FRIDAY, Oct. 19, 2018 (HealthDay News) — Contrary to the advice most cancer patients receive, light or moderate use of topical agents before radiation treatment does not appear to increase the radiation dose to the skin, according to a study published online Oct. 18 in JAMA Oncology.

Brian C. Baumann, M.D., from Washington University in St. Louis, and colleagues surveyed 133 patients and 108 clinicians to determine current practices regarding topical therapy use before radiation treatment. In addition, the researchers evaluated the dosimetric effect of topical agents by delivering 200 monitor units and measuring the dose at the surface and at a depth of 2 cm in a tissue-equivalent phantom with or without a petroleum-based ointment (Aquaphor, petrolatum 41 percent) and silver sulfadiazine cream, 1 percent.

The researchers found that the vast majority of patients (83.4 percent) and clinicians (91.4 percent) received or gave the advice to avoid applying topical agents before radiotherapy treatments. There was no difference in dosimetric measurements at either the surface or the 2-cm depth with or without a 1- to 2-mm application of either topical agent when using en face 6- or 15-megavoltage (MV) photons. At 15 to 60 degrees, the same application of topicals did not alter the surface dose as a function of beam incident, except for a 6 percent increase at 60 degrees with the silver sulfadiazine cream. However, with a thicker (≥3 mm) topical application, surface dose for 6- and 15-MV beams was significantly increased.

“Based on the results of this study, the use of topical agents just before radiation therapy can be safely liberalized, which may improve quality of life for patients undergoing radiation therapy, but very thick applications of topical agents just before radiation therapy should still be avoided,” Baumann said in a statement.

One author disclosed having served on advisory boards for IBA and Varian Medical Systems for proton therapy.

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