Publications by authors named "Shie Nishioka"

26 Publications

  • Page 1 of 1

Survey on utilization of flattening filter-free photon beams in Japan.

J Radiat Res 2021 Jul;62(4):726-734

Department of Information Technology and Medical engineering, Human Health Science, Graduate School of Medicine, Kyoto University, 53 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan.

To understand the current state of flattening filter-free (FFF) beam implementation in C-arm linear accelerators (LINAC) in Japan, the quality assurance (QA)/quality control (QC) 2018-2019 Committee of the Japan Society of Medical Physics (JSMP) conducted a 37-question survey, designed to investigate facility information and specifications regarding FFF beam adoption and usage. The survey comprised six sections: facility information, devices, clinical usage, standard calibration protocols, modeling for treatment planning (TPS) systems and commissioning and QA/QC. A web-based questionnaire was developed. Responses were collected between 18 June and 18 September 2019. Of the 846 institutions implementing external radiotherapy, 323 replied. Of these institutions, 92 had adopted FFF beams and 66 had treated patients using them. FFF beams were used in stereotactic radiation therapy (SRT) for almost all disease sites, especially for the lungs using 6 MV and liver using 10 MV in 51 and 32 institutions, respectively. The number of institutions using FFF beams for treatment increased yearly, from eight before 2015 to 60 in 2018. Farmer-type ionization chambers were used as the standard calibration protocol in 66 (72%) institutions. In 73 (80%) institutions, the beam-quality conversion factor for FFF beams was calculated from TPR20,10, via the same protocol used for beams with flattening filter (WFF). Commissioning, periodic QA and patient-specific QA for FFF beams also followed the procedures used for WFF beams. FFF beams were primarily used in high-volume centers for SRT. In most institutions, measurement and QA was conducted via the procedures used for WFF beams.
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http://dx.doi.org/10.1093/jrr/rrab042DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8273795PMC
July 2021

Neutron flux evaluation model provided in the accelerator-based boron neutron capture therapy system employing a solid-state lithium target.

Sci Rep 2021 Apr 13;11(1):8090. Epub 2021 Apr 13.

Division of Research and Development for Boron Neutron Capture Therapy, National Cancer Center Exploratory Oncology Research & Clinical Trial Center, Tsukiji 5-1-1, Chuo-ku, Tokyo, 104-0045, Japan.

An accelerator-based boron neutron capture therapy (BNCT) system employing a solid-state Li target can achieve sufficient neutron flux for treatment although the neutron flux is reduced over the lifetime of its target. In this study, the reduction was examined in the five targets, and a model was then established to represent the neutron flux. In each target, a reduction in neutron flux was observed based on the integrated proton charge on the target, and its reduction reached 28% after the integrated proton charge of 2.52 × 10 mC was delivered to the target in the system. The calculated neutron flux acquired by the model was compared to the measured neutron flux based on an integrated proton charge, and the mean discrepancies were less than 0.1% in all the targets investigated. These discrepancies were comparable among the five targets examined. Thus, the reduction of the neutron flux can be represented by the model. Additionally, by adequately revising the model, it may be applicable to other BNCT systems employing a Li target, thus furthering research in this direction. Therefore, the established model will play an important role in the accelerator-based BNCT system with a solid-state Li target in controlling neutron delivery and understanding the neutron output characteristics.
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http://dx.doi.org/10.1038/s41598-021-87627-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8044165PMC
April 2021

A dosimetric and centeredness comparison of the conventional and novel endobronchial applicators: A preliminary study.

Brachytherapy 2021 Mar-Apr;20(2):467-477. Epub 2021 Jan 19.

Department of Radiation Oncology, National Cancer Center Hospital, Chuo City, Tokyo, Japan.

Purpose: This study compared the applicator position relative to the tracheal wall and dosimetric parameters between conventional and novel applicators among patients receiving endobronchial brachytherapy (EBBT) for intratracheal tumors.

Methods And Materials: Data from 7 patients who received EBBT for intratracheal tumors were retrospectively analyzed; 4 and 3 patients were treated with conventional (2-wing) or novel (5-wing) applicators, respectively. Applicator centrality was evaluated using the distance between the center of the trachea and main bronchus (TMB) lumen and path of source (L). Dosimetric parameters, including plans normalized to D of the TMB = 45 Gy (normalized plan), were compared between the applicators.

Results: The mean and maximum values of L in cases of the 2-wing applicator group were approximately 5.0 mm and 10.0 mm, respectively. In the novel applicator group, the corresponding values were approximately 3.0 and 6.0 mm, respectively. In the normalized plan of the 2-wing applicator group, the ranges of median V of clinical target volume (CTV) and D of the TMB in all cases were 23.0-91.9% and 66.3-153.1 Gy, respectively. In the 5-wing applicator group, the corresponding values were 69.2-83.8% and 60.4-84.5 Gy, respectively.

Conclusions: In the 5-wing applicator group, the range was narrow in all dose-volume parameters except for D of the TMB. Compared to the conventional applicator, the 5-wing applicator can give a stable dose to the CTV and can reduce the maximum dose of the TMB. This suggests that stable EBBT can be given to any patient using the 5-wing applicator.
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http://dx.doi.org/10.1016/j.brachy.2020.11.005DOI Listing
January 2021

Dosimetric effect of the intestinal gas of online adaptive stereotactic body radiotherapy on target and critical organs without online electron density correction for pancreatic cancer.

Br J Radiol 2021 Mar 5;94(1119):20200239. Epub 2021 Feb 5.

Department of Radiation Oncology, National Cancer Center Hospital, Tokyo, Japan.

Objective: This study aimed to assess the dosimetric effect of intestinal gas of stereotactic magnetic resonance (MR)-guided adaptive radiation therapy (SMART) on target and critical organs for pancreatic cancer without online electron density correction (EDC).

Methods: Thirty pancreatic cancer patients who underwent online SMART were selected for this study. The treatment time of each stage and the total treatment time were recorded and analyzed. The concerned dose-volume parameters of target and organs-at-risk (OAR) were compared with and without an intestinal gas EDC using the Wilcoxon-signed rank test. Analysis items with value < 0.05 were considered statistically significant. The relationships between dosimetric differences and intestinal gas volume variations were investigated using the Spearman test.

Results: The average treatment time was 82 min, and the average EDC time was 8 min, which accounted for 10% of the overall treatment time. There were no significant differences in CTV (GTV), PTV, bowel, stomach, duodenum, and skin ( > 0.05) with respect to dose volume parameters. For the of gastrointestinal organs ( = 0.03), the mean dose of the liver ( = 0.002) and kidneys ( = 0.03 and = 0.04 for the left and right kidneys, respectively), there may be a risk of slight overestimation compared with EDC, and for the of the spinal cord ( = 0.02), there may be a risk of slight underestimation compared with EDC. A weak correlation for in the PTV and in the duodenum was observed.

Conclusion: For patients with similar inter-fractional intestinal gas distribution, EDC had little dosimetric effects on the of all GI organs and dose volume parameters of target in most plans.

Advances In Knowledge: By omitting the EDC of intestinal gas, the online SMART treatment time can be shortened.
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http://dx.doi.org/10.1259/bjr.20200239DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8011255PMC
March 2021

The use of hyperbaric oxygen to treat actinic rectal fistula after SpaceOAR use and radiotherapy for prostate cancer: a case report.

BMC Urol 2020 Dec 14;20(1):196. Epub 2020 Dec 14.

Department of Radiation Therapy, National Cancer Center Hospital, Tsukiji 5-1-1, Chuo-ku, Tokyo, Japan.

Background: In definitive radiation therapy for prostate cancer, the SpaceOAR® System, a hydrogel spacer, is widely used to decrease the irradiated dose and toxicity of rectum. On the other hand, periprostatic abscesses formation and rectal perforation are known as rare adverse effects of SpaceOAR. Nevertheless, there is a lack of reports clarifying the association between aggravation of abscesses and radiation therapy, and hyperbaric oxygen therapy (HBOT) is effective for a peri-SpaceOAR abscess and rectal perforation.

Case Presentation: We report a case of a 78-year-old high-risk prostate cancer patient. After SpaceOAR insertion into the correct space, he started to receive external beam radiation therapy (EBRT). He developed a fever, perineal pain and frequent urination after the completion of EBRT, and the magnetic resonance imaging (MRI) revealed a peri-SpaceOAR abscess. Scheduled brachytherapy was postponed, administration of antibiotics and opioid via intravenous drip was commenced, and transperineal drainage was performed. After the alleviation of the abscess, additional EBRT instead of brachytherapy was performed with MRI-guided radiation therapy (MRgRT). On the last day of the MRgRT, perineal pain reoccurred, and MRI and colonoscopy detected the rectal perforation. He received an intravenous antibiotics drip and HBOT, and fully recovered from the rectal perforation.

Conclusions: Our report indicates that EBRT can lead to a severe rectum complication by causing inflammation for patients with a peri-SpaceOAR abscess. Furthermore, HBOT was effective for the peri-SpaceOAR abscess and rectal perforation associated with EBRT.
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http://dx.doi.org/10.1186/s12894-020-00767-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7737272PMC
December 2020

Configuration analysis of the injection position and shape of the gel spacer in gynecologic brachytherapy.

Brachytherapy 2021 Jan-Feb;20(1):95-103. Epub 2020 Oct 1.

Department of Radiation Oncology, National Cancer Center Hospital, Tokyo, Japan.

Purpose: In this single-institution retrospective study, configuration analysis was performed to determine the optimal location and volume of hyaluronic acid gel spacer injection into the rectovaginal or vesicovaginal septum for effective dose reduction (DR) to the organs at risk (OARs), the rectum and bladder.

Methods And Materials: 70 and 50 intracavitary brachytherapy treatment plans used only vaginal cylinders with gel spacers for the rectal and bladder sides, respectively, whereas 28 did not use spacers. Correlation analysis was performed between the geometrical parameters and injection position of the gel spacers and the 2-cm covering doses of the OARs for each treatment.

Results: A higher DR was predicted for hyaluronic acid gel spacer injection within ±5 mm and ±2.5 mm in the lateral-medial direction from the midpoint on the rectal and bladder sides, and ±10 mm in the cranial-caudal direction from the midpoint on the rectal side. There were correlations between 2-cm covering doses and the gel spacer parameters: the volume on the rectal (p = 0.02) and bladder (p = 0.04) sides; the craniocaudal length on the rectal side (p << 0.05); and ventrodorsad thickness on each OAR (p << 0.05) sides. There was no significant difference in the DR between a volume of ∼10 cm and that of a higher volume (p >> 0.05).

Conclusions: A gel spacer volume of ∼10 cm provides sufficient OAR DR if its gravity point is on the midpoint between the cylinder applicator and OAR, and its craniocaudal length covers the active length of the cylinder applicator.
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http://dx.doi.org/10.1016/j.brachy.2020.08.021DOI Listing
October 2020

[Summary of the Report of Task Group 100 of the AAPM: Application of Risk Analysis Methods to Radiation Therapy Quality Management].

Igaku Butsuri 2020 ;40(1):28-34

Department of Radiation Oncology, National Cancer Center Hospital.

In 2016, the American Association of Physicists in Medicine (AAPM) has published a report of task group (TG) 100 with a completely new concept, entitled "application of risk analysis methods to radiation therapy quality management." TG-100 proposed implementation of risk analysis in radiotherapy to prevent harmful radiotherapy accidents. In addition, it enables us to conduct efficient and effective quality management in not only advanced radiotherapy such as intensity-modulated radiotherapy and image-guided radiotherapy but also new technology in radiotherapy. It should be noted that treatment process in modern radiotherapy is absolutely more complex and it needs skillful staff and adequate resources. TG-100 methodology could identify weakness in radiotherapy procedure through assessment of failure modes that could occur in overall treatment processes. All staff in radiotherapy have to explore quality management in radiotherapy safety.
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http://dx.doi.org/10.11323/jjmp.40.1_28DOI Listing
September 2020

Comparison of FBPA uptake with FDG uptake in cancer patients.

Appl Radiat Isot 2020 Mar 7;157:109019. Epub 2019 Dec 7.

Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1, Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan; Division of Research and Development for Boron Neutron Capture Therapy, Exploratory Oncology Research and Clinical Trial Center, National Cancer Center, 5-1-1, Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan. Electronic address:

For the patients who underwent fluorinated para-boronophenylalanine (FBPA) positron emission tomography (PET) and fluorodeoxyglucose (FDG) PET within a period of 2 weeks, maximum standardized uptake value (SUVmax), tumor-to-normal tissue ratio (TNR), and tumor-to-blood ratio (TBR) for FBPA were compared with SUVmax for FDG. A total of 30 patients were selected for comparison. SUVmax for FBPA was correlated the best with SUVmax for FDG. Subsequently, the SUVmax correlation between FBPA and FDG were verified among 82 patients. The correlation factor was 0.4825.
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http://dx.doi.org/10.1016/j.apradiso.2019.109019DOI Listing
March 2020

Characterization of the relationship between neutron production and thermal load on a target material in an accelerator-based boron neutron capture therapy system employing a solid-state Li target.

PLoS One 2019 22;14(11):e0225587. Epub 2019 Nov 22.

Department of Medical Physics, National Cancer Center Hospital, Chuo-ku, Tokyo, Japan.

An accelerator-based boron neutron capture therapy (BNCT) system that employs a solid-state Li target can achieve sufficient neutron flux derived from the 7Li(p,n) reaction. However, neutron production is complicated by the large thermal load expected on the target. The relationship between neutron production and thermal load was examined under various conditions. A target structure for neutron production consists of a Li target and a target basement. Four proton beam profiles were examined to vary the local thermal load on the target structure while maintaining a constant total thermal load. The efficiency of neutron production was evaluated with respect to the total number of protons delivered to the target structure. The target structure was also evaluated by observing its surface after certain numbers of protons were delivered. The yield of the sputtering effect was calculated via a Monte Carlo simulation to investigate whether it caused complications in neutron production. The efficiency of neutron production and the amount of damage done depended on the proton profile. A more focused proton profile resulted in greater damage. The efficiency decreased as the total number of protons delivered to the target structure increased, and the rate of decrease depended on the proton profile. The sputtering effect was not sufficiently large to be a main factor in the reduction in neutron production. The proton beam profile on the target structure was found to be important to the stable operation of the system with a solid-state Li target. The main factor in the rate of reduction in neutron production was found to be the local thermal load induced by proton irradiation of the target.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0225587PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6874357PMC
March 2020

Inter-fractional variations in the dosimetric parameters of accelerated partial breast irradiation using a strut-adjusted volume implant.

J Radiat Res 2020 Jan;61(1):123-133

Department of Medical Physics, National Cancer Center Hospital, Chuo-ku, Tsukiji 5-1-1, Tokyo, 104-0045, Japan.

The aim of the study was to evaluate inter-fractional dosimetric variations for high-dose rate breast brachytherapy using a strut-adjusted volume implant (SAVI). For the nine patients included, dosimetric constraints for treatment were as follows: for the planning target volume for evaluation (PTV_Eval), the volume receiving 90, 150 and 200% of the prescribed dose (V90%,150%,200%) should be >90%, ≤50 cm3 and ≤20 cm3, respectively; the dose covering 1 cm3 (D1cc) of the organs at risk should be ≤110% of the prescribed dose; and the air volume should be ≤10% of PTV_Eval. Differences in V90%,150%,200%, D1cc and air volume ($\Delta V$ and $\Delta D$) as inter-fractional dosimetric variations and SAVI displacements were measured with pretreatment and planning computed tomography (CT) images. Inter-fractional dosimetric variations were analyzed for correlations with the SAVI displacements. The patients were divided into two groups based on the distance of the SAVI from the surface skin to assess the relationship between the insertion position of the SAVI and dosimetric parameters. The median ΔV90%,150%,200% for the PTV_Eval in all patients was -0.3%, 0.2 cm3 and 0.2 cm3, respectively. The median (range) ΔD1cc for the chest wall and surface skin was -0.8% (-18.9 to 9.4%) and 0.3% (-7.6 to 5.3%), respectively. SAVI displacement did not correlate with inter-fractional dosimetric variations. In conclusion, the dose constraints were satisfied in most cases. However, there were inter-fractional dosimetric changes due to SAVI displacement.
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http://dx.doi.org/10.1093/jrr/rrz061DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7022137PMC
January 2020

Dummy-run for standardizing plan quality of intensity-modulated radiotherapy for postoperative uterine cervical cancer: Japan Clinical Oncology Group study (JCOG1402).

Radiat Oncol 2019 Jul 29;14(1):133. Epub 2019 Jul 29.

Radiation Therapy Center, Okinawa Chubu Hospital, Okinawa, 904-2293, Japan.

Background: The purpose of this study was to assess compliance with treatment planning in a dummy-run for a multicenter clinical trial involving patients with high-risk postoperative uterine cervical cancer using intensity-modulated radiation therapy (IMRT) (JCOG1402 trial).

Methods: For the dummy-run, we prepared a computed tomography dataset comprising two anonymized cases of post-hysterectomy cervical cancer. These were sent to the 47 participating institutions to assess institutional plan quality such as delineations and dose distributions.

Results: Central review showed 3 and 4 deviations per treatment plan on average. The deviations related to the nodal and vaginal cuff clinical target volume (CTV) delineation, which accounted for approximately 50% of the total deviations. The CTV vaginal cuff showed considerable differences in delineation compared with the nodal CTV. For the Dice similarity coefficient, case 1 showed a mean ± 1σ of 0.81 ± 0.03 and 0.60 ± 0.09 for the nodal and the CTV vaginal cuff, respectively, while these were 0.81 ± 0.04 and 0.54 ± 0.14, respectively, for case two. Of the 47 institutions, 10 were required to resubmit their treatment plan because the delineations, planning target volume margin, and required dose distributions were not in accordance with the JCOG1402 protocol.

Conclusions: The dummy-run test in postoperative uterine cervical cancer demonstrated substantial deviations in the delineations, particularly for the CTV vaginal cuff. The analysis data could provide helpful information on delineation and planning, allowing standardization of IMRT planning for postoperative uterine cervical cancer.

Trial Registration: Japanese Clinical Trial Registry #: UMIN000027017 at https://upload.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000030672;language=J.
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http://dx.doi.org/10.1186/s13014-019-1340-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6664568PMC
July 2019

[On-line Adaptive Radiotherapy Using MRI-Guided Technique].

Igaku Butsuri 2019;38(4):159-165

Department of Radiation Oncology, National Cancer Center Hospital.

In our institution, we installed MRI-guided radiotherapy system (MRIdian, ViewRay Inc.), allowing to perform on-line adaptive radiotherapy (ART). The MRIdian has three Co sources with 120 degrees apart, equipped with MRI system using a static magnetic field of 0.35 T. The tumor can be monitored and identified in real-time Cine-MRI during treatments, and gated-radiotherapy is possible based on the boundaries. On-line ART can provide the optimum delivery where high dose coverages to the tumor and sparing dose to health organs can be achieved. However, patient specific QA in on-line ART has a limitation of activities, because patients stay in the couth while planning. In this report, we summarized the commissioning of the MRIdian, and the patient specific QA established in on-line ART was described.
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http://dx.doi.org/10.11323/jjmp.38.4_159DOI Listing
July 2019

Dependence of neutrons generated by Li(p,n) reaction on Li thickness under free-air condition in accelerator-based boron neutron capture therapy system employing solid-state Li target.

Phys Med 2019 Feb 16;58:121-130. Epub 2019 Feb 16.

Department of Medical Physics, National Cancer Center Hospital, Tsukiji 5-1-1, Chuo-ku, Tokyo 104-0045, Japan; Division of Research and Development for Boron Neutron Capture Therapy, National Cancer Center Exploratory Oncology Research & Clinical Trial Center, Tsukiji 5-1-1, Chuo-ku, Tokyo 104-0045, Japan; Department of Radiation Oncology, National Cancer Center Hospital, Tsukiji 5-1-1, Chuo-ku, Tokyo 104-0045, Japan.

Purpose: An accelerator-based boron neutron capture therapy (BNCT) system with a solid-state Li target is reported to have degradation of the Li target. The degradation reduces the Li thickness, which may change spectra of the generated neutrons corresponding to the Li thickness. This study aims to examine the relationship between the Li thickness and the generated neutrons and to investigate the effects of the Li thickness on the absorbed dose in BNCT.

Method: The neutron energy spectra were calculated via Monte Carlo simulation for Li thicknesses ranging from 20 to 150 μm. Using the system, the saturated radioactivity of gold induced by reactions between Au and the generated neutrons was evaluated with the simulation and the measurement, and those were compared. Additionally, for each Li thickness, the saturated radioactivity was compared with the number of generated neutrons. The absorbed doses delivered by B(n,α)Li, N(n,p)C, H(n, g)H, and (n,n') reactions in water were also calculated for each Li thickness.

Results: The measurement and simulation indicated a reduction in the number of neutrons due to the degradation of the Li target. However, the absorbed doses were comparable for each Li thickness when the requisite number of neutrons for BNCT was delivered. Additionally, the saturated radioactivity of Au could be a surrogate for the number of neutrons even if the Li thickness was varied.

Conclusions: No notable effect to the absorbed dose was observed when required neutron fluence was delivered in the BNCT even if the degradation of the Li was observed.
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http://dx.doi.org/10.1016/j.ejmp.2019.02.010DOI Listing
February 2019

Monte Carlo modeling of a 60Co MRI-guided radiotherapy system on Geant4 and experimental verification of dose calculation under a magnetic field of 0.35 T.

J Radiat Res 2019 Jan;60(1):116-123

Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo, Japan.

Our purpose was to establish the commissioning procedure of Monte Carlo modeling on a magnetic resonance imaging-guided radiotherapy system (MRIdian, Viewray Inc.) under a magnetic field of 0.345 T through experimental measurements. To do this, we sought (i) to assess the depth-dose and lateral profiles generated by the Geant4 using either EBT3 film or the BJR-25 data; (ii) to assess the calculation accuracy under a magnetic field of 0.345 T. The radius of the electron trajectory caused by the electron return effect (ERE) in a vacuum was obtained both by the Geant4 and the theoretical methods. The surface dose on the phantom was calculated and compared with that obtained from the film measurements. The dose distribution in a phantom having two air gaps was calculated and measured with EBT 3 film. (i) The difference of depth-dose profile generated by the Geant4 from the BJR-25 data was 0.0 ± 0.8% and 0.3 ± 1.5% for field sizes of 4.5 and 27.3 cm2, respectively. Lateral dose profiles generated by Geant4 agreed well with those generated from the EBT3 film data. (ii) The radius of the electron trajectory generated by Geant4 agreed well with the theoretical values. A maximum of ~50% reduction of the surface dose under a magnetic field of 0.345 T was observed due to elimination of the electron contamination caused by the magnetic field, as determined by both the film measurements and the Geant4. Changes in the dose distributions in the air gaps caused by the ERE were observed on the Geant4 and in the film measurements. Gamma analysis (3%/3 mm) showed a pass rate of 95.1%. Commissioning procedures for the MRI-guided radiotherapy system on the Geant4 were established, and we concluded that the Geant4 had provided high calculation accuracy under a magnetic field of 0.345 T.
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http://dx.doi.org/10.1093/jrr/rry087DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6373691PMC
January 2019

[Efforts toward Patient Safety: Development of System and Education of Non-Technical Skill].

Igaku Butsuri 2018;38(2):62-67

Department of Radiation Oncology, National Cancer Center Hospital.

Advanced radiotherapy such as intensity-modulated radiotherapy offers many advantages of high accuracy and efficiency of radiotherapy. To date, many technical guidelines with description of quality assurance and quality control have been reported. However, some reports indicated that human factor and environment is major cause of radiotherapy incidents. If radiotherapy systems depend on automation and computer system, individual risk management is degraded and ability of preventing radiotherapy incidents weaken. Recently, the American Association of Physicists in Medicine (AAPM) task group-100 was reported and it has a new concept guideline, which proposed the comprehensive risk management and education of non-technical skills for overall radiotherapy processes. The TG-100 recommends implementation of process map, reporting system, risk assessment such as failure mode and effects analysis (FMEA) and fault tree analysis (FTA) especially for advanced radiotherapy. In this paper, we described effective and efficient procedures to improve the treatment processes and education of non-technical skills using the such management tools proposed by the TG-100 guide-lines.
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http://dx.doi.org/10.11323/jjmp.38.2_62DOI Listing
June 2019

Establishment of postal audit system in intensity-modulated radiotherapy by radiophotoluminescent glass dosimeters and a radiochromic film.

Phys Med 2018 Apr 24;48:119-126. Epub 2018 Apr 24.

Department of Radiation Oncology, Kindai University Faculty of Medicine, Osaka 589-8511, Japan.

We developed an efficient postal audit system to independently assess the delivered dose using radiophotoluminescent glass dosimeters (RPLDs) and the positional differences of fields using EBT3 film at the axial plane for intensity-modulated radiotherapy (IMRT). The audit phantom had a C-shaped target structure as a planning target volume (PTV) with four measurement points for the RPLDs and a cylindrical structure as the organ at risk (OAR) for one measurement point. The phantoms were sent to 24 institutions. Point dose measurements with a 0.6 cm PTW farmer chamber were also performed to justify glass dosimetry in IMRT. The measured dose with the RPLDs was compared to the calculated dose in the institution's treatment planning system (TPS). The mean ± 1.96σ of the ratio of the measured dose with the RPLDs to the farmer chamber was 0.997 ± 0.024 with no significant difference (p = .175). The investigations demonstrated that glass dosimetry was reliable with a high measurement accuracy comparable to the chamber. The mean ± 1.96σ for the dose differences with a reference of the TPS dose for the PTV and the OAR was 0.1 ± 2.5% and -2.1 ± 17.8%, respectively. The mean ± 1.96σ for the right-left and the anterior-posterior direction was -0.9 ± 2.8 and 0.5 ± 1.4 mm, respectively. This study is the first report to justify glass dosimetry for implementation in IMRT audit in Japan. We demonstrate that our postal audit system has high accuracy with a high-level criterion of 3%/3 mm.
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http://dx.doi.org/10.1016/j.ejmp.2018.03.013DOI Listing
April 2018

Positional uncertainty of vaginal cuff and feasibility of implementing portable bladder scanner in postoperative cervical cancer patients.

Phys Med 2018 Jan 1;45:1-5. Epub 2017 Dec 1.

Department of Radiation Oncology, National Cancer Center Hospital, Tokyo, Japan.

Purpose: To propose a geometrical margin for definition of the vaginal cuff PTV using only CT images of the full bladder (CT) in postoperative cervical cancer patients.

Methods: Twenty-nine operated cervical cancer patients underwent volumetric arc therapy with a bladder filling protocol. This study assessed bladder filling using a portable bladder scanner and cone-beam computed tomography (CBCT) during the entire treatment period. The measured bladder volumes with a BladderScan® were compared with the delineated volume on CBCT. Titanium clips in the vaginal cuff were analysed to assess geometrical uncertainty and the influence of rectal and bladder volume changes.

Results: BladderScan® showed good agreement with the delineated volume (R = 0.80). The volume changes in the bladder have a greater influence on the clip displacements than in the rectum. The 95th percentile of uncertainty of the clips in reference to CT in the right-left (RL), the superoinferior (SI), and the anteroposterior (AP) was 0.32, 0.65, and 1.15 cm, respectively. From this result and intra-fractional movements of the vaginal cuff reported by Haripotepornkul, a new geometrical margin was proposed for definition of the vaginal cuff planning target volume (PTV): 0.5, 0.9, and 1.4 cm in the RL, SI, and AP directions, respectively.

Conclusions: A new geometrical margin was proposed for definition of the vaginal cuff PTV based on CT, which will be needless of empty bladder at the planning CT scan. This method allows patients to reduce the burden and efficient routine CT scans can be improved.
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http://dx.doi.org/10.1016/j.ejmp.2017.11.018DOI Listing
January 2018

Evaluation of radioactivity in the bodies of mice induced by neutron exposure from an epi-thermal neutron source of an accelerator-based boron neutron capture therapy system.

Proc Jpn Acad Ser B Phys Biol Sci 2017 ;93(10):821-831

Department of Radiation Oncology, National Cancer Center Hospital.

This study aimed to evaluate the residual radioactivity in mice induced by neutron irradiation with an accelerator-based boron neutron capture therapy (BNCT) system using a solid Li target. The radionuclides and their activities were evaluated using a high-purity germanium (HP-Ge) detector. The saturated radioactivity of the irradiated mouse was estimated to assess the radiation protection needs for using the accelerator-based BNCT system. Na, Cl, Br, Br, Mn, and K were identified, and their saturated radioactivities were (1.4 ± 0.1) × 10, (2.2 ± 0.1) × 10, (3.4 ± 0.4) × 10, 2.8 ± 0.1, 8.0 ± 0.1, and (3.8 ± 0.1) × 10 Bq/g/mA, respectively. The Na activation rate at a given neutron fluence was found to be consistent with the value reported from nuclear-reactor-based BNCT experiments. The induced activity of each nuclide can be estimated by entering the saturated activity of each nuclide, sample mass, irradiation time, and proton current into the derived activation equation in our accelerator-based BNCT system.
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http://dx.doi.org/10.2183/pjab.93.051DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5790759PMC
November 2018

Independent assessment of source position for gynecological applicator in high-dose-rate brachytherapy.

J Contemp Brachytherapy 2017 Oct 19;9(5):477-486. Epub 2017 Oct 19.

Department of Radiation Oncology, National Cancer Center Hospital, Tokyo.

Purpose: The aim of this study is to describe a phantom designed for independent examination of a source position in brachytherapy that is suitable for inclusion in an external auditing program.

Material And Methods: We developed a phantom that has a special design and a simple mechanism, capable of firmly fixing a radiochromic film and tandem-ovoid applicators to assess discrepancies in source positions between the measurements and treatment planning system (TPS). Three tests were conducted: 1) reproducibility of the source positions ( = 5); 2) source movements inside the applicator tube; 3) changing source position by changing curvature of the transfer tubes. In addition, as a trial study, the phantom was mailed to 12 institutions, and 23 trial data sets were examined. The source displacement ΔX and ΔY (reference = TPS) were expressed according to the coordinates, in which the positive direction on the X-axis corresponds to the external side of the applicator perpendicular to source transfer direction Y-axis.

Results: Test 1: The 1σ fell within 1 mm irrespective of the dwell positions. Test 2: ΔX were greater around the tip of the applicator owing to the source cable. Test 3: All of the source position changes fell within 1 mm. For postal audit, the mean and 1.96σ in ΔX were 0.8 and 0.8 mm, respectively. Almost all data were located within a positive region along the X-axis due to the source cable. The mean and 1.96σ in ΔY were 0.3 and 1.6 mm, respectively. The variance in ΔY was greater than that in ΔX, and large uncertainties exist in the determination of the first dwell position. The 95% confidence limit was 2.1 mm.

Conclusions: In HDR brachytherapy, an effectiveness of independent source position assessment could be demonstrated. The 95% confidence limit was 2.1 mm for a tandem-ovoids applicator.
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http://dx.doi.org/10.5114/jcb.2017.70952DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5705831PMC
October 2017

Modeling the detection efficiency of an HP-Ge detector for use in boron neutron capture therapy.

Appl Radiat Isot 2017 Jul 2;125:80-85. Epub 2017 Apr 2.

Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.

The multi-foil method is commonly used to determine upon an energy spectrum of neutrons in boron neutron capture therapy. The method requires to measure the radioactivation of the foils. This study develops a simple modeling procedure of a high-purity Ge detector, which is used to measure the radioactivation, in order to calculate the detection efficiency with GEANT4. By changing four parameters from their manufacturing specifications of the detector, the simulated detection efficiency is able to reproduce the actual detection efficiency.
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http://dx.doi.org/10.1016/j.apradiso.2017.03.027DOI Listing
July 2017

Dosimetric impact of an air passage on intraluminal brachytherapy for bronchus cancer.

J Radiat Res 2016 Nov 7;57(6):637-645. Epub 2016 Sep 7.

Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.

The brachytherapy dose calculations used in treatment planning systems (TPSs) have conventionally been performed assuming homogeneous water. Using measurements and a Monte Carlo simulation, we evaluated the dosimetric impact of an air passage on brachytherapy for bronchus cancer. To obtain the geometrical characteristics of an air passage, we analyzed the anatomical information from CT images of patients who underwent intraluminal brachytherapy using a high-dose-rate Ir source (MicroSelectron V2r®, Nucletron). Using an ionization chamber, we developed a measurement system capable of measuring the peripheral dose with or without an air cavity surrounding the catheter. Air cavities of five different radii (0.3, 0.5, 0.75, 1.25 and 1.5 cm) were modeled by cylindrical tubes surrounding the catheter. A Monte Carlo code (GEANT4) was also used to evaluate the dosimetric impact of the air cavity. Compared with dose calculations in homogeneous water, the measurements and GEANT4 indicated a maximum overdose of 5-8% near the surface of the air cavity (with the maximum radius of 1.5 cm). Conversely, they indicated a minimum overdose of ~1% in the region 3-5 cm from the cavity surface for the smallest radius of 0.3 cm. The dosimetric impact depended on the size and the distance of the air passage, as well as the length of the treatment region. Based on dose calculations in water, the TPS for intraluminal brachytherapy for bronchus cancer had an unexpected overdose of 3-5% for a mean radius of 0.75 cm. This study indicates the need for improvement in dose calculation accuracy with respect to intraluminal brachytherapy for bronchus cancer.
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http://dx.doi.org/10.1093/jrr/rrw072DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5137293PMC
November 2016

Real patient data based cross verification of kilovoltage and megavoltage CT calibration for proton therapy.

Phys Med 2016 Feb 26;32(2):343-52. Epub 2016 Feb 26.

Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA. Electronic address:

Purpose: We propose a methodology to evaluate the stoichiometric calibration method on MVCT against the corresponding kVCT calibration using patient data.

Methods: Stoichiometric calibrations were conducted for a MVCT and a kVCT scanner, respectively. We retrospectively analyzed kVCT and MVCT images of 21 patients by picking small tissue volumes in kVCT images and performing image registration to locate the tissue volumes in corresponding MVCT images. We computed the difference between the mean proton stopping power derived through kVCT and MVCT calibration, taking into account the uncertainties in calibration, imaging, and image registration.

Results: kVCT and MVCT calibration curves were in good agreement for soft tissues such as muscle and brain, but showed statistically significant difference (p < 0.05) in stopping power of adipose (2.4 ± 1.7%) and bony structures such as spongiosa, and cranium (-3.2 ± 1.4 and -3.1 ± 2.1%, respectively).

Conclusion: The MVCT calibration might not agree with the corresponding kVCT calibration for some tissues.
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http://dx.doi.org/10.1016/j.ejmp.2016.01.477DOI Listing
February 2016

Experimental evaluation of actual delivered dose using mega-voltage cone-beam CT and direct point dose measurement.

Med Dosim 2013 21;38(2):153-9. Epub 2012 Dec 21.

Graduate School of Human Health Sciences, Tokyo Metropolitan University, Tokyo, Japan.

Radiation therapy in patients is planned by using computed tomography (CT) images acquired before start of the treatment course. Here, tumor shrinkage or weight loss or both, which are common during the treatment course for patients with head-and-neck (H&N) cancer, causes unexpected differences from the plan, as well as dose uncertainty with the daily positional error of patients. For accurate clinical evaluation, it is essential to identify these anatomical changes and daily positional errors, as well as consequent dosimetric changes. To evaluate the actual delivered dose, the authors proposed direct dose measurement and dose calculation with mega-voltage cone-beam CT (MVCBCT). The purpose of the present study was to experimentally evaluate dose calculation by MVCBCT. Furthermore, actual delivered dose was evaluated directly with accurate phantom setup. Because MVCBCT has CT-number variation, even when the analyzed object has a uniform density, a specific and simple CT-number correction method was developed and applied for the H&N site of a RANDO phantom. Dose distributions were calculated with the corrected MVCBCT images of a cylindrical polymethyl methacrylate phantom. Treatment processes from planning to beam delivery were performed for the H&N site of the RANDO phantom. The image-guided radiation therapy procedure was utilized for the phantom setup to improve measurement reliability. The calculated dose in the RANDO phantom was compared to the measured dose obtained by metal-oxide-semiconductor field-effect transistor detectors. In the polymethyl methacrylate phantom, the calculated and measured doses agreed within about +3%. In the RANDO phantom, the dose difference was less than +5%. The calculated dose based on simulation-CT agreed with the measured dose within±3%, even in the region with a high dose gradient. The actual delivered dose was successfully determined by dose calculation with MVCBCT, and the point dose measurement with the image-guided radiation therapy procedure.
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http://dx.doi.org/10.1016/j.meddos.2012.10.005DOI Listing
December 2013

In vivo proton dosimetry using a MOSFET detector in an anthropomorphic phantom with tissue inhomogeneity.

J Appl Clin Med Phys 2012 Mar 8;13(2):3699. Epub 2012 Mar 8.

National Cancer Center Hospital East, Kashiwa, Chiba, Japan.

When in vivo proton dosimetry is performed with a metal-oxide semiconductor field-effect transistor (MOSFET) detector, the response of the detector depends strongly on the linear energy transfer. The present study reports a practical method to correct the MOSFET response for linear energy transfer dependence by using a simplified Monte Carlo dose calculation method (SMC). A depth-output curve for a mono-energetic proton beam in polyethylene was measured with the MOSFET detector. This curve was used to calculate MOSFET output distributions with the SMC (SMC(MOSFET)). The SMC(MOSFET) output value at an arbitrary point was compared with the value obtained by the conventional SMC(PPIC), which calculates proton dose distributions by using the depth-dose curve determined by a parallel-plate ionization chamber (PPIC). The ratio of the two values was used to calculate the correction factor of the MOSFET response at an arbitrary point. The dose obtained by the MOSFET detector was determined from the product of the correction factor and the MOSFET raw dose. When in vivo proton dosimetry was performed with the MOSFET detector in an anthropomorphic phantom, the corrected MOSFET doses agreed with the SMC(PPIC) results within the measurement error. To our knowledge, this is the first report of successful in vivo proton dosimetry with a MOSFET detector.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5716407PMC
http://dx.doi.org/10.1120/jacmp.v13i2.3699DOI Listing
March 2012

Proton dose distribution measurements using a MOSFET detector with a simple dose-weighted correction method for LET effects.

J Appl Clin Med Phys 2011 Apr 4;12(2):3431. Epub 2011 Apr 4.

National Cancer Center Hospital East, Chiba 277-8577, Japan.

We experimentally evaluated the proton beam dose reproducibility, sensitivity, angular dependence and depth-dose relationships for a new Metal Oxide Semiconductor Field Effect Transistor (MOSFET) detector. The detector was fabricated with a thinner oxide layer and was operated at high-bias voltages. In order to accurately measure dose distributions, we developed a practical method for correcting the MOSFET response to proton beams. The detector was tested by examining lateral dose profiles formed by protons passing through an L-shaped bolus. The dose reproducibility, angular dependence and depth-dose response were evaluated using a 190 MeV proton beam. Depth-output curves produced using the MOSFET detectors were compared with results obtained using an ionization chamber (IC). Since accurate measurements of proton dose distribution require correction for LET effects, we developed a simple dose-weighted correction method. The correction factors were determined as a function of proton penetration depth, or residual range. The residual proton range at each measurement point was calculated using the pencil beam algorithm. Lateral measurements in a phantom were obtained for pristine and SOBP beams. The reproducibility of the MOSFET detector was within 2%, and the angular dependence was less than 9%. The detector exhibited a good response at the Bragg peak (0.74 relative to the IC detector). For dose distributions resulting from protons passing through an L-shaped bolus, the corrected MOSFET dose agreed well with the IC results. Absolute proton dosimetry can be performed using MOSFET detectors to a precision of about 3% (1 sigma). A thinner oxide layer thickness improved the LET in proton dosimetry. By employing correction methods for LET dependence, it is possible to measure absolute proton dose using MOSFET detectors.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5718688PMC
http://dx.doi.org/10.1120/jacmp.v12i2.3431DOI Listing
April 2011

Apparent absence of a proton beam dose rate effect and possible differences in RBE between Bragg peak and plateau.

Med Phys 2010 Oct;37(10):5376-81

National Cancer Center Hospital East, 6-5-1 Kashiwanoha, Kashiwa, Chiba 277-8577, Japan.

Purpose: Respiration-gated irradiation for a moving target requires a longer time to deliver single fraction in proton radiotherapy (PRT). Ultrahigh dose rate (UDR) proton beam, which is 10-100 times higher than that is used in current clinical practice, has been investigated to deliver daily dose in single breath hold duration. The purpose of this study is to investigate the survival curve and relative biological effectiveness (RBE) of such an ultrahigh dose rate proton beam and their linear energy transfer (LET) dependence.

Methods: HSG cells were irradiated by a spatially and temporally uniform proton beam at two different dose rates: 8 Gy/min (CDR, clinical dose rate) and 325 Gy/min (UDR, ultrahigh dose rate) at the Bragg peak and 1.75 (CDR) and 114 Gy/min (UDR) at the plateau. To study LET dependence, the cells were positioned at the Bragg peak, where the absorbed dose-averaged LET was 3.19 keV/microm, and at the plateau, where it was 0.56 keV/microm. After the cell exposure and colony assay, the measured data were fitted by the linear quadratic (LQ) model and the survival curves and RBE at 10% survival were compared.

Results: No significant difference was observed in the survival curves between the two proton dose rates. The ratio of the RBE for CDR/UDR was 0.98 +/- 0.04 at the Bragg peak and 0.96 +/- 0.06 at the plateau. On the other hand, Bragg peak/plateau RBE ratio was 1.15 +/- 0.05 for UDR and 1.18 +/- 0.07 for CDR.

Conclusions: Present RBE can be consistently used in treatment planning of PRT using ultrahigh dose rate radiation. Because a significant increase in RBE toward the Bragg peak was observed for both UDR and CDR, further evaluation of RBE enhancement toward the Bragg peak and beyond is required.
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http://dx.doi.org/10.1118/1.3490086DOI Listing
October 2010