Author: Thomas I. Banks, Bin Cai, Andrew R. Godley, Yang Kyun Park, Hao Peng, Rameshwar Prasad, Chenyang Shen, Shunyu Yan, Haozhao Zhang 👨🔬
Affiliation: Medical Artificial Intelligence and Automation (MAIA) Lab, Department of Radiation Oncology, UT Southwestern Medical Center, UT Southwestern Medical Center, University of Texas Southwestern Medical Center 🌍
Purpose:
The RefleXion® X1 (RefleXion Medical, Inc., Hayward, CA) uniquely integrates KVCT and PET as on-board image guidance for radiotherapy. It has been installed and commissioned for clinical use at our institution. This study aims to evaluate the feasibility and quality of treatment planning using the X1 system for KVCT-guided spinal stereotactic body radiation therapy (SBRT).
Methods:
A total of patients—five treated with single dose level SBRT and five with simultaneous integrated boost (SIB) SBRT plans—were selected for this retrospective study. Each case was planned using the RefleXion X1 treatment planning system (TPS) for a 1-pass treatment with a jaw size of 10 mm. The resulting plans were reviewed in accordance with our institutional planning guidelines to evaluate their clinical acceptability. To benchmark the planning quality, plans generated with X1 TPS were compared with clinically treated plans created using Eclipse TPS for TrueBeam LINAC (Varian Medical Systems, Palo Alto, CA). Clinically relevant metrics, including planning target volume (PTV) coverage, maximum point dose (0.035cc), conformity index (CI), and organs-at-risk (OAR) constraints were compared using paired t-tests with significance at p<0.05.
Results:
All RefleXion plans met institutional spinal SBRT guidelines and were clinically acceptable. Paired t-tests revealed no significant differences in all PTV metrics, including D_max (p=0.89), D_mean (p=0.43), and D_min (p=0.91). X1 plans demonstrated slightly higher average maximum cauda equina doses (X1: 14.21Gy, Eclipse: 12.74Gy, p=0.05), while achieving lower average D_0.35cc (X1: 13.92Gy, Eclipse: 15.49Gy, p=0.09) and comparable D_max (X1: 20.30Gy, Eclipse: 20.43Gy, p=0.90) for spinal cord. The average CI values for Eclipse and X1 plans were 1.18 and 1.20, respectively (p=0.73), indicating comparable conformity. Similarly, X1 plans demonstrated comparable dose sparing for other OARs.
Conclusion:
The RefleXion X1 system generates clinically acceptable treatment plans for complex spinal SBRT, with plan quality comparable to clinical plans previously treated at our institution.