A Novel Markerless Lung Tumor-Tracking Method Using Treatment MV Beam Imaging

Timothy Rozario,Xun Jia,Tsuicheng Chiu,Sergey Bereg,Mingli Chen,Weiguo Lu,Weihua Mao

doi:10.3390/app8122525

Abstract

A novel method was developed to track lung tumor motion in real time during radiation therapy with the purpose to allow target radiation dose escalation while simultaneously reducing the dose to sensitive structures, thereby increasing local control without increasing toxicity. This method analyzes beam’s eye view radiation therapy treatment megavoltage (MV) images with simulated digitally reconstructed radiographs (DRRs) as references. Instead of comparing global DRRs with projection images, this method incorporates a technique that divides the global composite DRR and the corresponding MV projection into sub-images called tiles. Registration is performed independently on tile pairs in order to reduce the effects of global discrepancies due to scattering or imaging modality differences. This algorithm was evaluated by phantom studies while simulated tumors were controlled to move with various patterns in a complex humanoid torso. Approximately 15,000 phantom MV images were acquired at nine gantry angles, with different tumors moving within ranges between 10 and 20 mm. Tumors were successfully identified on every projection with a total maximum/average error of 1.84/0.98 mm. This algorithm was also applied to over 5,000 frames of MV projections acquired during radiation therapy of five lung cancer patients. This tumor-tracking methodology is capable of accurately locating lung tumors during treatment without implanting any internal fiducial markers nor delivering extra imaging radiation doses.

Highlights

The fundamental goal of radiotherapy is to deliver targeted tumoricidal radiation doses while minimizing doses to critical structures and healthy tissues
The black dash lines correspond to the sinusoidal motion detected by markers, and the red solid lines are the differences between the detected positions and the corresponding actual positions. 2D motions could be evaluated by using motions in both directions
The deviation studies were performed on the tumor-tracking results for both large and small tumor phantoms at nine gantry angles when the tumors were moved with five different ranges

Summary

Introduction

The fundamental goal of radiotherapy is to deliver targeted tumoricidal radiation doses while minimizing doses to critical structures and healthy tissues. Large planning margins may be required to expand the target volume since respiratory motion can lead to lung tumor displacements of up to. The margins must be large enough to encompass the entire tumor motion range; if the margin is incorrectly determined, the lung tumor may move out of the planning target volume (PTV). Large margins produce larger PTVs, limiting the ability to deliver high doses to targets and subsequently compromising dose sparing to critical structures and normal tissues. Motion ranges are normally quantified by four-dimensional (4D) computed tomography (CT) scans, 4D CT results represent the regular motion patterns and lung tumor placements only at the time of CT scan planning.

Methods

Results

Conclusion