Fundamental evaluation of dose and dose distribution under applied topical agents and dressings used for skin care in radiotherapy

Purpose: Radiation dermatitis is a common adverse event in radiotherapy and is treated using topical agents or dressings; however, it may be exacerbated by increasing the skin dose during irradiation. This study investigated the effects on the dose and dose distribution assuming irradiation without wiping the agent off. Methods: Five types of topical products and dressings available in clinical settings were used in this study. These products were applied to a tough water phantom, and the dose and dose distributions of photon and electron beam were measured using an ionization chamber and an EBT3 Gafchromic film, respectively. For dose measurements, topical products were applied to thicknesses of 0, 1, 2, 3, 4, 5, and 10 mm, and 100 monitor units (MU) were irradiated. The dressings were pasted onto the phantom. For dose distribution measurements, the Gafchromic film was placed parallel to the radiation flux. The thicknesses of the topical products were 0, 1, and 5 mm. Results: The doses of 6 and 10 MV X-rays increased 0.35–0.82% and 0.25–0.55% with topical product thicknesses of 4 or 5 mm, respectively. In contrast, the electron beam dose decreased by 10.67% at 6 MeV and 2.11% at 12 MeV with a topical product thickness of 5 mm. The applied topical products shifted the X-ray and electron beam dose distributions toward the surface. However, the dressings did not affect the dose and dose distributions. Specifically, dose changes were less than 0.3% for all employed dressings. Conclusion: Based on the results of this study, we suggest that topical agents and dressings do not affect the dose and dose distribution except when topical agents are applied particularly thickly. However, the actual dose received by the skin needs to be investigated in the future.