No Need to Avoid Topical Agents Before Radiation Therapy
NEW YORK (Reuters Health) - Thin or moderate application of a topical agent before radiation therapy is unlikely to affect the skin dose, although a thick amount should be avoided, researchers say.
"Radiation dermatitis is common and often treated with topical therapy," Dr. Brian Baumann of Washington University in St. Louis told Reuters Health by email. "Patients are typically advised to avoid topical agents for several hours before daily radiotherapy out of concern that (the) agents might increase the radiation dose to the skin."
"This recommendation came into practice in the era of ortho-voltage radiation from the 1920s to the 1950s, which delivered a higher dose to the skin," he said. "With modern mega-voltage (MV) radiation treatments that deliver less dose to the skin, this recommendation may no longer be relevant."
To investigate, Dr. Baumann and colleagues conducted an online survey of patients and physicians regarding topical therapy use from January 2015 to March 2017. They also evaluated the effect of topical agents on skin dose preclinically by delivering radiation to tissue-equivalent simulations with and without the application of two common topical agents: a petroleum-based ointment and silver sulfadiazine cream, 1%.
Further, they tested the effect of topical agents and skin dose in a mouse model.
Altogether, as reported online October 18 in JAMA Oncology, they surveyed 133 cancer patients undergoing radiotherapy (median age, 60; 87.9% women) and105 clinicians involved in managing patient skin care during such therapy.
Advice to avoid applying topical agents before radiation treatments was received by 111 patients (83.4%) and was provided by 96 (91.4%) of the clinicians.
However, the study results showed that thinly or moderately applied topical agents, even if applied right before radiation therapy, had "minimal influence" on skin dose, regardless of beam energy or beam incidence.
Specifically, dosimetric measurements in the tissue-equivalent simulation showed no difference in the delivered dose at either the surface or at a 2-cm depth, with or without a 1- to 2-mm application of either topical agent tested when using en face 6- or 15-MV photons.
Similarly, such application did not alter the surface dose as a function of beam incident angle from 15 degrees to 60 degrees - except for a 6% increase at 60 degrees with the silver sulfadiazine cream.
However, in the simulations, surface doses for 6- and 15-MV beams increased significantly when the topical agents were applied thickly (3-mm or more). For 6 MV, the surface dose was 1.05 Gy with a thick layer of petroleum-based ointment and 1.02 Gy for silver sulfadiazine cream versus 0.88 Gy without either topical agent.
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, versus 0.52 Gy for no topicals.
With 6- and 9-million electron volts (MeV), there was a 2% to 5% increase in surface dose with the use of the topical agents; however, there were no dose differences at 2-cm depth.
Further, in the mouse radiation experiments, there were no differences in phosphorylated histone-positive foci or in terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining with or without topical agents of varying thickness.
"Our survey results demonstrated that avoiding topical agents prior to radiation treatments is still widespread," Dr. Baumann said.
However, he noted, "We found no increase in the measured surface dose in the presence or absence of topical agents, except in the case of a very thick (at least 3 mm application) of a skin cream or ointment, which represents an extreme scenario that we did not encounter in our clinic."
"We also performed pre-clinical studies in mice and found no increase in radiation-induced DNA double-stranded breaks or in apoptosis in the presence or absence of topical ointment of varying thickness," he added.
"In my opinion, the results suggest that clinical practice should change regarding the advice clinicians give regarding topical agent use prior to radiation therapy.," he stressed. "I would support efforts to add a guideline suggesting that topical agents can be applied in a more liberal fashion prior to radiation treatments."
Dr. Chelsea Pinnix of the University of Texas MD Anderson Cancer Center in Houston, coauthor of a related editorial, told Reuters Health by email, "This study should be instrumental in providing evidence to radiation oncologists that this practice is unnecessary, (which) will likely improve patient quality of life during radiation therapy, as they will feel comfortable applying creams to address radiation dermatitis without exacerbating skin toxicity."
"I personally will change my practice because of these data," she concluded.
JAMA Oncol 2018.