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Knowledge-based plan library-guided adaptive proton stereotactic ablative radiotherapy (SABR) for localized prostate
Keyur D Shah1, Chih-Wei Chang1, Duncan H Bohannon1
1Department of Radiation Oncology and Winship Cancer Institute, Emory University, Atlanta, Georgia, USA.
Medical Physics
|October 24, 2025
Summary
This study introduces a knowledge-based adaptive proton stereotactic ablative radiotherapy (SABR) workflow for prostate cancer. This method improves bladder and bladder neck sparing while ensuring robust target coverage by selecting optimal pre-generated plans.
Area of Science:
- Medical Physics
- Radiation Oncology
- Prostate Cancer Treatment
Background:
- Ultrahypofractionated proton stereotactic ablative radiotherapy (SABR) is an emerging treatment for localized prostate cancer (PCa).
- Proton SABR is susceptible to interfractional anatomical variations, necessitating adaptive strategies for robust target coverage and organ at risk (OAR) sparing.
- Traditional margin-based approaches and online re-optimization methods have limitations in managing these variations.
Purpose of the Study:
- To develop and evaluate a knowledge-based (KB) adaptive proton SABR workflow for prostate cancer.
- The workflow aims to account for prostate interfraction motion and density uncertainty (DU) by selecting the most clinically optimal plan from a set of pre-generated KB plans.
Main Methods:
- Retrospective analysis of 42 prostate cancer patients treated with five-fraction proton SABR and 45 with 28-fraction proton therapy.
- Development of Gaussian process regression (GPR) models to predict patient-specific prostate motion.
- Generation of three KB treatment plans per patient (KB-Nominal, KB-AS, KB-PI) and evaluation using Monte Carlo (MC) dose calculations under varying DU conditions.
- Plan quality assessment using ProKnow scoring, incorporating CTV coverage, conformity, and OAR doses.
Main Results:
- KB plans reduced bladder and bladder neck dose compared to the clinical plan while maintaining robust CTV coverage.
- KB-AS and KB-PI plans showed significant reductions in bladder V20.8Gy (26%) and rectum V17.6Gy (17%).
- KB plan selection was stable across DU variations, consistently achieving higher ProKnow scores than the clinical plan, comparable to Online Adaptive plans.
Conclusions:
- A knowledge-based plan-driven adaptive proton SABR workflow is feasible for prostate cancer treatment.
- Pre-generating motion-informed plans and selecting the optimal one ensures robust target coverage and improves OAR sparing.
- This framework offers a robust and effective adaptive strategy for proton SABR in prostate cancer.
