Avoiding skin creams right before radiation: Myth or sound advice?

Abstract

51 Background: Radiation dermatitis in breast cancer patients is common and often treated with topical creams. Patients are traditionally advised to avoid lotions for several hours before radiotherapy (RT) based on concern that creams might increase skin dose. With modern RT’s improved skin sparing, this recommendation may be irrelevant. We hypothesize that applying either metallic or non-metallic creams before treatment would have minimal effect on skin dose. Methods: We conducted an online, 24-question OncoLink survey of patients and providers to determine current skin cream practices. To evaluate the dosimetric effect of creams, we delivered 200 MU at 100 cm SSD and measured the dose at the surface and 2 cm depth in a tissue equivalent phantom, with or w/o 2 common skin creams, Aquaphor and silver sulfadiazine. We assessed the effect of various photon and electron energies, cream thicknesses and beam incidence on dose. The effect of creams on skin dose was also evaluated in C57BL/6 mice using γ-H2AX IHC staining. Results: 27 of 33 surveyed breast cancer patients (82%) and 43 of 45 providers (96%) either received or gave the advice to avoid applying creams prior to RT treatments. Measurements showed no difference in dose at the surface or 2 cm depth with or w/o a 1-2 mm application of either cream when using enface 6 or 15 MV photons. The same application of cream had no effect on surface dose as a function of beam incident angle from 15-60°, except for a 7% increase at 60° with the silver cream. Surface dose for 6 & 15 MV beams were significantly increased with a thicker (≥3 mm) layer of cream. For 6 MV, the surface dose was 105 cGy (Aquaphor), 102 cGy (silver cream) and 88 cGy (controls). For 15 MV, the doses were 70, 60 and 52 cGy. With 6 and 9 MeV electrons, there was only a 2-5% increase in surface dose with use of creams. There were no dose differences at 2 cm depth. Irradiated skin in mice showed no difference in γ-H2AX positive foci with or w/o creams. Conclusions: This is the first dosimetric assessment of the effect of skin creams for RT dermatitis. Our findings suggest that thin or moderately applied creams, even if applied just prior to RT, have minimal impact on skin dose, regardless of beam energy or beam incidence. Applying very thick amounts of cream just prior to RT increased surface dose and should be avoided.