Developing a novel quasi-3D movable water phantom for radiation therapy workable in the magnetic resonance environment

Jian-Kuen Wu; Ting-Yen Lee; Min-Chin Yu; Ming-Chih Kuo; Wei-Chuan Chen; Yi-Cheng Hsiao; Yu-Jen Wang

doi:10.21037/qims-23-189

Developing a novel quasi-3D movable water phantom for radiation therapy workable in the magnetic resonance environment

Quant Imaging Med Surg. 2023 Dec 1;13(12):7731-7740. doi: 10.21037/qims-23-189. Epub 2023 Sep 13.

Authors

Jian-Kuen Wu¹, Ting-Yen Lee², Min-Chin Yu³, Ming-Chih Kuo⁴, Wei-Chuan Chen⁵, Yi-Cheng Hsiao⁶, Yu-Jen Wang^{7

8}

Affiliations

¹ Division of Radiation Oncology, Departments of Oncology, National Taiwan University Hospital, Taipei.
² Department of Nuclear Medicine, National Taiwan University Hospital, Taipei.
³ Department of Radiation Oncology Taipei Medical University Hospital, Taipei.
⁴ Department of Medical Imaging, National Taiwan University Cancer Center, Taipei.
⁵ Department of Radiation Oncology, China Medical University Beigang Hospital, Yunlin.
⁶ Department of Medical Imaging, National Taiwan University Hospital, Taipei.
⁷ Department of Radiation Oncology, Fu Jen Catholic University Hospital, New Taipei City.
⁸ School of Medicine, College of Medicine, Fu Jen Catholic University, New Taipei City.

Abstract

Background: The use of magnetic resonance linear accelerators (MR-LINACs) for clinical treatment has opened up new possibilities and challenges in the field of radiation oncology. However, annual quality assurance (QA) is relatively understudied due to practical considerations. Thus, to overcome the difficulty of measuring the dose with a small water phantom for TRS-398 or TG-51 in all external beam radiation treatment unit environments, such as MR compatibility, we designed a remote phantom with a three-axis changeable capacity for QA.

Methods: The designed water phantom was tested under an MR environment. The water phantom system comprised of three parts: a phantom box, a dose measurement tool, and a PMD401 drive system. The UNIDOSE universal dosimeter was used to collect beam data. The manufacturer's developer tools were utilized to position the measurement. To ensure magnetic field homogeneity, a distortion phantom was prepared using sixty fish oil capsules aligned radially to distinguish the oil and free air. The phantom was scanned in both the MR simulator and computed tomography (CT), and the acquired images were analyzed to determine the position shift.

Results: The dimensions of the device are 30 cm in the X-axis, 20 cm in the Y-axis, and 17 cm in the Z-axis. Total cost of materials was no more than $10,000 US dollars. Our results indicate that the device can function normally in a regular 1.5 T MR environment without interference from the magnetic field. The water phantom's traveling speed was found to be approximately 5 mm/s with a position difference confined within 6 cm intervals during normal use. The distortion test results showed that the prepared MR environment has uniform magnetic field homogeneity.

Conclusions: In this study, we constructed a prototype water phantom device that can function in an MR simulator without interference between the magnetic field and electronic components. Compared to other commercially available MR-LINAC water phantoms, our device offers a more cost-effective solution for routine monthly QA. It can shorten the duration of QA tests and relieve the burden on medical physicists.

Keywords: Water phantom; low cost; magnetic resonance (MR); movable; radiation therapy.