Research presented at the 2026 AAPM Meeting in Vancouver by Richard Chase Mallory, MS; James A. McCulloch, DMP; Nicole H. Bunda-Randall, MS; and Kyle P. Woods, MS
Low-dose radiotherapy for knee osteoarthritis is being increasingly adopted to mitigate pain and inflammation in benign joint disorders, bringing scheduling problems with it. Every OA knee that needs a CT simulation slot competes with head and neck, lung, and other complex cases that also need that scanner time. The anatomy of the knee joint is geometrically simple and consistent from patient to patient, which raises a reasonable question: does a benign, palliative-intent AP-PA knee treatment need a CT sim at all?
Simulation-free radiotherapy already has a track record in palliative bone metastases, where Dr. Schuler showed real reductions in clinic load (Schuler et. al. 2024). A CAMP team led by Richard Chase Mallory took that paradigm and built a validated simulation-free workflow for knee OA, presented at this year’s Joint AAPM/COMP Meeting.
The Workflow
Two caliper measurements replace the CT dataset. AP and lateral knee separations are acquired during consultation or at a clinical sim/treat visit, then entered into an in-house spreadsheet built on simplified TG-71 formalism. The calculator handles equivalent squares, Sc and Sp lookups, TMR interpolation, and outputs per-field MUs for a standardized AP-PA plan: selectable energy, SAD setup, normalized to prescription dose at isocenter, with modest anterior weighting to prioritize dose to the patella and an option to utilize bolus. A built-in checksum flags any tampering with the underlying data tables before the calculation can be used.
The Validation
The team modeled knee phantoms in Eclipse spanning AP separations from 9.5 to 16.1 cm and calculated plans with AAA against the hand-calc output. Two findings carry the result.
MU consistency: across the full range of clinically relevant knee sizes, calculated MUs varied by only 2.4 MU. Knee size barely matters to the monitor units, which is exactly what you want from a workflow with no patient-specific imaging.
Setup robustness: shifting the isocenter up to 2 cm anterior or posterior on the 13.3 cm phantom changed dose to a calculation point at the inferior-posterior patella by only about 5 cGy, under 2% error, with the global hotspot moving 1% at the extremes. A 2 cm setup error is a generous bound for a joint you can palpate, and the dosimetry absorbs it.
One honest wrinkle: phantom scatter and TPR uncertainties for non-square geometries were significant enough to matter. A simple linear correction factor brought the spreadsheet into agreement with the TPS, and the correction can be re-derived at any clinic by cross-calibrating against a couple of simulated cases.
Practical Guardrails
The workflow ships with sensible limits. First-fraction single-field port imaging verifies initial setup; subsequent fractions rely on external landmarks, since repeated imaging dose is a proportionally meaningful addition to a 300 cGy prescription. Patients with AP separations outside the validated 9.5 to 16.1 cm range, or anyone needing a complex setup, default back to standard CT simulation.
Why It Matters
For clinics watching OA referrals climb, this removes the CT sim bottleneck from the equation entirely. Access improves, sim slots go back to the cases that need them, and dose consistency holds. Future work includes a formal FMEA, expanding the validated measurement range, prospective outcome tracking, and extending the method to other OA treatment sites.
Questions about implementing a simulation-free OA workflow? Reach the CAMP team through campphysics.com/contact.
References
- Ott OJ, et al. “DEGRO guidelines for the radiotherapy of non-malignant disorders.” Strahlentherapie und Onkologie (2015).
- Schuler T, et al. “Real-World Implementation of Simulation-Free Radiation Therapy (SFRT-1000): A propensity score-matched analysis.” International Journal of Radiation Oncology Biology Physics (2024).
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Last updated: July 2026
