS AND METHODS: Thirty-one patients referred for postoperative radiation therapy after lumpectomy were treated with PBI using our previously reported 3D-CRT technique. Ninety-four percent of patients had surgical clips outlining the lumpectomy cavity (mean: 6 clips). The clinical target volume (CTV) consisted of the lumpectomy cavity plus a 10-mm margin in 9 patients and 15-mm margin in 22 (median: 15 mm). The planning target volume consisted of the CTV plus a 10-mm margin for breathing motion and treatment setup uncertainties. The prescribed dose (PD) was 34 or 38.5 Gy (6 patients and 25 patients, respectively) in 10 fractions b.i.d. separated by 6 h and delivered in 5 consecutive days. Patients were treated in the supine position with 3-5 beams (mean: 4) designed to irradiate the CTV with <10% inhomogeneity and a comparable or lower dose to the heart, lung, and contralateral breast compared with standard whole-breast tangents. The median follow-up duration is 10 months (range: 1-30 months). Four patients have been followed >2 years, 6 >1.5 years, and 5 >1 year. The remaining 16 patients have been followed <12 months.
RESULTS: No skin changes greater than Grade 1 erythema were noted during treatment. At the initial 4-8-week follow-up visit, 19 patients (61%) experienced Grade 1 toxicity and 3 patients (10%) Grade 2 toxicity. No Grade 3 toxicities were observed. The remaining 9 patients (29%) had no observable radiation effects. Cosmetic results were rated as good/excellent in all evaluable patients at 6 months (n = 3), 12 months (n = 5), 18 months (n = 6), and in the 4 evaluable patients at >2 years after treatment. The mean coverage of the CTV by the 100% isodose line (IDL) was 98% (range: 54-100%, median: 100%) and by the 95% IDL, 100% (range: 99-100%). The mean coverage of the planning target volume by the 95% IDL was 100% (range: 97-100%). The mean percentage of the breast receiving 100% of the PD was 23% (range: 14-39%). The mean percentage of the breast receiving 50% of the PD was 47% (range: 34-60%).
CONCLUSIONS: Utilizing 3D-CRT to deliver PBI is technically feasible, and acute toxicity to date has been minimal. Additional follow-up will be needed to assess the long-term effects of these larger fraction sizes on normal-tissue sequelae and the impact of this fractionation schedule on treatment efficacy.