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The Children's Cancer Study Group has organised two therapeutic clinical trials designed to evaluate the efficacy of various types and doses of CNS prophylaxis in the treatment of childhood acute lymphoblastic leukaemia. Of 478 previously untreated patients who subsequently achieved an initial marrow remission, 299 were randomised to receive 2400 rad craniospinal radiation therapy (RT) or 2400 rad cranial RT plus intrathecal methotrexate (i.t. MTX) while the remaining 179 patients were randomised between the same two regimens using a radiation dose of 1800 rad. All patients received identical induction and maintenance chemotherapy. Comparison of the two studies indicated that reduction of the dose of CNS radiation from 2400 rad to 1800 rad did not result in a significant increase in the frequency of CNS relapse, bone marrow relapse, or death. Moreover, no significant differences were observed when analyses were done within prognostic risk groups. Randomised trials with RT doses lower than 1800 rad or with i.t. chemotherapy alone should be considered to determine the most effective and least toxic forms of CNS prophylaxis.

A retrospective comparison was made of three methods of central-nervous-system prophylaxis in childhood acute lymphoblastic leukaemia; (1) intrathecal methotrexate only; (2) intermediate-dose methotrexate infusion and intrathecal methotrexate and, (3) 2400 rads cranial irradiation and intrathecal methotrexate. The incidence of primary meningeal relapse was statistically significantly lower in both standard-risk patients (age grear than 24 months and less than or equal to 120 months white-cell count less than 20,000) and increased-risk patients (age less than or equal to 24 months or greater than 120 months and/or white-cell count greater than 20,000) whose central-nervous-system prophylaxis included cranial irradiation. The disease-free and overall survival of irradiated increased-risk patients was significantly better than that of unirradiated increased-risk patients. The disease-free survival of standard-risk patients who received intermediate-dose methotrexate was statistically superior to that of the remaining standard-risk patients. There were no significant differences in overall survival between the three groups of standard-risk patients.