Review of the SIN and Los Alamos Pion Trials.

Negative pi mesons (pions) were used to treat 227 patients at the Los Alamos Meson Production Facility (LAMPF) between 1974 and 1981. Persisting local control values for 129 patients treated with pions alone in the following tumor sites were recorded at a minimum post-treatment observation interval of 2.5 years in the following tumor sites: cerebral gliomas 3/29; head and neck, 8/31; lung, 1/7; pancreas, 0/17; large bowel, 3/13; cervix, 2/45; bladder, 3/4; prostate, 18/20; miscellaneous sites, 0/4. Late severe sequelae ranged from none to 30% for major sites. A dose-response relationship was seen for late severe sequelae with a high probability following dose levels of 4750 cGy (max) in approximately 38 fractions. RBE values for pions appeared to lie in the range of 1.4-1.6 for both acute normal tissue reactions and late sequelae. At the Swiss Institute for Nuclear Research (SIN), 126 patients were treated in Phase I-II protocol studies between 1982 and 1984 with a new technique of scanning with a focused spot of pions. With minimum observation intervals of only 6 months, the local complete response values in 67 evaluable patients treated with pions alone to selected sites are gliomas 1/15 (9 months); pancreas, 3/11; cervix, 4/8; bladder, 18/26 (at 1 year, 9/22); sarcomas, 4/5; biliary tract, 3/4. Late severe sequelae ranged from none to 50% for major sites. A steep dose-response relationship is seen for late severe sequelae with high probability following doses exceeding 3800 cGy (max) in 20 fractions and very low probability with doses below 3500 cGy (max).