Retrospective analysis of MV–kV imaging‐based fiducial tracking in prostate SBRT treatment

Abstract

Motion management is critical for prostate stereotactic body radiotherapy (SBRT) due to its high fractional dose and proximity to organs at risk. This study seeks to quantify the advantages of MV-kV tracking over kV imaging alone through a retrospective analysis of over 300 patients who underwent prostate SBRT treatment using MV-kV tracking. Methods: An MV-kV imaging-based fiducial tracking technique has been developed at our institute and become a standard clinical practice. This technique calculates three-dimensional (3D) fiducial displacement in real time from orthogonal kV and MV images acquired simultaneously. The patient will be repositioned if for two consecutive MV-kV data points, the motion is larger than a tolerance of 1.5 mm in any of the lateral, superior-inferior, and/or anterior-posterior directions. This study retrospectively analyzed detected 3D motions using an MV-kV approach of 324 patients who recently underwent prostate SBRT treatments. An algorithm was developed to recover the 2D motion components as if they were detected by kV or MV imaging alone. Results: Our results indicated that out-of -tolerance motions were primarily limited to the range of 1.5-3 mm (>95%). The motions are primarily anteriorposterior and superior-inferior, with less than 14.8% of the occurrences in the lateral direction. Compared to out-of -tolerance occurrences detected by MV-kV approach, kV alone caught 46.6% of motions in all three directions, and MV alone caught 46.7%. kV alone shows an overall missing rate of 45.8% for superior-inferior motions and 38.6% for lateral motions. It is also demonstrated that the detectability of motion in specific directions greatly depends on gantry angles, as does the missing rate. Conclusions: Our study demonstrated that MV-kV imaging-based intrafraction motion tracking is superior to single kV imaging for prostate SBRT in clinical practice.

Markerless motion tracking with simultaneous MV and kV imaging in spine SBRT treatment—a feasibility study

“…2D-2D registration tracks translational motion very well, and in many cases, it can give good estimates to correct for rotational motions (pitch, roll and yaw) by applying translational shifts only, as long as the center of rotational motion is away from PTV (which is often the case). This has been reported in MV-KV imaging-based motion tracking for prostate SBRT (Hunt et al 2016, Zhang et al 2016, Happersett et al 2019, Gorovets et al 2020, Crotteau et al 2022. However, in some cases, it is the intrinsic limitation that a 2D-2D registration together with translational shift cannot correct motion with rotational motion.…”

“…The proposed MV-kV motion tracking approach for spinal treatment is not limited to IMRT beams at static gantry angles, and it can be expanded to volume modulated arc therapy (VMAT) plans with some modifications. As previously reported, the MV-kV technique has been used for motion tracking in prostate SBRT (Hunt et al 2016, Happersett et al 2019, Crotteau et al 2022. In this technique, when KV is triggered, MLC apertures are open wider to expose at least one fiducial and the dose rate is reduced to acquire MV images (Happersett et al 2019).…”

“…To overcome these issues, we propose to combine kV imaging with simultaneous MV imaging for more effective motion tracking, referred to as MV-kV imaging hereafter. The advantages of including MV imaging for motion tracking are: (1) the stronger penetration power of the MV beam can sometimes generate better image quality than kV imaging beam at gantry angles where x-ray attenuation is heavy; (2) when the kV beam suffers from high attenuation in the patient's lateral direction, the 90-degree apart MV beam is at the anterior-posterior direction and can have better signal for motion detection; (3) Motion detected from MV beam's eye view has more dosimetry impact than that detected from KV beam's eye view (Yue et al 2011; (4) Simultaneously acquired MV-kV image pairs make it possible to calculate 6D motions in real-time (Hunt et al 2016, Crotteau et al 2022. Clinical experiences with simultaneous MV-kV imaging showed distinct advantages over single kV imaging system in detecting fiducial motions in three dimensions in real-time for prostate SBRT (Zhang et al 2016, Hunt et al 2016, Happersett et al 2019, Gorovets et al 2020, Crotteau et al 2022.…”