Evaluation of radiation therapy factors in prophylactic central nervous system irradiation for childhood leukemia: a report from the Children's Cancer Study Group

The results of six different types of central nervous system (CNS) prophylaxis were studied in two successive Children's Cancer Study Group clinical trials of children with acute leukemia. Radiation therapy doses and technical factors were analyzed in relation to survival, relapse-free survival, bone marrow and CNS relapse rates, and the toxicities encountered in 656 study children. They were randomized among: (1) 2400 rad to the craniospinal axis (CS) and 1200 rad to the abdomen and gonad, (2) 2400 rad CS, and (3) 2400 rad to the cranium (Cr) + IT/MTX. Hematologic, gastrointestinal and infectious disease compilations were highest in group 1. The patients were divided into low and high risk categories, defined as those with initial white blood cell counts below and above 20,000/cu mm for outcome analyses. No statistically significant differences were detected in the five-year rates for relapse-free survival or survival, nor fo CNS or bone marrow relapse among the 5 irradiated groups when equipment variables, total doses, field arrangements, fractionation, and protraction were analyzed. These results should be interpreted in the light of the group 4 children who had the highest CNS relapse rates (e.g., 33% for low risk patients vs 4 to 16% for their counterparts in the other 5 groups), but nonetheless had a generally similar bone marrow and survival experience. Exceptions to the foregoing are the better five-year survival rates of 64 and 73% respectively for group 3 and group 6 high-risk boys, contrasted with 25 to 42% for their counterparts in the other 4 groups