A Multicenter Prospective Trial of Diffusing Alpha-Emitter Radiation Therapy for Recurrent or Unresectable Cutaneous Cancers: Early Results from a Pilot Feasibility Study in the United States

Purpose/Objective(s)

Recurrent or unresectable cutaneous cancers may have limited treatment options. Diffusing alpha-emitter Radiation Therapy (DaRT, AlphaTau Medical, Tel Aviv, Israel) is a novel method of treating solid tumors using alpha-particle interstitial radiotherapy. A prior study conducted outside the United States demonstrated the feasibility, safety and efficacy of DaRT in patients with squamous cell carcinoma of the skin or mucosa of the head and neck. In this prospective multicenter trial conducted in the United States, we tested the hypothesis that DaRT for recurrent and unresectable cutaneous cancers was feasible, and also characterized preliminary safety and efficacy.

Materials/Methods

Patients with malignant skin or soft tissue tumors were recruited if they had limited treatment options, including recurrent disease, unresectable tumors, or those with metastases which could not be rendered disease-free with surgery. After baseline patient and tumor assessment, pre-treatment planning was performed. Patients underwent temporary DaRT placement to deliver a physical dose of 10 Gy to the tumor. Patients were followed for adverse events and tumor response 6, 12 and 24 weeks after removal. The primary objectives were to determine the feasibility of the procedure (based on successful implantation of DaRT device in the tumor) as well as the safety (based on adverse events (AEs) graded by CTCAE V5.0). Secondary objectives included response (based on RECIST V1.1 criteria), among others.

Results

Ten patients were recruited to the study and all successfully underwent the DaRT procedure, confirming feasibility. Median patient age was 72 years (range 57-92 years), with 6 men and 4 women participating. Six patients had recurrent disease, 4 were deemed unresectable and none had metastases. Tumors were located on the nose, chin, eyelid, scalp, neck, trunk, and extremities. The baseline mean tumor volume was 3.4 cm³ (range 0.65-12.65 cm³). Mean prescription dose coverage of the gross tumor volume was 91%, with all tumors having ≥85% coverage. No device-related grade 3 AEs were noted. Common AEs were grade 1-2 erythema, edema, and pruritis. At 12 weeks following treatment, there was a 100% complete response (CR) rate. Nine out of the ten CRs were confirmed by CT imaging.

Conclusion

This trial demonstrated the feasibility, and preliminary safety and efficacy of DaRT in the treatment of recurrent or unresectable cutaneous cancers. The favorable safety profile and high response rate are promising. A pivotal US trial for marketing approval is expected to be underway by the time of this presentation.