Experience with pion radiotherapy.

Forty-one patients with a total of 86 tumors were treated with negative pimesons (pions) at the Los Alamos Meson Physics Facility (LAMPF) through December 31, 1977. An additional 30 tumors in the total patient population were treated with 100 kVp x-rays to assess comparative effects on skin nodules and 8 patients received additive photon or electron radiation to pion-treated portals. Of 52 evaluable tumors in 20 patients treated with pions only and followed for 3 to 22 months, 81% (42 tumors) completely regressed; 6% (3 tumors) partially regressed; and 13% (7 tumors) did not respond, although 5 of the 7 have shown no growth for 10 months. Of eight tumors in seven patients treated with a combination of pions and conventional radiation, three tumors showed complete response and five tumors showed partial response, though the resected specimens in two (one with complete and one with partial response) revealed no tumor microscopically. Reactions in normal tissues have been mild, with some patients exhibiting no normal tissue reaction, as compared with relatively marked tumor response.