PO38: Commissioning and Workflow Development for a Real-Time, Ultrasound-Guided Prostate HDR Brachytherapy Program

Abstract

Purpose: This work presents the commissioning of a real-time, ultrasound (US)-guided HDR brachytherapy system (Elekta AB, Inc.), including the hardware, US imaging system, treatment planning system (TPS) (Oncentra Prostate), and the developed workflow.Materials and Methods: Commissioning tasks were separated into (1) US imaging, (2) stepper mechanicals, and (3) treatment planning aspects. Quality assurance US imaging measurements consisted of benchmarking the spatial resolution, accuracy, and low-contrast detectability. Mechanical tests were first performed to validate the electronic encoders used within the stepper and were later expanded to evaluate the needle free length calculation accuracy. Several system-integrated measurements were performed to verify needle positioning accuracy and imaging origin coincidence measurements using the needle free length measurement as a surrogate marker, as this remains one of the largest potential sources of error. The workflow was developed through a multi-disciplinary team, including physicians, radiation-therapists, nurses, physicists, administration staff, sterilization and anesthesia staff and included multi-dry-runs of the full procedure. A detailed description of each party's role was also developed, including checklists for the planning physicist, a secondary check physicist, and a radiation therapist.Results: Needle placement accuracy was verified to within 1 mm for both sagittal and transverse imaging planes. Needle reconstruction accuracy was also rigorously evaluated. The source strength was also calibrated with the interstitial needle and was found to be 1.14% lower than when measured in a plastic needle. The calibration length of each probe was redundantly check between the calculated and measured needle free length, which was found to be within 1 mm for a variety of scenarios. Dose calculations in the TPS and secondary dose calculation software were benchmarked against manual TG-43 calculations, which were within 1% for all calculated points. Source positioning and dummy coincidence was also verified. The US-guided HDR prostate procedure consisted of six primary components: (1) the delineation of personnel and their roles, (2) HDR suite preparation prior to the treatment day, (3) day of treatment preparations, (4) patient setup, (4) pre-needle insertion plan, (5) initial insertion and live reconstruction, and (6) final imaging and planning. A set of plan evaluation metrics were established based on the currently available guidelines (ABS, ESTRO, and RTOG) and the culmination of clinical experiences across multiple institutions.Conclusions: The commissioning of real-time, US-guided HDR prostate systems requires careful consideration among several facets including the image quality, dosimetric and mechanical accuracy. The TPS relies on each of these components to develop and administer a treatment plan, and as such, should be carefully examined.