横山　陽一 （ヨコヤマ　ヨウイチ）

Yokoyama, Yoichi

写真a

所属（所属キャンパス）

医学部 放射線科学教室（診断） （信濃町）

職名

助教（有期）

外部リンク
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  • Validation of musculoskeletal segmentation model with uncertainty estimation for bone and muscle assessment in hip-to-knee clinical CT images

    Soufi M., Otake Y., Iwasa M., Uemura K., Hakotani T., Hashimoto M., Yamada Y., Yamada M., Yokoyama Y., Jinzaki M., Kusano S., Takao M., Okada S., Sugano N., Sato Y.

    Scientific Reports 15 （ 1 ）  2025年12月

    　概要を見る

    Deep learning-based image segmentation has allowed for the fully automated, accurate, and rapid analysis of musculoskeletal (MSK) structures from medical images. However, current approaches were either applied only to 2D cross-sectional images, addressed few structures, or were validated on small datasets, which limit the application in large-scale databases. This study aimed to validate an improved deep learning model for volumetric MSK segmentation of the hip and thigh with uncertainty estimation from clinical computed tomography (CT) images. Databases of CT images from multiple manufacturers/scanners, disease status, and patient positioning were used. The segmentation accuracy, and accuracy in estimating the structures volume and density, i.e., mean HU, were evaluated. An approach for segmentation failure detection based on predictive uncertainty was also investigated. The model has improved all segmentation accuracy and structure volume/density evaluation metrics compared to a shallower baseline model with a smaller training database (N = 20). The predictive uncertainty yielded large areas under the receiver operating characteristic (AUROC) curves (AUROCs ≥.95) in detecting inaccurate and failed segmentations. Furthermore, the study has shown an impact of the disease severity status on the model’s predictive uncertainties when applied to a large-scale database. The high segmentation and muscle volume/density estimation accuracy and the high accuracy in failure detection based on the predictive uncertainty exhibited the model’s reliability for analyzing individual MSK structures in large-scale CT databases.

  • Chronological changes in etiology, pathological and imaging findings in primary liver cancer from 2001 to 2020

    Tsuzaki J., Ueno A., Masugi Y., Tamura M., Yamazaki S., Matsuda K., Kurebayashi Y., Sakai H., Yokoyama Y., Abe Y., Hayashi K., Hasegawa Y., Yagi H., Kitago M., Jinzaki M., Sakamoto M.

    Japanese Journal of Clinical Oncology 55 （ 4 ） 362 - 371 2025年04月

    ISSN  03682811

    　概要を見る

    Purpose: To achieve a historical perspective, the chronological changes in primary liver cancer over a 20-year period were investigated at a single institution, focusing on shifts in etiology and the impact on imaging and pathological findings using The Liver Imaging Reporting and Data System. Materials and methods: A retrospective study of surgically resected primary liver cancer in 680 patients from 2001 to 2020 resulted in 434 patients with 482 nodules being analyzed. Dynamic contrast-enhanced computed tomography imaging and the Liver Imaging Reporting and Data System 2018 classification were employed. Two pathologists and two radiologists independently evaluated specimens and images. Results: This study highlighted a significant decline in cases of viral hepatitis and cirrhosis in primary liver cancer patients but an increase in intrahepatic cholangiocarcinoma and scirrhous hepatocellular carcinoma. Notably, there was a rise in non-viral hepatitis cases, potentially pointing toward an increase in steatohepatitic hepatocellular carcinoma cases in the future. Intrahepatic cholangiocarcinoma, scirrhous hepatocellular carcinoma and steatohepatitic hepatocellular carcinoma tumors exhibited slightly different distributions in the Liver Imaging Reporting and Data System classification compared with ordinary hepatocellular carcinoma, which may reflect the presence of fibrosis and lipid in tumor parenchyma. Conclusions: Consistent with past reports, this study demonstrated the emergence of primary liver cancer against a backdrop of non-viral and non-cirrhotic liver. Liver Imaging Reporting and Data System has been consistently useful in diagnosing primary liver cancer; however, among the histological subtypes of hepatocellular carcinoma, an increase is anticipated in scirrhous hepatocellular carcinoma and steatohepatitic hepatocellular carcinoma, which may present imaging findings different from those of ordinary hepatocellular carcinoma. This development may necessitate a reevaluation of the current approach for diagnosing and treating hepatocellular carcinoma based solely on imaging.

  • Clinical Impact of Neoadjuvant Therapy for Resectable Pancreatic Ductal Adenocarcinoma: A Single-Center Retrospective Study

    Shimane G., Kitago M., Yagi H., Abe Y., Hasegawa Y., Hori S., Tanaka M., Tsuzaki J., Yokoyama Y., Masugi Y., Takemura R., Kitagawa Y.

    Annals of Surgical Oncology 32 （ 4 ） 2830 - 2840 2025年04月

    ISSN  10689265

    　概要を見る

    Background: Neoadjuvant therapy is recommended for treating resectable pancreatic ductal adenocarcinoma (PDAC); however, its appropriate use in patients with resectable PDAC remains debatable. Objective: This study aimed to identify independent poor prognostic factors and evaluate the clinical significance of neoadjuvant therapy in patients with resectable PDAC. Methods: We retrospectively reviewed consecutive patients diagnosed with resectable PDAC at our institute between January 2003 and December 2022. We analyzed poor prognostic factors at the time of diagnosis in patients who underwent upfront surgery using the Cox proportional hazards model for overall survival (OS). The prognostic score was calculated by adding the individual prognostic factor scores. Results: Overall, 359 patients were included in this study, with 308 patients undergoing upfront surgery and the remaining 51 patients receiving neoadjuvant therapy. The R0 resection rate was significantly higher in the neoadjuvant therapy group (70.6%) than in the upfront surgery group (64.0%). Multivariate analysis in the upfront surgery group revealed the following independent poor prognostic factors: tumor size ≥ 35 mm, serum albumin level ≤.5 g/dL, neutrophil-to-lymphocyte ratio ≥ 3.5, carbohydrate antigen 19-9 level ≥ 250 U/mL, and Duke pancreatic monoclonal antigen type 2 level ≥ 750 U/mL. Among patients with prognostic scores of 0–1 (n = 263), the intention-to-treat OS did not significantly differ between the neoadjuvant therapy and upfront surgery groups. Among those patients with a prognostic score of ≥ 2 (n = 96), the neoadjuvant therapy group had significantly longer intention-to-treat OS than the upfront surgery group. Conclusions: Prognostic score-based stratification can help identify patients who could benefit from neoadjuvant therapy.

  • Simultaneous quantification of lower limb skeletal posture and ground reaction forces using upright computed tomography: Potential implications for osteoarthritis assessment and treatment

    Ito A., Seki H., Sujino A., Nagura T., Yokoyama Y., Yamada M., Yamada Y., Jinzaki M., Ogihara N.

    Journal of Biomechanics 183 2025年04月

    ISSN  00219290

    　概要を見る

    Understanding the transmission of forces through the joints of the lower limb under weight-bearing conditions is critical for assessing the progression of knee and ankle osteoarthritis, as well as for developing effective surgical and preventive strategies. This study presents the first simultaneous quantification of three-dimensional skeletal posture and ground reaction force vectors during quiet standing, utilizing upright computed tomography and a custom-made force plate. We constructed the force plate using two six-axis force sensors, and the coordinate system of the CT was aligned with that of the force plate using metal spheres attached to the edges of the force plate. This system enabled precise measurement of ground reaction force vectors relative to the skeletal posture. The present study demonstrated that the load-bearing axis (the line connecting the femoral head center to the midpoint of the distal tibial plafond) in healthy subjects during quiet standing is not identical to the actual line of force application. The analysis revealed that the force vectors generally pass slightly medioposterior to the femoral head center. By providing a detailed view of how force is transmitted through the lower limb joints, this system potentially offers new insights into joint loading patterns that possibly contribute to osteoarthritis development.

  • Simulation Study of Upright Prostate Radiation Therapy: Comparison of Upright and Supine Anatomy and Dose-Volumetric Factors

    Oguma K., Yamada Y., Koike N., Fukada J., Yamada M., Yokoyama Y., Takeda A., Shigematsu N., Jinzaki M.

    Practical Radiation Oncology 2025年

    ISSN  18798500

    　概要を見る

    Purpose: This study aimed to assess the feasibility of upright radiation therapy for prostate cancer, compared to conventional supine radiation therapy, by quantitatively evaluating anatomic changes and their dosimetric impact through treatment planning simulations based on paired upright and supine positioning computed tomography (CT) images. Methods and Materials: This study compared pelvic organ anatomies and dose distributions, in hypothetical prostate cancer patients, between upright and supine prostate radiation therapy using paired CT images from asymptomatic volunteers. Anatomic changes in pelvic organ position, shape, volume, and rectal gas were quantitatively evaluated. Prostate radiation therapy was simulated on these CT images for volumetric modulated arc therapy with a prescribed dose of 60 Gy in 20 fractions. Dosimetric comparisons were performed using dose-volume histogram parameters based on a clinical protocol. Results: Fifty-one asymptomatic volunteers were registered. Compared to the supine position, pelvic organs in the upright position moved inferiorly (prostate: 2.8 mm ± 5.2, rectum: 2.9 mm ± 5.8, bladder: 3.7 mm ± 6.9, bowel: 25.2 mm ± 18.6; all P < .001). Rectal gas moved superiorly (4.8 mm ± 11.9; P = .004) and posteriorly (10.7 mm ± 23.5; P = .008). All dose-volume histogram parameters met the dose constraints, and the dose distributions of the upright and supine plans were clinically comparable in terms of organ-at-risk sparing and target coverage (P > .05). In some cases, the rectum curved more posteriorly in the upright position, allowing better sparing of high-dose areas, and the bladder moved inferiorly while expanding in the anterior-posterior direction in the upright position, preventing the small bowel from dropping into the radiation field. Conclusions: Our treatment planning simulation showed that upright radiation therapy for prostate cancer is feasible with a dose distribution comparable to that of conventional supine radiation therapy, despite significant anatomic changes in pelvic organ positioning between the upright and supine patient positions.

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  • 立位CTでの骨盤底障害と排尿障害の病態解明

    2023年04月
    -
    2026年03月

    横山 陽一, 若手研究, 補助金,  研究代表者

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  • Certificate of Merit

    Yoichi Yokoyama, Yoshitake Yamada, Minoru Yamada, Keiichi Narita, Takehiro Nakahara, Takeo Nagura, Masahiro Jinzaki, 2020年12月, Radiological Society of North America, Upright CT with Area Detectors for Whole-Body Scans: Performance and Visualization of the Effects of Gravity on Human

    受賞区分： 国内外の国際的学術賞

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