Outcomes Associated with the Use of Tissue Equivalent Bolus Tailored by Skin Involvement Status in Postmastectomy Radiotherapy: A Single-Blinded Randomized Clinical Trial

Abstract

<h3>Purpose/Objective(s)</h3> To assess the impact of tissue equivalent bolus in postmastectomy radiotherapy (PMRT), the present study compared the use of different bolus regimens tailored by skin involvement status. <h3>Materials/Methods</h3> Patients with breast cancer who required PMRT were recruited (NCT01925651) and divided in two subgroups: standard-risk (SR, without skin involvement) and high-risk (HR, with skin involvement). The SR was randomized between no bolus or 5mm-bolus on alternate days and the HR between 5mm-bolus on alternate days or 5mm-bolus daily. Skin changes were graded weekly with the Radiation Therapy Oncology Group (RTOG) toxicity scale (single-blinded). Subsequently, patients were followed to assess local control (LC) in the chest wall (CW). <h3>Results</h3> Fifty-eight patients were enrolled (34 SR and 24 HR). The median age was 48 years and 35.3% had BMI > 30 kg/m². All the baseline characteristics were similar between each arm within the same risk subgroup. The radiotherapy technique used was tridimensional (3D) in 30 cases (58.8%) and conventional (2D) in 21 cases (41.2%). Overall, the maximal radiodermatitis rates were 29.4% (G2) and 15.7% (G3). In the SR arms, there was no difference in the incidence of G2 radiodermatitis between no bolus and alternate days bolus (p=0.70), and no G3 event occurred. In the HR arms, the 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. G2 events occurred earlier with daily bolus, but four of the six G3 events occurred 1-3 weeks after the last RT fraction. After a median follow-up of 6.2 years, the 5-year LC was 95.8% (95%CI: 88.2%-100%) in the SR and 91.7% (95%CI: 77.3%-100%) in the HR subgroups. Per randomization arm, there was no LC difference between the SR arms (p=0.90) or between the HR arms (p=0.70). All CW failures occurred in the tangent field's margins and when using 2D technique. <h3>Conclusion</h3> Within the same risk subgroup, no difference in LC was detected with a more intense bolus regimen. Due to increased G3 radiodermatitis and location of the CW failures (field borders), further studies testing the benefit of increasing superficial dose within the field (by adding bolus or increasing its intensity) are warranted.