Comparison of Planned Versus Delivered Dose to Children Receiving Total Body Irradiation Using Volumetric Arc Therapy

Clinical documentation of total body irradiation (TBI) predominantly relies on pretreatment plans rather than actual delivered doses.

This study systematically characterizes actual dose distributions in volumetric modulated arc therapy TBI (VMAT-TBI) using real-world data.

We retrospectively analyzed treatment plans and daily image-guided radiation therapy (IGRT) fan-beam CT (FBCT) images from 47 pediatric patients treated with VMAT-TBI at two institutions (January 2024-June 2025). Based on the IGRT from the current treatment session, the corresponding positions of the beam centers on the FBCT were determined. The beams were then transferred onto the FBCT for dose recalculation, thereby estimating the actual radiation dose distribution delivered to the patient during that treatment session.

Significant deviations between planned and delivered doses were observed. The 12 Gy/6 fraction regimen showed the greatest variability: median V_90% (PTV volume receiving ≥90% prescribed dose) decreased from 98.3% to 97.8% (-0.7%), V_100% declined from 93.5% to 92.5% (-1.0%), and V_110% increased from 8.0% to 19.0% (+11.0%). No regions received >120% of the prescribed dose. Mean lung dose reached 83.0% of the prescription in the 1 Gy regimen (+5.5% deviation) and 70.5% in the 12 Gy regimen (+5.0% deviation). All kidney doses remained below 9 Gy. Both planned and delivered doses remained within clinically acceptable ranges for all regimens.

This first systematic evaluation of actual delivered doses in VMAT-TBI confirms the technique's dosimetric precision and safety. Our findings provide actionable evidence for optimizing VMAT-TBI implementation in clinical practice, particularly regarding dose verification protocols and adaptive strategies for low-dose regimens.