Study on the preparation of holmium-166 patch for skin cancer treatment

A radioactive patch containing holmium-166 bas been developed for skin cancer treatment. The flexible nonradioactive ¹⁶⁵Ho-film was prepared by dissolving polyurethane and ¹⁶⁵Ho(NO₃)₃. 5H₂O in a solvent mixture of DMF and THF, and subsequently extruding the mixture on an aluminum dish and air drying it. The resulting ¹⁶⁵Ho-film was easily converted to radioactive flexible ¹⁶⁶Ho-film by neutron irradiation in the 'HANARO' research reactor. The radioactive patch practically applicable to the treatment of the superficial skin cancer without using any adhesive agent could be prepared as a sandwich type patch by inserting the ¹⁶⁶Ho-film between two polyester film layers. The absorbed dose rates in skin by the ¹⁶⁶Ho-patch were computed by means of the EGS4 code system. Air and liquid water were used as transport materials. The number of histories was chosen as 40,000,000. The source was based on the disk type of ¹⁶⁶Ho-patch, and the target was designed to be a 0.5 mm height cylinder with the same diameter as that of the source. The dose rate distributions were obtained for source diameters ranging from 10-50 mm in 10 mm steps. The estimated dose rates for 37 MBq of five ¹⁶⁶Ho-patch sources in the increasing order of source diameter were 1.248 cGy/s(0. 96%), 0.324 cGy/s(0.83%), 0.145 cGy/s(0.92%), 0.082 cGy/s(0.93%), 0.053 cGy/s(1.02%) at a 0.5 mm target depth, respectively. On the basis of above results, the initial activity and irradiation period were determined so that the total absorbed dose for the treatment of squamous cell carcinoma was found to be 70-75 Gy. The disk type of the ¹⁶⁶Ho-patch was applied to animal models and patients with malignant skin cancer. Their efficacy and safety have been investigated for several months. Skin tumors could be successfully treated with the ¹⁶⁶Ho-patch in animal models and patients. The ease with which the ¹⁶⁶Ho-patch can be prepared in various types, and also its safety and effectiveness, make it an attractive device for skin cancer treatments