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Forsthoefel M, Hankins R, Ballew E, Frame C, DeBlois D, Pang D, Krishnan P, Unger K, Kowalczyk K, Lynch J, Dritschilo A, Collins SP, Lischalk JW. Prostate Cancer Treatment with Pencil Beam Proton Therapy Using Rectal Spacers sans Endorectal Balloons. Int J Part Ther 2022; 9:28-41. [PMID: 35774493 PMCID: PMC9238133 DOI: 10.14338/ijpt-21-00039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Accepted: 02/01/2022] [Indexed: 11/21/2022] Open
Abstract
Purpose Proton beam radiotherapy (PBT) has been used for the definitive treatment of localized prostate cancer with low rates of high-grade toxicity and excellent patient-reported quality-of-life metrics. Technological advances such as pencil beam scanning (PBS), Monte Carlo dose calculations, and polyethylene glycol gel rectal spacers have optimized prostate proton therapy. Here, we report the early clinical outcomes of patients treated for localized prostate cancer using modern PBS–PBT with hydrogel rectal spacing and fiducial tracking without the use of endorectal balloons. Materials and Methods This is a single institutional review of consecutive patients treated with histologically confirmed localized prostate cancer. Prior to treatment, all patients underwent placement of fiducials into the prostate and insertion of a hydrogel rectal spacer. Patients were typically given a prescription dose of 7920 cGy at 180 cGy per fraction using a Monte Carlo dose calculation algorithm. Acute and late toxicity were evaluated using the Common Terminology Criteria for Adverse Events (CTCAE), version 5. Biochemical failure was defined using the Phoenix definition. Results From July 2018 to April 2020, 33 patients were treated (median age, 75 years). No severe acute toxicities were observed. The most common acute toxicity was urinary frequency. With a median follow-up of 18 months, there were no high-grade genitourinary late toxicities; however, one grade 3 gastrointestinal toxicity was observed. Late erectile dysfunction was common. One treatment failure was observed at 21 months in a patient treated for high-risk prostate cancer. Conclusion Early clinical outcomes of patients treated with PBS–PBT using Monte Carlo–based planning, fiducial placement, and rectal spacers sans endorectal balloons demonstrate minimal treatment-related toxicity with good oncologic outcomes. Rectal spacer stabilization without the use of endorectal balloons is feasible for the use of PBS–PBT.
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Affiliation(s)
- Matthew Forsthoefel
- Department of Radiation Medicine, Georgetown University Hospital, Washington, DC, USA
| | - Ryan Hankins
- Department of Urology, Georgetown University Hospital, Washington, DC, USA
| | - Elizabeth Ballew
- Department of Radiation Medicine, Georgetown University Hospital, Washington, DC, USA
| | - Cara Frame
- Department of Radiation Medicine, Georgetown University Hospital, Washington, DC, USA
| | - David DeBlois
- Department of Radiation Medicine, Georgetown University Hospital, Washington, DC, USA
| | - Dalong Pang
- Department of Radiation Medicine, Georgetown University Hospital, Washington, DC, USA
| | - Pranay Krishnan
- Department of Radiology, Georgetown University Hospital, Washington, DC, USA
| | - Keith Unger
- Department of Radiation Medicine, Georgetown University Hospital, Washington, DC, USA
| | - Keith Kowalczyk
- Department of Urology, Georgetown University Hospital, Washington, DC, USA
| | - John Lynch
- Department of Urology, Georgetown University Hospital, Washington, DC, USA
| | - Anatoly Dritschilo
- Department of Radiation Medicine, Georgetown University Hospital, Washington, DC, USA
| | - Sean P. Collins
- Department of Radiation Medicine, Georgetown University Hospital, Washington, DC, USA
| | - Jonathan W. Lischalk
- Department of Radiation Oncology, Perlmutter Cancer Center at New York University Langone Hospital – Long Island, New York, NY, USA
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Poon DMC, Wu S, Ho L, Cheung KY, Yu B. Proton Therapy for Prostate Cancer: Challenges and Opportunities. Cancers (Basel) 2022; 14:cancers14040925. [PMID: 35205673 PMCID: PMC8870339 DOI: 10.3390/cancers14040925] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Revised: 02/10/2022] [Accepted: 02/11/2022] [Indexed: 01/02/2023] Open
Abstract
Simple Summary Reported clinical outcomes of proton therapy (PT) for localized prostate cancer are similar to photon-based external beam radiotherapy. Apparently, the dosimetric advantages of PT have yet to be translated to clinical benefits. The suboptimal clinical outcomes of PT might be attributable to inadequate dose prescription, as indicated by the ASCENDE-RT trial. Moreover, uncertainties involved in the treatment planning and delivery processes, as well as technological limitations in PT treatment systems, may lead to discrepancies between planned doses and actual doses delivered to patients. In this article, we reviewed the current status of PT for prostate cancer and discussed different clinical implementations that could potentially improve the clinical outcome of PT for prostate cancer. Various technological advancements under which uncertainties in dose calculations can be minimized, including MRI-guided PT, dual-energy photon-counting CT and high-resolution Monte Carlo-based treatment planning systems, are highlighted. Abstract The dosimetric advantages of proton therapy (PT) treatment plans are demonstrably superior to photon-based external beam radiotherapy (EBRT) for localized prostate cancer, but the reported clinical outcomes are similar. This may be due to inadequate dose prescription, especially in high-risk disease, as indicated by the ASCENDE-RT trial. Alternatively, the lack of clinical benefits with PT may be attributable to improper dose delivery, mainly due to geometric and dosimetric uncertainties during treatment planning, as well as delivery procedures that compromise the dose conformity of treatments. Advanced high-precision PT technologies, and treatment planning and beam delivery techniques are being developed to address these uncertainties. For instance, external magnetic resonance imaging (MRI)-guided patient setup rooms are being developed to improve the accuracy of patient positioning for treatment. In-room MRI-guided patient positioning systems are also being investigated to improve the geometric accuracy of PT. Soon, high-dose rate beam delivery systems will shorten beam delivery time to within one breath hold, minimizing the effects of organ motion and patient movements. Dual-energy photon-counting computed tomography and high-resolution Monte Carlo-based treatment planning systems are available to minimize uncertainties in dose planning calculations. Advanced in-room treatment verification tools such as prompt gamma detector systems will be used to verify the depth of PT. Clinical implementation of these new technologies is expected to improve the accuracy and dose conformity of PT in the treatment of localized prostate cancers, and lead to better clinical outcomes. Improvement in dose conformity may also facilitate dose escalation, improving local control and implementation of hypofractionation treatment schemes to improve patient throughput and make PT more cost effective.
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Affiliation(s)
- Darren M. C. Poon
- Comprehensive Oncology Centre, Hong Kong Sanatorium & Hospital, Hong Kong 999077, China;
| | - Stephen Wu
- Medical Physics Department, Hong Kong Sanatorium & Hospital, Hong Kong 999077, China; (L.H.); (K.Y.C.); (B.Y.)
- Correspondence: ; Tel.: +852-29171413
| | - Leon Ho
- Medical Physics Department, Hong Kong Sanatorium & Hospital, Hong Kong 999077, China; (L.H.); (K.Y.C.); (B.Y.)
| | - Kin Yin Cheung
- Medical Physics Department, Hong Kong Sanatorium & Hospital, Hong Kong 999077, China; (L.H.); (K.Y.C.); (B.Y.)
| | - Ben Yu
- Medical Physics Department, Hong Kong Sanatorium & Hospital, Hong Kong 999077, China; (L.H.); (K.Y.C.); (B.Y.)
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Fukumitsu N, Mima M, Demizu Y, Suzuki T, Ishida T, Matsushita K, Yamaguchi R, Fujisawa M, Soejima T. Separation effect and development of implantation technique of hydrogel spacer for prostate cancers. Pract Radiat Oncol 2021; 12:226-235. [PMID: 34801769 DOI: 10.1016/j.prro.2021.10.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2021] [Revised: 10/22/2021] [Accepted: 10/31/2021] [Indexed: 11/29/2022]
Abstract
PURPOSE The purpose was to improve the placement of a hydrogel spacer in prostate cancer patients receiving radiotherapy. METHODS AND MATERIALS One hundred and sixty patients with prostate cancer were classified into 3 groups as follows: group 1, no spacer (n = 30); group 2, spacer placed using conventional technique (n = 100); and group 3, spacer placed using new technique (n = 30). When placing the spacer, the tip of the needle was placed at the middle of the prostate gland (group 2) or at a level corresponding to a cranial:caudal ratio of 6:4 and as close to the prostate gland as possible (group 3). The separation effect was then examined and compared among the groups. RESULTS The separation in group 2 was larger than that in group 1 from the base to the apex (4 mm) level of the prostate, while the separation in group 3 was larger than that in group 2 from the middle to the apex (4 mm) level of the prostate. The separation values for the middle to the apex, the spacer thickness from the apex (10 mm) level to the apex, the rectal exclusion from the middle to the apex, and the laterality were correlated with the 50 and 60 Gray relative biological effectiveness (Gy(RBE)) rectal dose (p = 4.1 × 10-9 - 0.046). The separation vales were strongly correlated with the spacer thickness at the apex (10 mm) and apex (4 mm) (p = 1.1 × 10-18 - 1.8 × 10-17). The rectal volumes at 10-60 Gy(RBE) differed among the groups (p = 5.1 × 10-19 - 5.4 × 10-3). The rectal volumes in group 2 were smaller than those in group 1 at all dose levels, while those in group 3 were smaller than those in group 2 at dose levels of 30-50 Gy(RBE). CONCLUSIONS The separation, spacer thickness and rectal exclusion from the middle to the apex of the prostate and the laterality of the hydrogel spacer affected the reduction in the rectal dose. The rectal dose can be further reduced by implanting a spacer on the caudal and the prostate side.
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Affiliation(s)
| | - Masayuki Mima
- Department of Radiation Oncology, Kobe Proton Center
| | - Yusuke Demizu
- Department of Radiation Oncology, Kobe Proton Center
| | | | - Takaki Ishida
- Department of Urology, International Clinical Cancer Research Center, Kobe University
| | - Kei Matsushita
- Department of Urology, International Clinical Cancer Research Center, Kobe University
| | - Raizo Yamaguchi
- Department of Urology, International Clinical Cancer Research Center, Kobe University
| | - Masato Fujisawa
- Department of Urology, Kobe University Graduate School of Medicine
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Omi Y, Yasui K, Shimomura A, Muramatsu R, Iwata H, Ogino H, Furukawa A, Hayashi N. Dosimetric effects of quality assurance-related setup errors in passive proton therapy for prostate cancer with and without a hydrogel spacer. Radiol Phys Technol 2021; 14:328-335. [PMID: 34313911 DOI: 10.1007/s12194-021-00632-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Revised: 07/20/2021] [Accepted: 07/21/2021] [Indexed: 11/30/2022]
Abstract
The purpose of this study was to evaluate the effect of quality assurance (QA)-related setup errors in passive proton therapy for prostate cancer with and without a hydrogel spacer. We used 20 typical computed tomography (CT) images of prostate cancer: 10 patients with and 10 patients without spacers. The following 12 model errors were assumed: output error ± 2%, range error ± 1 mm, setup error ± 1 mm for three directions, and multileaf collimator (MLC) position error ± 1 mm. We created verification plans with model errors and compared the prostate-rectal (PR) distance and dose indices with and without the spacer. The mean PR distance at the isocenter was 1.1 ± 1.3 mm without the spacer and 12.9 ± 2.9 mm with the spacer (P < 0.001). The mean rectum V53.5 GyE, V50 GyE, and V34.5 GyE in the original plan were 2.3%, 4.1%, and 12.1% without the spacer and 0.1%, 0.4%, and 3.3% with the spacer (P = 0.0011, < 0.001, and < 0.001). The effects of the range and lateral setup errors were small; however, the effects of the vertical/long setup and MLC error were significant in the cases without the spacer. The means of the maximum absolute change from original plans across all scenarios in the rectum V53.5 GyE, V50 GyE, and V34.5 GyE were 1.3%, 1.5%, and 2.3% without the spacer, and 0.2%, 0.4%, and 1.3% with the spacer (P < 0.001, < 0.001, and = 0.0019). This study indicated that spacer injections were also effective in reducing the change in the rectal dose due to setup errors.
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Affiliation(s)
- Yuta Omi
- Anjo Kosei Hospital, 28 Higashi-Hirokute, Anjo-cho, Anjo, Aichi, 446-8602, Japan
| | - Keisuke Yasui
- Faculty of Radiological Technology, School of Health Sciences, Fujita Health University, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi, 470-1192, Japan.
| | - Akira Shimomura
- Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya, Aichi, 462-8508, Japan
| | - Rie Muramatsu
- Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya, Aichi, 462-8508, Japan
| | - Hiromitsu Iwata
- Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya, Aichi, 462-8508, Japan
| | - Hiroyuki Ogino
- Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya, Aichi, 462-8508, Japan
| | - Akari Furukawa
- Faculty of Radiological Technology, School of Health Sciences, Fujita Health University, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi, 470-1192, Japan
| | - Naoki Hayashi
- Faculty of Radiological Technology, School of Health Sciences, Fujita Health University, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi, 470-1192, Japan
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Fagundes M, Rodrigues MA, Olszewski S, Khan F, McKenzie C, Gutierrez A, Chuong M, Mehta M. Expanding the Utilization of Rectal Spacer Hydrogel for Larger Prostate Glands (>80 cc): Feasibility and Dosimetric Outcomes. Adv Radiat Oncol 2021; 6:100651. [PMID: 34195489 PMCID: PMC8233470 DOI: 10.1016/j.adro.2021.100651] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Revised: 11/26/2020] [Accepted: 01/05/2021] [Indexed: 11/30/2022] Open
Abstract
Purpose The Hydrogel Spacer Prospective Randomized Pivotal Trial achieved mean rectoprostatic spacing of 12.6 mm resulting in lowering of rectal V70 from 12.4% (without spacer) to 3.3% (with spacer) in patients with glands up to 80 cm3. The value of this approach in patients with larger glands is inadequately established. This study assesses the feasibility and dosimetric outcomes of perirectal spacing in patients with prostate cancer with larger glands (>80 cm3). Methods and Materials Between January 2017 and December 2019, 33 patients with prostate glands >80 cm3 (mean 108.1 cm3; range, 81.1-186.6 cm3) were treated, 15 with glands >80 to 100 cm3 and 18 >100 cm3. Median follow-up was 10 months (range, 3-26). The median international prostate symptom score was 9 (range, 1-18). Hydrogel was placed under local anesthesia in all cases. Treatment modality included intensity modulated radiation therapy in 15 and proton therapy (PT) in 18 patients. Treatment targeted the prostate plus seminal vesicles in 21 patients and 12 also had elective nodal irradiation. Conventional fractionation (CF) to 78 Gy in 39 fractions was used in 16 and moderate hypofractionation (HF) to 70 Gy in 28 fractions in 17 patients. Results In the CF group, mean rectum (r) V75, 70, 60, 50 was 0.87%, 2.25%, 5.61%, and 10.5%, respectively. For glands >80 to 100 cm3 and >100 cm3, rV70 was 2.55% and 2%, respectively. In HF patients, mean rV65, 63, 60, and 50 was 1.67%, 2.3%, 3.4%, and 8.6%. For glands >80 to 100 cm3 and >100 cm3, rV63 was 2% and 2.56%, respectively. Overall, the mean midgland rectoprostatic hydrogel separation was 9.3 mm (range, 4.7-19.4 mm). All patients tolerated treatment well; no acute grade 2 or higher adverse gastrointestinal events were observed. Conclusions Hydrogel placement is feasible in prostate glands larger than 80 cm3 with favorable dosimetric outcomes.
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Affiliation(s)
- Marcio Fagundes
- Radiation Oncology Department, Miami Cancer Institute, Miami, Florida
| | | | - Steve Olszewski
- Radiation Oncology Department, Miami Cancer Institute, Miami, Florida
| | - Fazal Khan
- Radiation Oncology Department, Miami Cancer Institute, Miami, Florida
| | - Craig McKenzie
- Radiation Oncology Department, Miami Cancer Institute, Miami, Florida
| | - Alonso Gutierrez
- Radiation Oncology Department, Miami Cancer Institute, Miami, Florida
| | - Michael Chuong
- Radiation Oncology Department, Miami Cancer Institute, Miami, Florida
| | - Minesh Mehta
- Radiation Oncology Department, Miami Cancer Institute, Miami, Florida
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Sato H, Kato T, Motoyanagi T, Takemasa K, Narita Y, Kato M, Matsumoto T, Oyama S, Yamaguchi H, Wada H, Murakami M. Preliminary analysis of prostate positional displacement using hydrogel spacer during the course of proton therapy for prostate cancer. JOURNAL OF RADIATION RESEARCH 2021; 62:294-299. [PMID: 33341901 PMCID: PMC7948841 DOI: 10.1093/jrr/rraa115] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 09/29/2020] [Indexed: 06/12/2023]
Abstract
In recent years, a novel technique has been employed to maintain a distance between the prostate and the rectum by transperineally injecting a hydrogel spacer (HS). However, the effect of HS on the prostate positional displacement is poorly understood, despite its stability with HS in place. In this study, we investigated the effect of HS insertion on the interfraction prostate motion during the course of proton therapy (PT) for Japanese prostate cancer patients. The study population consisted of 22 cases of intermediate-risk prostate cancer with 11 cases with HS insertion and 11 cases without HS insertion. The irradiation position and preparation were similar for both groups. To test for reproducibility, regular confirmation computed tomography (RCCT) was done four times during the treatment period, and five times overall [including treatment planning CT (TPCT)] in each patient. Considering the prostate position of the TPCT as the reference, the change in the center of gravity of the prostate relative to the bony anatomy in the RCCTs of each patient was determined in the left-right (LR), superior-inferior (SI) and anterior-posterior (AP) directions. As a result, no significant difference was observed across the groups in the LR and SI directions. Conversely, a significant difference was observed in the AP direction (P < 0.05). The proportion of the 3D vector length ≤5 mm was 95% in the inserted group, but 55% in the non-inserted group. Therefore, HS is not only effective in reducing rectal dose, but may also contribute to the positional reproducibility of the prostate.
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Affiliation(s)
- Hiroki Sato
- Department of Radiation Physics and Technology, Southern Tohoku Proton Therapy Center, Fukushima, Japan
| | - Takahiro Kato
- Corresponding author. Department of Radiation Physics and Technology, Southern Tohoku Proton Therapy Center, 172 Yatsuyamada 7 Chome, Koriyama City, Fukushima, 963-8563, Japan. Tel: +81-24-934-3888; Fax: +81-24-934-5393;
| | - Tomoaki Motoyanagi
- Department of Radiation Physics and Technology, Southern Tohoku Proton Therapy Center, Fukushima, Japan
| | - Kimihiro Takemasa
- Department of Radiation Physics and Technology, Southern Tohoku Proton Therapy Center, Fukushima, Japan
| | - Yuki Narita
- Department of Radiation Physics and Technology, Southern Tohoku Proton Therapy Center, Fukushima, Japan
| | - Masato Kato
- Department of Radiation Physics and Technology, Southern Tohoku Proton Therapy Center, Fukushima, Japan
| | - Takuya Matsumoto
- Department of Radiation Physics and Technology, Southern Tohoku Proton Therapy Center, Fukushima, Japan
| | - Sho Oyama
- Department of Radiation Physics and Technology, Southern Tohoku Proton Therapy Center, Fukushima, Japan
| | - Hisashi Yamaguchi
- Department of Radiation Oncology, Southern Tohoku Proton Therapy Center, Fukushima, Japan
| | - Hitoshi Wada
- Department of Radiation Oncology, Southern Tohoku Proton Therapy Center, Fukushima, Japan
| | - Masao Murakami
- Department of Radiation Oncology, Southern Tohoku Proton Therapy Center, Fukushima, Japan
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Maeda Y, Sato Y, Yamamoto K, Tamamura H, Sasaki M, Fuwa N, Takamatsu S, Kume K. Stability of daily rectal movement and effectiveness of replanning protocols for sparing rectal doses based on the daily CT images during proton treatment for prostate cancer. J Appl Clin Med Phys 2020; 21:109-121. [PMID: 32888359 PMCID: PMC7592984 DOI: 10.1002/acm2.13015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2020] [Revised: 05/04/2020] [Accepted: 07/29/2020] [Indexed: 12/25/2022] Open
Abstract
PURPOSE To evaluate the optimal period of replanning to spare the rectal dose by investigating daily rectal movements during computed tomography (CT) image-guided proton therapy for prostate cancer. MATERIALS AND METHODS To evaluate the optimum reference period for replanning, we analyzed 1483 sets of daily CT (dCT) images acquired from 40 prostate cancer patients and measured the daily rectal movement along the anterior-posterior direction based on the simulator CT (sCT) images and dCT images. We calculated daily dose distributions based on initial plans on the sCT images and replans on the dCT images for 13 representative patients, and evaluated daily dose volume histograms (DVHs) for the prostate, seminal vesicles, and rectum. RESULTS The rectal anterior side on the dCT images around the seminal vesicles largely deviated toward the anterior side relative to the position on the reference sCT images, but the deviation decreased by referring to the dCT images and became nearly zero when we referred to the dCT images after 10-day treatment. The daily DVH values for the prostate showed good dose coverage. For six patients showing rectal movement toward the anterior side, the daily rectal DVH (V77% ) showed a 3.0 ± 1.7 cc excess from the initial plan and this excess was correlated with 9.9 ± 6.8 mm rectal movement. To identify the patients (37.5% in total) for whom the replanning on the 10th-day and 20th-day CT images reduced the V77% excess to 0.4 ± 1.5 cc and -0.2 ± 1.3 cc, respectively, we evaluated the accumulated mean doses with a 1.2 cc criterion. CONCLUSION Our data demonstrate that the daily movement of the rectal anterior side tends to move toward the anterior side, which results in a rectal overdose, and the mean of the movement gradually decreases with the passage of days. In such cases, replanning with the reference CT after 10 days is effective to spare the rectal dose.
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Affiliation(s)
- Yoshikazu Maeda
- Proton Therapy Center, Fukui Prefectural Hospital, Fukui, Fukui, Japan
| | - Yoshitaka Sato
- Proton Therapy Center, Fukui Prefectural Hospital, Fukui, Fukui, Japan
| | - Kazutaka Yamamoto
- Proton Therapy Center, Fukui Prefectural Hospital, Fukui, Fukui, Japan
| | - Hiroyasu Tamamura
- Proton Therapy Center, Fukui Prefectural Hospital, Fukui, Fukui, Japan
| | - Makoto Sasaki
- Proton Therapy Center, Fukui Prefectural Hospital, Fukui, Fukui, Japan
| | - Nobukazu Fuwa
- Department of Radiotherapy, Ise Red Cross Hospital, Ise, Mie, Japan
| | - Shigeyuki Takamatsu
- Department of Radiation Therapy, Kanazawa University Hospital, Kanazawa, Ishikawa, Japan
| | - Kyo Kume
- Research & Development Department, The Wakasa Wan Energy Research Center, Tsuruga, Fukui, Japan
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