Accuracy verification of infrared marker-based dynamic tumor-tracking irradiation using the gimbaled x-ray head of the Vero4DRT (MHI-TM2000)a)

Authors

  • Mukumoto Nobutaka,

    1. Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan
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  • Nakamura Mitsuhiro,

    1. Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan
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    • b)

      Author to whom correspondence should be addressed. Electronic mail: m_nkmr@kuhp.kyoto-u.ac.jp; Telephone: +81-75-751-3762; Fax: +81-75-771-9749.

  • Sawada Akira,

    1. Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan and Department of Radiological Technology, Faculty of Medical Science, Kyoto College of Medical Science, Nantan 622-0041, Japan
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  • Suzuki Yasunobu,

    1. Advanced Mechanical Systems Department, Mitsubishi Heavy Industries Ltd., Hiroshima 733-8553, Japan
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  • Takahashi Kunio,

    1. Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan and Advanced Mechanical Systems Department, Mitsubishi Heavy Industries Ltd., Hiroshima 733-8553, Japan
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  • Miyabe Yuki,

    1. Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan
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  • Kaneko Shuji,

    1. Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan and Advanced Mechanical Systems Department, Mitsubishi Heavy Industries Ltd., Hiroshima 733-8553, Japan
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  • Mizowaki Takashi,

    1. Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan
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  • Kokubo Masaki,

    1. Department of Radiation Oncology, Kobe City Medical Center General Hospital, Kobe 650-0047, Japan and Division of Radiation Oncology, Institute of Biomedical Research and Innovation, Kobe 650-0047, Japan
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  • Hiraoka Masahiro

    1. Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan
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  • a)

    Presented, in part, at the 54th Annual Meeting of the American Association of Physicists in Medicine, Charlotte, July 29 to August 2, 2012.

Abstract

Purpose:

To verify the accuracy of an infrared (IR) marker-based dynamic tumor-tracking irradiation system (IR tracking) using the gimbaled x-ray head of the Vero4DRT (MHI-TM2000).

Methods:

The gimbaled 6-MV C-band x-ray head of the Vero4DRT can swing along the pan-and-tilt direction to track a moving target. During beam delivery, the Vero4DRT predicts the future three-dimensional (3D) target position in real time using a correlation model [four-dimensional (4D) model] between the target and IR marker motion, and then continuously transfers the corresponding tracking orientation to the gimbaled x-ray head. The 4D-modeling error (E4DM) and the positional tracking error (EP) were defined as the difference between the predicted and measured positions of the target in 4D modeling and as the difference between the tracked and measured positions of the target during irradiation, respectively. For the clinical application of IR tracking, we assessed the relationship between E4DM and EP for three 1D sinusoidal (peak-to-peak amplitude [A]: 20–40 mm, breathing period [T]: 2–4 s), five 1D phase-shifted sinusoidal (A: 20 mm, T: 4 s, phase shift [τ]: 0.2–2 s), and six 3D patient respiratory patterns.

Results:

The difference between the 95th percentile of the absoluteEP (EP95) and the mean (μ) + two standard deviations (SD) of absolute E4DM (E4DMμ+2SD) was within ±1 mm for all motion patterns. As the absolute correlation between the target and IR marker motions decreased from 1.0 to 0.1 for the 1D phase-shifted sinusoidal patterns, the E4DMμ+2SD and EP95 increased linearly, from 0.4 to 3.0 mm (R = −0.98) and from 0.5 to 2.2 mm (R = −0.95), respectively. There was a strong positive correlation between E4DMμ+2SD and EP95 in each direction [(lateral, craniocaudal, anteroposterior) = (0.99, 0.98, 1.00)], even for the 3D respiratory patterns; thus, EP95 was readily estimated from E4DMμ+2SD.

Conclusions:

Positional tracking errors correlated strongly with 4D-modeling errors in IR tracking. Thus, the accuracy of the 4D model must be verified before treatment, and margins are required to compensate for the 4D-modeling error.

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