The Effect of Bolus on Local Control for Patients Treated With Mastectomy and Radiation Therapy

Purpose: Bolus use during postmastectomy radiation therapy doubles the risk of grade 2 and 3 skin toxicity. Despite its unknown benefit, bolus is often prescribed during postmastectomy radiation therapy for patients without skin involvement. Methods and Materials: For women with breast cancer receiving photon 3-dimensional conformal radiation therapy, bolus was used routinely for chest walls but was omitted for breast reconstructions by about half of radiation oncologists from 2007 to 2011. Eligible patients had newly diagnosed invasive breast cancers without skin involvement (pT1-4a, any-N, M0) treated with adjuvant or neoadjuvant radiation therapy. For the bolus and no-bolus groups, we compared the cumulative incidence of local recurrence (LR) and locoregional recurrence (LRR) with distant recurrence and death as competing risks and breast cancer mortality (BCM). Multivariable analysis of LR and BCM included stage, subtype, lymphovascular invasion, grade, margin status, beam energy, bolus use, hormone therapy, chemotherapy, and reconstruction. Results: Systemic therapy was used for 98% of the 1887 patients. The bolus group had 1569 patients and the no-bolus group had 318 patients. Bolus was used in 51% (281/550) of patients treated with reconstruction and 96% (1288/1337) of patients treated without reconstruction. The 10-year outcomes (95% confidence interval) in patients treated with and without bolus were, respectively: LR 1.9% (1.3-2.7) versus 0.9% (0.3-2.6), LRR 3.1% (2.3-4.0) versus 3.2% (1.6-5.5), and BCM 19.4% (17.3-21.6) versus 18.3% (13.9-23.2). On multivariable analysis, bolus use was not associated with better LR (hazard ratio = 1.4 [0.3-6.4]) or BCM (hazard ratio = 0.8 [0.5-1.2]). Conclusions: For patients treated with mastectomy, radiation therapy, and modern systemic therapy, the cumulative incidence of LR was low, with or without bolus. Because bolus use increases toxicity and does not reduce LR or BCM, it should no longer be used routinely for patients without skin involvement who receive systemic therapy.