'Phantom Odors' a Common but Under-Reported Toxicity of Radiation Therapy

By Megan Brooks

November 01, 2021

NEW YORK (Reuters Health) - Patients who undergo proton-beam radiation therapy to tumors located in or adjacent to the olfactory region may develop phantosmia - the perception of a foul-smelling odor for which there is no external stimulus.

"Phantosmia is a frequent but underreported toxicity of radiation therapy," Dr. Shoshana Rosenzweig of the Icahn School of Medicine at Mount Sinai, in New York City, said in a presentation of the results at the American Society for Radiation Oncology (ASTRO) annual meeting.

The researchers reviewed the records of 100 patients, aged 39 years or younger, who received intensity-modulated proton-beam therapy (IMPT) for primary intracranial, metastatic intracranial, skull base, nasopharyngeal or sinonasal neoplasms between 2019 and 2020.

Twelve patients reported phantosmia during irradiation. None had previously received radiation therapy. The phantom odor was described as a "chlorine," "broccoli," "stale water," "metallic" or "noxious" smell.

Patients who reported phantosmia had a median age of 17 (range, 12 to 33 years); eight (67%) were male. Eleven (92%) had intracranial tumors.

"All patients who developed phantosmia received some radiation dose to the olfactory region. There was a significant association between craniospinal irradiation and the development of phantosmia toxicity," Dr. Rosenzweig reported in her poster presentation.

Phantosmia was categorized as mild in seven patients and moderate in five. Ten of the 12 patients experienced accompanying toxicities, including taste changes, visual disturbances, such as flashing and purple lights, and nausea or vomiting.

The patients with moderate phantosmia symptoms required an intervention or combination of interventions to continue treatment. Three received essential oils to smell during treatment, one of whom required the addition of chewing gum and an oral antiemetic. The two other patients also required the use of an oral antiemetic and one of them also used VicksVapoRub applied to the nasolabial folds during treatment. The other seven patients did not require any intervention to complete therapy, Dr, Rosenzweig reported.

"Phantosmia symptoms remained stable for 67% of patients, and improved with more fractions for 25% of patients and worsened for 8% of the patients who reported phantosmia. All patients were able to complete their radiation course as planned," she noted.

Craniospinal irradiation (CSI) was strongly correlated with phantosmia (odds ratio, 7.66; P=0.002) but use of chemotherapy with RT was not (OR, 1.09; P=0.90).

"This is the largest retrospective study to date investigating phantosmia among pediatric, adolescent and young adult patients receiving cranial proton beam therapy," Dr. Rosenzweig said.

"To improve patient's experience and treatment compliance, physician awareness of radiation-induced olfactory disturbances is necessary. Physicians treating pediatric, adolescent and young adult patients with cranial radiation, especially CSI, should discuss phantosmia as a potential side effect of treatment, ask patients about it during weekly status checks and be prepared to manage it in a timely fashion."

She said prospective studies are needed to elucidate mechanisms of phantosmia and further examine its incidence and associated with factors.

SOURCE: https://bit.ly/2ZvRpxR American Society for Radiation Oncology annual meeting, presented October 25, 2021.