Markerless tumor tracking using short kilovoltage imaging arcs for lung image-guided radiotherapy

Abstract

The ability to monitor tumor motion without implanted markers is clinically advantageous for lung image-guided radiotherapy (IGRT). Existing markerless tracking methods often suffer from overlapping structures and low visibility of tumors on kV projection images. We introduce the short arc tumor tracking (SATT) method to overcome these issues. The proposed method utilizes multiple kV projection images selected from a nine-degree imaging arc to improve tumor localization, and respiratory-correlated 4D cone-beam CT (CBCT) prior knowledge to minimize the effects of overlapping anatomies. The 3D tumor position is solved as an optimization problem with prior knowledge incorporated via regularization. We retrospectively validated SATT on 11 clinical scans from four patients with central tumors. These patients represent challenging scenarios for markerless tumor tracking due to the inferior adjacent contrast. The 3D trajectories of implanted fiducial markers were used as the ground truth for tracking accuracy evaluation. In all cases, the tumors were successfully tracked at all gantry angles. Compared to standard pre-treatment CBCT guidance alone, trajectory errors were significantly smaller with tracking in all cases, and the improvements were the most prominent in the superior-inferior (SI) direction. The mean 3D tracking error ranged from 2.2–9.9 mm, which was 0.4–2.6 mm smaller compared to pre-treatment CBCT. In conclusion, we were able to directly track tumors with inferior visibility on kV projection images using SATT. Tumor localization accuracies are significantly better with tracking compared to the current standard of care of lung IGRT. Future work involves the prospective evaluation and clinical implementation of SATT.

The first patient treatment of electromagnetic-guided real time adaptive radiotherapy using MLC tracking for lung SABR

“…The electromagnetic transponders provide an internal surrogate of the tumour and their location will affect the accuracy of their surrogate motion. Further research is directed towards markerless MLC tracking that would not require implantation of transponders, a potential source of toxicity, replaced with direct (image-based) tracking [31][32][33][34].…”

Patient reported outcomes of slow, single arc rotation: Do we need rotating gantries?

“…[23][24][25][26][27][28] As such, it is not unreasonable to hypothesise that anatomic deformation resulting from rotation could be adapted for. In modern radiotherapy, it is becoming increasingly common to measure and adapt for patient motion, and there is already a great deal of research focused on increasing this capacity.…”

A Bayesian approach for three-dimensional markerless tumor tracking using kV imaging during lung radiotherapy

“…Figure 1). Details on step 1 and step 2 can be found in the previous publication (Shieh et al , 2015a). This paper focuses on the novel Bayesian framework in step 3.…”

“…This dataset was included and described in the previous publication (Shieh et al , 2015a). More details of the datasets can be found in Roman et al (2012).…”

“…We have previously proposed a 3D markerless tumor tracking method to address the challenge of inferior tumor visibility by utilizing short kV imaging arcs and subtraction of overlapping anatomic structures (Shieh et al , 2015a). The limitation of the lack of ground truth was overcome by comparing the tracking results with the motions of implanted markers.…”