Occurrence and mechanism of visual phosphenes in external photon beam radiation therapy and how to influence them

• Published in: Radiotherapy and oncology Vol. 132; pp. 109 - 113
• Main Authors: de Kruijf, Willy, Timmers, Anke, Dekker, Janita, Böing-Messing, Florian, Rozema, Tom
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier B.V 01.03.2019
• Subjects: Cherenkov radiation; Female; Head and Neck Neoplasms - radiotherapy; Humans; Light flashes; Logistic Models; Male; Middle Aged; Phosphenes - physiology; Photon beam radiation therapy; Photons - adverse effects; Photons - therapeutic use; Photoreceptor proteins; Retina - radiation effects; Visual phosphenes; Photon beam radiation therapy; Cherenkov radiation; Light flashes; Photoreceptor proteins; Visual phosphenes
• ISSN: 0167-8140; 1879-0887
• DOI: 10.1016/j.radonc.2018.11.010

•Visual phosphenes are probably caused by photon activation of photochemicals either by the direct or scattered beam or by the Cherenkov radiation.•One could reduce the dose rate, keep the eyes open, or increase the illuminance to reduce visual phosphenes.•Visual phosphenes might be correlated with fatigue in radiation therapy. Two plausible mechanisms to explain the appearance of visual phosphenes are: direct activation of the photochemicals in the retina and the generation of Cherenkov radiation in the vitreous humour. In this clinical trial we investigated the occurrence of visual phosphenes in external photon beam radiation therapy. Logistic regression analysis is used to examine whether seeing light flashes and seeing steady light depended on the ambient light intensity and the dose. In total, 465 treatments of 25 patients were analysed. The odds of seeing light flashes multiply by 0,926 as the ambient light intensity increases by 10 lux. Similarly, the odds multiply by 1,604 as the dose to the retina increases by 10 cGy. The odds of seeing steady light multiply by 1,540 as the dose to the vitreous humour increases by 10 cGy. We postulate that one should reduce the dose rate, instruct patients to keep the eyes open and increase the illuminance in the treatment room to reduce the probability of experiencing visual phosphenes. We hypothesize that melanopsin is involved in the visual phosphenes and that fatigue of patients might be correlated with the observation of visual phosphenes.