One-year follow-up after fractionated ultra-high-dose-rate FLASH radiotherapy in patient with extramammary Paget disease of the scrotum.

Abstract

Objective: Ultrahigh-dose-rate radiotherapy (FLASH-RT) has been shown to reduce radiation-induced normal tissue injury in preclinical studies. Here, we describe the first patient worldwide to receive fractionated FLASH-RT.

Methods: An elderly male patient was diagnosed with extramammary Paget disease of the scrotum along with multiple lymph node and bone metastases. After 6 cycles of chemotherapy, the disease progressed in the scrotum. The scrotal lesions were evaluated for FLASH-RT. 9 MeV electron FLASH-RT was performed at a dose rate of 120 Gy/s. The field size was 5 cm × 5 cm, and the prescribed dose was 40 Gy in five fractions. Dosimetric verification was performed daily. Treatment response was evaluated at 3-month post FLASH-RT, and normal tissue toxicity was assessed from the beginning of FLASH-RT to 12-month post-irradiation.

Results: A 1-year follow-up was achieved for scrotal lesions treated with electron FLASH-RT in patients with extramammary Paget disease. Electron FLASH-RT was safe, and treatment-related adverse events were mild. Transient skin toxicity occurred 2-5 weeks post FLASH-RT, and exudation and burning pain were significantly alleviated. A complete response was achieved 2-3 months post FLASH-RT, and the tumor lesions were covered by the normal epithelium of the scrotum. At the end of the one-year follow-up, the tumor lesions continued to respond, and one-year survival was achieved without additional injury to the irradiated areas after FLASH-RT.

Conclusion: Fractionated electron FLASH-RT is feasible and safe for the treatment of extramammary Paget disease of the scrotum. Our findings support further exploration of electron FLASH-RT in patients with skin tumors.