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Park H, Paganetti H, Schuemann J, Jia X, Min CH. Monte Carlo methods for device simulations in radiation therapy. Phys Med Biol 2021; 66:10.1088/1361-6560/ac1d1f. [PMID: 34384063 PMCID: PMC8996747 DOI: 10.1088/1361-6560/ac1d1f] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Accepted: 08/12/2021] [Indexed: 11/12/2022]
Abstract
Monte Carlo (MC) simulations play an important role in radiotherapy, especially as a method to evaluate physical properties that are either impossible or difficult to measure. For example, MC simulations (MCSs) are used to aid in the design of radiotherapy devices or to understand their properties. The aim of this article is to review the MC method for device simulations in radiation therapy. After a brief history of the MC method and popular codes in medical physics, we review applications of the MC method to model treatment heads for neutral and charged particle radiation therapy as well as specific in-room devices for imaging and therapy purposes. We conclude by discussing the impact that MCSs had in this field and the role of MC in future device design.
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Affiliation(s)
- Hyojun Park
- Department of Radiation Convergence Engineering, Yonsei University, Wonju, Republic of Korea
| | - Harald Paganetti
- Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, United States of America
| | - Jan Schuemann
- Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, United States of America
| | - Xun Jia
- Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX 75235, United States of America
| | - Chul Hee Min
- Department of Radiation Convergence Engineering, Yonsei University, Wonju, Republic of Korea
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Choi HJ, Park H, Yi CY, Kim BC, Shin WG, Min CH. Determining the energy spectrum of clinical linear accelerator using an optimized photon beam transmission protocol. Med Phys 2019; 46:3285-3297. [PMID: 31055830 DOI: 10.1002/mp.13569] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 04/09/2019] [Accepted: 04/25/2019] [Indexed: 12/29/2022] Open
Abstract
PURPOSE The complex beam delivery techniques for patient treatment using a clinical linear accelerator (linac) may result in variations in the photon spectra, which can lead to dosimetric differences in patients that cannot be accounted for by current treatment planning systems (TPSs). Therefore, precise knowledge of the fluence and energy spectrum (ES) of the therapeutic beam is very important. However, owing to the high energy and flux of the beam, the ES cannot be measured directly, and validation of the spectrum modeled in the TPS is difficult. The aim of this study is to develop an efficient beam transmission measurement procedure for accurately reconstructing the ES of a therapeutic x-ray beam generated by a clinical linac. METHODS The attenuation of a 6 MV photon beam from an Elekta Synergy Platform clinical linac through different thicknesses of graphite and lead was measured using an ion chamber. The response of the ion chamber as a function of photon energy was obtained using the Monte Carlo (MC) method in the Geant4 simulation code. Using the curves obtained in the photon beam transmission measurements and the ion chamber energy response, the ES was reconstructed using an iterative algorithm based on a mathematical model of the spectrum. To evaluate the accuracy of the spectrum reconstruction method, the reconstructed ES (ESrecon ) was compared to that determined by the MC simulation (ESMC ). RESULTS The ion chamber model in the Geant4 simulation was well validated by comparing the ion chamber perturbation factors determined by the TRS-398 calibration protocol and EGSnrc; the differences were within 0.57%. The number of transmission measurements was optimized to 10 for efficient spectrum reconstruction according to the rate of increase in the spectrum reconstruction accuracy. The distribution of ESrecon obtained using the measured transmission curves was clearly similar to the reference, ESMC , and the dose distributions in water calculated using ESrecon and ESMC were similar within a 2% local difference. However, in a heterogeneous medium, the dose discrepancy between them was >5% when a complex beam delivery technique composed of 171 control points was used. CONCLUSIONS The proposed measurement procedure required a total time of approximately 1 h to obtain and analyze 20 transmission measurements. In addition, it was confirmed that the transmission curve of high-Z materials influences the accuracy of spectrum reconstruction more than that of low-Z materials. A well-designed transmission measurement protocol suitable for clinical environments could be an essential tool for better dosimetric accuracy in patient treatment and for periodic verification of the beam quality.
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Affiliation(s)
- Hyun Joon Choi
- Department of Radiation Convergence Engineering, Yonsei University, 1 Yeonsedae-gil, Heungeop-myeon, Wonju, 26493, Korea
| | - Hyojun Park
- Department of Radiation Convergence Engineering, Yonsei University, 1 Yeonsedae-gil, Heungeop-myeon, Wonju, 26493, Korea
| | - Chul Young Yi
- Center for Ionizing Radiation, Korea Research Institute of Standards and Science, Daejeon 34113, Korea
| | - Byoung-Chul Kim
- Center for Ionizing Radiation, Korea Research Institute of Standards and Science, Daejeon 34113, Korea
| | - Wook-Geun Shin
- Department of Radiation Convergence Engineering, Yonsei University, 1 Yeonsedae-gil, Heungeop-myeon, Wonju, 26493, Korea
| | - Chul Hee Min
- Department of Radiation Convergence Engineering, Yonsei University, 1 Yeonsedae-gil, Heungeop-myeon, Wonju, 26493, Korea
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Alashrah S, Kandaiya S, Maalej N, El-Taher A. Skin dose measurements using radiochromic films, TLDS and ionisation chamber and comparison with Monte Carlo simulation. RADIATION PROTECTION DOSIMETRY 2014; 162:338-344. [PMID: 24300340 DOI: 10.1093/rpd/nct315] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Estimation of the surface dose is very important for patients undergoing radiation therapy. The purpose of this study is to investigate the dose at the surface of a water phantom at a depth of 0.007 cm as recommended by the International Commission on Radiological Protection and International Commission on Radiation Units and Measurement with radiochromic films (RFs), thermoluminescent dosemeters and an ionisation chamber in a 6-MV photon beam. The results were compared with the theoretical calculation using Monte Carlo (MC) simulation software (MCNP5, BEAMnrc and DOSXYZnrc). The RF was calibrated by placing the films at a depth of maximum dose (d(max)) in a solid water phantom and exposing it to doses from 0 to 500 cGy. The films were scanned using a transmission high-resolution HP scanner. The optical density of the film was obtained from the red component of the RGB images using ImageJ software. The per cent surface dose (PSD) and percentage depth dose (PDD) curve were obtained by placing film pieces at the surface and at different depths in the solid water phantom. TLDs were placed at a depth of 10 cm in a solid water phantom for calibration. Then the TLDs were placed at different depths in the water phantom and were exposed to obtain the PDD. The obtained PSD and PDD values were compared with those obtained using a cylindrical ionisation chamber. The PSD was also determined using Monte Carlo simulation of a LINAC 6-MV photon beam. The extrapolation method was used to determine the PSD for all measurements. The PSD was 15.0±3.6% for RF. The TLD measurement of the PSD was 16.0±5.0%. The (0.6 cm(3)) cylindrical ionisation chamber measurement of the PSD was 50.0±3.0%. The theoretical calculation using MCNP5 and DOSXYZnrc yielded a PSD of 15.0±2.0% and 15.7±2.2%. In this study, good agreement between PSD measurements was observed using RF and TLDs with the Monte Carlo calculation. However, the cylindrical chamber measurement yielded an overestimate of the PSD. This is probably due to the ionisation chamber calibration factor that is only valid in charged particle equilibrium condition, which is not achieved at the surface in the build-up region.
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Affiliation(s)
- Saleh Alashrah
- Department of Physics, Qassim University, Qassim, Saudi Arabia Universiti Sains Malaysia, Penang, Malaysia
| | | | - Nabil Maalej
- Department of Physics, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia
| | - A El-Taher
- Department of Physics, Qassim University, Qassim, Saudi Arabia Physics Department, Faculty of Science, Al-Azher University, Assuit, Egypt
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Kumar S, Datta D, Sharma SD, Chourasiya G, Babu DAR, Sharma DN. Estimation of distance error by fuzzy set theory required for strength determination of HDR (192)Ir brachytherapy sources. J Med Phys 2014; 39:85-92. [PMID: 24872605 PMCID: PMC4035620 DOI: 10.4103/0971-6203.131281] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Revised: 01/20/2014] [Accepted: 03/26/2014] [Indexed: 11/04/2022] Open
Abstract
Verification of the strength of high dose rate (HDR) (192)Ir brachytherapy sources on receipt from the vendor is an important component of institutional quality assurance program. Either reference air-kerma rate (RAKR) or air-kerma strength (AKS) is the recommended quantity to specify the strength of gamma-emitting brachytherapy sources. The use of Farmer-type cylindrical ionization chamber of sensitive volume 0.6 cm(3) is one of the recommended methods for measuring RAKR of HDR (192)Ir brachytherapy sources. While using the cylindrical chamber method, it is required to determine the positioning error of the ionization chamber with respect to the source which is called the distance error. An attempt has been made to apply the fuzzy set theory to estimate the subjective uncertainty associated with the distance error. A simplified approach of applying this fuzzy set theory has been proposed in the quantification of uncertainty associated with the distance error. In order to express the uncertainty in the framework of fuzzy sets, the uncertainty index was estimated and was found to be within 2.5%, which further indicates that the possibility of error in measuring such distance may be of this order. It is observed that the relative distance li estimated by analytical method and fuzzy set theoretic approach are consistent with each other. The crisp values of li estimated using analytical method lie within the bounds computed using fuzzy set theory. This indicates that li values estimated using analytical methods are within 2.5% uncertainty. This value of uncertainty in distance measurement should be incorporated in the uncertainty budget, while estimating the expanded uncertainty in HDR (192)Ir source strength measurement.
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Affiliation(s)
- Sudhir Kumar
- Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, CTCRS, Anushaktinagar, Maharashtra, India
| | - D Datta
- Health Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai, Maharashtra, India
| | - S D Sharma
- Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, CTCRS, Anushaktinagar, Maharashtra, India
| | - G Chourasiya
- Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, CTCRS, Anushaktinagar, Maharashtra, India
| | - D A R Babu
- Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, CTCRS, Anushaktinagar, Maharashtra, India
| | - D N Sharma
- Health Safety and Environment Group, Bhabha Atomic Research Centre, Trombay, Mumbai, Maharashtra, India
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Chica U, Anguiano M, Vilches M, Lallena AM. Quality indexes based on water measurements for low and medium energy x-ray beams: A theoretical study with PENELOPE. Med Phys 2013; 41:012101. [DOI: 10.1118/1.4836556] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Chica U, Anguiano M, Lallena A. On the behavior of fc,Q factors with quality indexes for medium energy X-ray beams: A Monte Carlo study with penelope. Radiat Phys Chem Oxf Engl 1993 2013. [DOI: 10.1016/j.radphyschem.2013.03.034] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Legrand C, Hartmann GH, Karger CP. Experimental determination of the effective point of measurement and the displacement correction factor for cylindrical ionization chambers in a 6 MV photon beam. Phys Med Biol 2012; 57:6869-80. [DOI: 10.1088/0031-9155/57/21/6869] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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González-Castaño DM, González LB, Gago-Arias MA, Pardo-Montero J, Gómez F, Luna-Vega V, Sánchez M, Lobato R. A convolution model for obtaining the response of an ionization chamber in static non standard fields. Med Phys 2011; 39:482-91. [DOI: 10.1118/1.3666777] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Kumar S, Srinivasan P, Sharma SD, Mayya YS. A simplified analytical approach to estimate the parameters required for strength determination of HDR 192Ir brachytherapy sources using a Farmer-type ionization chamber. Appl Radiat Isot 2011; 70:282-9. [PMID: 21872480 DOI: 10.1016/j.apradiso.2011.08.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2011] [Revised: 06/29/2011] [Accepted: 08/06/2011] [Indexed: 01/10/2023]
Abstract
Measuring the strength of high dose rate (HDR) (192)Ir brachytherapy sources on receipt from the vendor is an important component of a quality assurance program. Owing to their ready availability in radiotherapy departments, the Farmer-type ionization chambers are also used to determine the strength of HDR (192)Ir brachytherapy sources. The use of a Farmer-type ionization chamber requires the estimation of the scatter correction factor along with positioning error (c) and the constant of proportionality (f) to determine the strength of HDR (192)Ir brachytherapy sources. A simplified approach based on a least squares method was developed for estimating the values of f and M(s). The seven distance method was followed to record the ionization chamber readings for parameterization of f and M(s). Analytically calculated values of M(s) were used to determine the room scatter correction factor (K(sc)). The Monte Carlo simulations were also carried out to calculate f and K(sc) to verify the magnitude of the parameters determined by the proposed analytical approach. The value of f determined using the simplified analytical approach was found to be in excellent agreement with the Monte Carlo simulated value (within 0.7%). Analytically derived values of K(sc) were also found to be in good agreement with the Monte Carlo calculated values (within 1.47%). Being far simpler than the presently available methods of evaluating f, the proposed analytical approach can be adopted for routine use by clinical medical physicists to estimate f by hand calculations.
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Affiliation(s)
- Sudhir Kumar
- Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, CTCRS, Anushaktinagar, Mumbai 400094, India
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Evaluation of scatter contribution and distance error by iterative methods for strength determination of HDR 192Ir brachytherapy source. Med Dosim 2009; 35:230-7. [PMID: 19931038 DOI: 10.1016/j.meddos.2009.06.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2009] [Accepted: 06/18/2009] [Indexed: 11/23/2022]
Abstract
High-dose rate (HDR) 192Ir brachytherapy sources are commonly used for management of malignancies by brachytherapy applications. Measurement of source strength at the hospital is an important dosimetry requirement. The use of 0.6-cm(3) cylindrical ionization chamber is one of the methods of measuring the source strength at the hospitals because this chamber is readily available for beam calibration and dosimetry. While using the cylindrical chamber for this purpose, it is also required to determine the positioning error of the ionization chamber, with respect to the source, commonly called a distance error (c). The contribution of scatter radiation (M(s)) from floor, walls, ceiling, and other materials available in the treatment room also need to be determined accurately so that appropriate correction can be applied while calculating the source strength from the meter reading. Iterative methods of Newton-Raphson and least-squares were used in this work to determine scatter contribution in the experimentally observed meter reading (pC/s) of a cylindrical ionization chamber. Monte Carlo simulation was also used to cross verify the results of the least-squares method. The experimentally observed, least-squares calculated and Monte Carlo estimated values of meter readings from HDR 192Ir brachytherapy source were in good agreement. Considering procedural simplicity, the method of least-squares is recommended for use at the hospitals to estimate values of f (constant of proportionality), c, and M(s) required to determine the strength of HDR 192Ir brachytherapy sources.
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González-Castaño DM, Hartmann GH, Sánchez-Doblado F, Gómez F, Kapsch RP, Pena J, Capote R. The determination of beam quality correction factors: Monte Carlo simulations and measurements. Phys Med Biol 2009; 54:4723-41. [DOI: 10.1088/0031-9155/54/15/006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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13
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Crop F, Reynaert N, Pittomvils G, Paelinck L, De Wagter C, Vakaet L, Thierens H. The influence of small field sizes, penumbra, spot size and measurement depth on perturbation factors for microionization chambers. Phys Med Biol 2009; 54:2951-69. [DOI: 10.1088/0031-9155/54/9/024] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Wulff J, Zink K, Kawrakow I. Efficiency improvements for ion chamber calculations in high energy photon beams. Med Phys 2008; 35:1328-36. [DOI: 10.1118/1.2874554] [Citation(s) in RCA: 164] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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González-Castaño D, Pena J, Sánchez-Doblado F, Hartmann GH, Gómez F, Leal A. The change of response of ionization chambers in the penumbra and transmission regions: impact for IMRT verification. Med Biol Eng Comput 2007; 46:373-80. [PMID: 17828563 DOI: 10.1007/s11517-007-0249-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2006] [Accepted: 08/20/2007] [Indexed: 10/22/2022]
Abstract
Significant deviations from the expected dose have been reported in the absolute dosimetry validation of an intensity modulated radiation therapy treatment when individual segments are analyzed. However, when full treatment is considered and all segment doses are added together, these discrepancies fade out, leading to overall dose deviations below a 5% action level. This contradictory behavior may be caused by a partial compensation between detector over-responding and under-responding for measurement conditions far from radiation equilibrium. We consider three treatment verification scenarios that may lead to ionization chamber miss-responding, namely: narrow beam irradiation, field penumbra location and multi-leaf collimator transmission contribution. In this work we have analyzed the response of three different ionization chambers with different active volume under these conditions by means of Monte Carlo (MC) simulation methods. Correction factors needed to convert the detector readout into actual dose to water were calculated by inserting the specific detector geometry (carefully modeled) into the simulations. This procedure required extensive use of parallel computing resources in order to achieve the desired level of uncertainty in the final results. The analysis of the simulations shows the relative contribution of each of the three previously mentioned miss-responding scenarios. Additionally, we provide some evidence on dose deviation compensation in multi-segment radiotherapy treatment verification.
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Affiliation(s)
- D González-Castaño
- Departamento de Física de Partículas, Universidad de Santiago de Compostela, Santiago de Compostela, Spain.
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Crop F, Reynaert N, Pittomvils G, Paelinck L, De Gersem W, De Wagter C, Vakaet L, De Neve W, Thierens H. Monte Carlo modeling of the ModuLeaf miniature MLC for small field dosimetry and quality assurance of the clinical treatment planning system. Phys Med Biol 2007; 52:3275-90. [PMID: 17505102 DOI: 10.1088/0031-9155/52/11/022] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The purpose of this investigation was the verification of both the measured data and quality of the implementation of the add-on ModuLeaf miniature multileaf collimator (ML mMLC) into the clinical treatment planning system for conformal stereotactic radiosurgery treatment. To this end the treatment head with ML mMLC was modeled in the BEAMnrc Monte Carlo (MC) code. The 6 MV photon beams used in the setup were first benchmarked with a set of measurements. A total ML mMLC transmission of 1.13% of the 10 x 10 cm2 open field dose was measured and reproduced with the BEAMnrc/DOSXYZnrc code. Correspondence between calculated and measured output factors (OFs) was within 2%. Correspondence between MC and measured profiles was within 2% dose and 2 mm distance, only for the smallest 0.5 x 0.5 cm2 field the results were within 3% dose. In the next step, the MC model was compared with Gafchromic film measurements and Pinnacle(3) 7.4 f (convolution superposition algorithm) calculated dose distributions, using a gamma evaluation comparison, for a multi-beam patient setup delivered to a Lucytrade mark phantom. The gamma evaluation of the MC versus Gafchromic film resulted in 3.4% of points not fulfilling gamma <or= 1 for a 2%/2 mm criterion, the Pinnacle(3) 7.4 f versus Gafchromic results 3.8% and Pinnacle versus MC less than 1%. For specific patients with lesions of 8 cc and 0.2 cc, Monte Carlo and Pinnacle simulations of the plans were performed and compared using DVH evaluation. DVHs corresponded within 2% dose and 2% volume.
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Affiliation(s)
- F Crop
- Department of Medical Physics, Ghent University, Proeftuinstraat 86, B-9000 Gent, Belgium.
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Sánchez-Doblado F, Hartmann GH, Pena J, Roselló JV, Russiello G, Gonzalez-Castaño DM. A new method for output factor determination in MLC shaped narrow beams. Phys Med 2007; 23:58-66. [PMID: 17568544 DOI: 10.1016/j.ejmp.2007.03.002] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2006] [Revised: 03/07/2007] [Accepted: 03/08/2007] [Indexed: 11/23/2022] Open
Abstract
A new method for the measurement of output factors of narrow beams is presented in this work. By combining a new large area parallel plane ionization chamber (PTW model T34070) with a relative film dosimetry the output factors of small square fields of a 6 MV beam shaped by a MLC were measured. Several detectors (three ionization chambers, two solid state detectors and film) and Monte Carlo simulation were also employed to validate this new methodology and also to determine those detectors more suitable for narrow beam output factor determination. The proposed method for output factor measurement has shown to be in a very good agreement with diamond, diode and Monte Carlo results while it is insensitive to position displacements. Several uncertainties associated to the process of narrow beam dosimetry have also been addressed.
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Affiliation(s)
- F Sánchez-Doblado
- Hospital Universitario Virgen Macarena, Servicio de Radiofísica, Sevilla, Spain.
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Pena J, González-Castaño DM, Gómez F, Sánchez-Doblado F, Hartmann GH. Automatic determination of primary electron beam parameters in Monte Carlo simulation. Med Phys 2007; 34:1076-84. [PMID: 17441253 DOI: 10.1118/1.2514155] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
In order to obtain realistic and reliable Monte Carlo simulations of medical linac photon beams, an accurate determination of the parameters that define the primary electron beam that hits the target is a fundamental step. In this work we propose a new methodology to commission photon beams in Monte Carlo simulations that ensures the reproducibility of a wide range of clinically useful fields. For such purpose accelerated Monte Carlo simulations of 2 x 2, 10 x 10, and 20 x 20 cm2 fields at SSD = 100 cm are carried out for several combinations of the primary electron beam mean energy and radial FWHM. Then, by performing a simultaneous comparison with the correspondent measurements for these same fields, the best combination is selected. This methodology has been employed to determine the characteristics of the primary electron beams that best reproduce a Siemens PRIMUS and a Varian 2100 CD machine in the Monte Carlo simulations. Excellent agreements were obtained between simulations and measurements for a wide range of field sizes. Because precalculated profiles are stored in databases, the whole commissioning process can be fully automated, avoiding manual fine-tunings. These databases can also be used to characterize any accelerators of the same model from different sites.
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Affiliation(s)
- Javier Pena
- Departamento de Física de Partículas, Facultade de Física, Universidade de Santiago de Compostela, Spain.
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