Meta-Analysis of Trials of Partial Breast Irradiation.

PURPOSE: Partial breast irradiation (PBI) is the delivery of radiotherapy (RT) limited to the tumor bed following breast conserving surgery (BCS). The results of recent trials of PBI compared to whole breast irradiation (WBI) have suggested conflicting results with respect to local control and toxicity. The purpose of this meta-analysis was to assess effectiveness of PBI and to compare the different techniques. METHODS: A meta-analysis of aggregate data from published randomized trials was performed to examine the effectiveness of PBI compared to WBI in patients with invasive breast cancer and ductal carcinoma in situ. Relevant data were extracted. The primary outcome was any ipsilateral breast event (invasive or non-invasive). Secondary outcomes included acute and late toxicity. The results of randomized trials were pooled using a fixed effects model and the inverse variance method. RESULTS: Fifteen trials involving 16,474 patients were identified. The majority of enrolled patients were > 60 years of age and had T1N0 grade I-II, disease treated with endocrine therapy. The percent of ipsilateral breast events was higher in patients treated with PBI compared to WBI [5.0% vs. 2.8%, risk ratio (RR)=1.72, 95% confidence interval (CI) 1.47-2.03]. Heterogeneity (p=0.0002) was observed between the 4 PBI techniques: external beam RT without CT planning [risk ratio (RR)=2.06, 95% CI 1.36-3.12]; brachytherapy (RR=1.21, 95% CI 0.65-2.25); intraoperative RT (RR=2.79, 95% CI 2.08-3.73); and external beam RT with CT planning (RR=1.25, 95% CI 0.99-1.58). When external beam RT without CT planning and intraoperative RT trials were excluded the percent of ipsilateral breast events was 3.3% vs 2.6% respectively, RR=1.25 (95% CI 1.00-1.55), p=0.05, and no heterogeneity was observed (p=0.92). Overall, acute toxicity was less with PBI and the effect on late toxicity varied by technique. CONCLUSIONS: Overall, WBI was more effective than PBI, but the effectiveness of PBI was technique related. PBI was less effective when given by external beam RT without CT planning or intraoperative therapy. While PBI given by multi-catheter brachytherapy or external beam RT with CT planning tended to be statistically less effective than WBI, the absolute difference between groups for ipsilateral breast events was very small (< 1%) supporting these approaches for women considering PBI.