Author: Carlos E. Cardenas, Udbhav S. Ram, Marcin Wierzbicki 👨🔬
Affiliation: The University of Alabama at Birmingham, University of Alabama at Birmingham, Juravinski Cancer Centre 🌍
Purpose:
This study aims to systematically evaluate the dosimetric properties and delivery efficiency of 6X-FFF and 10X-FFF beams for lung SBRT on the Varian TrueBeam STx using the Eclipse TPS 16.1 with the AcurosXB13.5 algorithm. Although 6X-FFF is well-documented for superior OAR sparing, 10X-FFF leverages higher dose rates to potentially reduce treatment times. We seek to quantify these inter-energy differences in dosimetry and assess delivery efficiency using a novel heterogeneous lung phantom.
Methods:
Ten SBRT lung cancer patients previously treated with 6X-FFF (7 peripheral cases with 4x48Gy and 3 central cases with 8x60Gy) were replanned using 10X-FFF under identical optimization objectives (re-planned using previously optimized 6X-FFF objectives). Dose Volume Histogram (DVH) data and clinical objectives were analyzed for comparison. A custom heterogeneous lung phantom was developed using low-cost materials (cork and acrylic) to replicate lung tissue, chest wall, and lesion densities.
Results:
Preliminary results from 10 replanned patients show that 6X-FFF demonstrates superior OAR sparing (~15% reduction in mean dose to proximal OARs) compared to 10X-FFF, consistent with prior studies. Dose gradients were observed to have higher fall offs with the lower 6X energy, where 10X beams contributed to lower (~7%) skin doses, due to deeper dose deposition. CT scans also confirmed material heterogeneity and density accuracy (0.265g/cc for lung tissue, 0.987g/cc chest wall and lesion).
Conclusion:
6X-FFF offers better OAR sparing, over 10XFFF, which is expected to provide lower beam-on times across all cases. Both energies provide clinically acceptable dose distributions with no significant differences in accuracy. The developed lung phantom serves as a reproducible tool for future multi-institutional studies. These findings guide energy selection in SBRT, balancing dosimetric precision with operational efficiency.