Dose Changes Caused by Placing a Surgical Mask Inside the Radiotherapy Treatment Field

Abstract

Background: The present study investigated the effect of the presence of medical masks in or near the radiotherapy (RT) treatment field during the COVID-19 pandemic, due to the widespread use of medical masks on the faces of patients undergoing RT. Methods: The dose distribution was calculated in a polymethyl methacrylate (PMMA) phantom using the Monaco treatment planning system, and then measured in a water phantom beneath the surgical medical mask (SMM) and near the mask, for photon energies of 6, 10, and 18 MV, and electron energies of 6, 8, 10, 12, and 15 MeV, emitted from a Versa HD linac. Results: According to the Monaco results, the difference in dose distribution between the area under the mask and the area outside the mask was observed only up to a depth of 20 mm. In electron radiation, this difference was observed up to a depth of 10 mm. Based on the measurement results, we found that at the entrance plane of the phantom, the masked readings increased by 1.2, 1.18, and 1.14 times compared to the unmasked mode for photon energies of 6, 10, and 18 MV, respectively. The masked readings increased by 3.1%, 3.4%, 3.2%, 2.6%, and 1.3% compared to the unmasked mode for 6, 8, 10, 12, and 15 MeV, respectively. Conclusions: Medical masks altered the dose distribution of both photon and electron radiation within the main treatment field and outside the main field, particularly at the surface. It is therefore recommended to keep patients’ medical masks out of the radiated field.