Feasibility, Treatment Planning, and Clinical Results of VMAT-Based Total Body Irradiation for Pediatric Patients:...

Total body irradiation (TBI) is a standard component of conditioning regimens for pediatric patients with acute lymphoblastic leukemia (ALL) undergoing hematopoietic stem cell transplantation (HSCT). Volumetric modulated arc therapy (VMAT) has emerged as a promising technique to improve dose conformity and organ-at-risk (OAR) sparing. This study evaluates the feasibility, dosimetric performance, and acute toxicity of a VMAT-based TBI (VMAT-TBI) technique implemented in a pediatric population.

Fifteen pediatric patients treated with myeloablative VMAT-TBI between August 2019 and December 2024 were retrospectively analyzed. Prescription regimens ranged from 9.9 to 12 Gy, delivered in three to six fractions. Planning objectives followed ESTRO-ACROP-SIOPE recommendations, with mean lung dose less than 8 Gy and mean kidney dose less than 10 Gy. Dosimetric coverage, OAR sparing, patient-specific quality assurance, image-guided verification, and clinical outcomes were assessed.

All treatment plans achieved adequate target coverage (mean PTV D95% = 96.6% ± 2.5%), with V110% = 19.1% ± 11.2% and V120% less than 1%. Mean lung and kidney doses were 7.8 ± 0.7 and 8.9 ± 1.1 Gy, respectively. Planned and measured dose distributions showed excellent agreement (gamma passing rates with 3%/3 mm criteria of 96.2% ± 4.6% with ArcCHECK diode array). After a median follow-up of 18 months, one late non-infectious pulmonary toxicity and one severe renal toxicity were observed.

VMAT-TBI is a feasible, effective technique for pediatric HSCT conditioning, providing excellent target coverage, OAR sparing, and acceptable toxicity. These findings support VMAT-TBI as a viable alternative to conventional TBI.