Validation of Geometric and Dosimetric Accuracy of Edge Accelerator Gating With Electromagnetic Tracking: A Phantom Study

Zhenhui Dai,Lin Zhu,Hua Zhang,Fei Li,Yaoqin Xie,Huaizhi Jin,Chunya Cai,Bailin Zhang,Xuetao Wang,Geng Yang

doi:10.1109/access.2019.2934858

Abstract

This work was to devise a comprehensive testing scheme to evaluate the geometric and dosimetric accuracy of the Edge accelerator gating with electromagnetic tracking (EMT) for its safety in clinical application. A CIRS thorax phantom was scanned with four-dimensional cone-beam CT (4D-CBCT) on an Edge accelerator while the simulated tumor was simultaneously tracked with an EMT system using Calypso. The geometric accuracy was validated by comparing the motion trajectories derived from Calypso and 4D-CBCT with the ground truth from motion control software. The two-dimensional and three-dimensional dynamic doses were measured with the Matrixx and ArcCHECK installed on a motion platform, both with and without EMT. For tumor motion with 5, 7.5 mm amplitudes, the average absolute differences of sample position between Calypso and the ground truth were 0.286±0.234 mm, 0.407±0.331 mm respectively. Dosimetric accuracy was validated with 3 mm/3% gamma criterion. The average gamma pass rates of 2D dynamic dose validation based on Matrixx were less than 46% without EMT, 97.3% using 2 mm gating limit, 96% using 3 mm gating limit and 93.4% using 5mm gating limit respectively. The mean 3D dynamic dose validation pass rates based on ArcCHECK were 65.9% without EMT, 96.2% using 3 mm gating limit, and 92.5% using 5 mm gating limit with EMT respectively. The geometric accuracy of the Calypso system in tracking the moving target area was stable at the submillimeter level. The dosimetric accuracy could be improved significantly with EMT using an appropriate gating limit.

Highlights

In radiation therapy, intra-fractional tumor motions significantly limit the accuracy of radiation delivery and bring potential harm to organs at risk (OAR) around the tumor during treatment [1]
To deliver high-dose radiation adapting to the intra-fractional tumor motion, real-time imaging and tracking of the tumor motion during the treatment had become a critical task in radiation therapy research [3]
The trajectory of the tumor from Calypso was in good agreement with the ground truth

Summary

Introduction

Intra-fractional tumor motions significantly limit the accuracy of radiation delivery and bring potential harm to organs at risk (OAR) around the tumor during treatment [1]. The position of thoracic organs and tissues is constantly changing during the treatment due to respiratory motion, which is likely to cause the edge of tumor to move outside the irradiation field, while healthy tissue may enter the irradiation field of. The plan, which will limit the total dose the patient can safely receive [2] To deliver high-dose radiation adapting to the intra-fractional tumor motion, real-time imaging and tracking of the tumor motion during the treatment had become a critical task in radiation therapy research [3]

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