Phantosmia Among Pediatric, Adolescent, and Young Adult Patients Receiving Proton Beam Therapy

Purpose: Phantosmia, an underreported toxicity of brain radiation therapy (RT), is defined as an olfactory disorder resulting in a malodorous phantom smell. This study aimed to characterize the incidence of phantosmia in patients treated with intensity modulated proton therapy (IMPT). Methods and Materials: In this institutional review board–approved retrospective study, the electronic medical record of a pencil beam scanning-only proton center was queried for patients ≤39 years of age who received IMPT for primary intracranial, metastatic intracranial, skull base, nasopharyngeal or sinonasal neoplasms between August 2019 and December 2020. Patient, clinical, and phantosmia-related characteristics were collected. The olfactory region was defined to include the olfactory bulb and tract. Phantosmia severity was graded by intervention use (mild, no intervention; moderate, supportive treatment; severe, RT discontinuation). Results: Ninety-nine patients met the inclusion criteria. Twelve patients (12.1%) reported phantosmia. Patients described perceiving a “chlorine,” “broccoli,” “stale water,” “metallic,” or “noxious” smell. Of the patients who reported phantosmia, median age was 17 (12-33) years, 66.7% were male, and 91.7% had intracranial tumors. None of the patients had prior RT. Chemoradiotherapy treatment did not correlate with phantosmia development (odds ratio, 1.09; 95% confidence interval, 0.32-3.70; P = .90). Ten patients experienced accompanying toxicities, including taste changes (n = 3), vision disturbances (n = 5), and nausea/emesis (n = 7). Phantosmia was mild (n = 7) or moderate (n = 5). All patients completed their RT course. Sixty-seven percent received craniospinal irradiation (CSI) while 33% received focal brain RT, with the olfactory region receiving doses as low as 0.5 Gy. Notably, 8 of 27 patients who received CSI (30%) reported phantosmia (odds ratio, 7.66; 95% confidence interval, 2.07-28.34; P = .002). Conclusions: In the first-ever study examining radiation-induced phantosmia among children and young adults treated with IMPT, all affected patients received irradiation dose to the olfactory region. Physician awareness of phantosmia, especially in the context of CSI, may improve the patient experience and treatment compliance. A prospective study is needed to elucidate frequency, severity, and phantosmia mechanism.