An Attempt to a New Neutron Capture Therapy Using Rhodium—The Anti-tumor Method Based on Beta Ray

Abstract

Neutron capture therapy (NCT) uses secondary particle to treat tumor. Boron has been applied to NCT in clinics, and gadolinium has also attracted the attention. Our group attempted a new candidate element, rhodium, because of its advantages, such as 100% natural abundance, long range (beta ray), neutron cross-section peak, and fitness to accelerator-based neutrons. To reduce toxicity and increase tumor accumulation, rhodium encapsulated liposomes (Rh-Lip) were synthesized. After 24 h exposure to rhodium solution, the cell viability increased to 90% when the rhodium concentration was diluted to 0.063 mg/mL; in contrast, it was up to 90% when rhodium concentration was diluted to 0.25 mg/mL in the Rh-Lip group. Moreover, in the Rh-Lip group, 387.3 ppm rhodium remained in the tumor 3 h after administration, but only 42.6 ppm remained in the rhodium solution group. After neutron irradiation, Rh-Lip showed a slower tumor growth rate and damage to tumor cells from pathological analysis, suggesting that rhodium is a potential element for NCT.