1992 年 7 巻 3 号 p. 285-289
In 7 patients the primary lesion of malignant melanoma was treated with proton beams in Proton Medical Research Center, University of Tsukuba. Four cases were male and the other 3 were female. Five cases were acral lentiginous melanomas and the other 2 were superficial spreading melanomas. Two cases received 3 to 8Gy fractions administrated 15 or 16 times in 24 or 44 days to a total dose of 90 or 91Gy. The other patients received even higher single doses than them, i.e. large fraction radiotherapy. They received 10 to 13Gy fractions administrated 7 to 11 times in 9 to 18 days to a total dose of 91 to 110Gy. Clinically the tumor reacted to the irradiation and in 6 cases showed partial regression of the size with erosive reaction, and in one case showed complete regression with complete healing of moist desquamation. Histological examinations were performed in 4 cases and they showed many melanoma cells degenerated. Electromicroscopic examination revealed that the organelle and the nucleus highly degenerated. Results indicated good local effects were obtained by proton beams, although additional modalities were requested to manage the remaining tumors.
Malignant melanoma is considered unresponsive to conventional radiation therapy in part due to a large shoulder on the radiation survival curve and higher dose fractions might be beneficial. The superior dose distribution of proton beams allows high-dose exposure to the target area with lesser dose to the surrounding normal tissues. And it enables one to treat malignant melanomas with as high single doses as 10 Gy like in the 5 cases, expecting that repair process of melanoma cells would be overcome. It is postulated that proton therapy should allow malignant melanoma to be treated with even higher doses resulting in improved local control rates.