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