Quantitative Effect of Bolus on Skin Dose in Postmastectomy Radiation Therapy

Background: In postmastectomy radiation therapy (PMRT), some centres prescribe the use of a tissue-equivalent bolus to the skin to reduce the risk of chest wall recurrence. The addition of bolus causes an increase in the skin dose, which may lead to increased risk of radiodermatitis. Radiodermatitis can decrease patients' overall quality of life, bringing into question the benefit of using the bolus. The purpose of this retrospective chart review was to quantify the increase in skin dose associated with the use of bolus in the PMRT setting. Materials and Methods: We evaluated 70 patients who underwent PMRT at our institution during 2012-2018. Two similar treatment plans were generated for each patient: one with bolus and one without. Skin dose-volume histogram values were evaluated, and statistical analysis was performed using MATLAB R2015b. Results: There was no significant difference in the maximum skin dose within a depth of 5 mm for bolus versus nonbolus plans (P = 0.4). However, within a depth of 3 mm, bolus plans had a maximum skin dose 7% +/- 2.5% higher than the nonbolus plans (P < .00001) . Mean skin dose within depths of 3 and 5 mm were both significantly higher (P < .00001) for bolus plans. The photon beam energy and chest wall separation showed minimal or no effect on skin dose. Conclusion: Given the differing opinions in the literature regarding the role for bolus in PMRT, there is still uncertainty of the optimal treatment method. This retrospective study demonstrates a 20%30% reduction in mean skin dose when bolus is not used.