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TBI delivery varies widely across institutions
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The use of total body irradiation for conditioning before hematopoietic cell transplantation varied widely among health care centers across 23 countries, study results showed.
Researchers, therefore, caution the interpretation of clinical studies designed to evaluate the safety and efficacy of the procedure.
“Because it is difficult to design multicenter randomized trials focused on total body irradiation techniques, every effort should be made to perform large retrospective studies addressing these issues,” Sebastian Giebel, MD, of the department of bone marrow transplantation and onco-hematology at the Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology in Poland, and colleagues wrote. “The results of the current survey may be useful for the planning of such analyses because we were able to identify the areas of particular heterogeneity … Based on the results of postulated retrospective analyses, attempts should be made to standardize the method to further improve results of the treatment.”
The researchers distributed questionnaires to all centers collaborating in the European Group for Blood and Marrow Transplantation. The questionnaires included 19 questions about various aspects of total body irradiation (TBI).
Responses from 56 centers in 23 countries were included in the final analysis. Fifty-one (91%) of the centers used the linear accelerator (LINAC), and five (9%) used the cobalt unit. Two centers also used helical tomotherapy units as an alternative to LINAC.
Study results showed the total maximum dose of TBI used for myeloablative transplantation ranged from 8 Gy to 14.4 Gy, and the dose per fraction ranged from 1.65 Gy to 8 Gy.
Researchers identified 16 dose/fractionation modalities, and the dose rate ranged from 2.25 centigrays per minute to 37.5 centigrays per minute.
Beams used in LINAC ranged from 6 megavolts to 25 megavolts. Study results showed nine various modalities of beam energy were recognized; slightly more than half of centers (51%) used 6 megavolts.
Sixty-four percent of centers used the “patient in 1 field” irradiation technique. Forty-one percent of centers immobilized patients during TBI, and 84% of centers shielded patients’ lungs during irradiation. The maximum accepted dose for the lungs ranged from 6 Gy to 14.4 Gy.
“TBI is an extremely heterogeneous treatment modality,” Giebel and colleagues wrote. “The findings of the current study should warrant caution in the interpretation of clinical studies involving TBI. Further investigation is needed to evaluate how methodological differences influence outcome. Efforts to standardize the method should be considered.”
Disclosure: The researchers report no relevant disclosures.
Perspective
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Edward A. Copelan, MD, FACP
The extreme heterogeneity of TBI techniques reflected in this survey of European transplant centers merits our full attention. Determination of whether one approach is better than another is particularly difficult in the field of hematopoietic cell transplantation, in large part due to the rarity of large randomized controlled trials. In order to address critical issues in the field, clinicians often must rely on the results of large observational studies, such as recent comparisons of “standard” TBI-based myeloablative conditioning with myeloablative IV busulfan-based regimens and with less intensive conditioning. Although heterogeneity in the administration of a therapy permits a generic assessment of its effectiveness in the real world, it prevents conclusions as to its potential benefit when optimally administered. Although less obvious, a close look reveals considerable variation even among prospective randomized trials in how rigidly the administration of TBI is defined. Even when total dose and fractionation are specified, differences in dose rate, treatment unit, technique, organ shielding and dosimetry may vary, emphasizing the need for careful design and conduct of these trials. More worrisome, however, are the complexities this survey exposes regarding interpretation of observational studies employing “standard” TBI. The study by Giebel and colleagues reminds us that, when comparing alternate approaches in transplantation and elsewhere, the devil is in the details.
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