Utility of cranial boost in addition to total body irradiation in the treatment of high risk acute lymphoblastic leukemia

Purpose: Total body irradiation (TBI) as part of a conditioning regimen before hematopoietic stem cell transplant (HSCT) is an important component in the management of acute lymphoblastic leukemia (ALL) that has relapsed or has other certain high-risk features. Controversy exists, however, as to whether a cranial boost in addition to TBI is necessary to prevent central nervous system (CNS) recurrences in these high-risk cases. Previous national trials have included a cranial boost in the absence of data to justify its use. Therefore, the aim of this study was to assess risk of CNS recurrence in ALL patients treated with TBI, to identify subsets of these high-risk patients at an increased or decreased risk of CNS recurrence after TBI, and to investigate whether regimens with higher doses of cranial irradiation further reduce the risk of CNS recurrence. Methods and Materials: Charts of 67 consecutively treated patients with ALL who received TBI before HSCT were reviewed. Data including patient demographics, clinical features at presentation, conditioning regimen, donor source, use of a cranial boost, remission stage at transplant, histologic subtype, cytogenetics, and extramedullary site of presentation were retrospectively collected and correlated with the risk of subsequent CNS recurrence. Results: At the time of analysis, 30 (45%) patients were alive with no evidence of disease, 8 (12%) were alive with recurrence of leukemia, 7 (10.5%) had recurrent ALL but with successful salvage, 7 (11%) died subsequent to recurrence, 14 (21%) died from complications related to HCST, and 1 patient was lost to follow-up (1.5%). Of the patients who recurred after HSCT, the relapses were hematologic in 13 (57%), CNS with or without simultaneous marrow involvement in 3 (13%), and other sites in 7 (30%). Forty-one (61%) patients did not receive an extracranial boost of irradiation with TBI. Two of these patients (4.9%) suffered CNS failures compared with 1 of 26 (3.8%) who received a cranial boost (p = 0.84). None of the 40 patients who presented only with hematologic disease developed a CNS recurrence despite the fact that only 13 of 40 of these patients received a cranial boost after TBI. Cranial boost was therefore not associated with a reduction in CNS recurrence, especially in patients with only hematologic disease at presentation for which there were no failures regardless of the use of additional cranial radiotherapy. Conclusions: Patients who present with hematologic disease only at the time of HSCT have a low risk of CNS recurrence after TBI regardless of the use of a cranial boost, suggesting that a cranial boost may not be necessary in these patients.