Kaplan-Meier estimate and cumulative relapse incidences for evaluation of the impact of preventive cranial radiotherapy. The curves compare the matching patients from ALL-BFM 90 and 95 who received presymptomatic cranial radiotherapy in trial ALL-BFM 90 yet were not irradiated in ALL-BFM 95 (pB-ALL, aged 1 year or older, no initial CNS involvement, risk group MR-90). (A) Event-free survival (P[log-rank] = .280). (B) Cumulative incidence of systemic relapses with CNS involvement (P[Gray] = .270) and isolated CNS relapses (P[Gray] < .001). Isol. CNS rel. indicates isolated relapse in the central nervous system; comb. CNS rel., combined relapse involving the central nervous system; 6y-pEFS, probability of event-free survival at 6 years; 6y-CI, cumulative incidence of relapses at 6 years; SE, standard error.