Annual Report 2024
Section of Radiation Safety and Quality Assurance
Hidenobu Tachibana, Kenji Hotta, Hiromi Baba, Kana Motegi, Ryo Takahashi, Hironori Kishida, Yuta Kobayashi, Ai Nakaoka, Saya Endo, Yugo Ebinuma, Tenyoh Suzuki, Morihisa Kumatabara
Introduction
Radiation therapy (RT) technologies have improved recently and will continue progressing. Although advanced technology has provided higher accuracy and precision in RT, it has introduced more complex situations and difficulties in performing the treatment adequately. RT errors can occur at several time points from the planning through treatment. The accuracy and precision of dose delivery in RT are essential, given the evidence that a 7%-10% change in the dose to the target volume may result in a significant change in tumor control probability. "Quality assurance in RT" is for all procedures that ensure consistency of the medical prescription and safe fulfillment of that prescription, as regards the dose to the target volume, together with the minimal dose to normal tissue, minimal exposure of personnel, and adequate patient monitoring aimed at determining the result of the treatment.
The primary aim of the Section of Radiation Safety and Quality Assurance is to develop quality assurance programs for photon, electron, and proton therapy machines, to check that quality requirements in photon and proton therapy products are met, and to adjust and correct the performance if the requirements are found not to be met. The second aim is to install and establish advanced technologies in clinical practices in the Department of Radiation Oncology. Our other goals are to develop high-precision RT such as intensity-modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT), respiratory-gating radiation therapy (RGRT), marker-tracking RT, image-guided radiation therapy (IGRT), stereotactic RT, and proton beam therapy (PBT) in cancer treatment.
The Team and What We Do
The Section of Radiation Safety and Quality Assurance is composed of medical physicists whose primary role is to appropriately manage invisible radiation to ensure its safe and effective medical use. We perform daily tasks including quality assurance (QA) of photon, electron, and proton therapy equipment; treatment planning for high-precision radiotherapy; introduction of new radiation therapy technologies that benefit patients; and support for clinical trials. Medical physicists are responsible for treatment planning and equipment QA, as well as supporting numerous investigator-initiated and physician-led clinical studies related to radiation therapy. We are also actively engaged in research and development aimed at advancing and improving the quality of radiotherapy. By integrating clinical practice and research, the team strives to enhance both the precision and safety of radiation therapy, while contributing to the education and training of the next generation of medical physicists.
Research Activities
During this fiscal year, the team published eight papers in international journals on topics such as three-dimensional dose and positional verification using gel dosimetry, proton beam measurement, and SRS accuracy evaluation, contributing to the advancement of radiation therapy QA.
Clinical Trials
1) Retrospective study on the effectiveness and safety of radiation therapy
2) Retrospective study on the prediction of adverse events in normal tissues in proton therapy
3) Retrospective study on the clinical implementation of robust treatment planning in intensity-modulated radiation therapy for head and neck cancer
4) Retrospective study on the clinical implementation of evidence-based decision-making for image-guided brachytherapy
Education
Our hospital provides treatments using different types of radiation, requiring medical physicists with expertise tailored to each radiation modality. At the same time, we believe that acquiring broad clinical knowledge and experience is essential for training. Our section includes medical physicists specializing in photon/electron and proton therapy, and we implement a rotation system to ensure that all staff gain practical experience across modalities. In fiscal year 2025, three new residents were assigned to the East Hospital. In addition, by the end of fiscal year 2024, five medical physics residents had completed their training program and obtained positions at our center, private companies, or research institutes.
Future Prospects
We will continue to promote activities integrating both clinical practice and research, aiming to further enhance the precision and safety of radiation therapy. We plan to apply advanced measurement technologies-such as gel dosimetry-to clinical QA and advance validation toward standardization. Furthermore, we will strengthen our educational system that allows cross-disciplinary experience in both photon and proton therapy, thereby contributing to the training of the next generation of medical physicists.
List of papers published in 2024
Journal
1. Yonemura M, Tachibana H, Kojima T, Seki K, Nakaichi T, Rachi T, Tachibana R, Akimoto T. Three-dimensional source position verification in image-guided high-dose-rate brachytherapy using an XCT-based gel dosimeter. Medical physics, 52:1243-1255, 2025
2. Baba H, Hotta K, Takahashi R, Motegi K, Sugama Y, Sakae T, Tachibana H. Quantification of beam size impact on intensity-modulated proton therapy with robust optimization in head and neck cancer-comparison with intensity-modulated radiation therapy. Journal of radiation research, 66:65-73, 2025
3. Takahashi Y, Oshika R, Tachibana R, Shirai K, Asakura H, Miyazaki M, Sagawa T, Takahashi S, Kuwae T, Kojima H, Nishiyama S, Nemoto H, Ishihara Y, Umeda M, Kijima K, Kobayashi D, Suzuki K, Nozawa Y, Hoshida K, Kitagawa T, Endo H, Matsunaga Y, Itagaki H, Ishida M, Kanahara S, Horita R, Hori D, Tachibana H. Spatial accuracy of dose delivery significantly impacts the planning target volume margin in linear accelerator-based intracranial stereotactic radiosurgery. Scientific reports, 15:3608, 2025
4. Takahashi S, Tachibana H, Oshika R, Tachibana R, Itou M. [Impact of Imaging and Reconstruction Parameters for Cone-beam Computed Tomography on Three-dimensional Star Shot Using an X-ray CT-based Gel Dosimeter]. Nihon Hoshasen Gijutsu Gakkai zasshi, 81:10, 2025
5. Bando H, Kumagai S, Kotani D, Mishima S, Irie T, Itahashi K, Tanaka Y, Habu T, Fukaya S, Kondo M, Tsushima T, Hara H, Kadowaki S, Kato K, Chin K, Yamaguchi K, Kageyama SI, Hojo H, Nakamura M, Tachibana H, Wakabayashi M, Fukui M, Fuse N, Koyama S, Mano H, Nishikawa H, Shitara K, Yoshino T, Kojima T. Atezolizumab following definitive chemoradiotherapy in patients with unresectable locally advanced esophageal squamous cell carcinoma - a multicenter phase 2 trial (EPOC1802). Nature cancer, 6:445-459, 2025
6. Tachibana H, Hoshino Y, Watanabe Y, Usui K, Mizukami S, Shibukawa S, Kodama T, Tachibana R. Quality assurance of magnetic resonance imaging for a polymer gel dosimeter using a 3D-printed phantom. Radiation Physics and Chemistry, 226:112196, 2025
7. Oshika R, Tachibana H, Seki K, Tachibana R, Moriya S, Sakae T. Technical Notes: Robustness of three-dimensional treatment and imaging isocenter testing using a new gel dosimeter and kilovoltage CBCT. Journal of applied clinical medical physics, 25:e14439, 2024
8. Tachibana H, Oshika R, Tachibana R, Seki K. Toward “on-line” X-ray computed tomography-based dosimetry using a new polymer gel with rapid response. Radiation Physics and Chemistry, 218:111570, 2024