KEY POINTS
- This single-center retrospective study included 15 children receiving myeloablative VMAT-based TBI from 2019–2024 before hematopoietic stem-cell transplantation. Median age was 6 years; 14 patients had acute lymphoblastic leukemia and one had cerebral T-cell lymphoma.
- Fractionation varied because 9 patients required anesthesia. Eight received 12 Gy in 6 fractions, four received 12 Gy in 4 fractions, two received 9.9 Gy in 3 fractions and one received 10 Gy in 4 fractions; seven anesthetized children therefore received non-standard once-daily schedules.
- Whole-body target coverage was clinically acceptable: mean PTV D95 was 96.6% ± 2.5%, D90 100.2% ± 1.5%, V110 19.1% ± 11.2%, and V120 only 0.2% ± 0.3%. The authors used multiple isocenters, skin flash and, after introduction of a rotatable tabletop, overlapping head-first and feet-first CT datasets.
- Organ sparing met contemporary pediatric TBI goals in most patients. Mean lung dose was 7.8 ± 0.7 Gy and, among 12 patients treated after renal constraints were implemented, mean kidney dose was 8.9 ± 1.1 Gy. In selected cases, VMAT also allowed individualized sparing—for example, pancreatic mean dose was reduced to 4.5 Gy in a child with severe prior pancreatitis.
- Reducing thoracic maximum dose rate from 600 to 100 MU/min lowered estimated mean lung dose rate from 48.9 to 23.0 cGy/min. Whether this precaution is biologically necessary for VMAT-TBI remains uncertain because contemporary evidence has not clearly linked higher VMAT dose rates with pulmonary toxicity.
- Patient-specific QA across 61 plans produced a mean 3%/3-mm ArcCHECK gamma passing rate of 96.2% ± 4.6%. Treatment remained logistically intensive: mean intrafraction time was approximately 39 minutes with the fixed-table workflow and 66 minutes with the rotatable tabletop.
- After median follow-up of 18 months, one child developed late BOOP/cryptogenic organizing pneumonia 9 months after TBI despite a mean lung dose of 7.6 Gy and recovered with corticosteroids. One patient developed grade 4 acute kidney injury after a 7.9-Gy mean renal dose and later died, although the renal event was considered multifactorial rather than radiation-induced.
CLINICAL TAKEAWAY
VMAT can deliver pediatric TBI with good whole-body coverage while meeting modern lung and kidney constraints and allowing patient-specific organ sparing. The technique is feasible but resource-intensive, and this small heterogeneous cohort cannot establish lower toxicity than conventional TBI.