Treatment of Squamous Cell Carcinoma by Alpha-Radiation Based Brachytherapy (Alpha Dart), a New Radiation Concept

Objectives: First clinical assessment in humans of feasibility and safety of a unique intratumoral alpha radiation based tumor ablation treatment termed Diffusing Alpha emitters Radiation Therapy (DaRT) in patients with skin and oral cavity squamous cell carcinoma.

Methods: In an ongoing clinical study, a new method utilizing alpha particles to treat solid tumors is first examined in humans. Radium-224 loaded sources, 1 cm long and 0.7 mm in diameter, each carrying a dose of 2 µCi (DaRT seeds) were inserted into solid tumors. Through a sequence of radioactive decays (Rn-220, Po-216, Pb-212, Bi-212, Po-212, Tl-208), highly destructive alpha particles are released in the tumor, covering a diameter of at least 5 mm.

17 patients (ages 66-94y, median 81y) with histopathologically confirmed skin/oral cavity SCC ≤ 5 centimeters in diameter were treated. Six patients had oral cavity SCC and nine had aggressive skin SCC. Eleven patients were treated within radiation failure fields (Radiation dosage >60 Gy). Seeds were placed 5-6mm apart. Adequate insertion and tumor coverage were confirmed by CT. 2-4 weeks after implantation the seeds were removed. Treatment effect was assessed six weeks after treatment by CT.

Results: Results are available for 15 subjects who reached the 30-day visit. All tumors responded to the treatment; Eleven tumors had a complete response and four tumors showed a partial response. No major toxicity was noted.

Conclusion: In this feasibility and safety human study, alpha particles based DaRT exhibited enhanced radiobiological potential. The treatment was effective against radioresistant SCC tumors without major toxicity.