Magnetic Resonance Imaging-Only Simulation for Prostate Magnetic Resonance Imaging-Guided Stereotactic Body Radiation...

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiology

Background:

• The Stereotactic MR-Guided Adaptive Radiation Therapy (SMART) protocol for prostate SBRT utilizes 3T-MRI for delineation and 0.35T MR-Linac for adaptation.
• Current workflows involve multiple simulation scans (CT, 3T-MRI, 0.35T-MRI), leading to logistical challenges and inefficiencies.

Purpose of the Study:

• To develop and validate an end-to-end MRI-only workflow for prostate SBRT.
• To eliminate the requirement for a planning CT scan (pCT), thereby improving workflow efficiency and reducing patient burden.

Main Methods:

• Ten prostate cancer patients underwent simulation using a 3T Siemens MAGNETOM Vida MRI scanner.
• High-resolution T2-weighted BLADE/DWI sequences were used for target delineation, and a T1-weighted DIXON VIBE sequence generated a synthetic CT (sCT) using a deep-learning algorithm.
• Treatment plans were created and delivered on a 0.35T MRIdian MR-Linac, with retrospective pCT-based plan recalculations on sCTs for validation using DVH and gamma index analysis.

Main Results:

• The MRI-only workflow was successfully implemented clinically.
• Dosimetric validation showed high fidelity between sCT and pCT calculations, with computed γ-indices of 96.80±1.33% (2%DD, 2mm DTA) and 99.98±0.03% (3%DD, 2mm DTA).
• Mean absolute differences in PTV D95% were minimal (0.06±0.14 Gy).

Conclusions:

• Integrating 3T MR simulation with 0.35T MR-Linac delivery via an sCT pathway is clinically feasible and dosimetrically robust.
• MRI-only simulation enhances workflow efficiency and reduces patient burden.
• This approach maintains the high-quality 3T delineation and MR-guidance characteristic of the SMART protocol.