From the Journals

Use of topical agents before RT may be safe

 

Key clinical point: Modest application of topical agents preceding radiotherapy (RT) treatment may be safe for patients.

Major finding: When common topicals were applied at a thickness of less than 2 mm, negligible effects on radiation dose were seen.

Study details: An online survey consisting of 133 patients and 108 clinicians, in addition to a tissue-equivalent phantom and mouse model preclinical study.

Disclosures: The study was funded by development funds from the University of Pennsylvania, Philadelphia. The authors had no disclosures relevant to this study.

Source: Baumann BC et al. JAMA Oncol. 2018 Oct 18. doi: 10.1001/jamaoncol.2018.4292.

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Radiotherapy myth debunked

The common practice of discontinuing topical therapies immediately prior to radiotherapy (RT) is likely an accepted myth, and through allowance of these agents, quality of life for patients may improve, according to Simon A. Brown, MD, and Chelsea C. Pinnix, MD, PhD.

The dogma stems from a period known as the “orthovoltage era,” which started in the 1920s, lasting into the 1950s. During this time, radiation oncologists recommended against the use of topical therapies or related agents directly preceding RT sessions, Dr. Brown and Dr. Pinnix wrote in invited commentary. The assumption was that using these agents could lead to increased dermatologic toxicities, because of the alleged bolus effects, or interactions with metal salts present in the topical. Bolus effects are sometimes beneficial, by reducing the delivered treatment dose in deeper tissues; but they also may be harmful, if unanticipated.

A similar study that took place in 1997, in which a group of researchers from the Medical College of Georgia, Augusta, investigated links between various topical agents and irradiation surface dose using a 6-MV photon beam. The results, similar to those reported by Dr. Baumann and his colleagues, showed that surface doses were affected only if agents were applied in a very thick manner, beyond what is considered normal. In addition, metal salts contained within the topical agents did not alter administered surface dose.

Taken together, the commentators stated that the common proposition that topical therapies must be avoided prior to RT is likely not relevant in many clinical situations.

Dr. Brown is affiliated with the department of radiation medicine at Oregon Health & Science University in Portland and Dr. Pinnix is with the department of radiation oncology at the University of Texas at the MD Anderson Cancer Center in Houston. These comments are adapted from their invited commentary.


 

REPORTING FROM JAMA ONCOLOGY

Moderate application of topical therapies directly prior to radiotherapy (RT) treatment sessions may be safe and might exhibit minimal effects on delivered treatment dose, investigators report.

The researchers found that although avoiding topical agents prior to radiation treatments was widespread, preclinical data indicate that there is no difference in the radiation dose on the skin with or without a 1- to 2-mm-thick layer of topical agent.

In an online survey, which queried 133 patients and 108 clinicians in relation to existing practices surrounding topical agent use, 83.4% of patients were informed to discontinue application of topical therapies directly before RT treatment sessions. In addition, 54.1% were told to clean and remove any enduring topical agents before treatment. Among clinicians, 91.4% reported to have received or given advice to stop application of topicals before obtaining RT treatment, Brian C. Baumann, MD, and his associates reported in JAMA Oncology.

However, in a preclinical study using a mouse- and tissue-equivalent phantom model to determine the dosimetric effects of concomitant topical agent use with daily RT treatments, Dr. Baumann, of Washington University in St. Louis, and his colleagues determined that when a topical agent was given prior to RT at a thickness below 2 mm, no changes were seen in radiation treatment dose, irrespective of depth, photon and electron energy level, or beam angle.

However, a proportionally thicker covering (3 mm or more) caused a bolus effect at the surface, which resulted in electron dose increases of 2%-5%, and photon increases of 15%-35%, when compared with controls.

Investigators measured radiation dose and photon beam intensity at various surface depths after applying two commonly used topical therapies, a healing ointment of 41% petrolatum or silver sulfadiazine cream 1%. The agents were administered using a thick (1-2 mm) application and proportionally thicker (3 mm or more) covering.

“Thin or moderately applied topical agents, even if applied just before RT, may have minimal influence on skin dose regardless of beam energy or beam incidence,” the investigators wrote. However, the findings do suggest that “applying very thick amounts of a topical agent before RT may increase the surface dose and should be avoided,” they said.

The authors reported that the study was funded by development funds from the University of Pennsylvania, Philadelphia. One of the coauthors, James M. Metz, MD, disclosed service on advisory boards for Ion Beam Applications and Varian Medical Systems for proton therapy; however, these roles were not relevant to this study.

SOURCE: Baumann BC et al. JAMA Oncol. 2018 Oct 18. doi: 10.1001/jamaoncol.2018.4292.

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