Myeloablative Total Body Irradiation With Volumetric Modulated Arc Therapy for Children-a Single Center Experience

Total body irradiation (TBI) is a critical component of conditioning therapy prior to allogeneic hematopoietic stem cell transplantation in pediatric acute lymphoblastic leukemia. Our institution implemented volumetric modulated arc therapy-TBI (VMAT-TBI) in 2023, aiming to improve target conformity and organ-at-risk sparing using standard linear accelerators. This study describes our initial 2-year institutional experience with VMAT-TBI, focusing on treatment planning and delivery metrics, as well as early clinical outcomes and acute toxicities in pediatric patients.

We conducted a review of 10 pediatric patients treated with VMAT-TBI at our institution from October 2023 to June 2025. All patients received myeloablative conditioning with 12 Gy in 6 fractions over 3 days, followed by intravenous etoposide preceding allogeneic hematopoietic stem cell transplantation. Data collected included treatment planning parameters, planning duration, delivery times, overall survival, relapse-free survival, and acute toxicities.

Treatment plans achieved robust target coverage (V ₁₀₀ > 90%) and met organ-at-risk constraints, with mean lung, kidney, and lens doses of 8.8 Gy, 8.7 Gy, and 8.5 Gy, respectively. Mean beam-on time per fraction was 21.3 minutes, and in-room time was 77 minutes. Image guided verification showed that online translation was within 3 mm and <1° rotation. The median follow-up was 19 months, with 1-year overall survival and relapse-free survival rates of 90%. Nonrelapse mortality at 1 year was 10%. The most common acute toxicity was mucositis, affecting 70% of patients (grades 2-3 in 40%), with a median onset of 2 days. Gastrointestinal toxicities, including vomiting (50%) and diarrhea (40%), occurred early, with a median onset of 2-3 days.

Our early institutional experience demonstrates that VMAT-TBI is safe, feasible, and effective in pediatric patients, achieving excellent target coverage and acceptable acute toxicity profiles. These findings support the viability of implementing VMAT-TBI even in resource-constrained settings.