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Das IJ, Khan AU, Dogan SK, Longo M. Grid/lattice therapy: consideration of small field dosimetry. Br J Radiol 2024; 97:1088-1098. [PMID: 38552328 PMCID: PMC11135801 DOI: 10.1093/bjr/tqae060] [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: 02/14/2024] [Revised: 03/11/2024] [Accepted: 03/14/2024] [Indexed: 05/31/2024] Open
Abstract
Small-field dosimetry used in special procedures such as gamma knife, Cyberknife, Tomotherapy, IMRT, and VMAT has been in evolution after several radiation incidences with very significant (70%) errors due to poor understanding of the dosimetry. IAEA-TRS-483 and AAPM-TG-155 have provided comprehensive information on small-fields dosimetry in terms of code of practice and relative dosimetry. Data for various detectors and conditions have been elaborated. It turns out that with a suitable detectors dose measurement accuracy can be reasonably (±3%) achieved for 6 MV beams for fields >1×1 cm2. For grid therapy, even though the treatment is performed with small fields created by either customized blocks, multileaf collimator (MLC), or specialized devices, it is multiple small fields that creates combined treatment. Hence understanding the dosimetry in collection of holes of small field is a separate challenge that needs to be addressed. It is more critical to understand the scattering conditions from multiple holes that form the treatment grid fields. Scattering changes the beam energy (softer) and hence dosimetry protocol needs to be properly examined for having suitable dosimetric parameters. In lieu of beam parameter unavailability in physical grid devices, MLC-based forward and inverse planning is an alternative path for bulky tumours. Selection of detectors in small field measurement is critical and it is more critical in mixed beams created by scattering condition. Ramification of small field concept used in grid therapy along with major consideration of scattering condition is explored. Even though this review article is focussed mainly for dosimetry for low-energy megavoltage photon beam (6 MV) but similar procedures could be adopted for high energy beams. To eliminate small field issues, lattice therapy with the help of MLC is a preferrable choice.
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Affiliation(s)
- Indra J Das
- Department of Radiation Oncology, Northwest Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, United States
| | - Ahtesham Ullah Khan
- San Bortolo Hospital, Medical Physics Department, Viale F. Rodolfi 37, 36100 Vicenza, Italy
| | - Serpil K Dogan
- Department of Radiation Oncology, Northwest Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, United States
| | - Mariaconcetta Longo
- San Bortolo Hospital, Medical Physics Department, Viale F. Rodolfi 37, 36100 Vicenza, Italy
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Rossi G, Failing T, Gainey M, Kollefrath M, Hensley F, Zink K, Baltas D. Determination of the dose rate around a HDR 192Ir brachytherapy source with the microDiamond and the microSilicon detector. Z Med Phys 2023; 33:463-478. [PMID: 36038432 PMCID: PMC10751698 DOI: 10.1016/j.zemedi.2022.07.004] [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: 05/10/2022] [Revised: 07/23/2022] [Accepted: 07/25/2022] [Indexed: 12/01/2022]
Abstract
PURPOSE To employ the microDiamond and the microSilicon detector (mDD and mSD, both PTW-Freiburg, Germany) to determine the dose rate around a HDR 192Ir brachytherapy source (model mHDR-v2r, Elekta AB, Sweden). METHODS The detectors were calibrated with a 60Co beam at the PTW Calibration Laboratory. Measurements around the 192Ir source were performed inside a PTW MP3 water phantom. The detectors were placed at selected points of measurement at radial distances r, ranging from 0.5 to 10 cm, keeping the polar angle θ = 90°. Additional measurements were performed with the mSD at fixed distances r = 1, 3 and 5 cm, with θ varying from 0 to 150°, 0 to 166°, and 0 to 168°, respectively. The corresponding mDD readings were already available from a previous work (Rossi et al., 2020). The beam quality correction factor of both detectors, as well as a phantom effect correction factor to account for the difference between the experimental geometry and that assumed in the TG-43 formalism, were determined using the Monte Carlo (MC) toolkit EGSnrc. The beam quality correction factor was factorized into energy dependence and volume-averaging correction factors. Using the abovementioned MC-based factors, the dose rate to water at the different points of measurement in TG-43 conditions was obtained from the measured readings, and was compared to the dose rate calculated according to the TG-43 formalism. RESULTS The beam quality correction factor was considerably closer to unity for the mDD than for the mSD. The energy dependence of the mDD showed a very weak radial dependence, similar to the previous findings showing a weak angular dependence as well (Rossi et al., 2020). Conversely, the energy dependence of the mSD decreased significantly with increasing distances, and also showed a considerably more pronounced angular dependence, especially for the smallest angles. The volume-averaging showed a similar radial dependence for both detectors: the correction had a maximal impact at 0.5 cm and then approached unity for larger distances, as expected. Concerning the angular dependence, the correction for the mSD was also similar to the one previously determined for the mDD (Rossi et al., 2020): a maximal impact was observed at θ = 0°, with values tending to unity for larger angles. In general, the volume-averaging was less pronounced for the mSD due to the smaller sensitive volume radius. After the application of the MC-based factors, differences between mDD dose rate measurements and TG-43 dose rate calculations ranged from -2.6% to +4.3%, with an absolute average difference of 1.0%. For the mSD, the differences ranged from -3.1% to +5.2%, with an absolute average difference of 1.0%. For both detectors, all differences but one were within the combined uncertainty (k = 2). The differences of the mSD from the mDD ranged from -3.9% to +2.6%, with the vast majority of them being within the combined uncertainty (k = 2). For θ ≠ 0°, the mDD was able to provide sufficiently accurate results even without the application of the MC-based beam quality correction factor, with differences to the TG-43 dose rate calculations from -1.9% to +3.4%, always within the combined uncertainty (k = 2). CONCLUSION The mDD and the mSD showed consistent results and appear to be well suitable for measuring the dose rate around HDR 192Ir brachytherapy sources. MC characterization of the detectors response is needed to determine the beam quality correction factor and to account for energy dependence and/or volume-averaging, especially for the mSD. Our findings support the employment of the mDD and mSD for source QA, TPS verification and TG-43 parameters determination.
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Affiliation(s)
- Giulio Rossi
- Division of Medical Physics, Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, Germany; German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany.
| | - Thomas Failing
- University of Applied Sciences Giessen, Institute of Medical Physics and Radiation Protection, Giessen, Germany; University Medical Center Göttingen, Department of Radiation Oncology, Göttingen, Germany
| | - Mark Gainey
- Division of Medical Physics, Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, Germany; German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Michael Kollefrath
- Division of Medical Physics, Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, Germany; German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Frank Hensley
- University Hospital of Heidelberg, Department of Radiation Oncology, Heidelberg, Germany
| | - Klemens Zink
- University of Applied Sciences Giessen, Institute of Medical Physics and Radiation Protection, Giessen, Germany; University Medical Center Giessen-Marburg, Department of Radiotherapy and Radiation Oncology, Marburg, Germany; Marburg Ionbeam Therapycenter (MIT), Marburg, Germany
| | - Dimos Baltas
- Division of Medical Physics, Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, Germany; German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
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Das IJ, Dogan SK, Gopalakrishnan M, Ding GX, Longo M, Franscescon P. Validity of equivalent square field concept in small field dosimetry. Med Phys 2022; 49:4043-4055. [PMID: 35344220 DOI: 10.1002/mp.15624] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Revised: 03/16/2022] [Accepted: 03/16/2022] [Indexed: 11/11/2022] Open
Abstract
PURPOSE The equivalent Square (ES) concept has been used for traditional radiation fields defined by the machine collimating system. For small fields, the concept Sclin was introduced based on measuring dosimetric field width (full-width half maximum, FWHM) of the cardinal axis of the beam profiles. The pros and cons of this concept are evaluated in small fields and compared with the traditional ES using area and perimeter (4A/P) method based on geometric field size settings e.g. light field settings. METHODS One hundred thirty-seven square and rectangular fields from 5-50 mm with every possible permutation (keeping one jaw fixed and varying other jaw from 5 mm to 50 mm) were utilized to measure FWHM for the validation of Sclin . Using a microSilicon detector and a scanning water tank, measurements were performed on an Elekta (Versa) machine with Agility head and a Varian TrueBeam with different MLC/Jaw design to evaluate the Sclin concept and to understand the effect of exchange factor in small fields. Field output factors were also measured for all 137 fields. RESULTS The data fitting for fields ranging from 5-50 mm between the traditional 4A/P method and Sclin shows differences and indicates a linear relationship with distinct separation of slope for Elekta and Varian machines. As Elekta does not have y jaws, the ES based on 4A/P < Sclin but for the Varian linac 4A/P > Sclin for square fields. Our measured data shows that both methods are equally valid but does vary by the machine design. The field output factor is dependent on the elongation factor as well as machine design. For fields with sides ≥10 mm, the exchange factor is nearly identical in both machines with magnitude up to 4% which is close to measurement uncertainty (±3%) but for small fields (<10 mm) the Elekta machine has higher exchange factors compared to the Varian machine. CONCLUSION The results demonstrate that the two concepts for defining equivalent field (Sclin and 4A/P) are equivalent and can be directly related through an empirical equation. This study confirms that 4A/P is still valid for small fields except for very small fields (≤10 mm) where source occlusion is a dominating factor. The Sclin method is potentially sensitive to measurement uncertainty due to measurement of FWHM which is machine, detector and user dependent, while the 4A/P method relies mainly on geometry of the machine and has less dependency on type of machine, detector and user. The exchange factors are comparable for both types of machines. The conclusion is based on data from an Elekta with Agility head and a Varian TrueBeam machine that may have potential for bias due to light field/collimator set up and alignment. Care should be taken in extrapolating these data to any other machine. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Indra J Das
- Department of Radiation Oncology, Northwestern Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Serpil K Dogan
- Department of Radiation Oncology, Northwestern Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Mahesh Gopalakrishnan
- Department of Radiation Oncology, Northwestern Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - George X Ding
- Department of Radiation Oncology, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA
| | - Mariaconcetta Longo
- Department of Radiation Oncology Ospedale Di Vicenza, Viale Rodolfi, Vicenza, 36100, Italy
| | - Paolo Franscescon
- Department of Radiation Oncology Ospedale Di Vicenza, Viale Rodolfi, Vicenza, 36100, Italy
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Duchaine J, Markel D, Bouchard H. A probabilistic approach for determining Monte Carlo beam source parameters: I. Modeling of a CyberKnife M6 unit. Phys Med Biol 2022; 67. [DOI: 10.1088/1361-6560/ac4ef7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Accepted: 01/26/2022] [Indexed: 11/12/2022]
Abstract
Abstract
Objective. During Monte Carlo modeling of external radiotherapy beams, models must be adjusted to reproduce the experimental measurements of the linear accelerator being considered. The aim of this work is to propose a new method for the determination of the energy and spot size of the electron beam incident on the target of a linear accelerator using a maximum likelihood estimation. Approach. For that purpose, the method introduced by Francescon et al (2008 Med. Phys.
35 504–13) is expanded upon in this work. Simulated tissue-phantom ratios and uncorrected output factors using a set of different detector models are compared to experimental measurements. A probabilistic formalism is developed and a complete uncertainty budget, which includes a detailed simulation of positioning errors, is evaluated. The method is applied to a CyberKnife M6 unit using four detectors (PTW 60012, PTW 60019, Exradin A1SL and IBA CC04), with simulations being performed using the EGSnrc suite. Main results. The likelihood distributions of the electron beam energy and spot size are evaluated, leading to
E
ˆ
=
7.42
±
0.17
MeV
and
F
ˆ
=
2.15
±
0.06
mm
. Using these results and a 95% confidence region, simulations reproduce measurements in 13 out of the 14 considered setups. Significance. The proposed method allows an accurate beam parameter optimization and uncertainty evaluation during the Monte Carlo modeling of a radiotherapy unit.
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Blum I, Tekin T, Delfs B, Schönfeld AB, Kapsch RP, Poppe B, Looe HK. The dose response of PTW microDiamond and microSilicon in transverse magnetic field under small field conditions. Phys Med Biol 2021; 66. [PMID: 34181591 DOI: 10.1088/1361-6560/ac0f2e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2021] [Accepted: 06/28/2021] [Indexed: 11/11/2022]
Abstract
The aim of the present work is to investigate the behavior of two diode-type detectors (PTW microDiamond 60019 and PTW microSilicon 60023) in transverse magnetic field under small field conditions. A formalism based on TRS 483 has been proposed serving as the framework for the application of these high-resolution detectors under these conditions. Measurements were performed at the National Metrology Institute of Germany (PTB, Braunschweig) using a research clinical linear accelerator facility. Quadratic fields corresponding to equivalent square field sizesSbetween 0.63 and 4.27 cm at the depth of measurement were used. The magnetic field strength was varied up to 1.4 T. Experimental results have been complemented with Monte Carlo simulations up to 1.5 T. Detailed simulations were performed to quantify the small field perturbation effects and the influence of detector components on the dose response. The does response of both detectors decreases by up to 10% at 1.5 T in the largest field size investigated. InS = 0.63 cm, this reduction at 1.5 T is only about half of that observed in field sizesS > 2 cm for both detectors. The results of the Monte Carlo simulations show agreement better than 1% for all investigated conditions. Due to normalization at the machine specific reference field, the resulting small field output correction factors for both detectors in magnetic fieldkQclin,QmsrBare smaller than those in the magnetic field-free case, where correction up to 6.2% at 1.5 T is required for the microSilicon in the smallest field size investigated. The volume-averaging effect of both detectors was shown to be nearly independent of the magnetic field. The influence of the enhanced-density components within the detectors has been identified as the major contributors to their behaviors in magnetic field. Nevertheless, the effect becomes weaker with decreasing field size that may be partially attributed to the deficiency of low energy secondary electrons originated from distant locations in small fields.
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Affiliation(s)
- Isabel Blum
- 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
| | - Björn Delfs
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
| | - Ann-Britt Schönfeld
- 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
| | - Hui Khee Looe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
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Delfs B, Blum I, Tekin T, Schönfeld AB, Kranzer R, Poppinga D, Giesen U, Langner F, Kapsch RP, Poppe B, Looe HK. The role of the construction and sensitive volume of compact ionization chambers on the magnetic field-dependent dose response. Med Phys 2021; 48:4572-4585. [PMID: 34032298 DOI: 10.1002/mp.14994] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Revised: 04/19/2021] [Accepted: 05/03/2021] [Indexed: 11/11/2022] Open
Abstract
PURPOSE The magnetic-field correction factors k B , Q of compact air-filled ionization chambers have been investigated experimentally and using Monte Carlo simulations up to 1.5 T. The role of the nonsensitive region within the air cavity and influence of the chamber construction on its dose response have been elucidated. MATERIALS AND METHODS The PTW Semiflex 3D 31021, PinPoint 3D 31022, and Sun Nuclear Cooperation SNC125c chambers were studied. The k B , Q factors were measured at the experimental facility of the German National Metrology Institute (PTB) up to 1.4 T using a 6 MV photon beam. The chambers were positioned with the chamber axis perpendicular to the beam axis (radial); and parallel to the beam axis (axial). In both cases, the magnetic field was directed perpendicular to both the beam axis and chamber axis. Additionally, the sensitive volumes of these chambers have been experimentally determined using a focused proton microbeam and finite element method. Beside the simulations of k B , Q factors, detailed Monte Carlo technique has been applied to analyse the secondary electron fluence within the air cavity, that is, the number of secondary electrons and the average path length as a function of the magnetic field strength. RESULTS A nonsensitive volume within the air cavity adjacent to the chamber stem for the PTW chambers has been identified from the microbeam measurements and FEM calculations. The dose response of the three investigated ionization chambers does not deviate by more than 4% from the field-free case within the range of magnetic fields studied in this work for both the radial and axial orientations. The simulated k B , Q for the fully guarded PTW chambers deviate by up to 6% if their sensitive volumes are not correctly considered during the simulations. After the implementation of the sensitive volume derived from the microbeam measurements, an agreement of better than 1% between the experimental and Monte Carlo k B , Q factors for all three chambers can be achieved. Detailed analysis reveals that the stem of the PTW chambers could give rise to a shielding effect reducing the number of secondary electrons entering the air cavity in the presence of magnetic field. However, the magnetic field dependence of their path length within the air cavity is shown to be weaker than for the SNC125c chamber, where the length of the air cavity is larger than its diameter. For this chamber it is shown that the number of electrons and their path lengths in the cavity depend stronger on the magnetic field. DISCUSSION AND CONCLUSION For clinical measurements up to 1.5 T, the required k B , Q corrections of the three chambers could be kept within 3% in both the investigated chamber orientations. The results reiterate the importance of considering the sensitive volume of fully guarded chambers, even for the investigated compact chambers, in the Monte Carlo simulations of chamber response in magnetic field. The resulting magnetic field-dependent dose response has been demonstrated to depend on the chamber construction, such as the ratio between length and the diameter of the air cavity as well as the design of the chamber stem.
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Affiliation(s)
- Björn Delfs
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
| | - Isabel Blum
- 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
| | - Ann-Britt Schönfeld
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
| | - Rafael Kranzer
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany.,PTW Freiburg, Freiburg, Germany
| | | | - Ulrich Giesen
- Hochenergetische Photonen- und Elektronenstrahlung, Physikalisch-Technische Bundesanstalt, PTB, Braunschweig, Germany
| | - Frank Langner
- Hochenergetische Photonen- und Elektronenstrahlung, Physikalisch-Technische Bundesanstalt, PTB, Braunschweig, Germany
| | - Ralf-Peter Kapsch
- Hochenergetische Photonen- und Elektronenstrahlung, Physikalisch-Technische Bundesanstalt, PTB, Braunschweig, Germany
| | - Björn Poppe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
| | - Hui Khee Looe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
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Das IJ, Francescon P, Moran JM, Ahnesjö A, Aspradakis MM, Cheng CW, Ding GX, Fenwick JD, Saiful Huq M, Oldham M, Reft CS, Sauer OA. Report of AAPM Task Group 155: Megavoltage photon beam dosimetry in small fields and non-equilibrium conditions. Med Phys 2021; 48:e886-e921. [PMID: 34101836 DOI: 10.1002/mp.15030] [Citation(s) in RCA: 50] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Revised: 05/06/2021] [Accepted: 06/02/2021] [Indexed: 12/14/2022] Open
Abstract
Small-field dosimetry used in advance treatment technologies poses challenges due to loss of lateral charged particle equilibrium (LCPE), occlusion of the primary photon source, and the limited choice of suitable radiation detectors. These challenges greatly influence dosimetric accuracy. Many high-profile radiation incidents have demonstrated a poor understanding of appropriate methodology for small-field dosimetry. These incidents are a cause for concern because the use of small fields in various specialized radiation treatment techniques continues to grow rapidly. Reference and relative dosimetry in small and composite fields are the subject of the International Atomic Energy Agency (IAEA) dosimetry code of practice that has been published as TRS-483 and an AAPM summary publication (IAEA TRS 483; Dosimetry of small static fields used in external beam radiotherapy: An IAEA/AAPM International Code of Practice for reference and relative dose determination, Technical Report Series No. 483; Palmans et al., Med Phys 45(11):e1123, 2018). The charge of AAPM task group 155 (TG-155) is to summarize current knowledge on small-field dosimetry and to provide recommendations of best practices for relative dose determination in small megavoltage photon beams. An overview of the issue of LCPE and the changes in photon beam perturbations with decreasing field size is provided. Recommendations are included on appropriate detector systems and measurement methodologies. Existing published data on dosimetric parameters in small photon fields (e.g., percentage depth dose, tissue phantom ratio/tissue maximum ratio, off-axis ratios, and field output factors) together with the necessary perturbation corrections for various detectors are reviewed. A discussion on errors and an uncertainty analysis in measurements is provided. The design of beam models in treatment planning systems to simulate small fields necessitates special attention on the influence of the primary beam source and collimating devices in the computation of energy fluence and dose. The general requirements for fluence and dose calculation engines suitable for modeling dose in small fields are reviewed. Implementations in commercial treatment planning systems vary widely, and the aims of this report are to provide insight for the medical physicist and guidance to developers of beams models for radiotherapy treatment planning systems.
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Affiliation(s)
- Indra J Das
- Department of Radiation Oncology, Northwestern Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | - Paolo Francescon
- Department of Radiation Oncology, Ospedale Di Vicenza, Vicenza, Italy
| | - Jean M Moran
- Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY, USA
| | - Anders Ahnesjö
- Medical Radiation Sciences, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - Maria M Aspradakis
- Institute of Radiation Oncology, Cantonal Hospital of Graubünden, Chur, Switzerland
| | - Chee-Wai Cheng
- Department of Radiation Oncology, University Hospitals Cleveland Medical Center, Cleveland, OH, USA
| | - George X Ding
- Department of Radiation Oncology, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - John D Fenwick
- Molecular and Clinical Cancer Medicine, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK
| | - M Saiful Huq
- Department of Radiation Oncology, University of Pittsburgh, School of Medicine and UPMC Hillman Cancer Center, Pittsburgh, PA, USA
| | - Mark Oldham
- Department of Radiation Oncology, Duke University Medical Center, Durham, NC, USA
| | - Chester S Reft
- Department of Radiation Oncology, University of Chicago, Chicago, IL, USA
| | - Otto A Sauer
- Department of Radiation Oncology, Klinik fur Strahlentherapie, University of Würzburg, Würzburg, Germany
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Rossi G, Gainey M, Kollefrath M, Hofmann E, Baltas D. Suitability of the microDiamond detector for experimental determination of the anisotropy function of High Dose Rate 192 Ir brachytherapy sources. Med Phys 2020; 47:5838-5851. [PMID: 32970875 DOI: 10.1002/mp.14488] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 09/07/2020] [Accepted: 09/13/2020] [Indexed: 11/06/2022] Open
Abstract
PURPOSE To investigate the suitability of the microDiamond detector (mDD) type 60019 (PTW-Freiburg, Germany) to measure the anisotropy function F(r,θ) of High Dose Rate (HDR) 192 Ir brachytherapy sources. METHODS The HDR 192 Ir brachytherapy source, model mHDR-v2r (Elekta AB, Sweden), was placed inside a water tank within a 4F plastic needle. Four mDDs (mDD1, mDD2, mDD3, and mDD4) were investigated. Each mDD was placed laterally with respect to the source, and measurements were performed at radial distances r = 1 cm, 3 and 5 cm, and polar angles θ from 0° to 168°. The Monte Carlo (MC) system EGSnrc was used to simulate the measurements and to calculate phantom effect, energy dependence and volume-averaging correction factors. F(r,θ) was determined according to TG-43 formalism from the detector reading corrected with the MC-based factors and compared to the consensus anisotropy function CON F(r,θ). RESULTS At 1 cm, the differences between measurements and MC simulations ranged from -0.8% to +0.8% for θ = 0° and from -2.1% to + 2.3% for θ ≠ 0°. At 3 and 5 cm, the differences ranged from +1.4% to +3.9% for θ = 0°, and from -0.4% to +2.9% for θ ≠ 0°. All differences were within the uncertainties (k = 2). At small angles, the phantom effect correction was up to -1.9%. This effect was mainly caused by the air between source and needle tip. The energy correction was angle-independent everywhere. For small angles at 1 cm, the volume-averaging correction was up to -2.9% and became less important for larger angles and distances. The differences of the measured F(r,θ) corrected with the MC-based factors to CON F(r,θ) ranged from -1.0% to +3.4% for mDD1, -2.2% to +4.2% for mDD2, -2.5% to +4.0% for mDD3, and -2.6% to +3.4% for mDD4. All differences were within the uncertainties (k = 2) except one at (3 cm, 0°). For all the mDDs, F(r,0°) was always higher than CON F(r,0°), with average differences of +3.1% (1 cm), +3.6% (3 cm), and +1.9% (5 cm). The inter-detector variability was within 2.9% (1 cm), 1.8% (3 cm), and 3.4% (5 cm). CONCLUSIONS A reproducible method and experimental setup were presented for measuring and validating F(r,θ) of an HDR 192 Ir brachytherapy source in a water phantom using the mDD. The phantom effect and the volume-averaging need to be taken into account, especially for the smaller distances and angles. Good agreement to CON F(r,θ) was obtained. The discrepancies at (1 cm, 0°), accurately predicted by the MC results, may suggest a reconsideration of CON F(r,θ), at least for this position. The slight overestimations at (3 cm,0°) and (5 cm,0°), both in comparison to CON F(r,θ) and MC results, may be due to an underestimation of the air volume between source and needle tip, dark current, intrinsic over-response of the mDDs, or radiation-induced charge imbalance in the detector's components. The results indicate that the mDD is a valuable tool for measurements with HDR 192 Ir brachytherapy sources and support its employment for the determination and validation of TG-43 parameters of such sources.
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Affiliation(s)
- Giulio Rossi
- Division of Medical Physics, Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Mark Gainey
- Division of Medical Physics, Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Michael Kollefrath
- Division of Medical Physics, Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Elena Hofmann
- Division of Medical Physics, Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Dimos Baltas
- Division of Medical Physics, Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
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9
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Rosenfeld AB, Biasi G, Petasecca M, Lerch MLF, Villani G, Feygelman V. Semiconductor dosimetry in modern external-beam radiation therapy. Phys Med Biol 2020; 65:16TR01. [PMID: 32604077 DOI: 10.1088/1361-6560/aba163] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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10
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Poppinga D, Kretschmer J, Brodbek L, Meyners J, Poppe B, Looe HK. Evaluation of the RUBY modular QA phantom for planar and non-coplanar VMAT and stereotactic radiations. J Appl Clin Med Phys 2020; 21:69-79. [PMID: 32797670 PMCID: PMC7592965 DOI: 10.1002/acm2.13006] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Revised: 05/25/2020] [Accepted: 07/02/2020] [Indexed: 01/14/2023] Open
Abstract
Purpose This study evaluates the clinical use of the RUBY modular QA phantom for linac QA to validate the integrity of IGRT workflows including the congruence of machine isocenter, imaging isocenter, and room lasers. The results have been benchmarked against those obtained with widely used systems. Additionally, the RUBY phantom has been implemented to perform system QA (End‐to‐End testing) from imaging to radiation for IGRT‐based VMAT and stereotactic radiations at an Elekta Synergy linac. Material and Methods The daily check of IGRT workflow was performed using the RUBY phantom, the Penta‐Guide, and the STEEV phantom. Furthermore, Winston–Lutz tests was carried out with the RUBY phantom and a ball‐bearing phantom to determine the offsets and the diameters of the isospheres of gantry, collimator, and couch rotations, with respect to the room lasers and kV‐imaging isocenter. System QA was performed with the RUBY phantom and STEEV phantom for eight VMAT treatment plans. Additionally, the visibility of the embedded objects within these phantoms in the images and the results of CT and MR image fusions were evaluated. Results All systems used for daily QA of IGRT workflows show comparable results. Calculated shifts based on CBCT imaging agree within 1 mm to the expected values. The results of the Winston–Lutz test based on kV imaging (2D planar and CBCT) or room lasers are consistent regardless of the system tested. The point dose values in the RUBY phantom agree to the expected values calculated using algorithms in Masterplan and Monte Carlo engine in Monaco within 3% of the clinical acceptance criteria. Conclusion All the systems evaluated in this study yielded comparable results in terms of linac QA and system QA procedures. A system QA protocol has been derived using the RUBY phantom to check the IGRT‐based VMAT and stereotactic radiations workflow at an Elekta Synergy linac.
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Affiliation(s)
| | - Jana Kretschmer
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
| | - Leonie Brodbek
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany.,Department of Radiation Oncology, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Jutta Meyners
- Radiotherapy Department, Imland Hospital, Rendsburg, Germany
| | - Bjoern Poppe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
| | - Hui Khee Looe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
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11
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Brace OJ, Alhujaili SF, Paino JR, Butler DJ, Wilkinson D, Oborn BM, Rosenfeld AB, Lerch MLF, Petasecca M, Davis JA. Evaluation of the PTW microDiamond in edge-on orientation for dosimetry in small fields. J Appl Clin Med Phys 2020; 21:278-288. [PMID: 32441884 PMCID: PMC7484886 DOI: 10.1002/acm2.12906] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Revised: 03/16/2020] [Accepted: 04/20/2020] [Indexed: 12/11/2022] Open
Abstract
Purpose The PTW microDiamond has an enhanced spatial resolution when operated in an edge‐on orientation but is not typically utilized in this orientation due to the specifications of the IAEA TRS‐483 code of practice for small field dosimetry. In this work the suitability of an edge‐on orientation and advantages over the recommended face‐on orientation will be presented. Methods The PTW microDiamond in both orientations was compared on a Varian TrueBeam linac for: machine output factor (OF), percentage depth dose (PDD), and beam profile measurements from 10 × 10 cm2 to a 0.5 × 0.5 cm2 field size for 6X and 6FFF beam energies in a water tank. A quantification of the stem effect was performed in edge‐on orientation along with tissue to phantom ratio (TPR) measurements. An extensive angular dependence study for the two orientations was also undertaken within two custom PMMA plastic cylindrical phantoms. Results The OF of the PTW microDiamond in both orientations agrees within 1% down to the 2 × 2 cm2 field size. The edge‐on orientation overresponds in the build‐up region but provides improved penumbra and has a maximum observed stem effect of 1%. In the edge‐on orientation there is an angular independent response with a maximum of 2% variation down to a 2 × 2 cm2 field. The PTW microDiamond in edge‐on orientation for TPR measurements agreed to the CC01 ionization chamber within 1% for all field sizes. Conclusions The microDiamond was shown to be suitable for small field dosimetry when operated in edge‐on orientation. When edge‐on, a significantly reduced angular dependence is observed with no significant stem effect, making it a more versatile QA instrument for rotational delivery techniques.
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Affiliation(s)
- Owen J Brace
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
| | - Sultan F Alhujaili
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
| | - Jason R Paino
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
| | - Duncan J Butler
- Australian Radiation Protection and Nuclear Safety Agency (ARPANSA), Yallambie, VIC, UK
| | - Dean Wilkinson
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia.,Illawarra Cancer Care Centre Wollongong Hospital Wollongong, Wollongong, NSW, Australia
| | - Brad M Oborn
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia.,Illawarra Cancer Care Centre Wollongong Hospital Wollongong, Wollongong, NSW, Australia
| | - Anatoly B Rosenfeld
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
| | - Michael L F Lerch
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
| | - Marco Petasecca
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
| | - Jeremy A Davis
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
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12
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Posar JA, Davis J, Large MJ, Basiricò L, Ciavatti A, Fraboni B, Dhez O, Wilkinson D, Sellin PJ, Griffith MJ, Lerch MLF, Rosenfeld A, Petasecca M. Characterization of an organic semiconductor diode for dosimetry in radiotherapy. Med Phys 2020; 47:3658-3668. [PMID: 32395821 DOI: 10.1002/mp.14229] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2020] [Revised: 04/15/2020] [Accepted: 05/01/2020] [Indexed: 12/14/2022] Open
Abstract
PURPOSE The development of novel detectors for dosimetry in advanced radiotherapy modalities requires materials that have a water equivalent response to ionizing radiation such that characterization of radiation beams can be performed without the need for complex calibration procedures and correction factors. Organic semiconductors are potentially an ideal technology in fabricating devices for dosimetry due to tissue equivalence, mechanical flexibility, and relatively cheap manufacturing cost. The response of a commercial organic photodetector (OPD), coupled to a plastic scintillator, to ionizing radiation from a linear accelerator and orthovoltage x-ray tube has been characterized to assess its potential as a dosimeter for radiotherapy. The radiation hardness of the OPD has also been investigated to demonstrate its longevity for such applications. METHODS Radiation hardness measurements were achieved by observing the response of the OPD to the visible spectrum and 70 keV x rays after pre-exposure to 40 kGy of ionizing radiation. The response of a preirradiated OPD to 6-MV photons from a linear accelerator in reference conditions was compared to a nonirradiated OPD with respect to direct and indirect (RP400 plastic scintillator) detection mechanisms. Dose rate dependence of the OPD was measured by varying the surface-to-source distance between 90 and 300 cm. Energy dependence was characterized from 29.5 to 129 keV with an x-ray tube. The percentage depth dose (PDD) curves were measured from 0.5 to 20 cm and compared to an ionization chamber. RESULTS The OPD sensitivity to visible light showed substantial degradation of the broad 450 to 600 nm peak from the donor after irradiation to 40 kGy. After irradiation, the spectral shape has a dominant absorbance peak at 370 nm, as the acceptor better withstood radiation damage. Its response to x rays stabilized to 30% after 35 kGy, with a 0.5% difference between 770 Gy increments. The OPD exhibited reproducible detection of ionizing radiation when coupled with a scintillator. Indirect detection showed a linear response from 25 to 500 cGy and constant response to dose rates from 0.31 Gy/pulse to 3.4 × 10-4 Gy/pulse. However, without the scintillator, response increased by 100% at low dose rates. Energy independence between 100 keV and 1.2 MeV advocates their use as a dosimeter without beam correction factors. A dependence on the scintillator thickness used during a comparison of the PDD to the ionizing chamber was identified. A 1-mm-thick scintillator coupled with the OPD demonstrated the best agreement of ± 3%. CONCLUSIONS The response of OPDs to ionizing radiation has been characterized, showing promising use as a dosimeter when coupled with a plastic scintillator. The mechanisms of charge transport and trapping within organic materials varies for visible and ionizing radiation, due to differing properties for direct and indirect detection mechanisms and observing a substantial decrease in sensitivity to the visible spectrum after 40 kGy. This study proved that OPDs produce a stable response to 6-MV photons, and with a deeper understanding of the charge transport mechanisms due to exposure to ionizing radiation, they are promising candidates as the first flexible, water equivalent, real-time dosimeter.
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Affiliation(s)
- Jessie A Posar
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Jeremy Davis
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Matthew J Large
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Laura Basiricò
- Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, Bologna, 40127, Italy
| | - Andrea Ciavatti
- Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, Bologna, 40127, Italy
| | - Beatrice Fraboni
- Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, Bologna, 40127, Italy
| | - Olivier Dhez
- ISORG, 60 Rue des berges, Parc Polyetc, Immeuble Tramontane, Grenoble, 38000, France
| | - Dean Wilkinson
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.,Illawarra Cancer Care Centre, Wollongong Hospital, Wollongong, NSW, 2500, Australia
| | - Paul J Sellin
- Department of Physics, University of Surrey, Guildford, Surrey, GU2 7XH, UK
| | - Matthew J Griffith
- Priority Research Centre for Organic Electronics, University of Newcastle, Callaghan, NSW, 2308, Australia.,School of Aeronautical, Mechanical and Mechatronic Engineering, University of Sydney, Camperdown, NSW, 2050, Australia
| | - Michael L F Lerch
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Anatoly Rosenfeld
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Marco Petasecca
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia
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13
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Weber C, Kranzer R, Weidner J, Kröninger K, Poppe B, Looe HK, Poppinga D. Small field output correction factors of the microSilicon detector and a deeper understanding of their origin by quantifying perturbation factors. Med Phys 2020; 47:3165-3173. [PMID: 32196683 PMCID: PMC7496769 DOI: 10.1002/mp.14149] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2019] [Revised: 01/31/2020] [Accepted: 03/13/2020] [Indexed: 11/09/2022] Open
Abstract
Purpose The aim of this study is the experimental and Monte Carlo‐based determination of small field correction factors for the unshielded silicon detector microSilicon for a standard linear accelerator as well as the Cyberknife System. In addition, a detailed Monte Carlo analysis has been performed by modifying the detector models stepwise to study the influences of the detector’s components. Methods Small field output correction factors have been determined for the new unshielded silicon diode detector, microSilicon (type 60023, PTW Freiburg, Germany) as well as for the predecessors Diode E (type 60017, PTW Freiburg, Germany) and Diode SRS (type 60018, PTW Freiburg, Germany) for a Varian TrueBeam linear accelerator at 6 MV and a Cyberknife system. For the experimental determination, an Exradin W1 scintillation detector (Standard Imaging, Middleton, USA) has been used as reference. The Monte Carlo simulations have been performed with EGSnrc and phase space files from IAEA as well as detector models according to manufacturer blueprints. To investigate the influence of the detector’s components, the detector models have been modified stepwise. Results The correction factors for the smallest field size investigated at the TrueBeam linear accelerator (equivalent dosimetric square field side length Sclin = 6.3 mm) are 0.983 and 0.939 for the microSilicon and Diode E, respectively. At the Cyberknife system, the correction factors of the microSilicon are 0.967 at the smallest 5‐mm collimator compared to 0.928 for the Diode SRS. Monte Carlo simulations show comparable results from the measurements and literature. Conclusion The microSilicon (type 60023) detector requires less correction than its predecessors, Diode E (type 60017) and Diode SRS (type 60018). The detector housing has been demonstrated to cause the largest perturbation, mainly due to the enhanced density of the epoxy encapsulation surrounding the silicon chip. This density has been rendered more water equivalent in case of the microSilicon detector to minimize the associated perturbation. The sensitive volume itself has been shown not to cause observable field size‐dependent perturbation except for the volume‐averaging effect, where the slightly larger diameter of the sensitive volume of the microSilicon (1.5 mm) is still small at the smallest field size investigated with corrections <2%. The new microSilicon fulfils the 5% correction limit recommended by the TRS 483 for output factor measurements at all conditions investigated in this work.
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Affiliation(s)
- Carolin Weber
- PTW Freiburg, Freiburg, 79115, Germany.,TU Dortmund University, Dortmund, 44227, Germany
| | | | | | | | - Björn Poppe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, 26121, Germany
| | - Hui Khee Looe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, 26121, Germany
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Kaveckyte V, Persson L, Malusek A, Benmakhlouf H, Alm Carlsson G, Carlsson Tedgren Å. Investigation of a synthetic diamond detector response in kilovoltage photon beams. Med Phys 2019; 47:1268-1279. [PMID: 31880809 DOI: 10.1002/mp.13988] [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: 06/03/2019] [Revised: 09/04/2019] [Accepted: 12/01/2019] [Indexed: 12/28/2022] Open
Abstract
PURPOSE An important characteristic of radiation dosimetry detectors is their energy response which consists of absorbed-dose and intrinsic energy responses. The former can be characterized using Monte Carlo (MC) simulations, whereas the latter (i.e., detector signal per absorbed dose to detector) is extracted from experimental data. Such a characterization is especially relevant when detectors are used in nonrelative measurements at a beam quality that differs from the calibration beam quality. Having in mind the possible application of synthetic diamond detectors (microDiamond PTW 60019, Freiburg, Germany) for nonrelative dosimetry of low-energy brachytherapy (BT) beams, we determined their intrinsic and absorbed-dose energy responses in 25-250 kV beams relative to a 60 Co beam, which is usually the reference beam quality for detector calibration in radiotherapy. MATERIAL AND METHODS Three microDiamond detectors and, for comparison, two silicon diodes (PTW 60017) were calibrated in terms of air-kerma free in air in six x-ray beam qualities (from 25 to 250 kV) and in terms of absorbed dose to water in a 60 Co beam at the national metrology laboratory in Sweden. The PENELOPE/penEasy MC radiation transport code was used to calculate the absorbed-dose energy response of the detectors (modeled based on blueprints) relative to air and water depending on calibration conditions. The MC results were used to extract the relative intrinsic energy response of the detectors from the overall energy response. Measurements using an independent setup with a single ophthalmic BEBIG I25.S16 125 I BT seed (effective photon energy of 28 keV) were used as a qualitative check of the extracted intrinsic energy response correction factors. Additionally, the impact of the thickness of the active volume as well as the presence of extra-cameral components on the absorbed-dose energy response of a microDiamond detector was studied using MC simulations. RESULTS The relative intrinsic energy response of the microDiamond detectors was higher by a factor of 2 in 25 and 50 kV beams compared to the 60 Co beam. The variation in the relative intrinsic energy response of silicon diodes was within 10% over the investigated photon energy range. The use of relative intrinsic energy response correction factors improved the agreement among the absorbed dose to water values determined using microDiamond detectors and silicon diodes, as well as with the TG-43 formalism-based calculations for the 125 I seed. MC study of microDiamond detector design features provided a possible explanation for inter-detector response variation at low-energy photon beams by differences in the effective thickness of the active volume. CONCLUSIONS MicroDiamond detectors had a non-negligible variation in the relative intrinsic energy response (factor of 2) which was comparable to that in the absorbed-dose energy response relative to water at low-energy photon beams. Silicon diodes, in contrast, had an absorbed-dose energy dependence on photon energy that varied by a factor of 6, whereas the intrinsic energy dependence on beam quality was within 10%. It is important to decouple these two responses for a full characterization of detector energy response especially when the user and reference beam qualities differ significantly, and MC alone is not enough.
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Affiliation(s)
- Vaiva Kaveckyte
- Radiation Physics, Department of Medical and Health Sciences, Linköping University, SE-581 85, Linköping, Sweden.,Department of Medical Radiation Physics and Nuclear Medicine, Karolinska University Hospital, SE-171 76, Stockholm, Sweden
| | - Linda Persson
- Swedish Radiation Safety Authority, SE-171 16, Stockholm, Sweden
| | - Alexandr Malusek
- Radiation Physics, Department of Medical and Health Sciences, Linköping University, SE-581 85, Linköping, Sweden
| | - Hamza Benmakhlouf
- Department of Medical Radiation Physics and Nuclear Medicine, Karolinska University Hospital, SE-171 76, Stockholm, Sweden
| | - Gudrun Alm Carlsson
- Radiation Physics, Department of Medical and Health Sciences, Linköping University, SE-581 85, Linköping, Sweden
| | - Åsa Carlsson Tedgren
- Radiation Physics, Department of Medical and Health Sciences, Linköping University, SE-581 85, Linköping, Sweden.,Department of Medical Radiation Physics and Nuclear Medicine, Karolinska University Hospital, SE-171 76, Stockholm, Sweden
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15
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Schönfeld AB, Poppinga D, Kranzer R, De Wilde RL, Willborn K, Poppe B, Looe HK. Technical Note: Characterization of the new microSilicon diode detector. Med Phys 2019; 46:4257-4262. [PMID: 31309594 PMCID: PMC6852691 DOI: 10.1002/mp.13710] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Revised: 06/24/2019] [Accepted: 06/24/2019] [Indexed: 12/31/2022] Open
Abstract
Purpose Dosimetric properties of the new microSilicon diode detector (60023) have been studied with focus on application in small‐field dosimetry. The influences of the dimensions of the sensitive volume and the density of the epoxy layer surrounding the silicon chip of microSilicon have been quantified and compared to its predecessor (Diode E 60017) and the microDiamond (60019, all PTW‐Freiburg, Germany). Methods Dose linearity has been studied in the range from 0.01 to 8.55 Gy and dose‐per‐pulse dependence from 0.13 to 0.86 mGy/pulse. The effective point of measurement (EPOM) was determined by comparing measured percentage depth dose curves with a reference curve (Roos chamber). Output ratios were measured for nominal field sizes from 0.5 × 0.5 cm2 to 4 × 4 cm2. The corresponding small‐field output correction factors, k, were derived with a plastic scintillation detector as reference. The lateral dose–response function, K(x), was determined using a slit beam geometry. Results MicroSilicon shows linear dose response (R2 = 1.000) in both low and high dose range up to 8.55 Gy with deviations of only up to 1% within the dose‐per‐pulse values investigated. The EPOM was found to lie (0.7 ± 0.2) mm below the front detector’s surface. The derived k for microSilicon (0.960 at seff = 0.55 cm) is similar to that of microDiamond (0.956), while Diode E requires larger corrections (0.929). This improved behavior of microSilicon in small‐fields is reflected in the slightly wider K(x) compared to Diode E. Furthermore, the amplitude of the negative values in K(x) at the borders of the sensitive volume has been reduced. Conclusions Compared to its predecessor, microSilicon shows improved dosimetric behavior with higher sensitivity and smaller dose‐per‐pulse dependence. Profile measurements demonstrated that microSilicon causes less perturbation in off‐axis measurements. It is especially suitable for the applications in small‐field output factors and profile measurements.
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Affiliation(s)
- Ann-Britt Schönfeld
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
| | | | | | | | - Kay Willborn
- Clinic for Radiation Therapy, Pius Hospital, Oldenburg, Germany
| | - Björn Poppe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
| | - Hui Khee Looe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
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16
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Poppinga D, Kranzer R, Ulrichs AB, Delfs B, Giesen U, Langner F, Poppe B, Looe HK. Three-dimensional characterization of the active volumes of PTW microDiamond, microSilicon, and Diode E dosimetry detectors using a proton microbeam. Med Phys 2019; 46:4241-4245. [PMID: 31292964 PMCID: PMC6851623 DOI: 10.1002/mp.13705] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Revised: 06/28/2019] [Accepted: 06/28/2019] [Indexed: 11/09/2022] Open
Abstract
PURPOSE The purpose of this work is the three-dimensional characterization of the active volumes of commercial solid-state dosimetry detectors. Detailed knowledge of the dimensions of the detector's active volume as well as the detector housing is of particular interest for small-field photon dosimetry. As shown in previous publications from different groups, the design of the detector housing influences the detector signal for small photon fields. Therefore, detailed knowledge of the active volume dimension and the surrounding materials form the basis for accurate Monte Carlo simulations of the detector. METHODS A 10 MeV proton beam focused by the microbeam system of the Physikalisch-Technische Bundesanstalt was used to measure two-dimensional response maps of a synthetic diamond detector (microDiamond, type 60019, PTW Freiburg) and two silicon detectors (microSilicon, type 60023, PTW Freiburg and Diode E, type 60017, PTW Freiburg). In addition, the thickness of the active volume of the new microSilicon was measured using the method developed in a previous study. RESULTS The analysis of the response maps leads to active area of 1.18 mm2 for the Diode E, 1.75 mm2 for the microSilicon, and 3.91 mm2 for the microDiamond detector. The thickness of the active volume of the microSilicon detector was determined to be (17.8 ± 2) µm. CONCLUSIONS This study provides detailed geometrical data of the dosimetric active volume of three different solid-state detector types.
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Affiliation(s)
| | | | - Ann-Britt Ulrichs
- 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
| | - Ulrich Giesen
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
| | - Frank Langner
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
| | - Björn Poppe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
| | - Hui Khee Looe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
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