Isodose 20 Gy found as a threshold dose for radiation recall dermatitis

Radiation recall is a rare phenomenon that can be observed in the field of radiotherapy, months or years after irradiation when a patient is exposed to certain pharmaceutical agents. In this report, we relate a case of radiation recall dermatitis induced after the application of a topical natural cream, 2 years after the initial radiotherapy treatment. Skin reactions were severe and limited to the irradiated volume, whereas a large part of the skin where the cream was applied outside the radiation field was strictly normal. More precisely, the radiation recall dermatitis matched with the isodose 20 Gy, whereas no recall reaction was observed in the lower dose areas (5, 10 or 15 Gy) despite these areas were also largely exposed to the cream. In conclusion, this is the first report that could provide a threshold dose for the occurrence of a radiation recall dermatitis, which was not observed below 20 Gy, in the context of this topical reagent.