Partial-Breast Irradiation: Review of Modern Trials

Purpose of Review Following partial mastectomy, whole-breast irradiation (WBI), delivered over 3 to 6 weeks, has been the standard adjuvant radiation approach for early-stage breast cancer. A growing body of literature over the past decade has suggested that irradiation of the partial breast, including the tumor bed plus a margin, may be a suitable alternative for appropriately selected patients. The use of partial breast irradiation (PBI) has been studied in multiple prospective randomized trials, now with up to 10 years of follow-up, establishing similar safety and efficacy compared with WBI. Advantages of PBI include (1) reduced treatment duration, (2) potential reductions in treatment-related toxicity, (3) improved cosmetic outcomes, and (4) reduced costs. The purpose of this article is to review appropriate patient selection criteria, clinical and toxicity outcomes data, clinical consensus practice guidelines, and the various PBI techniques. Recent Findings The National Surgical Adjuvant Breast and Bowel Project (NSABP) B39/Radiation Therapy Oncology Group (RTOG) 0413 study (NRG Oncology) is the most recently published (abstract form only) prospective randomized trial comparing PBI using 3D conformal external beam radiation therapy (3D-CRT, 38.5 Gy/10 fractions, twice daily) or brachytherapy (interstitial catheters or applicator based, 34 Gy/10 fractions, twice daily), vs. WBI (50 Gy +/- tumor a bed boost). With a median follow-up of 10.2 years, the 10-year ipsilateral breast tumor recurrence-free interval was 95.2% vs. 95.9% for PBI and WBI, although it did not meet the statistical significance for equivalence. Similarly, the randomized trial of accelerated partial breast irradiation using 3-dimensional conformal radiotherapy (RAPID) trial is a prospective randomized trial comparing primarily 3D-CRT (38.5 Gy/10 fractions, twice daily) with WBI, (42.5 Gy/16 daily fractions or 50 Gy/25 daily fractions +/- tumor bed boost). Rates of ipsilateral breast tumor recurrence (IBTR) at 8 years were not statistically significantly different (PBI vs WBI, 3% vs. 2.8%; HR = 1.27; 90% VI, 0.84-1.91). There is a growing body of literature supporting the use of PBI in appropriately selected patients and its use should continue to increase.