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Riis HL, Engstrøm KH, Andersen CE. Recombination and polarity effects of Farmer chambers in a strong magnetic field. Phys Med 2024; 123:103406. [PMID: 38875931 DOI: 10.1016/j.ejmp.2024.103406] [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: 04/30/2023] [Revised: 04/08/2024] [Accepted: 06/05/2024] [Indexed: 06/16/2024] Open
Abstract
PURPOSE Ionisation chamber based reference dosimetry in magnetic resonance linear accelerators (MRL) aimed for radiotherapy requires correction for recombination losses. Published studies have found that such corrections can be carried out using the two-voltage method. These studies have, however, not included comparison with recombination corrections based on the Niatel method, which can be seen as a robust reference method due to its clear separation of initial and volume recombination and its explicit account of the pulsed nature of the dose delivery. The primary objective of this work therefore was to carry out such a comparison. MATERIALS AND METHODS Four Farmer-type chambers (PTW-30006 and PTW-30013) were placed in a water phantom in 1.5 T Elekta Unity MRL. The chambers were oriented antiparallel or perpendicular to the static magnetic field B0 and irradiated at a source-to-surface distance of 133.5 cm with a 10 × 10 cm2 field size. RESULTS The two-voltage method gave results in agreement (within 0.1%) with the recombination corrections derived from the Niatel method. The recombination corrections from three Niatel parameter sets (one based on a Varian Truebeam and two obtained directly in the MRL) deviated less than 0.1% from each other. A systematic shift in the recombination correction of less than 0.05% was observed if polarity corrections were not applied. CONCLUSIONS The study supports the use of the two-voltage method in MRLs based on its excellent agreement with the Niatel method. This work, therefore, complements existing knowledge as previous studies have not included a comparison with the Niatel method.
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Affiliation(s)
- Hans Lynggaard Riis
- Odense University Hospital, Department of Oncology, Odense, Denmark; University of Southern Denmark, Department of Clinical Research, Odense, Denmark.
| | | | - Claus E Andersen
- Technical University of Denmark, Department of Health Technology, Roskilde, Denmark
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Jermain PR, Muir B, McEwen M, Niu Y, Pang D. Accurate machine-specific reference and small-field dosimetry for a self-shielded neuro-radiosurgical system. Med Phys 2024; 51:4423-4433. [PMID: 38695760 DOI: 10.1002/mp.17111] [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: 01/05/2024] [Revised: 03/14/2024] [Accepted: 04/18/2024] [Indexed: 06/05/2024] Open
Abstract
BACKGROUND The newly available ZAP-X stereotactic radiosurgical system is designed for the treatment of intracranial lesions, with several unique features that include a self-shielding, gyroscopic gantry, wheel collimation, non-orthogonal kV imaging, short source-axis distance, and low-energy megavoltage beam. Systematic characterization of its radiation as well as other properties is imperative to ensure its safe and effective clinical application. PURPOSE To accurately determine the radiation output of the ZAP-X with a special focus on the smaller diameter cones and an aim to provide useful recommendations on quantification of small field dosimetry. METHODS Six different types of detectors were used to measure relative output factors at field sizes ranging from 4 to 25 mm, including the PTW microSilicon and microdiamond diodes, Exradin W2 plastic scintillator, Exradin A16 and A1SL ionization chambers, and the alanine dosimeter. The 25 mm cone served as the reference field size. Absolute dose was determined with both TG-51-based dosimetry using a calibrated PTW Semiflex ion chamber and measurements using alanine dosimeters. RESULTS The average radiation output factors (maximum deviation from the average) measured with the microDiamond, microSilicon, and W2 detectors were: for the 4 mm cone, 0.741 (1.0%); for the 5 mm cone: 0.817 (1.0%); for the 7.5 mm cone: 0.908 (1.0%); for the 10 mm cone: 0.946 (0.4%); for the 12.5 mm cone: 0.964 (0.2%); for the 15 mm cone: 0.976 (0.1%); for the 20 mm cone: 0.990 (0.1%). For field sizes larger than 10 mm, the A1SL and A16 micro-chambers also yielded consistent output factors within 1.5% of those obtained using the microSilicon, microdiamond, and W2 detectors. The absolute dose measurement obtained with alanine was within 1.2%, consistent with combined uncertainties, compared to the PTW Semiflex chamber for the 25 mm reference cone. CONCLUSION For field sizes less than 10 mm, the microSilicon diode, microDiamond detector, and W2 scintillator are suitable devices for accurate small field dosimetry of the ZAP-X system. For larger fields, the A1SL and A16 micro-chambers can also be used. Furthermore, alanine dosimetry can be an accurate verification of reference and absolute dose typically measured with ion chambers. Use of multiple suitable detectors and uncertainty analyses were recommended for reliable determination of small field radiation outputs.
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Affiliation(s)
- Peter R Jermain
- Department of Radiation Medicine, Medstar Georgetown University Hospital, Washington, District of Columbia, USA
| | - Bryan Muir
- Metrology Research Centre, National Research Council, Ottawa, Ontario, Canada
| | - Malcolm McEwen
- Metrology Research Centre, National Research Council, Ottawa, Ontario, Canada
| | - Ying Niu
- Department of Radiation Medicine, Medstar Georgetown University Hospital, Washington, District of Columbia, USA
| | - Dalong Pang
- Department of Radiation Medicine, Medstar Georgetown University Hospital, Washington, District of Columbia, USA
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Yousif YAM, Daniel J, Healy B, Hill R. A study of polarity effect for various ionization chambers in kilovoltage x-ray beams. Med Phys 2024; 51:4513-4523. [PMID: 38669346 DOI: 10.1002/mp.17096] [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: 09/28/2023] [Revised: 03/01/2024] [Accepted: 03/21/2024] [Indexed: 04/28/2024] Open
Abstract
BACKGROUND Ionization chambers play an essential role in dosimetry measurements for kilovoltage (kV) x-ray beams. Despite their widespread use, there is limited data on the absolute values for the polarity correction factors across a range of commonly employed ionization chambers. PURPOSE This study aimed to investigate the polarity effects for five different ionization chambers in kV x-ray beams. METHODS Two plane-parallel chambers being the Advanced Markus and Roos and three cylindrical chambers; 3D PinPoint, Semiflex and Farmer chamber (PTW, Freiburg, Germany), were employed to measure the polarity correction factors. The kV x-ray beams were produced from an Xstrahl 300 unit (Xstrahl Ltd., UK). All measurements were acquired at 2 cm depth in a PTW-MP1 water tank for beams between 60 kVp (HVL 1.29 mm Al) and 300 kVp (HVL 3.08 mm Cu), and field sizes of 2-10 cm diameter for 30 cm focus-source distance (FSD) and 4 × 4 cm2 - 20 × 20 cm2 for 50 cm FSD. The ionization chambers were connected to a PTW-UNIDOS electrometer, and the polarity effect was determined using the AAPM TG-61 code of practice methodology. RESULTS The study revealed significant polarity effects in ionization chambers, especially in those with smaller volumes. For the plane-parallel chambers, the Advanced Markus chamber exhibited a maximum polarity effect of 2.5%, whereas the Roos chamber showed 0.3% at 150 KVp with the 10 cm circular diameter open-ended applicator. Among the cylindrical chambers at the same beam energy and applicator, the Pinpoint chamber exhibited a 3% polarity effect, followed by Semiflex with 1.7%, and Farmer with 0.4%. However, as the beam energy increased to 300 kVp, the polarity effect significantly increased reaching 8.5% for the Advanced Markus chamber and 13.5% for the PinPoint chamber at a 20 × 20 cm2 field size. Notably, the magnitude of the polarity effect increased with both the field size and beam energy, and was significantly influenced by the size of the chamber's sensitive volume. CONCLUSIONS The findings demonstrate that ionization chambers can exhibit substantial polarity effects in kV x-ray beams, particularly for those chambers with smaller volumes. Therefore, it is important to account for polarity corrections when conducting relative dose measurements in kV x-ray beams to enhance the dosimetry accuracy and improve patient dose calculations.
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Affiliation(s)
- Yousif A M Yousif
- Crown Princess Mary Cancer Centre, Westmead Hospital, Wentworthville, New South Wales, Australia
- North West Cancer Centre, Tamworth Hospital, Tamworth, New South Wales, Australia
| | - John Daniel
- North West Cancer Centre, Tamworth Hospital, Tamworth, New South Wales, Australia
- Department of Radiation Oncology, Calvary Mater Newcastle, Newcastle, New South Wales, Australia
| | - Brendan Healy
- Australian Clinical Dosimetry Service (ACDS), Yallambie, Victoria, Australia
| | - Robin Hill
- Department of Radiation Oncology, Chris O'Brien Lifehouse, Camperdown, New South Wales, Australia
- Institute of Medical Physics, School of Physics, University of Sydney, Camperdown, New South Wales, Australia
- Arto Hardy Family Biomedical Innovation Hub, Chris O'Brien Lifehouse, Camperdown, New South Wales, Australia
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Evaluation of the polarity effect of Roos parallel plate ionization chamber in build-up region. POLISH JOURNAL OF MEDICAL PHYSICS AND ENGINEERING 2022. [DOI: 10.2478/pjmpe-2022-0015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Abstract
Purpose: Despite widespread studying of the polarity effect of Roos parallel plate ion chamber in electron beams as mentioned in several protocols, no investigations have up till now studied this effect in photon beams in the build-up region. It is important to examine its polarity effect in the build-up region for photon beams, so this is the first work that focuses in to evaluate the polarity effect of the Roos chamber in the surface and build-up region and comparing its effect with other chambers.
Methods: In this study, the Roos chamber was irradiated by a Theratron 780E 60Co beam to a known polarity effect. The Polarity effects of 5×5 up to 35×35 cm2 field sizes at positive and negative polarizing voltages were measured in the build-up region from surface to 0.7 cm in a solid water phantom.
Results: The polarity ratios (PRs) were obtained at 1.020 ± 0.00 and 1.015 ± 0.00 for field sizes 5 × 5 up to 35 × 35 cm2, respectively. For the same fields, the percentage of polarity effects (%PEs) was obtained at 1.99% ± 0.00% and 1.47% ± 0.02%, respectively. The results found that the %PEs decrease with increased field sizes and depths. Moreover, the %PEs exhibited a decrease with an increased percentage surface dose (%SD). The uncertainty of %PE was estimated as 0.01% for all measurements in this study.
Conclusions: As a result, the average %PE of the Roos chamber described here is equal to 0.756% ± 0.013% for all depths and field sizes for the 60Co γ-ray beam. It has introduced a less percentage of polarity effect than other chambers.
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Kodama T, Yasui K, Nishioka S, Miyaura K, Takakura T, Katayose T, Nakamura M. Survey on utilization of flattening filter-free photon beams in Japan. JOURNAL OF RADIATION RESEARCH 2021; 62:726-734. [PMID: 34036361 PMCID: PMC8273795 DOI: 10.1093/jrr/rrab042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Revised: 03/08/2021] [Indexed: 06/12/2023]
Abstract
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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Affiliation(s)
- Takumi Kodama
- Department of Radiation Oncology, Saitama Cancer Center, 780 Ooazakomuro, Inamachi, Kitaadachi-gun, Saitama 362-0806, Japan
| | - Keisuke Yasui
- Faculty of Radiological Technology, School of Health Science, Fujita Health University, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi 470–1192, Japan
| | - Shie Nishioka
- Department of Medical Physics, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104–0045, Japan
| | - Kazunori Miyaura
- Graduate School of Health Sciences, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142–8666, Japan
| | - Toru Takakura
- Department of Radiation Therapy, Uji-Tokushukai Medical Center, 145 Ishibashi, Makichima-cho, Uji-shi, Kyoto 611–0041, Japan
| | - Tetsurou Katayose
- Department of Radiation Oncology, Chiba Cancer Center, 666-2 Nitona-cho, Chuo-ku, Chiba 260–8717, Japan
| | - Mitsuhiro Nakamura
- 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
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Martin-Martin G, Walter S, Guibelalde E. Dose accuracy improvement on head and neck VMAT treatments by using the Acuros algorithm and accurate FFF beam calibration. ACTA ACUST UNITED AC 2021; 26:73-85. [PMID: 33948305 DOI: 10.5603/rpor.a2021.0014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Accepted: 12/22/2020] [Indexed: 11/25/2022]
Abstract
Background The purpose of this study was to assess dose accuracy improvement and dosimetric impact of switching from the anisotropic analytical algorithm (AA) to the Acuros XB algorithm (AXB) when performing an accurate beam calibration in head and neck (H&N) FFF-VMAT treatments. Materials and methods Twenty H&N cancer patients treated with FFF-VMAT techniques were included. Calculations were performed with the AA and AXB algorithm (dose-to-water - AXBw- and dose-to-medium - AXBm-). An accurate beam calibration was used for AXB calculations. Dose prescription to the tumour (PTV70) and at-risk-nodal region (PTV58.1) were 70 Gy and 58.1 Gy, respectively. A PTV70_bone including bony structures in PTV70 was contoured. Dose-volume parameters were compared between the algorithms. Statistical tests were used to analyze the differences in mean values and the correlation between compliance with the D95 > 95% requirement and occurrence of local recurrence. Results AA systematically overestimated the dose compared to AXB algorithm with mean dose differences within 1.3 Gy/2%, except for the PTV70_bone (2.2 Gy/3.2%). Dose differences were significantly higher for AXBm calculations when including accurate beam calibration (maximum dose differences up to 2.8 Gy/4.1% and 4.2 Gy/6.3% for PTV70 and PTV70_bone, respectively). 80% of AA-calculated plans did not meet the D95 > 95% requirement after recalculation with AXBm and accurate beam calibration. The reduction in D95 coverage in the tumour was not clinically relevant. Conclusions Using the AXBm algorithm and carefully reviewing the beam calibration procedure in H&N FFF-VMAT treatments ensures (1) dose accuracy increase by approximately 3%; (2) a consequent dose increase in targets; and (3) a dose reporting mode that is consistent with the trend of current algorithms.
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Affiliation(s)
- Guadalupe Martin-Martin
- Medical Physics and Radiation Protection Service, Hospital Universitario de Fuenlabrada, Madrid, Spain
| | - Stefan Walter
- Department of Medicine and Public Health, Rey Juan Carlos University, Alcorcón, Spain
| | - Eduardo Guibelalde
- Medical Physics Group, Department of Radiology, University Complutense of Madrid, Madrid, Spain
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Martin-Martin G, Walter S, Guibelalde E. Dosimetric impact of failing to apply correction factors to ion recombination in percentage depth dose measurements and the volume-averaging effect in flattening filter-free beams. Phys Med 2020; 77:176-180. [DOI: 10.1016/j.ejmp.2020.07.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/04/2020] [Revised: 07/02/2020] [Accepted: 07/05/2020] [Indexed: 10/23/2022] Open
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