Evaluation of integrated respiratory gating systems on a Novalis Tx system

Zheng Chang,Zhiheng Wang,TongHai Liu,Jing Cai,Qing Chen,Fang‐Fang Yin

doi:10.1120/jacmp.v12i3.3495

Abstract

The purpose of this study was to investigate the accuracy of motion tracking and radiation delivery control of integrated gating systems on a Novalis Tx system. The study was performed on a Novalis Tx system, which is equipped with Varian Real‐time Position Management (RPM) system, and BrainLAB ExacTrac gating systems. In this study, the two systems were assessed on accuracy of both motion tracking and radiation delivery control. To evaluate motion tracking, two artificial motion profiles and five patients' respiratory profiles were used. The motion trajectories acquired by the two gating systems were compared against the references. To assess radiation delivery control, time delays were measured using a single‐exposure method. More specifically, radiation is delivered with a 4 mm diameter cone within the phase range of 10%–45% for the BrainLAB ExacTrac system, and within the phase range of 0%–25% for the Varian RPM system during expiration, each for three times. Radiochromic films were used to record the radiation exposures and to calculate the time delays. In the work, the discrepancies were quantified using the parameters of mean and standard deviation (SD). Pearson's product‐moment correlational analysis was used to test correlation of the data, which is quantified using a parameter of r. The trajectory profiles acquired by the gating systems show good agreement with those reference profiles. A quantitative analysis shows that the average mean discrepancies between BrainLAB ExacTrac system and known references are 1.5 mm and 1.9 mm for artificial and patient profiles, with the maximum motion amplitude of 28.0 mm. As for the Varian RPM system, the corresponding average mean discrepancies are 1.1 mm and 1.7 mm for artificial and patient profiles. With the proposed single‐exposure method, the time delays are found to be 0.20±0.03 seconds and 0.09±0.01 seconds for BrainLAB ExacTrac and Varian RPM systems, respectively. The results indicate the systems can track motion and control radiation delivery with reasonable accuracy. The proposed single‐exposure method has been demonstrated to be feasible in measuring time delay efficiently.PACS numbers: 87.56.bd, 87.56.‐v, 87.55.‐x

Highlights

Evaluation of the integrated respiratory gating system was performed on a Novalis Tx system, which is equipped with Varian real-time position management (RPM) gating system (VarianMedical Systems, Palo Alto, CA) and BrainLAB ExacTrac gating system (BrainLAB, Heimstetten, Germany)
A quantitative analysis shows that the average mean discrepancy of the trajectory profiles between the BrainLAB ExacTrac gating system and the reference profiles is 1.5 mm
Accuracy of motion tracking and radiation delivery control in the BrainLAB ExacTrac and Varian Realtime Position Management (RPM) respiratory gating systems was investigated on a Novalis Tx system

Summary

Introduction

72 Chang et al.: Evaluation of integrated gating systems few years, various techniques have been proposed to overcome this challenge, which include but are not limited to respiratory gating, breath-hold, forced shallow breathing, and respiration synchronized techniques.[3,4,5,6,7] Among these techniques, respiratory gating is commonly used, in which radiation is delivered within a particular portion of the patient’s breathing cycle or a duty cycle.[6,7,8,9,10,11,12] The gating method usually obtains a respiratory motion signal from an external surrogate. Among the characteristics of a gating system, motion tracking and radiation delivery control are two fundamental features. In a respiratory gated radiotherapy, the gating phase for treatment delivery is required to coincide with the corresponding phase as determined during simulation. In this regard, time delay is the most basic parameter controlling delivery accuracy, which must be measured and verified. An efficient single-exposure method is used to measure the time delay. In addition to radiation delivery control, motion tracking is another fundamental feature of a gating system. In this work, integrated gating systems on the Novalis Tx system were evaluated using both quantitative motion tracking analyses and efficient time delay measurements

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