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Nakao M, Ozawa S, Miura H, Yamada K, Hayata M, Hayashi K, Kawahara D, Nakashima T, Ochi Y, Okumura T, Kunimoto H, Kawakubo A, Kusaba H, Nozaki H, Habara K, Tohyama N, Nishio T, Nakamura M, Minemura T, Okamoto H, Ishikawa M, Kurooka M, Shimizu H, Hotta K, Saito M, Nakano M, Tsuneda M, Nagata Y. CT number calibration audit in photon radiation therapy. Med Phys 2024; 51:1571-1582. [PMID: 38112216 DOI: 10.1002/mp.16887] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2023] [Revised: 06/29/2023] [Accepted: 11/26/2023] [Indexed: 12/21/2023] Open
Abstract
BACKGROUND Inadequate computed tomography (CT) number calibration curves affect dose calculation accuracy. Although CT number calibration curves registered in treatment planning systems (TPSs) should be consistent with human tissues, it is unclear whether adequate CT number calibration is performed because CT number calibration curves have not been assessed for various types of CT number calibration phantoms and TPSs. PURPOSE The purpose of this study was to investigate CT number calibration curves for mass density (ρ) and relative electron density (ρe ). METHODS A CT number calibration audit phantom was sent to 24 Japanese photon therapy institutes from the evaluating institute and scanned using their individual clinical CT scan protocols. The CT images of the audit phantom and institute-specific CT number calibration curves were submitted to the evaluating institute for analyzing the calibration curves registered in the TPSs at the participating institutes. The institute-specific CT number calibration curves were created using commercial phantom (Gammex, Gammex Inc., Middleton, WI, USA) or CIRS phantom (Computerized Imaging Reference Systems, Inc., Norfolk, VA, USA)). At the evaluating institute, theoretical CT number calibration curves were created using a stoichiometric CT number calibration method based on the CT image, and the institute-specific CT number calibration curves were compared with the theoretical calibration curve. Differences in ρ and ρe over the multiple points on the curve (Δρm and Δρe,m , respectively) were calculated for each CT number, categorized for each phantom vendor and TPS, and evaluated for three tissue types: lung, soft tissues, and bones. In particular, the CT-ρ calibration curves for Tomotherapy TPSs (ACCURAY, Sunnyvale, CA, USA) were categorized separately from the Gammex CT-ρ calibration curves because the available tissue-equivalent materials (TEMs) were limited by the manufacturer recommendations. In addition, the differences in ρ and ρe for the specific TEMs (ΔρTEM and Δρe,TEM , respectively) were calculated by subtracting the ρ or ρe of the TEMs from the theoretical CT-ρ or CT-ρe calibration curve. RESULTS The mean ± standard deviation (SD) of Δρm and Δρe,m for the Gammex phantom were -1.1 ± 1.2 g/cm3 and -0.2 ± 1.1, -0.3 ± 0.9 g/cm3 and 0.8 ± 1.3, and -0.9 ± 1.3 g/cm3 and 1.0 ± 1.5 for lung, soft tissues, and bones, respectively. The mean ± SD of Δρm and Δρe,m for the CIRS phantom were 0.3 ± 0.8 g/cm3 and 0.9 ± 0.9, 0.6 ± 0.6 g/cm3 and 1.4 ± 0.8, and 0.2 ± 0.5 g/cm3 and 1.6 ± 0.5 for lung, soft tissues, and bones, respectively. The mean ± SD of Δρm for Tomotherapy TPSs was 2.1 ± 1.4 g/cm3 for soft tissues, which is larger than those for other TPSs. The mean ± SD of Δρe,TEM for the Gammex brain phantom (BRN-SR2) was -1.8 ± 0.4, implying that the tissue equivalency of the BRN-SR2 plug was slightly inferior to that of other plugs. CONCLUSIONS Latent deviations between human tissues and TEMs were found by comparing the CT number calibration curves of the various institutes.
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Affiliation(s)
- Minoru Nakao
- Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Department of Radiation Oncology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
| | - Shuichi Ozawa
- Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Department of Radiation Oncology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
| | - Hideharu Miura
- Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Department of Radiation Oncology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
| | - Kiyoshi Yamada
- Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
| | - Masahiro Hayata
- Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
| | - Kosuke Hayashi
- Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
| | - Daisuke Kawahara
- Department of Radiation Oncology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
| | - Takeo Nakashima
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
- Radiation Therapy Section, Department of Clinical Support, Hiroshima University Hospital, Hiroshima, Japan
| | - Yusuke Ochi
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Radiation Therapy Section, Department of Clinical Support, Hiroshima University Hospital, Hiroshima, Japan
| | - Takuro Okumura
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Radiation Therapy Section, Department of Clinical Support, Hiroshima University Hospital, Hiroshima, Japan
| | - Haruhide Kunimoto
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Radiation Therapy Department, Hiroshima Prefectural Hospital, Hiroshima, Japan
| | - Atsushi Kawakubo
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Radiation Therapy Department, Hiroshima City Hiroshima Citizens Hospital, Hiroshima, Japan
| | - Hayate Kusaba
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Radiation Therapy Department, Hiroshima City Hiroshima Citizens Hospital, Hiroshima, Japan
| | - Hiroshige Nozaki
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Division of Radiology, Hiroshima Red Cross Hospital & Atomic-bomb Survivors Hospital, Hiroshima, Japan
| | - Kosaku Habara
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Division of Radiology, Hiroshima Red Cross Hospital & Atomic-bomb Survivors Hospital, Hiroshima, Japan
| | - Naoki Tohyama
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
- Division of Medical Physics, Tokyo Bay Makuhari Clinic for Advanced Imaging, Cancer Screening, and High-Precision Radiotherapy, Chiba, Japan
| | - Teiji Nishio
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
- Medical Physics Laboratory, Division of Health Science, Graduate School of Medicine, Osaka University, Osaka, Japan
| | - Mitsuhiro Nakamura
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
- Department of Radiation Oncology and Image-Applied Therapy, Kyoto University, Kyoto, Japan
- Department of Advanced Medical Physics, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Toshiyuki Minemura
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
- Division of Medical Support and Partnership, Institute for Cancer Control, National Cancer Center, Tokyo, Japan
| | - Hiroyuki Okamoto
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
- Radiation Safety and Quality Assurance Division, National Cancer Center Hospital, Tokyo, Japan
| | - Masayori Ishikawa
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
- Faculty of Health Sciences, Hokkaido University, Hokkaido, Japan
| | - Masahiko Kurooka
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
- Department of Radiation Therapy, Tokyo Medical University Hospital, Tokyo, Japan
| | - Hidetoshi Shimizu
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
- Department of Radiation Oncology, Aichi Cancer Center Hospital, Aichi, Japan
| | - Kenji Hotta
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
- Radiation Safety and Quality Assurance division, National Cancer Center Hospital East, Chiba, Japan
- Particle Therapy Division, Exploratory Oncology Research and Clinical Trial Center, National Cancer Center, Chiba, Japan
| | - Masahide Saito
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
- Department of Radiology, University of Yamanashi, Yamanashi, Japan
| | - Masahiro Nakano
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
- Department of Radiation Oncology, Kitasato University School of Medicine, Kanagawa, Japan
| | - Masato Tsuneda
- Medical Physics Working Group in Japan Clinical Oncology Group - Radiation Therapy Study Group, Tokyo, Japan
- Graduate School of Medicine, Chiba University, Chiba, Japan
| | - Yasushi Nagata
- Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
- Department of Radiation Oncology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
- Technical Support Working Group in Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan
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Tsunemine S, Ozawa S, Nakao M, Miura H, Saito A, Kawahara D, Onishi Y, Onishi T, Okawa F, Terai A, Hashiguchi T, Yamasaki H, Maruta T, Murakami Y, Nagata Y. Tolerance levels of mass density for adaptive helical tomotherapy using MVCT. JOURNAL OF RADIATION RESEARCH 2022; 64:195-201. [PMCID: PMC9855312 DOI: 10.1093/jrr/rrac071] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Revised: 12/30/2022] [Indexed: 01/02/2024]
Abstract
Daily dose distributions for adaptive radiotherapy (ART) using helical tomotherapy (HT) are calculated using megavoltage computed tomography (MVCT). Generally, the MVCT number is converted to mass density (MD) using an MD calibration table (MVCT-MD table). The aims of this study are to calculate the tolerance levels of the MD for ART and to evaluate the tolerance levels using clinical patient plans. These tolerance levels of MD were calculated based on the tissue maximum ratio (TMR) of 6MV flattening-filter-free (FFF) beam of HT and the effective tissue thickness data from an International Commission on Radiological Protection 110 phantom data for lung, adipose/muscle and cartilage/spongy-bone. These tolerance levels were determined by considering both the MD causing a dose error of 2% and the variation in MVCT numbers. Subsequently, the stability of the MD values was estimated with the standard deviations (SD) in the MVCT number over 6 months. The dose distribution for clinical patient plans was calculated using the MVCT-MD table with added tolerance levels. These tolerance levels were determined as MD differences causing a dose error of 2%, and were ± 0.049 g/cm3, ± 0.030 g/cm3 and ± 0.049 g/cm3 for lung, adipose/muscle and cartilage/spongy-bone, respectively. The calculated dose distribution errors using the MVCT-MD table added tolerance levels were within 2%. We proposed these tolerance levels in MD for the quality control of the MVCT-MD table.
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Affiliation(s)
- Shogo Tsunemine
- Program of Medicine Doctoral Course, Graduate School of Biomedical and Health Sciences, Hiroshima University, 1-2-3, Kasumi, Minamiku, Hiroshima, 734-8553 Japan
- Department of Radiology, National Hospital Organization Himeji Medical Center, 68, Hommachi, Himeji, Hyogo, 670-8520, Japan
| | - Shuichi Ozawa
- Department of Radiology, National Hospital Organization Himeji Medical Center, 68, Hommachi, Himeji, Hyogo, 670-8520, Japan
- Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, 3-2-2, Futabanosato, Higashiku, Hiroshima, 732-0057, Japan
- Department of Radiation Oncology, Graduate School of Biomedical and Health Sciences, Hiroshima University, 1-2-3, Kasumi, Minamiku, Hiroshima, 734-8553 Japan
| | - Minoru Nakao
- Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, 3-2-2, Futabanosato, Higashiku, Hiroshima, 732-0057, Japan
- Department of Radiation Oncology, Graduate School of Biomedical and Health Sciences, Hiroshima University, 1-2-3, Kasumi, Minamiku, Hiroshima, 734-8553 Japan
| | - Hideharu Miura
- Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, 3-2-2, Futabanosato, Higashiku, Hiroshima, 732-0057, Japan
- Department of Radiation Oncology, Graduate School of Biomedical and Health Sciences, Hiroshima University, 1-2-3, Kasumi, Minamiku, Hiroshima, 734-8553 Japan
| | - Akito Saito
- Department of Radiation Oncology, Graduate School of Biomedical and Health Sciences, Hiroshima University, 1-2-3, Kasumi, Minamiku, Hiroshima, 734-8553 Japan
| | - Daisuke Kawahara
- Department of Radiation Oncology, Graduate School of Biomedical and Health Sciences, Hiroshima University, 1-2-3, Kasumi, Minamiku, Hiroshima, 734-8553 Japan
| | - Yasuhiko Onishi
- Department of Radiology, National Hospital Organization Himeji Medical Center, 68, Hommachi, Himeji, Hyogo, 670-8520, Japan
| | - Takashi Onishi
- Department of Radiology, National Hospital Organization Himeji Medical Center, 68, Hommachi, Himeji, Hyogo, 670-8520, Japan
| | - Fumito Okawa
- Department of Radiology, National Hospital Organization Himeji Medical Center, 68, Hommachi, Himeji, Hyogo, 670-8520, Japan
| | - Atsushi Terai
- Department of Radiology, National Hospital Organization Himeji Medical Center, 68, Hommachi, Himeji, Hyogo, 670-8520, Japan
| | - Taiki Hashiguchi
- Department of Radiology, National Hospital Organization Himeji Medical Center, 68, Hommachi, Himeji, Hyogo, 670-8520, Japan
| | - Hidetoshi Yamasaki
- Department of Radiology, National Hospital Organization Himeji Medical Center, 68, Hommachi, Himeji, Hyogo, 670-8520, Japan
| | - Tsutomu Maruta
- Department of Therapeutic Radiology, National Hospital Organization Himeji Medical Center, 68, Hommachi, Himeji, Hyogo, 670-8520, Japan
| | - Yuji Murakami
- Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, 3-2-2, Futabanosato, Higashiku, Hiroshima, 732-0057, Japan
- Department of Radiation Oncology, Graduate School of Biomedical and Health Sciences, Hiroshima University, 1-2-3, Kasumi, Minamiku, Hiroshima, 734-8553 Japan
| | - Yasushi Nagata
- Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, 3-2-2, Futabanosato, Higashiku, Hiroshima, 732-0057, Japan
- Department of Radiation Oncology, Graduate School of Biomedical and Health Sciences, Hiroshima University, 1-2-3, Kasumi, Minamiku, Hiroshima, 734-8553 Japan
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Buang S, Ab Razak NNAN, Aziz MZA, Raof N. Evaluation of brass alloy density as tissue equivalence bolus using electron density phantom and optical density method. Appl Radiat Isot 2022; 187:110310. [PMID: 35714516 DOI: 10.1016/j.apradiso.2022.110310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 05/09/2022] [Accepted: 05/30/2022] [Indexed: 11/19/2022]
Abstract
The brass mesh bolus alloy has been shown to be a promising substitute for tissue-equivalent bolus to increase the surface dose during breast cancer radiotherapy treatment. This study is aimed to evaluate the brass alloy density in order to better understand the brass qualities as a bolus in radiotherapy. The mass density of brass alloy determined in this work are using solid approaches, i) traditional density method, ii) Computed Tomography (CT) number using electron density phantom and CT scan and iii) mean pixel value via ImageJ software. According to ANOVA F (2,6) 2.982, p0.126, there was no statistically significant difference between the groups. As a result, all methods for calculating the density of brass alloy are valid. The X2 test of CT number of brass plug to breast substitute in electron density phantom indicates no association. Density analysis using computed tomography and an electron density phantom, as well as the traditional density method and Image J analysis, were all shown to be acceptable methods for estimating the density of the brass alloy. Considering this, brass alloy can be considered as a potential substitute for tissue-equivalent bolus with further extensive of research in conjunction to CT number.
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Affiliation(s)
- Sakinah Buang
- School of Physics, Universiti Sains Malaysia, Malaysia.
| | | | | | - NurSyatina Raof
- Advanced Medical Dental Institute, Universiti Sains Malaysia, Malaysia
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Andersson P, Pettersson N, Lindberg A, Swanpalmer J, Chakarova R. Effects of lung tissue characterization in radiotherapy of breast cancer under deep inspiration breath hold when using Monte Carlo dosimetry. Phys Med 2021; 90:83-90. [PMID: 34563835 DOI: 10.1016/j.ejmp.2021.09.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 08/05/2021] [Accepted: 09/13/2021] [Indexed: 10/20/2022] Open
Abstract
PURPOSE To investigate the sensitivity of Monte Carlo (MC) calculated lung dose distributions to lung tissue characterization in external beam radiotherapy of breast cancer under Deep Inspiration Breath Hold (DIBH). METHODS EGSnrc based MC software was employed. Mean lung densities for one hundred patients were analysed. CT number frequency and clinical dose distributions were calculated for 15 patients with mean lung density below 0.14 g/cm3. Lung volume with a pre-defined CT numbers was also considered. Lung tissue was characterized by applying different CT calibrations in the low-density region and air-lung tissue thresholds. Dose impact was estimated by Dose Volume Histogram (DVH) parameters. RESULTS Mean lung densities below 0.14 g/cm3 were found in 10% of the patients. CT numbers below -960 HU dominated the CT frequency distributions with a high rate of CT numbers at -990 HU. Mass density conversion approach influenced the DVH shape. V4Gy and V8Gy varied by 7% and 5% for the selected patients and by 9% and 3.5% for the pre-defined lung volume. V16Gy and V20Gy, were within 2.5%. Regions above 20 Gy were affected. Variations in air- lung tissue differentiation resulted in DVH parameters within 1%. Threshold at -990 HU was confirmed by the CT number frequency distributions. CONCLUSIONS Lung dose distributions were more sensitive to variations in the CT calibration curve below lung (inhale) density than to air-lung tissue differentiation. Low dose regions were mostly affected. The dosimetry effects were found to be potentially important to 10% of the patients treated under DIBH.
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Affiliation(s)
- P Andersson
- Institute of Clinical Sciences, Department of Medical Radiation Science, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; RISE Research Institutes of Sweden, Materials and Production, Gothenburg, Sweden
| | - N Pettersson
- Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Gothenburg, Sweden
| | - A Lindberg
- Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Gothenburg, Sweden
| | - J Swanpalmer
- Institute of Clinical Sciences, Department of Medical Radiation Science, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Gothenburg, Sweden
| | - R Chakarova
- Institute of Clinical Sciences, Department of Medical Radiation Science, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Gothenburg, Sweden.
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Nakao M, Ozawa S, Miura H, Yamada K, Habara K, Hayata M, Kusaba H, Kawahara D, Miki K, Nakashima T, Ochi Y, Tsuda S, Seido M, Morimoto Y, Kawakubo A, Nozaki H, Nagata Y. Development of a CT number calibration audit phantom in photon radiation therapy: A pilot study. Med Phys 2020; 47:1509-1522. [PMID: 32026482 PMCID: PMC7216906 DOI: 10.1002/mp.14077] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Revised: 01/30/2020] [Accepted: 01/31/2020] [Indexed: 01/24/2023] Open
Abstract
PURPOSE In photon radiation therapy, computed tomography (CT) numbers are converted into values for mass density (MD) or relative electron density to water (RED). CT-MD or CT-RED calibration tables are relevant for human body dose calculation in an inhomogeneous medium. CT-MD or CT-RED calibration tables are influenced by patient imaging (CT scanner manufacturer, scanning parameters, and patient size), the calibration process (tissue-equivalent phantom manufacturer, and selection of tissue-equivalent material), differences between tissue-equivalent materials and standard tissues, and the dose calculation algorithm applied; however, a CT number calibration audit has not been established. The purposes of this study were to develop a postal audit phantom, and to establish a CT number calibration audit process. METHODS A conventional stoichiometric calibration conducts a least square fit of the relationships between the MD, material weight, and measured CT number, using two parameters. In this study, a new stoichiometric CT number calibration scheme has been empirically established, using three parameters to harmonize the calculated CT number with the measured CT number for air and lung tissue. In addition, the suitable material set and the minimal number of materials required for stoichiometric CT number calibration were determined. The MDs and elemental weights from the International Commission on Radiological Protection Publication 110 were used as standard tissue data, to generate the CT-MD and CT-RED calibration tables. A small-sized, CT number calibration phantom was developed for a postal audit, and stoichiometric CT number calibration with the phantom was compared to the CT number calibration tables registered in the radiotherapy treatment planning systems (RTPSs) associated with five radiotherapy institutions. RESULTS When a least square fit was performed for the stoichiometric CT number calibration with the three parameters, the calculated CT number showed better agreement with the measured CT number. We established stoichiometric CT number calibration using only two materials because the accuracy of the process was determined not by the number of used materials but by the number of elements contained. The stoichiometric CT number calibration was comparable to the tissue-substitute calibration, with a dose difference less than 1%. An outline of the CT number calibration audit was demonstrated through a multi-institutional study. CONCLUSIONS We established a new stoichiometric CT number calibration method for validating the CT number calibration tables registered in RTPSs. We also developed a CT number calibration phantom for a postal audit, which was verified by the performances of multiple CT scanners located at several institutions. The new stoichiometric CT number calibration has the advantages of being performed using only two materials, and decreasing the difference between the calculated and measured CT numbers for air and lung tissue. In the future, a postal CT number calibration audit might be achievable using a smaller phantom.
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Affiliation(s)
- Minoru Nakao
- Hiroshima High‐Precision Radiotherapy Cancer Center3‐2‐2, Futabanosato, Higashi‐kuHiroshima732‐0057Japan
- Department of Radiation OncologyGraduate School of Biomedical & Health SciencesHiroshima University1‐2‐3 Kasumi, Minami‐kuHiroshima734‐8551Japan
| | - Shuichi Ozawa
- Hiroshima High‐Precision Radiotherapy Cancer Center3‐2‐2, Futabanosato, Higashi‐kuHiroshima732‐0057Japan
- Department of Radiation OncologyGraduate School of Biomedical & Health SciencesHiroshima University1‐2‐3 Kasumi, Minami‐kuHiroshima734‐8551Japan
| | - Hideharu Miura
- Hiroshima High‐Precision Radiotherapy Cancer Center3‐2‐2, Futabanosato, Higashi‐kuHiroshima732‐0057Japan
- Department of Radiation OncologyGraduate School of Biomedical & Health SciencesHiroshima University1‐2‐3 Kasumi, Minami‐kuHiroshima734‐8551Japan
| | - Kiyoshi Yamada
- Hiroshima High‐Precision Radiotherapy Cancer Center3‐2‐2, Futabanosato, Higashi‐kuHiroshima732‐0057Japan
| | - Kosaku Habara
- Hiroshima High‐Precision Radiotherapy Cancer Center3‐2‐2, Futabanosato, Higashi‐kuHiroshima732‐0057Japan
| | - Masahiro Hayata
- Hiroshima High‐Precision Radiotherapy Cancer Center3‐2‐2, Futabanosato, Higashi‐kuHiroshima732‐0057Japan
| | - Hayate Kusaba
- Hiroshima High‐Precision Radiotherapy Cancer Center3‐2‐2, Futabanosato, Higashi‐kuHiroshima732‐0057Japan
| | - Daisuke Kawahara
- Department of Radiation OncologyGraduate School of Biomedical & Health SciencesHiroshima University1‐2‐3 Kasumi, Minami‐kuHiroshima734‐8551Japan
| | - Kentaro Miki
- Department of Radiation OncologyHiroshima University Hospital1‐2‐3 Kasumi, Minami‐kuHiroshima734‐8551Japan
| | - Takeo Nakashima
- Radiation Therapy SectionDepartment of Clinical SupportHiroshima University Hospital1‐2‐3 Kasumi, Minami‐kuHiroshima734‐8551Japan
| | - Yusuke Ochi
- Radiation Therapy SectionDepartment of Clinical SupportHiroshima University Hospital1‐2‐3 Kasumi, Minami‐kuHiroshima734‐8551Japan
| | - Shintaro Tsuda
- Radiation Therapy SectionDepartment of Clinical SupportHiroshima University Hospital1‐2‐3 Kasumi, Minami‐kuHiroshima734‐8551Japan
| | - Mineaki Seido
- Department of RadiologyHiroshima Prefectural Hospital1‐5‐54, Ujinakanda, Minami‐kuHiroshima734‐8530Japan
| | - Yoshiharu Morimoto
- Department of RadiologyHiroshima Prefectural Hospital1‐5‐54, Ujinakanda, Minami‐kuHiroshima734‐8530Japan
| | - Atsushi Kawakubo
- Radiation Therapy DepartmentHiroshima City Hiroshima Citizens Hospital7‐33, Motomachi, Naka‐kuHiroshima730‐8518Japan
| | - Hiroshige Nozaki
- Division of RadiologyHiroshima Red Cross Hospital & Atomic‐bomb Survivors Hospital1‐9‐6, Senda, Naka‐kuHiroshima730‐8619Japan
| | - Yasushi Nagata
- Hiroshima High‐Precision Radiotherapy Cancer Center3‐2‐2, Futabanosato, Higashi‐kuHiroshima732‐0057Japan
- Department of Radiation OncologyGraduate School of Biomedical & Health SciencesHiroshima University1‐2‐3 Kasumi, Minami‐kuHiroshima734‐8551Japan
- Department of Radiation OncologyHiroshima University Hospital1‐2‐3 Kasumi, Minami‐kuHiroshima734‐8551Japan
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