Implant geometry and detection rates of prostate fiducial markers after transrectal ultrasound-guided perineal implantation for image-guided 6D-tracking in robotic stereotactic body radiotherapy.

Abstract

Purpose: Fiducial markers (FM) are essential in prostate robotic stereotactic body radiotherapy (SBRT). Accuray® (Madison, WI, USA) provides an implantation guideline for reliable detection. We report on complication rates and analyze how the geometrical implantation quality correlated with subsequent detection rates. We also investigated whether factors such as single vs. double FM, body mass index (BMI), prostatic gland volume, and implantation-to-treatment interval were predictive for geometry and detection quality.

Methods: A retrospective analysis of 64 patients receiving transrectal ultrasound (TRUS)-guided transperineal implantation of ≥ 3 prostate FM and robotic SBRT between January 2011 and May 2021 was performed. Adverse events (AE) were classified according to the Society of Interventional Radiology (SIR) classification system. Digitally reconstructed radiographs (DRR) and the planning CT constituted the basis for implant geometry calculations. Marker detection rates were obtained from the Synchrony® (Accuray®) log.

Results: Complication rates were low, with mostly mild AE. Double FM significantly improved the rate of obtaining an optimal implantation geometry. High FM detection rates during treatment could be achieved independent of implantation geometry and type of FM. BMI and prostatic gland volume did not correlate with geometry and detection quality. An implantation-to-treatment interval of > 42 days was predictive for lower detection rates.

Conclusion: Transperineal intraprostatic FM implantation is a safe procedure. We recommend the use of double markers for reduction of trauma (two punctures instead of four) and, hence, increased patient comfort. Double FM were significantly predictive for achieving an optimal implantation geometry, which was borderline significant for improved marker detection rates over the course of the five-fraction treatment.