Small-Vault Total Body Irradiation Using Jaw-Defined Sweeping Arc Delivery
Abstract
Purpose
Total Body Irradiation (TBI) for patients with hematological malignancies aims to deliver a prescribed dose within ±10% to the entire body as conditioning for bone marrow transplantation. Existing TBI techniques are often complex and resource-intensive. We present a novel TBI approach using Treatment Planning System (TPS) -optimized jaw-defined arcs, suitable for a small treatment vault.
Methods
Patients are treated in both supine and prone positions on a support structure close to the floor, aligned in the gantry’s rotation plane, at a nominal source-to-surface distance (SSD) of 200 cm. A full-body beam spoiler is placed approximately 20 cm above them. The linear accelerator (linac) delivers a 10 MV arc (310°-50°) with arc weighting adjusted every 5° to account for SSD variation, scatter, beam spoiler attenuation, patient thickness, and lung sparing. Field is fixed at 30×40 cm2 and encompasses patient laterally while sweeping longitudinally. The dose is calculated on the patient's CT within the TPS. TPS calculations under these non-standard conditions were validated using ion chamber measurements in slab phantoms at multiple depths and positions. Additional TPS calculations evaluated the impact of energy (6 MV vs 10 MV) and field size (20x40, 30x40, 40x40 cm2). Two full-body anthropomorphic phantoms, with and without lung and bone inserts, were used for dose verification, with diode measurements at eight anatomical locations.
Results
TPS accuracy was within 3%. The 10 MV with 30 x 40 cm2 arc configuration provided the best coverage and homogeneity. In the anthropomorphic phantom plans, more than 95% of the body received the prescribed dose within ±10%, with diode measurements within 5% of the prescribed dose.
Conclusion
This technique enables efficient, uniform, CT-based TBI using linac capabilities without vault-size limitations. Planning can be completed in under one hour, with total treatment delivery of approximately 30 minutes.