Treatment Plan Delivery Accuracy of the ViewRay System in Two-Headed Mode

Jong Min Park; So-Yeon Park; Hong-Gyun Wu; Jung-in Kim

doi:10.14316/pmp.2016.27.3.169

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Park, Park, Wu, and Kim: Treatment Plan Delivery Accuracy of the ViewRay System in Two-Headed Mode

Original Article

Progress in Medical Physics 2016;27(3):169-174.

Published online: 19 September 2016

DOI: https://doi.org/10.14316/pmp.2016.27.3.169

Treatment Plan Delivery Accuracy of the ViewRay System in Two-Headed Mode

Jong Min Park^∗,^†,^‡,^§, So-Yeon Park^∗,^†,^‡, Hong-Gyun Wu^∗,^†,^‡,^║, Jung-in Kim^∗,^†,^‡

^∗Department of Radiation Oncology, Seoul National University Hospital, Seoul Korea

^†Biomedical Research Institute, Seoul National University Hospital, Seoul Korea

^‡Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Korea

^§Center for Convergence Research on Robotics, Advanced Institutes of Convergence Technology, Suwon, Korea

^║Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Korea

Correspondence: Jung-in Kim (madangin@gmail.com) Tel: 82-2-2072-3573, Fax: 82-2-765-3317

Received 22 September 201623 September 2016 Accepted 24 September 2016

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The aim of this study is to investigate the delivery accuracy of intensity-modulated radiation therapy (IMRT) plans in the two-headed mode of the ViewRay^TM system in comparison with that of the normal operation treatment plan of the machine. For this study, a total of eight IMRT plans and corresponding verification plans were generated (four head and neck, two liver, and two prostate IMRT plans). The delivered dose distributions were measured using ArcCHECK^TM with the insertion of an ionization chamber. We measured the delivered dose distributions in three-headed mode (normal operation of the machine), two-headed mode with head 1 disabled, two-headed mode with head 2 disabled, and two-headed mode with head 3 disabled. Therefore, a total of four measurements were performed for each IMRT plan. The global gamma passing rates (3%/3 mm) in three-headed mode, head 1 disabled, head 2 disabled, and head 3 disabled were 99.9±0.1%, 99.8±0.3%, 99.6±0.7%, and 99.7±0.4%, respectively. The difference in the gamma passing rates of the three- and two-headed modes was insignificant. With 2%/2 mm, the rates were 96.6±3.6%, 97.2±3.5%, 95.7±6.2%, and 95.5±4.3%, respectively. Between three-headed mode and head 3 disabled, a statistically significant difference was observed with a p-value of 0.02; however, the difference was minimal (1.1%). The chamber readings showed differences of approximately 1% between three- and two-headed modes, which were minimal. Therefore, the treatment plan delivery in the two-headed mode of the ViewRay^TM system seems accurate and robust.

Keywords: MRI-guided radiation therapy system, Two-headed mode, Co-60, Intensity modulated radiation therapy

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Fig. 1

Measured dose distributions with the ArcCHECK^TM of the intensity modulated radiation therapy (IMRT) plan for the treatment of head and neck cancer. The failed points by the gamma-index method with a 2%/2 mm gamma criterion are shown in red (measured value＞calculated value) and blue (measured value＜calculated value) colors. The distributions of the three-headed mode (a), two-headed mode with head 1 disabled (b), two-headed mode with head 2 disabled (c) and two-headed mode with head 3 disabled (d) are shown.

Fig. 2

Measured dose distributions with the ArcCHECK^TM of the intensity modulated radiation therapy (IMRT) plan for the treatment of head and neck cancer. The failed points by the gamma-index method with a 3%/3 mm gamma criterion are shown in red (measured value＞calculated value) and blue (measured value＜calculated value) colors. The distributions of the three-headed mode (a), two-headed mode with head 1 disabled (b), two-headed mode with head 2 disabled (c) and two-headed mode with head 3 disabled (d) are shown.

Table 1.

Gamma passing rates of three-headed mode and two-headed mode.

Gamma passing rate	Three-headed mode	Head 1 disabled	Head 2 disabled	Head 3 disabled
2%/2 mm
Average value	96.6±3.6	97.2±3.5	95.7±6.2	95.5±4.3
Maximum value	99.7	100.0	99.9	98.8
Minimum value	89.1	88.1	80.1	85.8
3%/3 mm
Average value	99.9±0.1	99.8±0.3	99.5±0.8	99.6±0.6
Maximum value	100.0	100.0	100.0	100.0
Minimum value	99.6	99.0	97.6	98.3

Table 2.

The average, maximum, and minimum values of the percent difference in the measured charges with a chamber.

	Head 1 disabled	Head 2 disabled	Head 3 disabled
Average value	1.0±1.2	1.0±0.5	0.9±0.4
Maximum value	3.8	1.8	1.4
Minimum value	0.0	0.3	0.1

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