Feasibility of Total Body Irradiation (TBI) Treatment Planning Using High-Resolution Multileaf Collimators Compared to Conventional Mlc Systems
Abstract
Purpose
To assess the feasibility and dosimetric performance of volumetric-modulated arc therapy (VMAT) for total body irradiation (TBI) using high-resolution multileaf collimators (HR-MLCs).
Methods
TBI treatment plans were developed for patients using a commercial treatment planning system for a clinical linear accelerator. Three VMAT plans were generated for each patient: Conventional: Standard geometry using 4–5 midline isocenters and a multileaf collimator with a 40×40 cm maximum field size. HR-Single: Same isocenter configuration using a high-resolution MLC with a reduced field size of 22×32 cm. HR-Dual: Modified geometry with laterally split isocenters (±10 cm from midline) to account for the limited field size of the HR-MLC, preserving midline isocenters for setup reproducibility. Each plan used 2 arcs per isocenter (HR-Dual: 8 total isocenters) with asymmetric jaws along the cranial-caudal axis. Dosimetric endpoints included D80, D50, D10, lung mean dose, Dmax, homogeneity index (HI), conformality index (CI), and monitor units (MU).
Results
HR-Dual plans demonstrated comparable target coverage and conformality to conventional MLC plans. Lung mean dose was not significantly different (62.7% vs. 58.7%, p = 0.56), and Dmax increased modestly by 4%. HR-Single plans were clinically unacceptable, with significant increases in lung dose (+34%) and Dmax (+41%). While HR-Dual plans exhibited greater homogeneity (HI = 0.56 vs. 0.44), they required a 38% increase in MU on average, reflecting higher plan complexity and treatment time.
Conclusion
TBI using high-resolution MLCs is feasible when employing a dual-isocenter VMAT technique, achieving dosimetric quality comparable to that of conventional large-aperture MLC systems. However, increased complexity and treatment time must be considered. Use of high-resolution MLCs for TBI should be considered only when conventional large-field MLC-equipped linacs are not available.