Author: Awens Alphonse, Nebi Demez, Michael Kasper, Noufal Manthala Padannayil, Shyam Pokharel, Suresh Rana, Samuel Richter, Lauren A. Rigsby, Tino Romaguera, Hina Saeed, Nishan Shrestha, Somol Sunny 👨🔬
Affiliation: Lynn Cancer Institute, Boca Raton Regional Hospital, Baptist Health South Florida 🌍
Purpose: This study evaluates the necessity and potential benefits of online adaptive stereotactic body radiotherapy (SBRT) for prostate cancer using the ViewRay MR-Linac system. By leveraging real-time MR imaging and daily adaptive planning workflows, dosimetric outcomes were compared across reference plans, deformable registration (adaptive) plans, and rigid registration (non-adaptive) plans.
Methods: Five prostate cancer patients treated with SBRT (8×5 Gy) on the ViewRay MR-Linac system were retrospectively analyzed. Reference plans, daily delivered fractions, and MR image sets were exported to Velocity software to evaluate dose accumulation for targets and organs at risk (OARs). Three planning scenarios were assessed: (1) the reference plan, based on the initial planning dataset; (2) deformable registration plans, simulating daily anatomical adaptation; and (3) rigid registration plans, representing conventional non-adaptive IGRT. Dosimetric indices were analyzed for the targets and OARs, including the bladder, rectum, urethra, penile bulb, and femoral heads.
Results: Coverage (V100%) to target volumes was highest in reference plans, followed by deformable and rigid registration plans: Prostate_40Gy (98.8%, 97.0%, 95.3%), PTV_36.25Gy (97.1%, 93.5%, 94.9%), and SeminalVes_38Gy (100%, 99.4%, 98.7%). While adaptive and non-adaptive plans showed slightly reduced coverage compared to reference plans, all remained within clinically acceptable limits. OAR doses were also comparable across scenarios. Bladder D0.03cc doses were 37.5Gy (reference), 36.9Gy (adaptive), and 36.5Gy (rigid), while rectum D0.03cc doses were 35.8Gy, 37.2Gy, and 35.2Gy. Urethral D0.03cc doses were 38.9Gy (reference), 40.8Gy (adaptive), and 41.0Gy (rigid). Penile bulb and femoral head doses showed no substantial variation.
Conclusion: Daily adaptive radiotherapy for prostate cancer enhances target coverage and OAR sparing compared to non-adaptive plans, particularly in cases of anatomical changes, urethral sparing, or dose escalation. For patients with stable anatomy, less frequent adaptation may suffice, ensuring optimal clinical outcomes and efficient use of the ViewRay MR-Linac system.