Randomized clinical trial of tissue equivalent bolus prescription in postmastectomy radiotherapy stratified by skin involvement status

PURPOSE: To assess the impact and optimize the prescription of tissue-equivalent bolus in postmastectomy radiotherapy (PMRT), we compared the use of different bolus regimens tailored by skin involvement status. METHODS: Patients with breast cancer who required PMRT were recruited (NCT01925651) and classified into two groups: standard-risk (SR, without skin involvement) and high-risk (HR, with skin involvement). SR was randomized between no bolus or 5 mm-bolus on alternate days and HR between 5 mm-bolus on alternate days or daily. Conventional fractionation (50.4 Gy; 1.8 Gy/daily) was used. Acute skin toxicity was evaluated blindly and the radiodermatitis-specific toxicity index [rads-TI] calculated. Subsequently, patients were followed up to assess oncologic outcomes, focusing on chest wall (CW) local control. RESULTS: Fifty-eight patients were enrolled (34 SR and 24 HR). Baseline characteristics were similar between arms within the same risk group. Overall, maximal radiodermatitis rates were 29.4 % (G2) and 15.7 % (G3). In the SR group, no difference existed in G2 radiodermatitis incidence between the subgroups (p = 0.70) and no G3 events occurred. In the HR group, incidences of G2 (100 % vs 44.5 %, p = 0.01) and G3 radiodermatitis (70 % vs 11.1 %, p = 0.02) were higher with daily bolus. After adjusting for confounders, the daily bolus had a higher incidence of G2 (p = 0.03), G3 radiodermatitis (p = 0.04), and worse rads-TI (p < 0.01). After a median follow-up of 6.2 years, the 5-year local control was 95.8 % (95 %CI: 88.2 %–100 %) in the SR and 91.7 % (95 %CI: 77.3 %–100 %) in the HR groups. Per risk group, there was no difference in local control between the SR (p = 0.90) or the HR bolus regimens (p = 0.70). CONCLUSION: Daily 5 mm bolus prescription significantly increased the overall toxicity burden. In this preliminary study, within the same risk group, no detriment in CW local control was detected with less intense bolus regimens (SR: no bolus; HR: alternate-days bolus). Additionally, the rads-TI was able to distinguish overall radiodermatitis burden.