Researchers debunk rule that patients should avoid topical agents before radiotherapy treatments
Research published in the Journal of the American Medical Association: Oncology debunked the widely accepted rule that cancer patients should not use topical skin treatments before radiation treatments.
“Thin or moderately applied topical agents, even if applied just before radiotherapy, may have minimal influence on skin dose regardless of beam energy or beam incidence,” wrote lead author Brian C. Baumann, MD, of Washington University in St. Louis and the University of Pennsylvania, and colleagues.
Baumann and colleagues noted patients are typically advised to avoid topical agents for several hours before daily radiotherapy as the concern is the agent may increase the radiation dose to the skin. They sought to assess whether applying metallic or nonmetallic topical agents before radiation treatment alters the skin dose.
The researchers first developed and issued a 24-question anonymous online survey to 241 patients and clinicians to gauge current practices for topical agent use before radiotherapy.
They found that 83 percent of patients had been advised to avoid topical agents immediately before radiotherapy and 54 percent were advised to wipe off any residual topicals before the radiotherapy session. Additionally, they found 91 percent of physicians advised patients to avoid topical agent application and 84 percent of the physicians said it was to avoid the bolus effect. About 93 percent of physicians asked their patients not to use metal-containing topical agents immediately before radiotherapy because of the bolus effect and electron scatter from metals.
The researchers then used optically stimulated luminescent dosimeters (OSLDs) to measure the amount of surface radiation absorbed with each dose of radiation.
“Results of our dosimetric analysis suggest that thin or moderately thick applications of topical agents, even if applied immediately before radiotherapy, only minimally alter the dose to the skin regardless of beam energy or beam angles,” Baumann and colleagues wrote. “Very thick applications of a topical agent just before radiotherapy may have a bolus effect with increased surface dose and should be avoided.”
The researchers measured the dose using a tissue-equivalent phantom with beams of four energy levels—6-MV, 15-MV and 6-MeV and 9-MeV electrons, which were administered at five different beam angles—0°, 15°, 30°, 45° and 60°. Some of the phantoms had petroleum-based ointment (Aquaphor) or silver sulfadiazine cream.
There was no difference in dose at the surface or 2-cm depth with or without a “relatively thick” 1- to 2-mm topical agent using 6-MV or 15-MV energy levels. Additionally, there was no increased surface dose with 1- to 2-mm applications of either agents at various beam angles. The only exception was a 6 percent increase at 60° with the silver sulfadiazine cream.
For 6-MV, the surface dose was 1.05 Gy with a thick layer of petroleum-based ointment and 1.02 Gy for sliver sulfadiazine cream vs. 0.88 Gy without topical agents. For 15-MV, the doses were 0.70 Gy for a thick layer of petroleum-based ointment and 0.60 Gy for silver sulfadiazine cream vs. 0.52 Gy for the control phantoms.
That said, when 3 mm or more was applied to the phantoms, a bolus effect was observed; however, the increase in the surface dose was only an additional 2 to 5 percent.
“The very thick application used in this study was designed to represent an extreme situation that is very unlikely to occur in the clinic,” the researchers noted.
Parallel studies were completed on mice, and the use of a petroleum-based ointment did not affect the surface dose.
“We suggest that patients be advised that applying thin or moderate amounts of a topical agent, even right before radiotherapy, is acceptable and unlikely to increase toxic effects to the skin,” the researchers concluded. “Allowing patients to apply topical agents regardless of the timing with respect to radiotherapy will simplify patient instructions and reduce patient confusion and anxiety because many patients are concerned that having any residual topicals on their skin at the time of radiotherapy will increase toxic effects to the skin.”
As a senior news writer for TriMed, Subrata covers cardiology, clinical innovation and healthcare business. She has a master’s degree in communication management and 12 years of experience in journalism and public relations.