1
|
Failing T, Hensley FW, Keil B, Zink K. Investigations on the beam quality correction factor for ionization chambers in high-energy brachytherapy dosimetry. Phys Med Biol 2024; 69:165002. [PMID: 39009012 DOI: 10.1088/1361-6560/ad638b] [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: 11/30/2023] [Accepted: 07/15/2024] [Indexed: 07/17/2024]
Abstract
Objective. To enhance the investigations on MC calculated beam quality correction factors of thimble ionization chambers from high-energy brachytherapy sources and to develop reliable reference conditions in source and detector setups in water.Approach. The response of five different ionization chambers from PTW-Freiburg and Standard Imaging was investigated for irradiation by a high dose rate Ir-192 Flexisource in water. For a setup in a Beamscan water phantom, Monte Carlo simulations were performed to calculate correction factors for the chamber readings. After exact positioning of source and detector the absorbed dose rate at the TG-43 reference point at one centimeter nominal distance from the source was measured using these factors and compared to the specification of the calibration certificate. The Monte Carlo calculations were performed using the restricted cema formalism to gain further insight into the chamber response. Calculations were performed for the sensitive volume of the chambers, determined by the methods currently used in investigations of dosimetry in magnetic fields.Main results. Measured dose rates and values from the calibration certificate agreed within the combined uncertainty (k= 2) for all chambers except for one case in which the full air cavity was simulated. The chambers showed a distinct directional dependence. With the restricted cema formalism calculations it was possible to examine volume averaging and energy dependence of the perturbation factors contributing to the beam quality correction factor also differential in energy.Significance. This work determined beam quality correction factors to measure the absorbed dose rate from a brachytherapy source in terms of absorbed dose to water for a variety of ionization chambers. For the accurate dosimetry of brachytherapy sources with ionization chambers it is advisable to use correction factors based on the sensitive volume of the chambers and to take account for the directional dependence of chamber response.
Collapse
Affiliation(s)
- T Failing
- Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences, Gießen, Germany
| | - F W Hensley
- Department for Radiotherapy and Radiooncology, University Medical Center Heidelberg, Heidelberg, Germany
| | - B Keil
- Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences, Gießen, Germany
- Department for Diagnostic and Interventional Radiology, Philipps-University Marburg, Marburg, Germany
- LOEWE Research Cluster for Advanced Medical Physics in Imaging and Therapy (ADMIT), TH Mittelhessen University of Applied Sciences, Giessen, Germany
| | - K Zink
- Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences, Gießen, Germany
- LOEWE Research Cluster for Advanced Medical Physics in Imaging and Therapy (ADMIT), TH Mittelhessen University of Applied Sciences, Giessen, Germany
- Department for Radiotherapy and Radiooncology, University Medical Center Giessen-Marburg, Marburg, Germany
- Marburg Iontherapy Center (MIT), Marburg, Germany
| |
Collapse
|
2
|
Rogers DWO. Reflections on a life with Monte Carlo in Medical Physics. Med Phys 2023. [PMID: 36779658 DOI: 10.1002/mp.16278] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Accepted: 01/31/2023] [Indexed: 02/14/2023] Open
Abstract
The author reminisces about some of his experiences working with Monte Carlo techniques for Medical Physics applications.
Collapse
Affiliation(s)
- David W O Rogers
- Carleton Laboratory for Radiotherapy Physics, Physics Department, Carleton University, Ottawa, Canada
| |
Collapse
|
3
|
Walter AE, DeWerd LA. Feasibility of implementing a megavoltage ionization chamber calibration service at the secondary standards level. Radiat Phys Chem Oxf Engl 1993 2022. [DOI: 10.1016/j.radphyschem.2022.110699] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
|
4
|
Mirzakhanian L, Bassalow R, Zaks D, Huntzinger C, Seuntjens J. IAEA-AAPM TRS-483-based reference dosimetry of the new RefleXion biology-guided radiotherapy (BgRT) machine. Med Phys 2021; 48:1884-1892. [PMID: 33296515 DOI: 10.1002/mp.14631] [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: 07/26/2019] [Revised: 10/10/2020] [Accepted: 11/18/2020] [Indexed: 11/07/2022] Open
Abstract
PURPOSE The purpose of this study is to provide data for the calibration of the recent RefleXion TM biology-guided radiotherapy (BgRT) machine (Hayward, CA, USA) following the International Atomic Energy Agency (IAEA) and the American Association of Physicists in Medicine (AAPM) TRS-483 code of practice (COP) (Palmans et al. International Atomic Energy Agency, Vienna, 2017) and (Mirzakhanian et al. Med Phys, 2020). METHODS In RefleXion BgRT machine, reference dosimetry was performed using two methodologies described in TRS-483 and (Mirzakhanian et al. Med Phys, 2020) In the first approach (Approach 1), the generic beam quality correction factor k Q A , Q 0 f A , f ref was calculated using an accurate Monte Carlo (MC) model of the beam and of six ionization chamber types. The k Q A , Q 0 f A , f ref is a beam quality factor that corrects N D , w , Q 0 f ref (absorbed dose to water calibration coefficient in a calibration beam quality Q 0 ) for the differences between the response of the chamber in the conventional reference calibration field f ref with beam quality Q 0 at the standards laboratory and the response of the chamber in the user's A field f A with beam quality Q A . Field A represents the reference calibration field that does not fulfill msr conditions. In the second approach (Approach 2), a square equivalent field size was determined for field A of 10 × 2 cm 2 and 10 × 3 cm 2 . Knowing the equivalent field size, the beam quality specifier for the hypothetical 10 × 10 cm 2 field size was derived. This was used to calculate the beam quality correction factor analytically for the six chamber types using the TRS-398. (Andreo et al. Int Atom Energy Agency 420, 2001) Here, TRS-398 was used instead of TRS-483 since the beam quality correction values for the chambers used in this study are not tabulated in TRS-483. The accuracy of Approach 2 is studied in comparison to Approach 1. RESULTS Among the chambers, the PTW 31010 had the largest k Q A , Q 0 f A , f ref correction due to the volume averaging effect. The smallest-volume chamber (IBA CC01) had the smallest correction followed by the other microchambers Exradin-A14 and -A14SL. The equivalent square fields sizes were found to be 3.6 cm and 4.8 cm for the 10 × 2 cm 2 and 10 × 3 cm 2 field sizes, respectively. The beam quality correction factors calculated using the two approaches were within 0.27% for all chambers except IBA CC01. The latter chamber has an electrode made of steel and the differences between the correction calculated using the two approaches was the largest, that is, 0.5%. CONCLUSIONS In this study, we provided the k Q A , Q 0 f A , f ref values as a function of the beam quality specifier at the RefleXion BgRT setup ( TPR 20 , 10 ( S ) and % d d ( 10 , S ) x ) for six chamber types. We suggest using the first approach for calibration of the RefleXion BgRT machine. However, if the MC correction is not available for a user's detector, the user can use the second approach for estimating the beam quality correction factor to sufficient accuracy (0.3%) provided the chamber electrode is not made of high Z material.
Collapse
Affiliation(s)
| | - Rostem Bassalow
- RefleXion Medical, 25841 Industrial Blvd, Hayward, California, 94545, USA
| | - Daniel Zaks
- RefleXion Medical, 25841 Industrial Blvd, Hayward, California, 94545, USA
| | - Calvin Huntzinger
- RefleXion Medical, 25841 Industrial Blvd, Hayward, California, 94545, USA
| | - Jan Seuntjens
- Medical Physics Unit, McGill University, Montreal, Quebec, H4A 3J1, Canada
| |
Collapse
|
5
|
Performance characteristics of some cylindrical ion chamber dosimeters in Megavoltage (MV) photon beam according to TRS-398 dosimetry protocol. Radiat Phys Chem Oxf Engl 1993 2021. [DOI: 10.1016/j.radphyschem.2020.109299] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
|
6
|
Bouchard H. Reference dosimetry of modulated and dynamic photon beams. Phys Med Biol 2021; 65:24TR05. [PMID: 33438582 DOI: 10.1088/1361-6560/abc3fb] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In the late 1980s, a new technique was proposed that would revolutionize radiotherapy. Now referred to as intensity-modulated radiotherapy, it is at the core of state-of-the-art photon beam delivery techniques, such as helical tomotherapy and volumetric modulated arc therapy. Despite over two decades of clinical application, there are still no established guidelines on the calibration of dynamic modulated photon beams. In 2008, the IAEA-AAPM work group on nonstandard photon beam dosimetry published a formalism to support the development of a new generation of protocols applicable to nonstandard beam reference dosimetry (Alfonso et al 2008 Med. Phys. 35 5179-86). The recent IAEA Code of Practice TRS-483 was published as a result of this initiative and addresses exclusively small static beams. But the plan-class specific reference calibration route proposed by Alfonso et al (2008 Med. Phys. 35 5179-86) is a change of paradigm that is yet to be implemented in radiotherapy clinics. The main goals of this paper are to provide a literature review on the dosimetry of nonstandard photon beams, including dynamic deliveries, and to discuss anticipated benefits and challenges in a future implementation of the IAEA-AAPM formalism on dynamic photon beams.
Collapse
Affiliation(s)
- Hugo Bouchard
- Département de physique, Université de Montréal, Complexe des sciences, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, Québec H2V 0B3, Canada. Centre de recherche du Centre hospitalier de l'Université de Montréal, 900 Rue Saint-Denis, Montréal, Québec H2X 0A9, Canada. Département de radio-oncologie, Centre hospitalier de l'Université de Montréal (CHUM), 1051 Rue Sanguinet, Montréal, Québec H2X 3E4, Canada
| |
Collapse
|
7
|
Czarnecki D, Zink K, Pimpinella M, Borbinha J, Teles P, Pinto M. Monte Carlo calculation of quality correction factors based on air kerma and absorbed dose to water in medium energy x-ray beams. Phys Med Biol 2020; 65:245042. [PMID: 33120372 DOI: 10.1088/1361-6560/abc5c9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Clinical dosimetry is typically performed using ion chambers calibrated in terms of absorbed dose to water. As primary measurement standards for this quantity for low and medium energy x-rays are available only since a few years, most dosimetry protocols for this photon energy range are still based on air kerma calibration. For that reason, data for beam quality correction factors [Formula: see text], necessary for the application of dose to water based protocols, are scarce in literature. Currently the international IAEA TRS-398 Code of Practice is under revision and new [Formula: see text] factors for a large number of ion chambers will be introduced in the update of this protocol. Several international groups provided the IAEA with experimental and Monte Carlo based data for this revision. Within the European Community the EURAMET 16NRM03 RTNORM project was initiated for that purpose. In the present study, Monte Carlo based results for the beam quality correction factors in medium energy x-ray beams for six ion chambers applying different Monte Carlo codes are presented. Additionally, the perturbation factor p Q , necessary for the calculation of dose to water from an air kerma calibration coefficient, was determined. The beam quality correction factor [Formula: see text] for the chambers varied in the investigated energy range by about 4%-5%, and for five out of six chambers the data could be fitted by a simple logarithmic function, if the half-value-layer was used as the beam quality specifier. Corresponding data using different Monte Carlo codes for the same ion chamber agreed within 0.5%. For the perturbation factor p Q , the data did not obey a comparable simple relationship with the beam quality specifier. The variation of p Q for all ion chambers was in the range of 3%-4%. Compared to recently published data, our p Q data is around 1% larger, although the same Monte Carlo code has been used. Compared to the latest experimental data, there are even deviations in the range of 2%.
Collapse
Affiliation(s)
- Damian Czarnecki
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen (THM), Giessen, Germany
| | | | | | | | | | | |
Collapse
|
8
|
Andreo P, Burns DT, Kapsch RP, McEwen M, Vatnitsky S, Andersen CE, Ballester F, Borbinha J, Delaunay F, Francescon P, Hanlon MD, Mirzakhanian L, Muir B, Ojala J, Oliver CP, Pimpinella M, Pinto M, de Prez LA, Seuntjens J, Sommier L, Teles P, Tikkanen J, Vijande J, Zink K. Determination of consensus k Q values for megavoltage photon beams for the update of IAEA TRS-398. ACTA ACUST UNITED AC 2020; 65:095011. [DOI: 10.1088/1361-6560/ab807b] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
9
|
Tikkanen J, Zink K, Pimpinella M, Teles P, Borbinha J, Ojala J, Siiskonen T, Gomà C, Pinto M. Calculated beam quality correction factors for ionization chambers in MV photon beams. Phys Med Biol 2020; 65:075003. [PMID: 31995531 DOI: 10.1088/1361-6560/ab7107] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The beam quality correction factor, [Formula: see text], which corrects for the difference in the ionization chamber response between the reference and clinical beam quality, is an integral part of radiation therapy dosimetry. The uncertainty of [Formula: see text] is one of the most significant sources of uncertainty in the dose determination. To improve the accuracy of available [Formula: see text] data, four partners calculated [Formula: see text] factors for 10 ionization chamber models in linear accelerator beams with accelerator voltages ranging from 6 MV to 25 MV, including flattening-filter-free (FFF) beams. The software used in the calculations were EGSnrc and PENELOPE, and the ICRU report 90 cross section data for water and graphite were included in the simulations. Volume averaging correction factors were calculated to correct for the dose averaging in the chamber cavities. A comparison calculation between partners showed a good agreement, as did comparison with literature. The [Formula: see text] values from TRS-398 were higher than our values for each chamber where data was available. The [Formula: see text] values for the FFF beams did not follow the same [Formula: see text], [Formula: see text] relation as beams with flattening filter (values for 10 MV FFF beams were below fits made to other data on average by 0.3%), although our FFF sources were only for Varian linacs.
Collapse
Affiliation(s)
- J Tikkanen
- Radiation and Nuclear Safety Authority (STUK), Helsinki, Finland. Helsinki Institute of Physics, University of Helsinki, Helsinki, Finland
| | | | | | | | | | | | | | | | | |
Collapse
|
10
|
Renaud J, Palmans H, Sarfehnia A, Seuntjens J. Absorbed dose calorimetry. ACTA ACUST UNITED AC 2020; 65:05TR02. [DOI: 10.1088/1361-6560/ab4f29] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
|
11
|
Baumann K, Horst F, Zink K, Gomà C. Comparison of penh, fluka, and Geant4/topas for absorbed dose calculations in air cavities representing ionization chambers in high-energy photon and proton beams. Med Phys 2019; 46:4639-4653. [PMID: 31350915 PMCID: PMC6851981 DOI: 10.1002/mp.13737] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 07/01/2019] [Accepted: 07/16/2019] [Indexed: 12/16/2022] Open
Abstract
PURPOSE The purpose of this work is to analyze whether the Monte Carlo codes penh, fluka, and geant4/topas are suitable to calculate absorbed doses andf Q / f Q 0 ratios in therapeutic high-energy photon and proton beams. METHODS We used penh, fluka, geant4/topas, and egsnrc to calculate the absorbed dose to water in a reference water cavity and the absorbed dose to air in two air cavities representative of a plane-parallel and a cylindrical ionization chamber in a 1.25 MeV photon beam and a 150 MeV proton beam - egsnrc was only used for the photon beam calculations. The physics and transport settings in each code were adjusted to simulate the particle transport as detailed as reasonably possible. From these absorbed doses, f Q 0 factors, f Q factors, andf Q / f Q 0 ratios (which are the basis of Monte Carlo calculated beam quality correction factors k Q , Q 0 ) were calculated and compared between the codes. Additionally, we calculated the spectra of primary particles and secondary electrons in the reference water cavity, as well as the integrated depth-dose curve of 150 MeV protons in water. RESULTS The absorbed doses agreed within 1.4% or better between the individual codes for both the photon and proton simulations. The f Q 0 and f Q factors agreed within 0.5% or better for the individual codes for both beam qualities. The resultingf Q / f Q 0 ratios for 150 MeV protons agreed within 0.7% or better. For the 1.25 MeV photon beam, the spectra of photons and secondary electrons agreed almost perfectly. For the 150 MeV proton simulation, we observed differences in the spectra of secondary protons whereas the spectra of primary protons and low-energy delta electrons also agreed almost perfectly. The first 2 mm of the entrance channel of the 150 MeV proton Bragg curve agreed almost perfectly while for greater depths, the differences in the integrated dose were up to 1.5%. CONCLUSION penh, fluka, and geant4/topas are capable of calculating beam quality correction factors in proton beams. The differences in the f Q 0 and f Q factors between the codes are 0.5% at maximum. The differences in thef Q / f Q 0 ratios are 0.7% at maximum.
Collapse
Affiliation(s)
- Kilian‐Simon Baumann
- Department of Radiotherapy and RadiooncologyUniversity Medical Center Giessen‐MarburgMarburgGermany
- Institute of Medical Physics and Radiation ProtectionUniversity of Applied SciencesGiessenGermany
| | - Felix Horst
- Institute of Medical Physics and Radiation ProtectionUniversity of Applied SciencesGiessenGermany
- GSI Helmholtzzentrum für SchwerionenforschungDarmstadtGermany
| | - Klemens Zink
- Department of Radiotherapy and RadiooncologyUniversity Medical Center Giessen‐MarburgMarburgGermany
- Institute of Medical Physics and Radiation ProtectionUniversity of Applied SciencesGiessenGermany
- Frankfurt Institute for Advanced Studies (FIAS)FrankfurtGermany
| | - Carles Gomà
- Department of Oncology, Laboratory of Experimental RadiotherapyKU LeuvenLeuvenBelgium
| |
Collapse
|
12
|
Bourgouin A, Cojocaru C, Ross C, McEwen M. Determination of
W
air
in high‐energy electron beams using graphite detectors. Med Phys 2019; 46:5195-5208. [DOI: 10.1002/mp.13772] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2019] [Revised: 07/09/2019] [Accepted: 08/01/2019] [Indexed: 11/09/2022] Open
Affiliation(s)
- Alexandra Bourgouin
- Department of Physics Carleton University Ottawa ON K1S 5B6 Canada
- Ionizing Radiation Standards National Research Council of Canada Ottawa ON K1A 0R6Canada
| | - Claudiu Cojocaru
- Ionizing Radiation Standards National Research Council of Canada Ottawa ON K1A 0R6Canada
| | - Carl Ross
- Ionizing Radiation Standards National Research Council of Canada Ottawa ON K1A 0R6Canada
| | - Malcolm McEwen
- Ionizing Radiation Standards National Research Council of Canada Ottawa ON K1A 0R6Canada
| |
Collapse
|
13
|
Hartmann GH, Zink K. A Monte Carlo study on the PTW 60019 microDiamond detector. Med Phys 2019; 46:5159-5172. [DOI: 10.1002/mp.13721] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Revised: 07/02/2019] [Accepted: 07/03/2019] [Indexed: 11/12/2022] Open
Affiliation(s)
| | - Klemens Zink
- Institute of Medical Physics and Radiation Protection (IMPS) University of Applied Sciences Giessen 35390Giessen Germany
- Department for Radiotherapy and Radiooncology University Medical Center Giessen‐Marburg 35043Marburg Germany
- Frankfurt Institute for Advanced Studies (FIAS), Goethe‐University 60438Frankfurt Germany
| |
Collapse
|
14
|
Rahimi SA, Hashemi B, Mahdavi SR. Estimation of Dosimetric Parameters based on K NR and K NCSF Correction Factors for Small Field Radiation Therapy at 6 and 18 MV Linac Energies using Monte Carlo Simulation Methods. J Biomed Phys Eng 2019; 9:37-50. [PMID: 30881933 PMCID: PMC6409371] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Accepted: 12/24/2016] [Indexed: 06/09/2023]
Abstract
BACKGROUND Estimating dosimetric parameters for small fields under non-reference conditions leads to significant errors if done based on conventional protocols used for large fields in reference conditions. Hence, further correction factors have been introduced to take into account the influence of spectral quality changes when various detectors are used in non-reference conditions at different depths and field sizes. OBJECTIVE Determining correction factors (KNR and KNCSF) recommended recently for small field dosimetry formalism by American Association of Physicists in Medicine (AAPM) for different detectors at 6 and 18 MV photon beams. METHODS EGSnrc Monte Carlo code was used to calculate the doses measured with different detectors located in a slab phantom and the recommended KNR and KNCSF correction factors for various circular small field sizes ranging from 5-30 mm diameters. KNR and KNCSF correction factors were determined for different active detectors (a pinpoint chamber, EDP-20 and EDP-10 diodes) in a homogeneous phantom irradiated to 6 and 18 MV photon beams of a Varian linac (2100C/D). RESULTS KNR correction factor estimated for the highest small circular field size of 30 mm diameter for the pinpoint chamber, EDP-20 and EDP-10 diodes were 0.993, 1.020 and 1.054; and 0.992, 1.054 and 1.005 for the 6 and 18 MV beams, respectively. The KNCSF correction factor estimated for the lowest circular field size of 5 mm for the pinpoint chamber, EDP-20 and EDP-10 diodes were 0.994, 1.023, and 1.040; and 1.000, 1.014, and 1.022 for the 6 and 18 MV photon beams, respectively. CONCLUSION Comparing the results obtained for the detectors used in this study reveals that the unshielded diodes (EDP-20 and EDP-10) can confidently be recommended for small field dosimetry as their correction factors (KNR and KNCSF) was close to 1.0 for all small field sizes investigated and are mainly independent from the electron beam spot size.
Collapse
Affiliation(s)
- S A Rahimi
- PhD Candidate, Department of Medical Physics, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran
- Assistant Professor, Department of Basic Sciences, Faculty of Health Sciences, Mazandaran University of Medical Sciences, Sari, Iran
| | - B Hashemi
- Associate Professor, Department of Medical Physics, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran
| | - S R Mahdavi
- Associate Professor, Department of Medical Physics, Faculty of Medicine, Iran University of Medical Sciences, Tehran, Iran
| |
Collapse
|
15
|
Francescon P, Kilby W, Satariano N, Orlandi C, Elshamndy S. The impact of inter-unit variations on small field dosimetry correction factors, with application to the CyberKnife system. Phys Med Biol 2019; 64:035006. [PMID: 30561377 DOI: 10.1088/1361-6560/aaf971] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Small field dosimetry correction factors are usually determined from calculations or measurements using one specific example of a treatment system. The sensitivity of the corrections to inter-unit variation is therefore not evaluated. We propose two methods for this evaluation that could be applied to any system. We use them to assess the variability in [Formula: see text] for the CyberKnife System caused by design changes between pre-M6 and M6 versions, and to the variability in [Formula: see text] and [Formula: see text] resulting from measured beam-data variations across 139 units. We also perform measurements to investigate the differences in [Formula: see text] reported for microchambers in a CyberKnife-specific study versus TRS-483. The results show that [Formula: see text] is smaller for the M6 version than pre-M6 versions by 0.4% for a Farmer chamber, and 0.1% for shorter chambers. The presence or absence of a lead filter within the treatment head had no significant impact on [Formula: see text]. The beam-data analysis showed inter-unit variations in [Formula: see text] of ±0.8% (2 s.d.) for Farmer chambers and ⩽ ±0.5% for shorter cavities (<10 mm) pre-M6, reducing to 0.4% and 0.2% respectively with M6. Inter-unit [Formula: see text] variations for microDiamond and microchambers were ⩽ ±1% at 5 mm field size, except for microchambers with axis perpendicular to the beam where this was > ±2%. Differences of up to 9% were confirmed between Output Factors measured using a microchamber and corrected using TRS-483 [Formula: see text], and a consensus dataset for the same treatment unit determined using multiple detectors and Monte Carlo simulation. A set of practical recommendations for small field dosimetry with the CyberKnife System is derived from these results.
Collapse
Affiliation(s)
- P Francescon
- Department of Radiation Oncology, Ospedale Di Vicenza, I-36100 Vicenza, Italy
| | | | | | | | | |
Collapse
|
16
|
Reynolds M, St-Aubin J. Monte Carlo determination of k Q and k Qmsr values for the exradin A26 ionisation chamber for the Varian TrueBeam. Phys Med Biol 2018; 63:195006. [PMID: 30207987 DOI: 10.1088/1361-6560/aae0e9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We have calculated conversion factors, k Q for the A26 micro ionisation chamber along with machine specific reference beam quality factors, k Qmsr, for a number of field sizes and beam qualities for the Varian TrueBeam accelerator. The A12 ionisation chamber was simulated alongside the A26, so as to validate against known literature values. Both ionisation chambers were modelled from manufacturer data sheets and schematics. The egs_chamber Monte Carlo user code was used to simulate each absorbed dose relevant to the beam quality conversion factors k Q and k Qmsr. Tabulated spectra for beam energies of 4 through 25 MV were used in the k Q calculations for both investigated chambers. Varian TrueBeam phase space files for 6 MV flattened as well as 6 and 10 MV unflattened beams were used in the simulations of the A26 chamber in field sizes from 2 × 2 cm square to 20 × 20 cm square in order to determine k Qmsr values. The PDD(10)x values of the tabulated spectra were found to be within variation between studies, with an average deviance of 0.4% from one prior study. The simulated A12 k Q values matched the accepted literature values with an average variation of <0.1%. The A26 k Q values match the manufacturer provided values to within 0.5%. For all investigated field sizes the k Qmsr values are within 0.006 of unity. There is no published data for this chamber for a direct comparison, but there is similarity between these results and results from other chambers regularly used in similar circumstances. Furthermore, the agreement of the simulated k Q values to knowns, and the agreement of the PDD(10)x factors would suggest the correctness and accuracy of the study.
Collapse
Affiliation(s)
- M Reynolds
- Department of Oncology, Medical Physics Division, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada. Author to whom correspondence should be addressed
| | | |
Collapse
|
17
|
Czarnecki D, Poppe B, Zink K. Impact of new ICRU Report 90 recommendations on calculated correction factors for reference dosimetry. Phys Med Biol 2018; 63:155015. [PMID: 29974869 DOI: 10.1088/1361-6560/aad148] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In 2016 the ICRU published a new report dealing with key data for ionizing radiation dosimetry (ICRU Report 90). New recommendations have been made for the mean excitation energies I for air, graphite and liquid water as well as for the graphite density to use when evaluating the density effect. In addition, the ICRU Report 90 discusses renormalized photoelectric cross sections, but refuses to give a recommendation on the use of renormalization factors. However, the Consultative Committee for Ionizing Radiation recommends to use renormalized photoeffect cross sections. Goal of the present work is to evaluate the impact of these new recommendations on clinical reference dosimetry for high energy photon and electron beams. The beam quality correction factor k Q was calculated by Monte Carlo simulations for compact and parallel plate ionization chambers. In case of photons seven phase space files from clinical accelerators and twelve spectra taken from literature from 4 MV to 24 MV and additionally a 60Co source were applied. As electron source thirteen electron spectra available in literature were used in the range of 4 MeV-21 MeV. The new ICRU recommendations have a small impact on Monte Carlo calculated k Q values for the chosen ionization chambers in the range of 0.1%-0.35% only-the difference increases for higher photon energies. The impact of the ICRU Report 90 recommendations on Monte Carlo calculated stopping power ratios s w,a , perturbation factors p and beam quality correction factors k Q was investigated and confirmed a decrese of s w,a by a fraction of a percent for photon and electron beams. This study indicates that the impact of the new ICRU recommendation is within 0.35%. The determined deviations should be taken into account, when widely published Monte Carlo calculated values are examined.
Collapse
Affiliation(s)
- Damian Czarnecki
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen, Giessen, Germany. University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
| | | | | |
Collapse
|
18
|
Mainegra-Hing E, Muir BR. On the impact of ICRU report 90 recommendations on k Q factors for high-energy photon beams. Med Phys 2018; 45:3904-3908. [PMID: 29862534 DOI: 10.1002/mp.13027] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Revised: 05/04/2018] [Accepted: 05/28/2018] [Indexed: 02/28/2024] Open
Abstract
PURPOSE To assess the impact of the ICRU report 90 recommendations on the beam-quality conversion factor, kQ , used for clinical reference dosimetry of megavoltage linac photon beams. METHODS The absorbed dose to water and the absorbed dose to the air in ionization chambers representative of those typically used for linac photon reference dosimetry are calculated at the reference depth in a water phantom using Monte Carlo simulations. Depth-dose calculations in water are also performed to investigate changes in beam quality specifiers. The calculations are performed in a cobalt-60 beam and MV photon beams with nominal energy between 6 MV and 25 MV using the EGSnrc simulation toolkit. Inputs to the calculations use stopping-power data for graphite and water from the original ICRU-37 report and the new proposed values from the recently published ICRU-90 report. Calculated kQ factors are compared using the two different recommendations for key dosimetry data and measured kQ factors. RESULTS Less than about 0.1% effects from ICRU-90 recommendations on the beam quality specifiers, the photon component of the percentage depth-dose at 10 cm, %dd(10)x , and the tissue-phantom ratio at 20 cm and 10 cm, TPR1020, are observed. Although using different recommendations for key dosimetric data impact water-to-air stopping-power ratios and ion chamber perturbation corrections by up to 0.54% and 0.40%, respectively, we observe little difference (≤0.14%) in calculated kQ factors. This is contradictory to the predictions in ICRU-90 that suggest differences up to 0.5% in high-energy photon beams. A slightly better agreement with experimental values is obtained when using ICRU-90 recommendations. CONCLUSION Users of the addendum to the TG-51 protocol for reference dosimetry of high-energy photon beams, which recommends Monte Carlo calculated kQ factors, can rest assured that the recommendations of ICRU report 90 on basic data have little impact on this central dosimetric parameter.
Collapse
Affiliation(s)
- Ernesto Mainegra-Hing
- Measurement Science and Standards, National Research Council of Canada, Ottawa, ON, K1A 0R6, Canada
| | - Bryan R Muir
- Measurement Science and Standards, National Research Council of Canada, Ottawa, ON, K1A 0R6, Canada
| |
Collapse
|
19
|
Malkov VN, Rogers DWO. Monte Carlo study of ionization chamber magnetic field correction factors as a function of angle and beam quality. Med Phys 2018; 45:908-925. [DOI: 10.1002/mp.12716] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Revised: 10/31/2017] [Accepted: 11/25/2017] [Indexed: 11/08/2022] Open
Affiliation(s)
- Victor N. Malkov
- Carleton Laboratory for Radiotherapy Physics; Physics Dept; Carleton University; Ottawa ON Canada
| | - D. W. O. Rogers
- Carleton Laboratory for Radiotherapy Physics; Physics Dept; Carleton University; Ottawa ON Canada
| |
Collapse
|
20
|
Muir BR, McEwen MR. Technical Note: On the use of cylindrical ionization chambers for electron beam reference dosimetry. Med Phys 2017; 44:6641-6646. [PMID: 28913919 DOI: 10.1002/mp.12582] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Revised: 07/26/2017] [Accepted: 08/31/2017] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To investigate the use of cylindrical chambers for electron beam dosimetry independent of energy by studying the variability of relative ion chamber perturbation corrections, one of the main concerns for electron beam dosimetry with cylindrical chambers. METHODS Measurements are made with sets of cylindrical and plane-parallel reference-class chambers as a function of depth in water in 8 MeV and 18 MeV electron beams. The ratio of chamber readings for similar chambers is normalized in a high-energy electron beam and can be thought of as relative perturbation corrections. Data are plotted as a function of mean electron energy at depth for a range of depths close to the phantom surface to R80 , the depth at which the ionization falls to 80% of its maximum value. Additional, similar measurements are made in a Virtual Water® phantom with cylindrical chambers at the reference depth in a 4 MeV electron beam. RESULTS The variability of relative ion chamber perturbation corrections for nominally identical cylindrical Farmer-type chambers is found to be less than 0.4%, no worse than plane-parallel chambers with similar specifications. CONCLUSIONS This work discusses several issues related to the use of plane-parallel ion chambers and suggests that reference-class cylindrical chambers may be appropriate for reference dosimetry of all electron beams. This would simplify the reference dosimetry procedure and improve accuracy of beam calibration.
Collapse
Affiliation(s)
- Bryan R Muir
- Measurement Science and Standards, National Research Council of Canada, Ottawa, ON, K1A 0R6, Canada
| | - Malcolm R McEwen
- Measurement Science and Standards, National Research Council of Canada, Ottawa, ON, K1A 0R6, Canada
| |
Collapse
|
21
|
Zoros E, Moutsatsos A, Pappas EP, Georgiou E, Kollias G, Karaiskos P, Pantelis E. Monte Carlo and experimental determination of correction factors for gamma knife perfexion small field dosimetry measurements. Phys Med Biol 2017; 62:7532-7555. [PMID: 28796643 DOI: 10.1088/1361-6560/aa8590] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Detector-, field size- and machine-specific correction factors are required for precise dosimetry measurements in small and non-standard photon fields. In this work, Monte Carlo (MC) simulation techniques were used to calculate the [Formula: see text] and [Formula: see text] correction factors for a series of ionization chambers, a synthetic microDiamond and diode dosimeters, used for reference and/or output factor (OF) measurements in the Gamma Knife Perfexion photon fields. Calculations were performed for the solid water (SW) and ABS plastic phantoms, as well as for a water phantom of the same geometry. MC calculations for the [Formula: see text] correction factors in SW were compared against corresponding experimental results for a subset of ionization chambers and diode detectors. Reference experimental OF data were obtained through the weighted average of corresponding measurements using TLDs, EBT-2 films and alanine pellets. [Formula: see text] values close to unity (within 1%) were calculated for most of ionization chambers in water. Greater corrections of up to 6.0% were observed for chambers with relatively large air-cavity dimensions and steel central electrode. A phantom correction of 1.006 and 1.024 (breaking down to 1.014 from the ABS sphere and 1.010 from the accompanying ABS phantom adapter) were calculated for the SW and ABS phantoms, respectively, adding up to [Formula: see text] corrections in water. Both measurements and MC calculations for the diode and microDiamond detectors resulted in lower than unit [Formula: see text] correction factors, due to their denser sensitive volume and encapsulation materials. In comparison, higher than unit [Formula: see text] results for the ionization chambers suggested field size depended dose underestimations (being significant for the 4 mm field), with magnitude depending on the combination of contradicting phenomena associated with volume averaging and electron fluence perturbations. Finally, the presence of 0.5 mm air-gap between the diodes' frontal surface and their phantom-inserts may considerably influence OF measurements, reaching 4.6% for the Razor diode.
Collapse
Affiliation(s)
- E Zoros
- Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, 75 Mikras Asias, 115 27 Athens, Greece
| | | | | | | | | | | | | |
Collapse
|
22
|
Muir BR, Cojocaru CD, McEwen MR, Ross CK. Electron beam water calorimetry measurements to obtain beam quality conversion factors. Med Phys 2017; 44:5433-5444. [DOI: 10.1002/mp.12463] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 06/20/2017] [Accepted: 07/02/2017] [Indexed: 11/06/2022] Open
Affiliation(s)
- Bryan R. Muir
- Measurement Science and Standards; National Research Council of Canada; Ottawa ON K1A 0R6 Canada
| | - Claudiu D. Cojocaru
- Measurement Science and Standards; National Research Council of Canada; Ottawa ON K1A 0R6 Canada
| | - Malcolm R. McEwen
- Measurement Science and Standards; National Research Council of Canada; Ottawa ON K1A 0R6 Canada
| | - Carl K. Ross
- Measurement Science and Standards; National Research Council of Canada; Ottawa ON K1A 0R6 Canada
| |
Collapse
|
23
|
Sorriaux J, Testa M, Paganetti H, Bertrand D, Lee JA, Palmans H, Vynckier S, Sterpin E. Consistency in quality correction factors for ionization chamber dosimetry in scanned proton beam therapy. Med Phys 2017; 44:4919-4927. [DOI: 10.1002/mp.12434] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Revised: 05/22/2017] [Accepted: 06/08/2017] [Indexed: 11/09/2022] Open
Affiliation(s)
- Jefferson Sorriaux
- Center of Molecular Imaging, Radiotherapy and Oncology; Institut de Recherche Expérimentale et Clinique; Université catholique de Louvain; Avenue Hippocrate 54 1200 Brussels Belgium
- ICTEAM Institute; Université catholique de Louvain; Chemin du Cyclotron 6 1348 Louvain-la-Neuve Belgium
| | - Mauro Testa
- Department of Radiation Convergence Engineering; Yonsei University; Wonju 220-710 Korea
| | - Harald Paganetti
- Department of Radiation Oncology; Massachusetts General Hospital; Harvard Medical School; Boston MA 02114 USA
| | - Damien Bertrand
- Ion Beam Applications S.A; Chemin du Cyclotron 3 1348 Louvain-la-Neuve Belgium
| | - John Aldo Lee
- Center of Molecular Imaging, Radiotherapy and Oncology; Institut de Recherche Expérimentale et Clinique; Université catholique de Louvain; Avenue Hippocrate 54 1200 Brussels Belgium
- ICTEAM Institute; Université catholique de Louvain; Chemin du Cyclotron 6 1348 Louvain-la-Neuve Belgium
| | - Hugo Palmans
- Medical Physics Department; EBG MedAustron GmbH; Wiener Neustadt A-2700 Austria
- Acoustics and Ionising Radiation Division; National Physical Laboratory; Teddington TW11 OLW UK
| | - Stefaan Vynckier
- Département de Radiothérapie; Cliniques Universitaires Saint-Luc; Avenue Hippocrate 54 1200 Brussels Belgium
| | - Edmond Sterpin
- Center of Molecular Imaging, Radiotherapy and Oncology; Institut de Recherche Expérimentale et Clinique; Université catholique de Louvain; Avenue Hippocrate 54 1200 Brussels Belgium
- Department of Oncology; Laboratory of Experimental Radiotherapy; Katholieke Universiteit Leuven; O&N Herestraat 49 - box 818 3000 Leuven Belgium
| |
Collapse
|
24
|
Malkov VN, Rogers DWO. Sensitive volume effects on Monte Carlo calculated ion chamber response in magnetic fields. Med Phys 2017. [PMID: 28636763 DOI: 10.1002/mp.12421] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
PURPOSE The development of magnetic resonance-guided radiation therapy (MRgRT) necessitates accurate Monte Carlo (MC) models of ion chambers for computing ion chamber corrections to compensate for the presence of the magnetic field. This study evaluates the sensitivity of the ion chamber dose response in a magnetic field on the collection volume used in the MC simulation. METHODS The EGSnrc system's egs_chamber application is used with a recently developed and validated magnetic field transport code. The calculated dose to the sensitive volume of the chamber per unit incident photon fluence, normalized to that at 0 T, is evaluated as a function of magnetic field for the PTW 30013, PTW 31006, PTW 31010, Exradin A12S, and Exradin A1SL chambers. The sensitive region is varied by excluding the volume corresponding to either 0, 0.5, or 1 mm of distance away from the stem. The photon field, magnetic field, and ion chamber are all oriented perpendicular to each other as in the majority of published experimental works. RESULTS The calculations for a Co-60 source demonstrate that variations from the 0 mm simulations are on the order of several percent with a maximum deviation, occurring at 0.5 T, of 1.75 ± 0.03% and 3.39 ± 0.06% for the 0.5 mm or 1 mm simulations, respectively, for a 0.057 cm3 A1SL chamber. Larger volume chambers showed smaller, but still non-negligible, variations. Simulations of the A1SL chamber with a 7 MV photon source, corresponding to the Elekta MR-linac machine, demonstrate that the effect is slightly reduced but still persists with a maximum deviation of 1.97 ± 0.08% for the 1 mm reduction. CONCLUSIONS Usually, the geometric sensitive volume of the ion chamber is used in MC calculation as a substitute for the potentially unknown, smaller, true collection volume (governed by the complex electric field distribution inside the chamber). The calculations in this study demonstrate that even a small variation in simulated volume can lead to fairly large variations in the MC calculated ion chamber response in a magnetic field. This is an important effect that must be addressed to ensure proper calibration of MRgRT machines using MC ion chamber correction factors. This effect may play a role, even where there is no magnetic field, in small-field dosimetry when volume averaging effect are important.
Collapse
Affiliation(s)
- Victor N Malkov
- Department of Physics, Carleton Laboratory for Radiotherapy Physics, Carleton University, Ottawa, ON, Canada
| | - D W O Rogers
- Department of Physics, Carleton Laboratory for Radiotherapy Physics, Carleton University, Ottawa, ON, Canada
| |
Collapse
|
25
|
Czarnecki D, Poppe B, Zink K. Monte Carlo-based investigations on the impact of removing the flattening filter on beam quality specifiers for photon beam dosimetry. Med Phys 2017; 44:2569-2580. [DOI: 10.1002/mp.12252] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Revised: 03/13/2017] [Accepted: 03/21/2017] [Indexed: 01/07/2023] Open
Affiliation(s)
- Damian Czarnecki
- Institute of Medical Physics and Radiation Protection; University of Applied Sciences Giessen; Wiesenstrasse 14 Giessen D-35390 Germany
- 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
| | - Klemens Zink
- Institute of Medical Physics and Radiation Protection; University of Applied Sciences Giessen; Giessen D-35390 Germany
- Department of Radiotherapy and Radiation Oncology; University Medical Center Giessen and Marburg; Marburg D-35043 Germany
- Frankfurt Institute for Advanced Studies (FIAS); Ruth-Moufang-Straße 1; 60438 Frankfurt am Main Germany
| |
Collapse
|
26
|
Osinga-Blättermann JM, Brons S, Greilich S, Jäkel O, Krauss A. Direct determination of k Q for Farmer-type ionization chambers in a clinical scanned carbon ion beam using water calorimetry. Phys Med Biol 2017; 62:2033-2054. [DOI: 10.1088/1361-6560/aa5bac] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
27
|
Bouchard H, Kamio Y, Palmans H, Seuntjens J, Duane S. Detector dose response in megavoltage small photon beams. II. Pencil beam perturbation effects. Med Phys 2016; 42:6048-61. [PMID: 26429280 DOI: 10.1118/1.4930798] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To quantify detector perturbation effects in megavoltage small photon fields and support the theoretical explanation on the nature of quality correction factors in these conditions. METHODS In this second paper, a modern approach to radiation dosimetry is defined for any detector and applied to small photon fields. Fano's theorem is adapted in the form of a cavity theory and applied in the context of nonstandard beams to express four main effects in the form of perturbation factors. The pencil-beam decomposition method is detailed and adapted to the calculation of perturbation factors and quality correction factors. The approach defines a perturbation function which, for a given field size or beam modulation, entirely determines these dosimetric factors. Monte Carlo calculations are performed in different cavity sizes for different detection materials, electron densities, and extracameral components. RESULTS Perturbation effects are detailed with calculated perturbation functions, showing the relative magnitude of the effects as well as the geometrical extent to which collimating or modulating the beam impacts the dosimetric factors. The existence of a perturbation zone around the detector cavity is demonstrated and the approach is discussed and linked to previous approaches in the literature to determine critical field sizes. CONCLUSIONS Monte Carlo simulations are valuable to describe pencil beam perturbation effects and detail the nature of dosimetric factors in megavoltage small photon fields. In practice, it is shown that dosimetric factors could be avoided if the field size remains larger than the detector perturbation zone. However, given a detector and beam quality, a full account for the detector geometry is necessary to determine critical field sizes.
Collapse
Affiliation(s)
- Hugo Bouchard
- Acoustics and Ionising Radiation Team, National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United Kingdom
| | - Yuji Kamio
- Centre hospitalier de l'Université de Montréal (CHUM), 1560 Sherbrooke Est, Montréal, Québec H2L 4M1, Canada
| | - Hugo Palmans
- Acoustics and Ionising Radiation Team, National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United KingdomMedical Physics, EBG MedAustron GmbH, Wiener Neustadt A-2700, Austria
| | - Jan Seuntjens
- Medical Physics Unit, McGill University, Montréal, Québec H3G 1A4, Canada
| | - Simon Duane
- Acoustics and Ionising Radiation Team, National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United Kingdom
| |
Collapse
|
28
|
Gersh JA, Willett B. Determination of kQ using MLC-collimated rectangular fields for absolute dosimetry of the CyberKnife. J Appl Clin Med Phys 2015; 16:273–280. [PMID: 26699583 PMCID: PMC5690991 DOI: 10.1120/jacmp.v16i6.5720] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Revised: 08/03/2015] [Accepted: 08/02/2015] [Indexed: 11/23/2022] Open
Abstract
Traditional CyberKnife (CK) calibration uses TG‐51, which requires kQ to be defined using the standard reference condition of 100 cm SSD in a 10 cm×10 cm field. Since the CK is calibrated using a 6 cm fixed‐aperture collimating cone at 80 cm SAD, the BJR‐25 method is commonly used to relate circular‐field PDDs to square‐field PDDs for kQ determination. Using the InCise MLC system, the CK is able to deliver rectangular fields, allowing a more direct measurement of %dd(10 cm) using conventional reference conditions. We define the PDD correction factor (CPDD) as the ratio of %dd(10 cm) measured using CK reference conditions to that measured using standard TG‐51 reference conditions. Using four ionization chambers (A1SL, CC08, CC13, and A19), %dd(10 cm) is measured using a 6 cm fixed cone at 80 cm SSD and at 100 cm SSD using an effective 10 cm×10 cm MLC‐collimated field. These values are used to calculate CPDD, while the latter is used to directly calculate a kQ value. This direct kQ value is then compared to values determined using the BJR‐25 method. Using the MLC system, this study demonstrates conversion between the %dd(10 cm) measured using CyberKnife reference conditions and TG‐51 reference conditions. These values provide the means for derivation of a kQ curve as a function of direct measurements of %dd(10 cm) using a 6 cm fixed‐aperture collimating cone at 80 cm SSD. PACS number: 87.55.Qr
Collapse
Affiliation(s)
- Jacob A Gersh
- Gibbs Cancer Center and Research Institute and Spectrum Medical Physics, LLC.
| | | |
Collapse
|
29
|
Ganesan R, McEwen MR, Orton CG. Point/Counterpoint. Calibration of radiotherapy ionization chambers using Co-60 is outdated and should be replaced by direct calibration in linear accelerator beams. Med Phys 2015; 42:5003-6. [PMID: 26328950 DOI: 10.1118/1.4922710] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Affiliation(s)
- Ramanathan Ganesan
- Radiotherapy Section, Medical Radiation Services Branch, Australian Radiation Protection and Nuclear Safety Agency, Yallambie 3085, Victoria, Australia (Tel: 61 3 9433 2273; E-mail: )
| | - Malcolm R McEwen
- Ionizing Radiation Standards, National Research Council, Ottawa, Ontario K1A OR6, Canada (Tel: 613-993-2197 Ext: 226; E-mail: )
| | | |
Collapse
|
30
|
Bouchard H, de Pooter J, Bielajew A, Duane S. Reference dosimetry in the presence of magnetic fields: conditions to validate Monte Carlo simulations. Phys Med Biol 2015; 60:6639-54. [DOI: 10.1088/0031-9155/60/17/6639] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
31
|
Shimizu M, Morishita Y, Kato M, Tanaka T, Kurosawa T, Takata N, Saito N, Ramanathan G, Harty PD, Oliver C, Wright T, Butler DJ. Comparison of the NMIJ and the ARPANSA standards for absorbed dose to water in high-energy photon beams. RADIATION PROTECTION DOSIMETRY 2015; 164:181-186. [PMID: 25209996 DOI: 10.1093/rpd/ncu272] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2014] [Accepted: 07/30/2014] [Indexed: 06/03/2023]
Abstract
The authors report the results of an indirect comparison of the standards of absorbed dose to water in high-energy photon beams from a clinical linac and (60)Co radiation beam performed between the National Metrology Institute of Japan (NMIJ) and the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). Three ionisation chambers were calibrated by the NMIJ in April and June 2013 and by the ARPANSA in May 2013. The average ratios of the calibration coefficients for the three ionisation chambers obtained by the NMIJ to those obtained by the ARPANSA were 0.9994, 1.0040 and 1.0045 for 6-, 10- and 15-MV (18 MV at the ARPANSA) high-energy photon beams, respectively. The relative standard uncertainty of the value was 7.2 × 10(-3). The ratio for (60)Co radiation was 0.9986(66), which is consistent with the results published in the key comparison of BIPM.RI(I)-K4.
Collapse
Affiliation(s)
- M Shimizu
- National Metrology Institute of Japan, AIST, Tsukuba, Japan
| | - Y Morishita
- National Metrology Institute of Japan, AIST, Tsukuba, Japan
| | - M Kato
- National Metrology Institute of Japan, AIST, Tsukuba, Japan
| | - T Tanaka
- National Metrology Institute of Japan, AIST, Tsukuba, Japan
| | - T Kurosawa
- National Metrology Institute of Japan, AIST, Tsukuba, Japan
| | - N Takata
- National Metrology Institute of Japan, AIST, Tsukuba, Japan
| | - N Saito
- National Metrology Institute of Japan, AIST, Tsukuba, Japan
| | - G Ramanathan
- Australian Radiation Protection and Nuclear Safety Agency, Yallambie, Australia
| | - P D Harty
- Australian Radiation Protection and Nuclear Safety Agency, Yallambie, Australia
| | - C Oliver
- Australian Radiation Protection and Nuclear Safety Agency, Yallambie, Australia
| | - T Wright
- Australian Radiation Protection and Nuclear Safety Agency, Yallambie, Australia School of Chemistry and Physics, University of Adelaide, Adelaide, Australia
| | - D J Butler
- Australian Radiation Protection and Nuclear Safety Agency, Yallambie, Australia
| |
Collapse
|
32
|
Muir BR, Rogers DWO. Monte Carlo calculations of electron beam quality conversion factors for several ion chamber types. Med Phys 2014; 41:111701. [DOI: 10.1118/1.4893915] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
|
33
|
Muir BR, McEwen MR, Rogers DWO. Determination of relative ion chamber calibration coefficients from depth-ionization measurements in clinical electron beams. Phys Med Biol 2014; 59:5953-69. [PMID: 25211012 DOI: 10.1088/0031-9155/59/19/5953] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A method is presented to obtain ion chamber calibration coefficients relative to secondary standard reference chambers in electron beams using depth-ionization measurements. Results are obtained as a function of depth and average electron energy at depth in 4, 8, 12 and 18 MeV electron beams from the NRC Elekta Precise linac. The PTW Roos, Scanditronix NACP-02, PTW Advanced Markus and NE 2571 ion chambers are investigated. The challenges and limitations of the method are discussed. The proposed method produces useful data at shallow depths. At depths past the reference depth, small shifts in positioning or drifts in the incident beam energy affect the results, thereby providing a built-in test of incident electron energy drifts and/or chamber set-up. Polarity corrections for ion chambers as a function of average electron energy at depth agree with literature data. The proposed method produces results consistent with those obtained using the conventional calibration procedure while gaining much more information about the behavior of the ion chamber with similar data acquisition time. Measurement uncertainties in calibration coefficients obtained with this method are estimated to be less than 0.5%. These results open up the possibility of using depth-ionization measurements to yield chamber ratios which may be suitable for primary standards-level dissemination.
Collapse
Affiliation(s)
- B R Muir
- Measurement Science and Standards, National Research Council of Canada, Ottawa, ON, K1A 0R6, Canada
| | | | | |
Collapse
|
34
|
Krauss A, Kapsch RP. Experimental determination ofkQfactors for cylindrical ionization chambers in 10 cm × 10 cm and 3 cm × 3 cm photon beams from 4 MV to 25 MV. Phys Med Biol 2014; 59:4227-46. [DOI: 10.1088/0031-9155/59/15/4227] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
35
|
McEwen M, DeWerd L, Ibbott G, Followill D, Rogers DWO, Seltzer S, Seuntjens J. Addendum to the AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon beams. Med Phys 2014; 41:041501. [PMID: 24694120 PMCID: PMC5148035 DOI: 10.1118/1.4866223] [Citation(s) in RCA: 201] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Revised: 02/03/2014] [Accepted: 02/06/2014] [Indexed: 11/07/2022] Open
Abstract
An addendum to the AAPM's TG-51 protocol for the determination of absorbed dose to water in megavoltage photon beams is presented. This addendum continues the procedure laid out in TG-51 but new kQ data for photon beams, based on Monte Carlo simulations, are presented and recommendations are given to improve the accuracy and consistency of the protocol's implementation. The components of the uncertainty budget in determining absorbed dose to water at the reference point are introduced and the magnitude of each component discussed. Finally, the consistency of experimental determination of ND,w coefficients is discussed. It is expected that the implementation of this addendum will be straightforward, assuming that the user is already familiar with TG-51. The changes introduced by this report are generally minor, although new recommendations could result in procedural changes for individual users. It is expected that the effort on the medical physicist's part to implement this addendum will not be significant and could be done as part of the annual linac calibration.
Collapse
Affiliation(s)
- Malcolm McEwen
- National Research Council, 1200 Montreal Road, Ottawa, Ontario, Canada
| | - Larry DeWerd
- University of Wisconsin, 1111 Highland Avenue, Madison, Wisconsin 53705
| | - Geoffrey Ibbott
- Department of Radiation Physics, M D Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030
| | - David Followill
- IROC Houston QA Center, Radiological Physics Center, 8060 El Rio Street, Houston, Texas 77054
| | - David W O Rogers
- Carleton Laboratory for Radiotherapy Physics, Physics Department, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada
| | - Stephen Seltzer
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899
| | - Jan Seuntjens
- Medical Physics Unit, McGill University, 1650 Cedar Avenue, Montreal, Québec, Canada
| |
Collapse
|
36
|
Sterpin E, Sorriaux J, Souris K, Vynckier S, Bouchard H. A Fano cavity test for Monte Carlo proton transport algorithms. Med Phys 2013; 41:011706. [DOI: 10.1118/1.4835475] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
37
|
Muir BR, Rogers DWO. Monte Carlo calculations for reference dosimetry of electron beams with the PTW Roos and NE2571 ion chambers. Med Phys 2013; 40:121722. [DOI: 10.1118/1.4829577] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
|
38
|
Andreo P, Wulff J, Burns DT, Palmans H. Consistency in reference radiotherapy dosimetry: resolution of an apparent conundrum when60Co is the reference quality for charged-particle and photon beams. Phys Med Biol 2013; 58:6593-621. [DOI: 10.1088/0031-9155/58/19/6593] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
39
|
Ubrich F, Wulff J, Engenhart-Cabillic R, Zink K. Correction factors for source strength determination in HDR brachytherapy using the in-phantom method. Z Med Phys 2013; 24:138-52. [PMID: 24021956 DOI: 10.1016/j.zemedi.2013.08.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2013] [Revised: 07/23/2013] [Accepted: 08/04/2013] [Indexed: 11/17/2022]
Abstract
For the purpose of clinical source strength determination for HDR brachytherapy sources, the German society for Medical Physics (DGMP) recommends in their report 13 the usage of a solid state phantom (Krieger-phantom) with a thimble ionization chamber. In this work, the calibration chain for the determination of the reference air-kerma rate Ka,100 and reference dose rate to waterDw,1 by ionization chamber measurement in the Krieger-phantom was modeled via Monte Carlo simulations. These calculations were used to determine global correction factors k(tot), which allows a user to directly convert the reading of an ionization chamber calibrated in terms of absorbed dose to water, into the desired quantity Ka,100 or Dw,1. The factor k(tot) was determined for four available (192)Ir sources and one (60)Co source with three different thimble ionization chambers. Finally, ionization chamber measurements on three μSelectron V2 HDR sources within the Krieger-phantom were performed and Ka,100 was determined according to three different methods: 1) using a calibration factor in terms of absorbed dose to water with the global correction factor [Formula: see text] according DGMP 13 2) using a global correction factor calculated via Monte Carlo 3) using a direct reference air-kerma rate calibration factor determined by the national metrology institute PTB. The comparison of Monte Carlo based [Formula: see text] with those from DGMP 13 showed that the DGMP data were systematically smaller by about 2-2.5%. The experimentally determined [Formula: see text] , based on the direct Ka,100 calibration were also systematically smaller by about 1.5%. Despite of these systematical deviations, the agreement of the different methods was in almost all cases within the 1σ level of confidence of the interval of their respective uncertainties in a Gaussian distribution. The application of Monte Carlo based [Formula: see text] for the determination of Ka,100 for three μSelectron V2 sources revealed the smallest deviation to the manufacturer's source certificate. With the calculated [Formula: see text] for a (60)Co source, the user is now able to accurately determine Ka,100 of a HDR (60)Co source via in-phantom measurement. Moreover, using the presented global correction factor [Formula: see text] , the user is able to determine the future source specification quantity Dw,1 with the same in-phantom setup.
Collapse
Affiliation(s)
- Frank Ubrich
- Department of Radiotherapy and Radiation Oncology, University Hospital Giessen-Marburg, Marburg, Germany.
| | - Jörg Wulff
- current working address: Varian Medical Systems Particle Therapy GmbH, Bergisch-Gladbach, Germany; Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences (THM) Giessen, Germany
| | - Rita Engenhart-Cabillic
- Department of Radiotherapy and Radiation Oncology, University Hospital Giessen-Marburg, Marburg, Germany
| | - Klemens Zink
- Department of Radiotherapy and Radiation Oncology, University Hospital Giessen-Marburg, Marburg, Germany; Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences (THM) Giessen, Germany
| |
Collapse
|
40
|
Anton M, Kapsch RP, Krauss A, von Voigts-Rhetz P, Zink K, McEwen M. Difference in the relative response of the alanine dosimeter to megavoltage x-ray and electron beams. Phys Med Biol 2013; 58:3259-82. [DOI: 10.1088/0031-9155/58/10/3259] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
41
|
Erazo F, Lallena AM. Calculation of beam quality correction factors for various thimble ionization chambers using the Monte Carlo code PENELOPE. Phys Med 2013; 29:163-70. [DOI: 10.1016/j.ejmp.2012.01.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/17/2011] [Revised: 12/31/2011] [Accepted: 01/05/2012] [Indexed: 10/14/2022] Open
|
42
|
Gago-Arias A, Antolín E, Fayos-Ferrer F, Simón R, González-Castaño DM, Palmans H, Sharpe P, Gómez F, Pardo-Montero J. Correction factors for ionization chamber dosimetry in CyberKnife: Machine-specific, plan-class, and clinical fields. Med Phys 2013; 40:011721. [DOI: 10.1118/1.4773047] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
43
|
Ali ESM, McEwen MR, Rogers DWO. Detailed high-accuracy megavoltage transmission measurements: a sensitive experimental benchmark of EGSnrc. Med Phys 2012; 39:5990-6003. [PMID: 23039637 DOI: 10.1118/1.4745561] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE There are three goals for this study: (a) to perform detailed megavoltage transmission measurements in order to identify the factors that affect the measurement accuracy, (b) to use the measured data as a benchmark for the EGSnrc system in order to identify the computational limiting factors, and (c) to provide data for others to benchmark Monte Carlo codes. METHODS Transmission measurements are performed at the National Research Council Canada on a research linac whose incident electron parameters are independently known. Automated transmission measurements are made on-axis, down to a transmission value of ∼1.7%, for eight beams between 10 MV (the lowest stable MV beam on the linac) and 30 MV, using fully stopping Be, Al, and Pb bremsstrahlung targets and no fattening filters. To diversify energy differentiation, data are acquired for each beam using low-Z and high-Z attenuators (C and Pb) and Farmer chambers with low-Z and high-Z buildup caps. Experimental corrections are applied for beam drifts (2%), polarity (2.5% typical maximum, 6% extreme), ion recombination (0.2%), leakage (0.3%), and room scatter (0.8%)-the values in parentheses are the largest corrections applied. The experimental setup and the detectors are modeled using EGSnrc, with the newly added photonuclear attenuation included (up to a 5.6% effect). A detailed sensitivity analysis is carried out for the measured and calculated transmission data. RESULTS The developed experimental protocol allows for transmission measurements with 0.4% uncertainty on the smallest signals. Suggestions for accurate transmission measurements are provided. Measurements and EGSnrc calculations agree typically within 0.2% for the sensitivity of the transmission values to the detector details, to the bremsstrahlung target material, and to the incident electron energy. Direct comparison of the measured and calculated transmission data shows agreement better than 2% for C (3.4% for the 10 MV beam) and typically better than 1% for Pb. The differences can be explained by acceptable photon cross section changes of ≤0.4%. CONCLUSIONS Accurate transmission measurements require accounting for a number of influence quantities which, if ignored, can collectively introduce errors larger than 10%. Accurate transmission calculations require the use of the most accurate data and physics options available in EGSnrc, particularly the more accurate bremsstrahlung angular sampling option and the newly added modeling of photonuclear attenuation. Comparison between measurements and calculations implies that EGSnrc is accurate within 0.2% for relative ion chamber response calculations. Photon cross section uncertainties are the ultimate limiting factor for the accuracy of the calculated transmission data (Monte Carlo or analytical).
Collapse
Affiliation(s)
- E S M Ali
- Department of Physics, Carleton University, Ottawa, Ontario, Canada.
| | | | | |
Collapse
|
44
|
Sterpin E, Mackie TR, Vynckier S. Monte Carlo computed machine-specific correction factors for reference dosimetry of TomoTherapy static beam for several ion chambers. Med Phys 2012; 39:4066-72. [DOI: 10.1118/1.4722752] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
45
|
Zink K, Wulff J. Beam quality corrections for parallel-plate ion chambers in electron reference dosimetry. Phys Med Biol 2012; 57:1831-54. [DOI: 10.1088/0031-9155/57/7/1831] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
46
|
Muir BR, McEwen MR, Rogers DWO. Beam quality conversion factors for parallel-plate ionization chambers in MV photon beams. Med Phys 2012; 39:1618-31. [DOI: 10.1118/1.3687864] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
47
|
Francescon P, Cora S, Satariano N. Calculation of kQclin,Qmsrfclin,fmsr for several small detectors and for two linear accelerators using Monte Carlo simulations. Med Phys 2011; 38:6513-27. [DOI: 10.1118/1.3660770] [Citation(s) in RCA: 134] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|