Patient specific methods for room‐mounted x‐ray imagers for monoscopic/stereoscopic prostate motion monitoring

Abstract

PurposeTo investigate the improvement of combined monoscopic/stereoscopic prostate motion monitoring with room‐mounted dual x‐ray systems by adopting patient specific methods.MethodsThe linac couch was used as a motion stage to simulate 40 highly dynamic real patient prostate trajectories. For each trajectory, 40 s pretreatment and 120 s treatment periods were extracted to represent a typical treatment fraction. Motion was monitored via continuous stereoscopic x‐ray imaging of a single gold fiducial and images were retrospectively divided into periods of stereoscopic and monoscopic imaging to simulate periodic blocking of the room‐mounted system by the gantry during arc‐based therapy. The accuracy of the combined motion monitoring was assessed by comparison with the linac couch log files. To estimate 3‐D marker position during monoscopic imaging, the use of population statistics was compared to both maximum likelihood estimation and stereoscopic localization based estimation of individualized prostate probability density functions (PDFs) from the pretreatment period. The inclusion of intrafraction updating was compared to pretreatment initialization alone.ResultsCombined mono/stereoscopic localization was successfully implemented. During the transitions from stereoscopic to monoscopic imaging, fiducial localization exhibits sharp discontinuities when population PDFs were employed. Patient specific PDFs successfully reduced the localization error when estimated from stereoscopic localizations, whereas maximum likelihood estimation (MLE) was too unstable in the room‐mounted geometry. Intrafraction stereoscopic updating provided further increases in accuracy. Residual error tended to decrease throughout the treatment fraction, as the patient‐specific PDFs became more refined.ConclusionsThis is the first demonstration of toggled monoscopic/stereoscopic localization using room‐mounted dual x‐ray imagers, enabling continuous intrafraction motion monitoring for these systems. We showed that both pretreatment individualization and intrafraction updating should be used to provide the most accurate motion monitoring.

Estimation of patient-size dependent imaging dose for stereoscopic/monoscopic real-time kV image guidance in lung and prostate SBRT

“…By acquiring continuous stereoscopic projections with two views during treatment, real-time tumor monitoring can be achieved with Cyberknife (Hamamoto et al 2015, Jung et al 2015, Nakayama et al 2018 or SyncTracX (Shiinoki et al 2016) systems. Similarly, real-time tumor monitoring in ExacTrac system has been reported for prostate (Stevens et al 2016(Stevens et al , 2017 and lung sites.…”

“…Vendor recommended image acquisition techniques (kVp and mAs) were used depending on patient sizes as per tables 1 and 2. During a realistic treatment fraction, one of the x-ray tubes would be periodically blocked by the rotating linac gantry (Stevens et al 2016(Stevens et al , 2017. Therefore, real-time imaging were divided in to stereoscopic and monoscopic periods based on the gantry angle (figure 1(a)) to calculate realistic imaging dose by assuming that the dose rate and gantry speed is constant over the VMAT arcs.…”

Toward a pre-clinical irradiator using clinical infrastructure

“…3). Similar to previous work [30][31][32], in each projection the BB and field edge were automatically detected using a maximum convolution approach. This involved using a convolution kernel with the central pixels set to negative one and surrounded by a one-pixel border with a positive value such that the total value of the kernel is zero.…”

Performance optimization of capacitive motion sensing (CMS) system for intra-fraction motion detection during stereotactic radiosurgery

“…In-room x-ray stereoscopic imaging allows for determination of the 3D location of anatomy based on two planar x-ray projections [24][25][26]. However real-time monitoring with this technique would require continuous exposure to ionizing radiation [27][28][29][30] and is physically challenging due to obstruction of the imaging system by the gantry/couch geometry during treatment delivery.…”