Tanaka, Tomoaki



School of Medicine, Department of Radiology (Radiation Oncology) (Shinanomachi)



Career 【 Display / hide

  • 2010.04


  • 2012.04


  • 2013.04


  • 2014.04


Academic Background 【 Display / hide

  • 2008.03

    岐阜大学, 医学部, 医学科

    University, Graduated

Licenses and Qualifications 【 Display / hide

  • 放射線科専門医, 2013.08

  • 放射線治療専門医, 2016.08


Research Areas 【 Display / hide

  • Radiation science

Research Keywords 【 Display / hide

  • radiation therapy

Research Themes 【 Display / hide

  • radiation therapy, 



Papers 【 Display / hide

  • Distribution analysis of hydrogel spacer and evaluation of rectal dose reduction in Japanese prostate cancer patients undergoing stereotactic body radiation therapy

    Kobayashi H., Eriguchi T., Tanaka T., Ogata T., Ishida M., Nakajima Y., Kumabe A., Kosugi M.

    International Journal of Clinical Oncology (International Journal of Clinical Oncology)  26 ( 4 ) 736 - 743 2021.04

    ISSN  13419625

     View Summary

    Background: To report on our primary experience with the placement of a hydrogel spacer following stereotactic body radiation therapy (SBRT) in low- and intermediate-risk prostate cancer patients and assess its impact on dosimetry as well as acute toxicity. Methods: A total of 70 patients treated with SBRT (total dose of 36.25 Gy) in 5 fractions were included. Hydrogel spacers were inserted in 53 patients along with gold fiducial markers. For dosimetry, we trisected the rectum on the sagittal image of magnetic resonance imaging and defined it as the upper rectum (UR), middle rectum (MR), and lower rectum (LR). We compared the dose to each part of the rectum with and without hydrogel spacer using dose volume histograms. Genitourinary (GU) and gastrointestinal (GI) toxicity assessments were conducted until 6 months of follow-up visits. Results: The median volume of the hydrogel spacer was 12.3 mL. Overall, the hydrogel spacer could significantly reduce the rectal dose in the middle-to-high-dose region (V20–V35). The rectum doses at the UR and MR were significantly lower in the spacer group in the middle to high dose region (V20–V35); the dose at the LR was significantly lower in the spacer group in the high-dose region (V30–V35). There was no grade ≥ 3 toxicity observed, but grade 2 toxicity of GU and GI occurred in 17.1% and 1.4% of the patients, respectively. Conclusion: Hydrogel spacers could contribute to rectal dose reduction, especially in high dose regions, by creating a prostate–rectum distance.

  • Relationship between radiation doses and erectile function deterioration in patients with localized prostate cancer treated with permanent prostate brachytherapy

    Shigeta K., Kikuchi E., Matsushima M., Ogihara K., Kosaka T., Mizuno R., Tanaka T., Shigematsu N., Oya M.

    International Journal of Urology (International Journal of Urology)  27 ( 12 ) 1087 - 1093 2020.12

    ISSN  09198172

     View Summary

    © 2020 The Japanese Urological Association Objectives: To investigate the relationship between radiation doses in prostate brachytherapy and deterioration of erectile function in patients with localized prostate cancer. Methods: A longitudinal survey study was carried out among 261 prostate cancer patients who received prostate brachytherapy. A total of 48 patients were potent at baseline and they did not receive any supplemental therapy preoperatively. Dosimetry parameters of the whole prostate gland, prostate apex, urethra and rectum were collected using the VariSeed 8.0 treatment planning system (Varian Medical Systems, Palo Alto, CA, USA). We carried out a logistic regression analysis to clarify the relationship between radiation doses and erectile function deterioration, which was assessed using the International Index of Erectile Function-15 questionnaire. Results: The median patient age was 66 years (range 53–70 years) with a median follow-up time of 44 months (36–71 months). The mean total International Index of Erectile Function-15 score decreased from 49.9 at baseline to 34.7 after 12 months (P < 0.001), but gradually plateaued within 36 months. Erectile function deterioration was noted in 32 (66.7%) patients 36 months after prostate brachytherapy. In an analysis of risk factors for erectile function deterioration after prostate brachytherapy, age ≥70 years (P = 0.029), prostate V100 ≥95% (P = 0.024), apex V100 ≥95% (P = 0.024), apex V150 ≥70% (P = 0.009) and apex D90 ≥150 Gy (P = 0.011) correlated with erectile function deterioration. A multivariate analysis identified an age of ≥70 years (odds ratio 7.91, P = 0.024) and apex V150 ≥70% (odds ratio 7.75, P = 0.007) as independent risk factors for erectile function deterioration after prostate brachytherapy. Conclusions: An excessive radiation dose, particularly to the prostate apex area, and an advanced age might have a negative impact on the preservation of potency after prostate brachytherapy.

  • Predictive factors of long-term rectal toxicity following permanent iodine-125 prostate brachytherapy with or without supplemental external beam radiation therapy in 2216 patients.

    Tomoki Tanaka, Atsunori Yorozu, Shinya Sutani, Yasuto Yagi, Toru Nishiyama, Yutaka Shiraishi, Toshio Ohashi, Takashi Hanada, Shiro Saito, Kazuhito Toya, Naoyuki Shigematsu

    Brachytherapy (Brachytherapy)  17 ( 5 ) 799 - 807 2018.09

    Research paper (scientific journal), Joint Work,  ISSN  15384721

     View Summary

    © 2018 American Brachytherapy Society Purpose: We analyzed factors associated with rectal toxicity after iodine-125 prostate brachytherapy (BT) with or without external beam radiation therapy (EBRT). Methods and Materials: In total, 2216 prostate cancer patients underwent iodine-125 BT with or without EBRT between 2003 and 2013. The median followup was 6.9 years. Cox proportional hazards modeling was used for univariate and multivariate analyses to assess clinical and dosimetric factors associated with rectal toxicity. Dosimetric parameters from 1 day after implantation (Day 1) and 1 month after implantation (Day 30) were included in the analyses. Results: The 7-year cumulative incidence of Grade 2 or higher rectal toxicity was 5.7% in all patients. The multivariate analysis revealed that antiplatelet or anticoagulant therapy, neoadjuvant androgen deprivation therapy, treatment modality, Day 1 rectal volume receiving 100% of the prescribed dose (RV 100 ), and the Day 30 minimal percent of the prescribed dose delivered to 30% of the rectum (RD 30 ) were associated with rectal toxicity. Day 1 RV 100 was a common predictor in both BT-alone and the BT + EBRT groups. The 5-year cumulative incidence of Grade 2 or higher rectal toxicity was 12.6%, 5.9%, and 1.7% for BT + 3-dimensional conformal radiation therapy, BT + intensity-modulated radiation therapy, and the BT-alone groups, respectively (p < 0.001). Conclusions: Rectal dosimetric parameters in BT were associated with late rectal toxicity. Although the risk of rectal toxicity was higher when EBRT was combined with BT, with proper and achievable rectal dose constraints intensity-modulated radiation therapy yielded less toxicity than 3-dimensional conformal radiation therapy.

  • Prostate-specific antigen nadir within 12 months as an early surrogate marker of biochemical failure and distant metastasis after low-dose-rate brachytherapy or external beam radiotherapy for localized prostate cancer.

    Nishimura S, Ohashi T, Momma T, Sakayori M, Eriguchi T, Tanaka T, Yamashita S, Kosaka T, Oya M, Shigematsu N

    Cancer Med (Cancer Medicine)  7 ( 5 ) 1794 - 1801 2018.03

    Research paper (scientific journal), Joint Work

     View Summary

    © 2018 The Authors. Cancer Medicine published by John Wiley & Sons Ltd. Prostate-specific antigen nadir (nPSA) after radiotherapy for localized prostate cancer has been investigated as a predictor. However, nPSA usually requires several years, limiting its clinical utility. We investigated the significance of nPSA within 12 months (nPSA12) after low-dose-rate prostate brachytherapy (LDR-PB) or external beam radiotherapy (EBRT) on treatment outcomes. Between 2006 and 2014, 663 patients with prostate cancer were treated with LDR-PB or EBRT at two institutions. Four hundred and seventy-four men received LDR-PB and 189 men received EBRT, without androgen deprivation therapy. The Kaplan–Meier method was used for biochemical failure (BF)-free survival (BFFS) and distant metastasis (DM)-free survival (DMFS) analyses, and multivariable Cox regression analysis was performed. The median follow-up was 61.3 months. The median nPSA12 in the LDR-PB and EBRT cohorts was 0.7 and 1.0 ng/mL, respectively. The 7-year BFFS and DMFS rates in LDR-PB patients with nPSA12 ≤ 0.7 ng/mL were 99.1% and 99.5%, respectively; when nPSA12 was >0.7 ng/mL, they were 90.2% and 94.8%, respectively. In EBRT patients with nPSA12 ≤ 1.0 ng/mL, BFFS and DMFS rates were 85.4% and 98.5%, respectively; when nPSA12 was >1.0 ng/mL, they were 67.1% and 87.2%, respectively. nPSA12 was an independent predictor of BF and DM in both cohorts (LDR-PB, P = 0.004 and 0.020, respectively; EBRT, P = 0.005 and 0.041, respectively). The nPSA12 after LDR-PB or EBRT is significantly associated with treatment outcomes of prostate cancer. Higher nPSA12 may identify patients at high risk of relapse who might benefit from salvage treatment.

  • Variability of treatment planning of seed implantation: A Japanese multicenter simulation study.

    Ishiyama H, Nakano M, Toya K, Kota R, Kikuchi K, Yamaguchi T, Kono N, Kawakami S, Tsutsumi Y, Tanaka T, Eriguchi T, Ohga S, Yamaguchi T, Takagawa Y, Morita M, Katayama N, Ohashi T, Aoki M, Yorozu A, Saito S

    Brachytherapy 16 ( 5 ) 1013 - 1020 2017.09

    Research paper (scientific journal), Joint Work

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Papers, etc., Registered in KOARA 【 Display / hide

Presentations 【 Display / hide

  • Seed migration to the vertebral venous plexus after low-dose-rate prostate brachytherapy

    Tanaka Tomoaki

    日本放射線腫瘍学会第29回学術大会, 2016.10, Poster (general)

  • 前立腺癌に対するIMRT併用小線源療法における直腸毒性の軽減

    Tanaka Tomoaki

    日本放射線腫瘍学会第26回学術大会, 2013.10, Oral Presentation(general)

  • 前立腺癌に対するIMRTの初期経験

    Tanaka Tomoaki

    第443回日本医学放射線学会関東地方会, 2013.06, Oral Presentation(general)

  • 放射線治療中の膵臓の位置に関する検討

    Tanaka Tomoaki

    第71回日本医学放射線学会総会, 2012.04, Oral Presentation(general)

  • ミリプラチンを用いた肝細胞癌に対する肝動脈化学塞栓療法の初期経験

    Tanaka Tomoaki

    第6回日本IVR学会 関東地方会, 2011.07, Oral Presentation(general)


Courses Taught 【 Display / hide







Courses Previously Taught 【 Display / hide

  • 放射線医学

    Keio University, 2017, Full academic year, Major subject, Laboratory work/practical work/exercise, 3h


  • 放射線科学

    Keio University, 2016, Full academic year, Major subject, Laboratory work/practical work/exercise, 3h

  • 放射線医学

    Keio University, 2015, Full academic year, Major subject, Laboratory work/practical work/exercise, 3h

  • 放射線科学

    Keio University, 2014, Full academic year, Major subject, Laboratory work/practical work/exercise, 3h

  • 放射線科学

    Keio University, 2014, Full academic year, Major subject, Laboratory work/practical work/exercise, 3h


Memberships in Academic Societies 【 Display / hide

  • 日本医学放射線学会

  • 日本放射線腫瘍学会