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Kannan M, Saminathan S, Shwetha B, Chandraraj V, Raj DG, Ganesh KM. Validation of Microionization Chambers in Small-field Dosimetry. J Med Phys 2024; 49:285-293. [PMID: 39131427 PMCID: PMC11309149 DOI: 10.4103/jmp.jmp_9_24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2024] [Revised: 02/21/2024] [Accepted: 03/03/2024] [Indexed: 08/13/2024] Open
Abstract
Aim This study aims to validate the Razor Nano Chamber (RNC) and Razor Chamber (RC) dosimetric characteristics in a small field. The dosimetric parameters of the two chambers were compared. Materials and Methods The chamber characteristics of leakage (pre and post), stability, energy dependency, dose linearity, dose rate effect, stem effect, angular dependency, ion recombination effect, and polarity effect were studied. Relative dose measurements of the percentage depth dose, profile measurement, and output factor (OF) measurements were performed for small fields. All measurements were performed in a Theratron 780E telecobalt unit and an Elekta Versa HD™ Linear Accelerator. Results and Discussion The measured pre- and postirradiation leakage and energy dependency were within 0.5% of the acceptable limit. In the stability check, the standard error and standard error of mean were 0.047% and 0.068%, respectively, for both RNC and RC. The deviation in the angular responses of the RNC and RC ion chambers was negligible. In the ion recombination measurements, both the RNC and RC were overestimated for the 10 flattening filter-free photon beam. In small fields, there were no significant differences in the kpol values for either chamber. The RNC showed good agreement in the relative dose measurements compared to the RC. Conclusion RNC and RC showed good agreement in small-field dosimetry. The RNC angular dependency and OF showed a superior response compared to the RC because of the small volume spherical shape and high spatial resolution, which gives a reduced penumbra and no volume averaging effect.
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Affiliation(s)
- Mageshraja Kannan
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - Sathiyan Saminathan
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - B. Shwetha
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - Varatharaj Chandraraj
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - D. Gowtham Raj
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - K. M. Ganesh
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
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Mateus D, Greco C, Peralta L. Field output correction factors of small static field for IBA razor nanochamber. Biomed Phys Eng Express 2023; 10:015004. [PMID: 37939486 DOI: 10.1088/2057-1976/ad0ae0] [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: 07/26/2023] [Accepted: 11/08/2023] [Indexed: 11/10/2023]
Abstract
Purpose.The goal of this work is present results of field output factors (OF) using an IBA CC003 (Razor NanoChamber) and compare these results with PTW 60019 (MicroDiamond) and IBA Razor Diode. The experimental results for IBA CC003 were also compared with Monte Carlo (MC) Simulation, using Penelope and Ulysses programs. In addition, field output correction factors (kQclin,Qmsrfclin,fmsr) for IBA CC003 were derived with three different methods: (1) using PTW 60019 and IBA Razor as reference detectors; (2) comparison between MC and experimental measurements; and (3) using only MC.Material and Methods. The beam collimation included in this study were (1) square field size between 10 × 10 and 0.5 × 0.5 cm2defined by the MLC and jaws and (2) cones of different diameters. For IBA CC003 it was determined the polarity and ion collection efficiency correction factors in parallel and perpendicular orientation.Results.The results indicate (1) the variation of polarity effect with the field size is relevant for the determination of OF using IBA CC003, especially for parallel orientation; (2) there is no significant variation of the ion collection efficiency with the field size using IBA CC003 in parallel orientation; (3) OF differences between IBA CC003 and PTW 60019/IBA Razor, and experimental and MC results, increase with decreasing field size;ThekQclin,Qmsrfclin,fmsrresults indicate (1) using the first and second method,kQclin,Qmsrfclin,fmsrincrease with decreasing field size, which can be related with the influence of the volume effect and (2) using the third method,kQclin,Qmsrfclin,fmsrdecrease with decreasing field size, which can be explained by the perturbation effect.Conclusions. Our results demonstrate the need of applyingkQclin,Qmsrfclin,fmsrfor IBA CC003 forSclin≤1 cm, to compensate for volume averaging and perturbations effects.
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Affiliation(s)
- D Mateus
- Faculdade de Ciências da Universidade de Lisboa, Lisboa, Portugal
- Mercurius Health S.A, Lisboa, Portugal
- Fundação Champalimaud, Lisboa, Portugal
| | - C Greco
- Fundação Champalimaud, Lisboa, Portugal
| | - L Peralta
- Faculdade de Ciências da Universidade de Lisboa, Lisboa, Portugal
- Laboratório de Instrumentação e Física Experimental de Partículas, Lisboa, Portugal
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Kannan M, Saminathan S, Chandraraj V, Raj DG, Ganesh KM. Evaluation of International Atomic Energy Agency Technical Report Series-483 Detector-specific Output Correction Factor for Various Collimator Systems. J Med Phys 2023; 48:281-288. [PMID: 37969152 PMCID: PMC10642599 DOI: 10.4103/jmp.jmp_59_23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Revised: 06/25/2023] [Accepted: 07/01/2023] [Indexed: 11/17/2023] Open
Abstract
Aim In this study, a 6MV flattening filter (FF) and 6MV FF Free (FFF) photon beam small-field output factors (OF) were measured with various collimators using different detectors. The corrected OFs were compared with the treatment planning system (TPS) calculated OFs. Materials and Methods OF measurements were performed with four different types of collimators: Varian Millennium multi-leaf collimator (MLC), Elekta Agility MLC, Apex micro-MLC (mMLC) and a stereotactic cone. Ten detectors (four ionization chambers and six diodes) were used to perform the OF measurements at a depth of 10 cm with a source-to-surface distance of 90 cm. The corrected OF was calculated from the measurements. The corrected OFs were compared with existing TPS-generated OFs. Results The use of detector-specific output correction factor (OCF) in the PTW diode P detector reduced the OF uncertainty by <4.1% for 1 cm × 1 cm Sclin. The corrected OF was compared with TPS calculated OF; the maximum variation with the IBA CC01 chamber was 3.75%, 3.72%, 1.16%, and 0.90% for 5 mm stereotactic cone, 0.49 cm × 0.49 cm Apex mMLC, 1 cm × 1 cm Agility MLC, and 1 cm × 1 cm Millennium MLC, respectively. Conclusion The technical report series-483 protocol recommends that detector-specific OCF should be used to calculate the corrected OF from the measured OF. The implementation of OCF in the TPS commissioning will reduce the small-field OF variation by <3% for any type of detector.
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Affiliation(s)
- Mageshraja Kannan
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - Sathiyan Saminathan
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - Varatharaj Chandraraj
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - D. Gowtham Raj
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - K. M. Ganesh
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
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Kannan M, Saminathan S, Chandraraj V, Gowtham Raj D, Ganesh KM. Determination of small-field output factors for beam-matched linear accelerators using various detectors and comparison of detector-specific output correction factors using IAEA Technical Report Series 483 protocol. Rep Pract Oncol Radiother 2023; 28:241-254. [PMID: 37456703 PMCID: PMC10348327 DOI: 10.5603/rpor.a2023.0024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2022] [Accepted: 04/06/2023] [Indexed: 07/18/2023] Open
Abstract
Background Beam matching is widely used to ensure that linear accelerators used in radiotherapy have equal dosimetry characteristics. Small-field output factors (OF) were measured using different detectors infour beam-matched linear accelerators and the measured OFs were compared with existing treatment planning system (TPS) Monte Carlo algorithm calculated OFs. Materials and methods Three Elekta Versa HDTM and one Elekta InfinityTMlinear accelerators with photon energies of 6 MV flattening filter (FF), 10 MVFF, 6 MV flattening filter free (FFF) and 10 MVFFF were used in this study. All the Linac'swere beam-matched, Dosimetry beam data were ± 1% compare with Reference Linac. Ten different type of detectors (four ionizationchambers and six diode detectors) were used for small-field OF measurements. The OFs were measured for field sizes of 1 × 1 to 10 × 10 cm2, and normalized to 10 × 10 cm2 field size. The uncorrected and corrected OFs were calculated from these measurements. The corrected OF was compare with existing treatment planning system (TPS) Monte Carlo algorithm calculated OFs. Results The small-field corrected and Uncorrected OF variations among the linear accelerators was within 1% for all energies and detectors. An increase in field size led to a reduction in the difference between OFs among the detectors, which was the case for all energies. The RSD values decreased with increasing field size. The TRS 483 provided Detector-specificoutput-correction factor (OCF) reduced uncertainty in small-field measurements. Conclusion It is necessary to implement the OF-correction of small fields in a TPS. Special care must be taken to incorporate the corrected small-field OF in a TPS.
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Affiliation(s)
- Mageshraja Kannan
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - Sathiyan Saminathan
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - Varatharaj Chandraraj
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - D Gowtham Raj
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - K M Ganesh
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
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Kawata K, Ono T, Hirashima H, Tsuruta Y, Fujimoto T, Nakamura M, Nakata M. Effect of angular dependence for small-field dosimetry using seven different detectors. Med Phys 2023; 50:1274-1289. [PMID: 36583601 DOI: 10.1002/mp.16198] [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: 10/20/2022] [Revised: 12/14/2022] [Accepted: 12/19/2022] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND Small-field dosimetry is challenging for radiotherapy dosimetry because of the loss of lateral charged equilibrium, partial occlusion of the primary photon source by the collimating devices, perturbation effects caused by the detector materials and their design, and the detector size relative to the radiation field size, which leads to a volume averaging effect. Therefore, a suitable tool for small-field dosimetry requires high spatial resolution, tissue equivalence, angular independence, and energy and dose rate independence to achieve sufficient accuracy. Recently, with the increasing use of combinations of coplanar and non-coplanar beams for small-field dosimetry, there is a need to clarify angular dependence for dosimetry where the detector is oriented at various angles to the incident beam. However, the effect of angular dependence on small-field dosimetry with coplanar and non-coplanar beams has not been fully clarified. PURPOSE This study clarified the effect of angular dependence on small-field dosimetry with coplanar and non-coplanar beams using various detectors. METHODS Seven different detectors were used: CC01, RAZOR, RAZOR Nano, Pinpoint 3D, stereotactic field diode (SFD), microSilicon, and microDiamond. All measurements were taken using a TrueBeam STx with 6 MV and 10 MV flattening filter-free (FFF) energies using a water-equivalent spherical phantom with a source-to-axis distance of 100 cm. The detector was inserted in a perpendicular orientation, and the gantry was rotated at 15° increments from the incidence beam angle. A multi-leaf collimator (MLC) with four field sizes of 0.5 × 0.5, 1 × 1, 2 × 2, and 3 × 3 cm2 , and four couch angles from 0°, 30°, 60°, and 90° (coplanar and non-coplanar) were adopted. The angular dependence response (AR) was defined as the ratio of the detector response at a given irradiation gantry angle normalized to the detector response at 0°. The maximum AR differences were calculated between the maximum and minimum AR values for each detector, field size, energy, and couch angle. RESULTS The maximum AR difference for the coplanar beam was within 3.3% for all conditions, excluding the maximum AR differences in 0.5 × 0.5 cm2 field for CC01 and RAZOR. The maximum AR difference for non-coplanar beams was within 2.5% for fields larger than 1 × 1 cm2 , excluding the maximum AR differences for RAZOR Nano, SFD, and microSilicon. The Pinpoint 3D demonstrated stable AR tendencies compared to other detectors. The maximum difference was within 2.0%, except for the 0.5 × 0.5 cm2 field and couch angle at 90°. The tendencies of AR values for each detector were similar when using different energies. CONCLUSION This study clarified the inherent angular dependence of seven detectors that were suitable for small-field dosimetry. The Pinpoint 3D chamber had the smallest angular dependence of all detectors for the coplanar and non-coplanar beams. The findings of this study can contribute to the calculation of the AR correction factor, and it may be possible to adapt detectors with a large angular dependence on coplanar and non-coplanar beams. However, note that the gantry sag and detector-specific uncertainties increase as the field size decreases.
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Affiliation(s)
- Kohei Kawata
- Division of Clinical Radiology Service, Kyoto University Hospital, Kyoto, Japan
| | - Tomohiro Ono
- Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Hideaki Hirashima
- Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Yusuke Tsuruta
- Division of Clinical Radiology Service, Kyoto University Hospital, Kyoto, Japan
- Department of Advanced Medical Physics, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Takahiro Fujimoto
- Division of Clinical Radiology Service, Kyoto University Hospital, Kyoto, Japan
| | - Mitsuhiro Nakamura
- Department of Advanced Medical Physics, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Manabu Nakata
- Division of Clinical Radiology Service, Kyoto University Hospital, Kyoto, Japan
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Parveen N, Ramachandran P, Seshadri V, Perrett B, Fielding A. Comparison and Validation of Multiple Detectors against Monte Carlo Simulation for the Use of Small-Field Dosimetry. J Med Phys 2022; 47:235-242. [PMID: 36684698 PMCID: PMC9847003 DOI: 10.4103/jmp.jmp_35_22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Revised: 06/30/2022] [Accepted: 07/20/2022] [Indexed: 11/11/2022] Open
Abstract
Aim The aim of this study was to compare the Exradin W2 scintillator, PTW microDiamond, IBA Razor Nano, and IBA Razor chamber detectors for small-field dose measurements and validate the measured data against the EGSnrc user code and observe the variation between daisy-chained and direct measurement methods for the above detectors. Materials and Methods The W2 scintillator, microDiamond, Razor Nano, and Razor chamber detectors were used to measure the in-plane and cross-plane profiles and the output factors (OFs) at 10 cm depth, and 90 source-to-surface distance for 6MV X-rays (Elekta Versa HD). The field sizes ranged from 0.5 cm × 0.5 cm to 5 cm × 5 cm. The BEAMnrc/DOSXYZnrc user codes (EGSnrc) were used to simulate the reference profiles. Gamma analysis was performed to compare the measured and simulated dose distributions. Results The OFs measured with the W2 scintillator, microDiamond, Razor Nano chamber, Razor chamber, and the calculated Monte Carlo (MC) showed agreement to within 1% for the 3 cm × 3 cm field size. The uncertainty in the MC simulation was observed to be 0.4%. The percent difference in OFs measured using daisy-chained and direct measurement methods was within 0.15%, 0.4%, 1.4%, and 2.4% for microDiamond, W2 scintillator, Nano, and Razor chamber detectors, respectively. Conclusion The lateral beam profiles and OFs of W2 scintillator, microDiamond, Razor Nano, and Razor chambers exhibit good agreement with the MC simulation within the nominal field sizes. Our results demonstrate that we can achieve considerable time-saving by directly measuring small-field OFs without daisy-chained methods using microDiamond and W2 scintillator. In terms of ease of use, sensitivity, reproducibility, and from a practical standpoint, we recommend microDiamond for small-field dosimetry.
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Affiliation(s)
- Nazia Parveen
- Therapeutic Physics, Radiation Oncology, Cancer Services, Princess Alexandra Hospital, Woolloongabba, Queensland, Australia
| | - Prabhakar Ramachandran
- Therapeutic Physics, Radiation Oncology, Cancer Services, Princess Alexandra Hospital, Woolloongabba, Queensland, Australia
| | - Venkatakrishnan Seshadri
- Therapeutic Physics, Radiation Oncology, Cancer Services, Princess Alexandra Hospital, Woolloongabba, Queensland, Australia
| | - Ben Perrett
- Therapeutic Physics, Radiation Oncology, Cancer Services, Princess Alexandra Hospital, Woolloongabba, Queensland, Australia
| | - Andrew Fielding
- School of Chemistry and Physics, Queensland University of Technology (QUT), Brisbane, Australia
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Cavallone M, Jorge PG, Moeckli R, Bailat C, Flacco A, Prezado Y, Delorme R. Determination of the ion collection efficiency of the Razor Nano Chamber for ultra-high dose-rate electron beams. Med Phys 2022; 49:4731-4742. [PMID: 35441716 PMCID: PMC9539950 DOI: 10.1002/mp.15675] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Revised: 04/07/2022] [Accepted: 04/12/2022] [Indexed: 11/10/2022] Open
Abstract
Background Ultra‐high dose‐rate (UHDR) irradiations (>40 Gy/s) have recently garnered interest in radiotherapy (RT) as they can trigger the so‐called “FLASH” effect, namely a higher tolerance of normal tissues in comparison with conventional dose rates when a sufficiently high dose is delivered to the tissue. To transfer this to clinical RT treatments, adapted methods and practical tools for online dosimetry need to be developed. Ionization chambers remain the gold standards in RT but the charge recombination effects may be very significant at such high dose rates, limiting the use of some of these dosimeters. The reduction of the sensitive volume size can be an interesting characteristic to reduce such effects. Purpose In that context, we have investigated the charge collection behavior of the recent IBA Razor™ Nano Chamber (RNC) in UHDR pulses to evaluate its potential interest for FLASH RT. Methods In order to quantify the RNC ion collection efficiency (ICE), simultaneous dose measurements were performed under UHDR electron beams with dose‐rate‐independent Gafchromic™ EBT3 films that were used as the dose reference. A dose‐per‐pulse range from 0.01 to 30 Gy was investigated, varying the source‐to‐surface distance, the pulse duration (1 and 3 μs investigated) and the LINAC gun grid tension as irradiation parameters. In addition, the RNC measurements were corrected from the inherent beam shot‐to‐shot variations using an independent current transformer. An empirical logistic model was used to fit the RNC collection efficiency measurements and the results were compared with the Advanced Markus plane parallel ion chamber. Results The RNC ICE was found to decrease as the dose‐per‐pulse increases, starting from doses above 0.2 Gy/pulse and down to 40% of efficiency at 30 Gy/pulse. The RNC resulted in a higher ICE for a given dose‐per‐pulse in comparison with the Markus chamber, with a measured efficiency found higher than 85 and 55% for 1 and 10 Gy/pulse, respectively, whereas the Markus ICE was of 60 and 25% for the same doses. However, the RNC shows a higher sensitivity to the pulse duration than the Advanced Markus chamber, with a lower efficiency found at 1 μs than at 3 μs, suggesting that this chamber could be more sensitive to the dose rate within the pulse. Conclusions The results confirmed that the small sensitive volume of the RNC ensures higher ICE compared with larger chambers. The RNC was thus found to be a promising online dosimetry tool for FLASH RT and we proposed an ion recombination model to correct its response up to extreme dose‐per‐pulses of 30 Gy.
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Affiliation(s)
- Marco Cavallone
- Institut Curie, PSL Research University, Radiation Oncology Department, Proton Therapy Centre, Centre Universitaire, Orsay, 91898, France.,Laboratoire d'Optique Appliquée, ENSTA Paris, École Polytechnique, CNRS-UMR7639, Institut Polytechnique de Paris, Palaiseau Cedex, 91762, France
| | | | - Raphaël Moeckli
- Institute of Radiation Physics, Lausanne University Hospital, Lausanne, Switzerland
| | - Claude Bailat
- Institute of Radiation Physics, Lausanne University Hospital, Lausanne, Switzerland
| | - Alessandro Flacco
- Laboratoire d'Optique Appliquée, ENSTA Paris, École Polytechnique, CNRS-UMR7639, Institut Polytechnique de Paris, Palaiseau Cedex, 91762, France
| | - Yolanda Prezado
- Institut Curie, Université PSL, CNRS UMR3347, Inserm U1021, Signalisation Radiobiologie et Cancer, Orsay, 91400, France.,Université Paris-Saclay, CNRS UMR3347, Inserm U1021, Signalisation Radiobiologie et Cancer, Orsay, 91400, France
| | - Rachel Delorme
- University of Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, Grenoble, 38000, France.,Imagerie et Modélisation en Neurobiologie et Cancérologie (IMNC), CNRS Univ Paris-Sud, Université Paris-Saclay, Orsay, F-91400, France
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Partanen M, Niemelä J, Ojala J, Keyriläinen J, Kapanen M. Properties of IBA Razor Nano Chamber in small-field radiation therapy using 6 MV FF, 6 MV FFF, and 10 MV FFF photon beams. Acta Oncol 2021; 60:1419-1424. [PMID: 34596486 DOI: 10.1080/0284186x.2021.1979644] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
BACKGROUND Small megavoltage photon fields are increasingly used in modern radiotherapy techniques such as stereotactic radiotherapy. Therefore, it is important to study the reliability of dosimetry in the small-field conditions. The IBA Razor Nano Chamber (Nano chamber) ionization chamber is particularly intended for small-field measurements. In this work, properties of the Nano chamber were studied with both measurements and Monte Carlo (MC) simulations. MATERIAL AND METHODS The measurements and MC simulations were performed with 6 MV, 6 MV FFF and 10 MV FFF photon beams from the Varian TrueBeam linear accelerator. The source-to-surface distance was fixed at 100 cm. The measurements and MC simulations included profiles, percentage depth doses (PDD), and output factors (OF) in square jaw-collimated fields. The MC simulations were performed with the EGSnrc software system in a large water phantom. RESULTS The measured profiles and PDDs obtained with the Nano chamber were compared against IBA Razor Diode, PTW microDiamond and the PTW Semiflex ionization chamber. These results indicate that the Nano chamber is a high-resolution detector and thus suitable for small field profile measurements down to field sizes 2 × 2 cm2 and appropriate for the PDD measurements. The field output correction factors kQclin, Qmsrfclin, fmsr and field OFs ΩQclin, Qmsrfclin, fmsr were determined according to TRS-483 protocol In the 6 MV FF and FFF beams, the determined correction factors kQclin, Qmsrfclin, fmsr were within 1.2% for the field sizes of 1 × 1 cm2-3 × 3 cm2 and the experimental and MC defined field output factors ΩQclin,Qmsrfclin,fmsr showed good agreement. CONCLUSION The Nano chamber with its small cavity volume is a potential detector for the small-field dosimetry. In this study, the properties of this detector were characterized with measurements and MC simulations. The determined correction factors kQclin, Qmsrfclin, fmsr are novel results for the NC in the TrueBeam fields.
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Affiliation(s)
- Mari Partanen
- Unit of Radiotherapy, Department of Oncology, Tampere University Hospital, Tampere, Finland
- Department of Medical Physics, Medical Imaging Center, Tampere University Hospital, Tampere, Finland
| | - Jarkko Niemelä
- Department of Medical Physics, Turku University Hospital, Turku, Finland
- Department of Oncology and Radiotherapy, Turku University Hospital, Turku, Finland
- Department of Physics and Astronomy, University of Turku, Turku, Finland
| | - Jarkko Ojala
- Unit of Radiotherapy, Department of Oncology, Tampere University Hospital, Tampere, Finland
- Department of Medical Physics, Medical Imaging Center, Tampere University Hospital, Tampere, Finland
| | - Jani Keyriläinen
- Department of Medical Physics, Turku University Hospital, Turku, Finland
- Department of Oncology and Radiotherapy, Turku University Hospital, Turku, Finland
| | - Mika Kapanen
- Unit of Radiotherapy, Department of Oncology, Tampere University Hospital, Tampere, Finland
- Department of Medical Physics, Medical Imaging Center, Tampere University Hospital, Tampere, Finland
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Debnath SBC, Tonneau D, Fauquet C, Tallet A, Goncalves A, Darreon J. Dosimetric characterization of a small-scale (Zn,Cd)S:Ag inorganic scintillating detector to be used in radiotherapy. Phys Med 2021; 84:15-23. [PMID: 33813200 DOI: 10.1016/j.ejmp.2021.03.022] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Revised: 03/14/2021] [Accepted: 03/20/2021] [Indexed: 12/01/2022] Open
Abstract
PURPOSE In modern radiotherapy techniques, to ensure an accurate beam modeling process, dosimeters with high accuracy and spatial resolution are required. Therefore, this work aims to propose a simple, robust, and a small-scale fiber-integrated X-ray inorganic detector and investigate the dosimetric characteristics used in radiotherapy. METHODS The detector is based on red-emitting silver-activated zinc-cadmium sulfide (Zn,Cd)S:Ag nanoclusters and the proposed system has been tested under 6 MV photons with standard dose rate used in the patient treatment protocol. The article presents the performances of the detector in terms of dose linearity, repeatability, reproducibility, percentage depth dose distribution, and field output factor. A comparative study is shown using a microdiamond dosimeter and considering data from recent literature. RESULTS We accurately measured a small field beam profile of 0.5 × 0.5 cm2 at a spatial resolution of 100 µm using a LINAC system. The dose linearity at 400 MU/min has shown less than 0.53% and 1.10% deviations from perfect linearity for the regular and smallest field. Percentage depth dose measurement agrees with microdiamond measurements within 1.30% and 2.94%, respectively for regular to small field beams. Besides, the stem effect analysis shows a negligible contribution in the measurements for fields smaller than 3x3 cm2. This study highlights the drastic decrease of the convolution effect using a point-like detector, especially in small dimension beam characterization. Field output factor has shown a good agreement while comparing it with the microdiamond dosimeter. CONCLUSION All the results presented here anticipated that the developed detector can accurately measure delivered dose to the region of interest, claim accurate depth dose distribution hence it can be a suitable candidate for beam characterization and quality assurance of LINAC system.
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Affiliation(s)
| | - Didier Tonneau
- Aix Marseille Université, CNRS, CINaM UMR 7325, 13288 Marseille, France
| | - Carole Fauquet
- Aix Marseille Université, CNRS, CINaM UMR 7325, 13288 Marseille, France
| | - Agnes Tallet
- Institut Paoli-Calmettes, 13009 Marseille, France
| | - Anthony Goncalves
- Institut Paoli-Calmettes, 13009 Marseille, France; Aix Marseille Université, CNRS UMR 7258, INSERM UMR 1068, CRCM, 13009 Marseille, France
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Gul A, Fukuda S, Mizuno H, Taku N, Kakakhel MB, Mirza SM. Feasibility study of using Stereotactic Field Diode for field output factors measurement and evaluating three new detectors for small field relative dosimetry of 6 and 10 MV photon beams. J Appl Clin Med Phys 2020; 21:23-36. [PMID: 33078544 PMCID: PMC7700919 DOI: 10.1002/acm2.13007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2020] [Revised: 06/29/2020] [Accepted: 07/10/2020] [Indexed: 11/23/2022] Open
Abstract
This study assesses the feasibility of using stereotactic field diode (SFD) as an alternate to gaf chromic films for field output factor (FF) measurement and further evaluating three new detectors for small field dosimetry. Varian 21EX linear accelerator was used to generate 6 and 10 MV beams of nominal square fields ranging from 0.5 × 0.5 cm2 to 10 × 10 cm2. One passive (EBT3 films) and five active detectors including IBA RAZOR diode(RD), SFD, RAZOR nanochamber (RNC), pinpoint chamber (PTW31023), and semiflex chamber (PTW31010) were employed. FFs were measured using films and SFD while beam profiles and percentage depth dose (PDD) distribution were acquired with active detectors. Polarity (kpol) and recombination (ks) effects of ion chambers were determined and corrected for output ratio measurement. Correction factors (CF) of RD, RNC, and PTW31023 in axial and radial orientation were also measured. Stereotactic field diode measured FFs have shown good agreement with films (with difference of <1%). RD and RNC measured beam profiles were within 3% deviation from the SFD values. Variation in kpol with field size for RNC and PTW31023 was up to 4% and 0.4% (for fields ≥ 1 × 1 cm2), respectively, while variation in ks of PTW31023 was <0.2 %. The maximum values of CF have been calculated to be 5.2%, 2.0%, 13.6%, and 25.5% for RD, RNC, PTW31023‐axial, and PTW31023‐radial respectively. This study concludes that SFD with appropriate CFs as given in TRS 483 may be used for measuring FFs as an alternate to EBT3 films. Whereas RD and RNC may be used for beam profile and PDD measurement in small fields. Considering the limit of usability of 2%, RNC may be used without CF for FF measurement in the smallfields investigated in this study.
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Affiliation(s)
- Attia Gul
- QST Hospital, National Institutes for Quantum and Radiological Science and Technology, Chiba, Japan.,Department of Physics & Applied Mathematics, Pakistan Institute of Engineering and Applied Sciences (PIEAS), Islamabad, Pakistan
| | - Shigekazu Fukuda
- QST Hospital, National Institutes for Quantum and Radiological Science and Technology, Chiba, Japan
| | - Hideyuki Mizuno
- QST Hospital, National Institutes for Quantum and Radiological Science and Technology, Chiba, Japan
| | - Nakaji Taku
- QST Hospital, National Institutes for Quantum and Radiological Science and Technology, Chiba, Japan
| | - M Basim Kakakhel
- Department of Physics & Applied Mathematics, Pakistan Institute of Engineering and Applied Sciences (PIEAS), Islamabad, Pakistan
| | - Sikander M Mirza
- Department of Physics & Applied Mathematics, Pakistan Institute of Engineering and Applied Sciences (PIEAS), Islamabad, Pakistan
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11
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Yamauchi R, Igari M, Kasai Y, Hariu M, Suda Y, Kawachi T, Katayose T, Mizuno N, Miyasaka R, Saitoh H. Estimation of the cable effect in megavoltage photon beam by measurement and Monte Carlo simulation. Med Phys 2020; 47:5324-5332. [PMID: 32786073 DOI: 10.1002/mp.14450] [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: 06/14/2019] [Revised: 05/12/2020] [Accepted: 08/05/2020] [Indexed: 11/12/2022] Open
Abstract
PURPOSE Ionization chambers are widely used for dosimetry with megavoltage photon beams. Several properties of ionization chambers, including the cable effect, polarity effect, and ion recombination loss, are described in standard dosimetry protocols. The cable effect is categorized as the leakage current and Compton current, and careful consideration of these factors has been described not only in reference dosimetry but also in large fields. However, the mechanism of Compton current in the cable has not been investigated thoroughly. The cable effect of ionization chambers in 6 MV X-ray beam was evaluated by measurement, and the mechanism of Compton current was investigated by Monte Carlo simulation. MATERIALS AND METHODS Four PTW ionization chambers (TM30013, TM31010, TM31014, and TM31016) with the same type of mounted cable, but different ionization volumes, were used to measure output factor (OPF) and cable effect measurement. The OPF was measured to observe any variation resulting from the cable effect. The cable effect was evaluated separately for the leakage current and Compton current, and its charge per absorbed dose to water per cable length was estimated by a newly proposed method. The behavior of electrons and positrons in the core wire was analyzed and the Compton current for the photon beam was estimated by Monte Carlo simulation. RESULTS In OPF measurement, the difference in the electrometer readings by polarity became obvious for the mini- or microchamber and its difference tended to be larger for a chamber with a smaller ionization volume. For the cable effect measurement, it was determined that the contribution of the leakage current to the cable effect was ignorable, while the Compton current was dominant. The charge due to the Compton current per absorbed dose to water per cable length was estimated to be 0.36 ± 0.03 pC Gy-1 cm-1 for PTW ionization chambers. As a result, the contribution of the Compton current to the electrometer readings was estimated to be 0.002% cm-1 for the Farmer-type, 0.011% cm-1 for the scanning, and 0.088% cm-1 for microchambers, respectively. By the simulation, it was determined that the Compton current for MV x-ray could be explained by not only recoil electrons due to Compton scattering but also positron due to pair production. The Compton current estimated by the difference in outflowing and inflowing charge was 0.45 pC Gy-1 cm-1 and was comparable with the measured value. CONCLUSION The cable effect, which includes the leakage current and Compton current, was quantitatively estimated for several chambers from measurements, and the mechanism of Compton current was investigated by Monte Carlo simulation. It was determined that the Compton current is a dominant component of the cable effect and its charge is consistently positive and nearly the same, irrespective of the ionization chamber volume. The contribution of Compton current to the electrometer readings was estimated for chambers. The mechanism of Compton current was analyzed and it was confirmed that the Compton current can be estimated from the difference in outflowing and inflowing charge to and from the core wire.
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Affiliation(s)
- Ryohei Yamauchi
- Department of Radiation Oncology, St. Luke's International Hospital, 9-1 Akashi-cho, Chuo-ku, Tokyo, 104-8560, Japan.,Graduate School of Human Health Sciences, Tokyo Metropolitan University, 7-2-10 Higashi-ogu, Arakawa-ku, Tokyo, 116-0012, Japan
| | - Mitsunobu Igari
- Department of Radiation Oncology, International Medical Center, Saitama Medical University, 1397-1, Yamane, Hidaka-City, Saitama, 350-1298, Japan
| | - Yuya Kasai
- Division of Radiation, National Hospital Organization Tokyo National Hospital, 3-1-1 Takeoka, Kiyose-City, Tokyo, 204-8585, Japan
| | - Masatsugu Hariu
- Department of Radiation Oncology, Saitama Medical Center, Saitama Medical University, 1981 Kamoda, Kawagoe City, Saitama, 350-8550, Japan
| | - Yuhi Suda
- Graduate School of Human Health Sciences, Tokyo Metropolitan University, 7-2-10 Higashi-ogu, Arakawa-ku, Tokyo, 116-0012, Japan.,Department of Radiotherapy, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, 3-18-22 Honkomagome, Bunkyo-ku, Tokyo, 113-8677, Japan
| | - Toru Kawachi
- Department of Radiation Oncology, Chiba Cancer Center, 666-2 Nitona-cho, Chuo-ku, Chiba, 260-8717, Japan
| | - Tetsurou Katayose
- Department of Radiation Oncology, Chiba Cancer Center, 666-2 Nitona-cho, Chuo-ku, Chiba, 260-8717, Japan
| | - Norifumi Mizuno
- Department of Radiation Oncology, St. Luke's International Hospital, 9-1 Akashi-cho, Chuo-ku, Tokyo, 104-8560, Japan
| | - Ryohei Miyasaka
- Graduate School of Human Health Sciences, Tokyo Metropolitan University, 7-2-10 Higashi-ogu, Arakawa-ku, Tokyo, 116-0012, Japan.,Department of Radiation Oncology, Chiba Cancer Center, 666-2 Nitona-cho, Chuo-ku, Chiba, 260-8717, Japan
| | - Hidetoshi Saitoh
- Graduate School of Human Health Sciences, Tokyo Metropolitan University, 7-2-10 Higashi-ogu, Arakawa-ku, Tokyo, 116-0012, Japan
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12
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Wegener S, Sauer OA. The effective point of measurement for depth-dose measurements in small MV photon beams with different detectors. Med Phys 2019; 46:5209-5215. [PMID: 31461533 DOI: 10.1002/mp.13788] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Revised: 07/11/2019] [Accepted: 08/06/2019] [Indexed: 11/07/2022] Open
Abstract
PURPOSE The effective point of measurement (EPOM) of cylindrical ionization chambers differs from their geometric center. The exact shift depends on chamber construction details, above all the chamber size, and to some degree on the field-size and beam quality. It generally decreases as the chamber dimensions get smaller. In this work, effective points of measurement in small photon fields of a range of cylindrical chambers of different sizes are investigated, including small chambers that have not been studied previously. METHODS In this investigation, effective points of measurement for different ionization chambers (Farmer type, scanning chambers, micro-ionization chambers) and solid state detectors were determined by measuring depth-ionization curves in a 6 MV beam in field sizes between 2 × 2 cm2 and 10 × 10 cm2 and comparing those curves with curves measured with plane-parallel chambers. RESULTS It was possible to average the results to one shift per detector, as the results were sufficiently independent of the studied field sizes. For cylindrical ion chambers, shifts of the EPOM were determined to be between 0.49 and 0.30 times the inner chamber radius from the reference point. CONCLUSIONS We experimentally confirmed the previously reported decrease of the EPOM shift with decreasing detector size. Highly accurate data for a large range of detectors, including new very small ones, were determined. Thus, small chambers noticeably differ from the 0.5-times to 0.6-times the inner chamber radius recommendations in current dosimetry protocols. The detector-individual EPOMs need to be considered for measurements of depth-dose curves.
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Affiliation(s)
- Sonja Wegener
- Radiation Oncology, University of Wuerzburg, Josef-Schneider-Str. 11, 97080, Wuerzburg, Germany
| | - Otto A Sauer
- Radiation Oncology, University of Wuerzburg, Josef-Schneider-Str. 11, 97080, Wuerzburg, Germany
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13
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Looe HK, Büsing I, Tekin T, Brant A, Delfs B, Poppinga D, Poppe B. The polarity effect of compact ionization chambers used for small field dosimetry. Med Phys 2018; 45:5608-5621. [DOI: 10.1002/mp.13227] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2018] [Revised: 09/24/2018] [Accepted: 09/28/2018] [Indexed: 11/07/2022] Open
Affiliation(s)
- Hui Khee Looe
- University Clinic for Medical Radiation Physics Medical Campus Pius Hospital Carl von Ossietzky University Oldenburg Germany
| | - Isabel Büsing
- University Clinic for Medical Radiation Physics Medical Campus Pius Hospital Carl von Ossietzky University Oldenburg Germany
| | - Tuba Tekin
- University Clinic for Medical Radiation Physics Medical Campus Pius Hospital Carl von Ossietzky University Oldenburg Germany
| | - Andre Brant
- University Clinic for Medical Radiation Physics Medical Campus Pius Hospital Carl von Ossietzky University Oldenburg Germany
| | - Björn Delfs
- University Clinic for Medical Radiation Physics Medical Campus Pius Hospital Carl von Ossietzky University Oldenburg Germany
| | | | - Björn Poppe
- University Clinic for Medical Radiation Physics Medical Campus Pius Hospital Carl von Ossietzky University Oldenburg Germany
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14
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Wegener S, Sauer OA. Electrometer offset current due to scattered radiation. J Appl Clin Med Phys 2018; 19:274-281. [PMID: 30298980 PMCID: PMC6236832 DOI: 10.1002/acm2.12458] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Revised: 05/14/2018] [Accepted: 08/27/2018] [Indexed: 11/05/2022] Open
Abstract
Relative dose measurements with small ionization chambers in combination with an electrometer placed in the treatment room ("internal electrometer") show a large dependence on the polarity used. While this was observed previously for percent depth dose curves (PDDs), the effect has not been understood or preventable. To investigate the polarity dependence of internal electrometers used in conjunction with a small-volume ionization chamber, we placed an internal electrometer at a distance of 1 m from the isocenter and exposed it to different amounts of scattered radiation by varying the field size. We identified irradiation of the electrometer to cause a current of approximately -1 pA, regardless of the sign of the biasing voltage. For low-sensitivity detectors, such a current noticeably distorts relative dose measurements. To demonstrate how the current systematically changes PDDs, we collected measurements with nine ionization chambers of different volumes. As the chamber volume decreased, signal ratios at 20 and 10 cm depth (M20/M10) became smaller for positive bias voltage and larger for negative bias voltage. At the size of the iba CC04 (40 mm³) the difference of M20/M10 was around 1% and for the smallest studied chamber, the iba CC003 chamber (3 mm³), around 7% for a 10 × 10 cm² field. When the electrometer was moved further from the source or shielded, the additional current decreased. Consequently, PDDs at both polarities were brought into alignment at depth even for the 3 mm³ ionization chamber. The apparent polarity effect on PDDs and lateral beam profiles was reduced considerably by shielding the electrometer. Due to normalization the effect on output values was low. When measurements with a low-sensitivity probe are carried out in conjunction with an internal electrometer, we recommend careful monitoring of the particular setup by testing both polarities, and if deemed necessary, we suggest shielding the electrometer.
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Affiliation(s)
- Sonja Wegener
- Department of Radiation Oncology, University of Wuerzburg, Wuerzburg, Germany
| | - Otto A Sauer
- Department of Radiation Oncology, University of Wuerzburg, Wuerzburg, Germany
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Veselsky T, Novotny J, Pastykova V, Koniarova I. Determination of small field synthetic single-crystal diamond detector correction factors for CyberKnife, Leksell Gamma Knife Perfexion and linear accelerator. Phys Med 2017; 44:66-71. [DOI: 10.1016/j.ejmp.2017.11.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/22/2017] [Revised: 10/09/2017] [Accepted: 11/09/2017] [Indexed: 10/18/2022] Open
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