Commissioning and Early Clinical Experience with a Preplan-Based MRI-Assisted Radiosurgery (MARS) HDR Prostate Brachytherapy Workflow
Abstract
Purpose
Preplanning is a standard practice for MRI-Assisted Radiosurgery (MARS) LDR prostate brachytherapy; however, HDR procedures often rely on generic needle patterns rather than individualized preplans. Implementing a patient-specific HDR preplan provides an opportunity for QA feedback, improved procedural safety, and increased clinical efficiency intraoperatively. Furthermore, it serves as a robust educational tool for HDR training for trainees. This study evaluates and commissions a commercially available preplanning treatment planning system (TPS), MIM Symphony HDR.
Methods
The preplanning TPS enabled clinicians to preplan virtual needle compositions on the virtual Martinez template (Elekta) and virtual needle digitization on a pre-implant diagnostic MRI, which was resliced to reflect the dorsal lithotomy position used during needle implants. Preplanned needle digitization and contouring were exported to a standard TPS (Oncentra) for optimization and dose calculation. Data transfer integrity was validated by comparing DICOM coordinates of the needle tips and 10th dwell positions, alongside contour volumes. Martinez template and BK ultrasound were also commissioned, and the overall workflow was developed. Three patients were treated using the preplan technique with 240mm plastic needles implanted with ultrasound guidance. Pre- and post-implant dosimetry was compared.
Results
Technical specifications of the digital template and needles were successfully verified in both TPS platforms. Data transfer between two TPS platforms was accurate, with maximum coordinate difference <0.2 mm for needle positions, and volume differences <3% for the prostate, bladder, and rectum. Intraoperative needle positions successfully replicated the patient-specific preplans, requiring only minor adjustments to match day-of-treatment anatomy variations. Post-implant dosimetry met or exceeded preplanned dosimetry for both the target and OARs goals, with treated target V100% within 3% of the preplanned value.
Conclusion
A patient-specific MARS HDR preplanning workflow was successfully commissioned and deemed clinically feasible. Early clinical experience of three implants suggests improved efficiency of workflow and efficacy of dosimetry.