Simulation-Free Radiation Therapy for Knee Osteoarthritis: A Streamlined, Dosimetrically Robust, Measurement-Based Approach
Abstract
Purpose
Simulation-free-radiation-therapy (SFRT) could improve patient access, efficiency, and clinical throughput for benign indications such as knee osteoarthritis. For sites with limited geometric complexity and inter-patient variability, simplified planning approaches based on external measurements may provide sufficient dosimetric accuracy. This work investigates the feasibility of incorporating SFRT into a clinical workflow for osteoarthritis knee treatments using hand-calculated AP–PA plans derived from external measurements.
Methods
A Simless-RT workflow was developed where anterior–posterior (AP) and lateral knee separations are acquired during consultation. These measurements are used to generate a hand-calculated AP–PA treatment plan via a simplified TG-71 formalism. To assess dosimetric robustness to patient anatomy, three simulated knee phantoms were constructed in Eclipse, corresponding to the average reported knee AP separation (133mm) and ±2 standard deviations (105mm and 161mm). Standardized AP–PA plans were calculated using 10MV photons, SAD setup, 20×15cm fields, and normalization to 300cGy at isocenter, with modest anterior beam weighting to increase dose to the patella.
Results
Across the range of knee separations studied, calculated monitor units (MUs) demonstrated minimal variation. The smallest phantom (105mm) required 26.7MU on the AP field, while the largest phantom (161mm) required 28.1MU. The observed MU variation across ±2 standard deviations in knee size was less than 6%, suggesting relative insensitivity of the AP–PA plan to realistic anatomic variation.
Conclusion
These results demonstrate that hand-calculated AP–PA knee plans derived from simple external measurements are dosimetrically robust across a clinically relevant range of knee sizes. The limited variation in MUs supports the feasibility of SFRT for osteoarthritis knees, enabling plan generation without CT simulation while maintaining consistent dose delivery. This approach may reduce resource utilization and improve patient access while preserving dosimetric reliability. Future work will focus on further validation, clinical implementation, and failure mode analysis.