A new method to reconstruct intra-fractional prostate motion in volumetric modulated arc therapy

Abstract

Intra-fractional motion is a concern during prostate radiation therapy, as it may cause deviations between planned and delivered radiation doses. Because accurate motion information during treatment delivery is critical to address dose deviation, we developed the Projection Marker Matching Method (PM3), a novel method for prostate motion reconstruction in volumetric modulated arc therapy. The purpose of this method is to reconstruct in-treatment prostate motion trajectory using projected positions of implanted fiducial markers measured in kV x-ray projection images acquired during treatment delivery. We formulated this task as a quadratic optimization problem. The objective function penalized the distance from the reconstructed 3D position of each fiducial marker to the corresponding straight line, defined by the x-ray projection of the marker. Rigid translational motion of the prostate and motion smoothness along the temporal dimension were assumed and incorporated into the optimization model. We tested the motion reconstruction method in both simulation and phantom experimental studies. We quantified the accuracy using 3D normalized root-mean-square (RMS) error defined as the norm of a vector containing ratios between the absolute RMS errors and corresponding motion ranges in three dimensions. In the simulation study with realistic prostate motion trajectories, the 3D normalized RMS error was on average 0.164 (range from 0.097 to 0.333). In an experimental study, a prostate phantom was driven to move along a realistic prostate motion trajectory. The 3D normalized RMS error was 0.172. We also examined the impact of the model parameters on reconstruction accuracy, and found that a single set of parameters can be used for all the tested cases to accurately reconstruct the motion trajectories. The motion trajectory derived by PM3 may be incorporated into novel strategies, including 4D dose reconstruction and adaptive treatment replanning to address motion-induced dose deviation.

Real-time intrafraction motion monitoring in external beam radiotherapy

“…Cardiac activity can also have a substantial effect on the position of lung tumours, mediastinal lymph nodes (Seppenwoolde et al 2002, Schmidt et al 2016, Scherman Rydhög et al 2017 or liver tumours (Kitamura et al 2003. Erratic motion of the prostate, including rotation, was also reported in several studies (Aubry et al 2004, Ghilezan et al 2005, Kupelian et al 2007, Langen et al 2008, Poulsen et al 2008b, Ng et al 2012, Huang et al 2015, Tynan et al 2016, Chi et al 2017.…”

A method to reconstruct intra-fractional liver motion in rotational radiotherapy using linear fiducial markers

“…The proposed approach is the extension of the PM 3 method that was previously developed by our group (Chi et al 2017). Different from the previous method that can only reconstruct 3-DoF translational motion, the new approach considered both translational and rotational components.…”

“…In each projection image, four endpoints of the two markers were identified. We extended the projection marker matching method (PM 3 ), which was previously developed by our group to reconstruct 3D intrafractional translational motion (Chi et al 2017), to enable the calculations of the rotational components, therefore enabling 6 degree-of-freedom (DoF) motion tracking. Compared to existing methods for 6-DoF motion reconstruction, the contribution of this work is twofold.…”

Experimental and numerical studies on kV scattered x-ray imaging for real-time image guidance in radiation therapy

“…Motion information may be obtained by tracking implanted fiducial markers or certain anatomical surrogates (Mao et al 2008, Cerviño et al 2009, Ng et al 2012, Poulsen et al 2014, Chi et al 2017, 2019. However, the makerbased methods introduce risks to patients due to the invasiveness of the procedure, and marker migration leads to the concern of tumor position accuracy.…”