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Bai L, Xiao Q, Wang Q, Zhao J, Li G, Bai S. Dosimetric characteristics of a 2D silicon diode array for stereotactic radiotherapy end-to-end patient-specific QA. Radiat Phys Chem Oxf Engl 1993 2020. [DOI: 10.1016/j.radphyschem.2020.108885] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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Gotz M, Ka L, Tölli H, Pawelke J. Correction for volume recombination in liquid ionization chambers at high dose-per-pulse. Med Phys 2019; 46:3692-3699. [PMID: 31102553 DOI: 10.1002/mp.13600] [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: 10/17/2018] [Revised: 05/13/2019] [Accepted: 05/13/2019] [Indexed: 11/09/2022] Open
Abstract
PURPOSE To determine the volume recombination at high dose-per-pulse in liquid ionization chambers (LIC) and to ascertain whether existing calculation methods verified in air-filled chambers may be used to calculate a correction factor. METHODS Two LICs, one filled with 2,2,4-trimethylpentane (isooctane) the other with tetramethylsilane (TMS), were irradiated in a pulsed, 20 MeV electron beam. Via reference measurements with a Faraday cup, the saturation correction for volume recombination was determined for dose-per-pulse values ranging from about 5 mGy to 1 Gy for both chambers at a pulse duration of 693 ns. In addition, the isooctane chamber was irradiated with pulses of varying duration, ranging from 5 ps to 10 ms, at a dose-per-pulse of about 76.5 mGy. The dose-per-pulse-dependent measurements were compared to calculations based on Boag's models (with and without a free electron fraction), the two-dose-rate method, and a numerical calculation. The pulse duration dependent measurements were compared only to a numerical calculation that iteratively calculates the charge transport and loss in a 1D model of an ionization chamber. RESULTS In TMS only Boag's model with a free electron fraction and the numerical calculation are in good agreement with the experimental data. However, in isooctane, good agreement is observed between the experimental data, the numerical calculation as well as the two-dose-rate method, and Boag's model including a free electron fraction. Only Boag's model without a free electron fraction shows a good agreement with lesser extend. Furthermore, the pulse duration-dependent data for isooctane are well described by the numerical model. CONCLUSION With isooctane as an active medium, a LIC could be directly used in a field with high dose-per-pulse utilizing the well-established two-dose-rate method to correct the volume recombination. In addition, pulsed fields with variable pulse duration are easily modeled for this medium using a numerical calculation. Other media, as exemplified by the TMS-filled chamber, might require additional considerations, such as including a fraction of free electrons in the consideration of volume recombination.
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Affiliation(s)
- Malte Gotz
- OncoRay - National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden - Rossendorf, Fetscherstr. 74, PF 41, 01307, Dresden, Germany
| | - Leonhard Ka
- OncoRay - National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden - Rossendorf, Fetscherstr. 74, PF 41, 01307, Dresden, Germany.,Institute of Radiooncology - OncoRay, Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany
| | - Heikki Tölli
- Department of Radiation Sciences, Radiation Physics, Umeå University, SE- 901 87, Umeå, Sweden
| | - Jörg Pawelke
- OncoRay - National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden - Rossendorf, Fetscherstr. 74, PF 41, 01307, Dresden, Germany.,Institute of Radiooncology - OncoRay, Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany
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Brualla-González L, Vázquez-Luque A, Zapata M, González-Castaño DM, Luna-Vega V, Guiu-Souto J, Prieto-Pena J, García T, Granero D, Vicedo A, Rosellò J, Pombar M, Gómez F, Pardo-Montero J. Development and clinical characterization of a novel 2041 liquid-filled ionization chambers array for high-resolution verification of radiotherapy treatments. Med Phys 2018; 45:1771-1781. [PMID: 29446083 DOI: 10.1002/mp.12816] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Revised: 12/10/2017] [Accepted: 02/03/2018] [Indexed: 11/10/2022] Open
Abstract
PURPOSE The aim of this study was to present a novel 2041 liquid-filled ionization chamber array for high-resolution verification of radiotherapy treatments. MATERIALS AND METHODS The prototype has 2041 ionization chambers of 2.5 × 2.5 mm2 area filled with isooctane. The detection elements are arranged in a central square grid of 43 × 43, totally covering an area of 107.5 × 107.5 mm2 . The central inline and cross-line are extended to 227 mm and the diagonals to 321 mm to be able to perform profile measurements of large fields. We have studied stability, pixel response uniformity, dose rate dependence, depth and field size dependence and anisotropy. We present results for output factors, tongue-and-groove, garden fence, small field profiles, irregular fields, and verification of dose planes of patient treatments. RESULTS Comparison with other detectors used for small field dosimetry (SFD, CC13, microDiamond) has shown good agreement. Output factors measured with the device for square fields ranging from 10 × 10 to 100 × 100 mm2 showed relative differences within 1%. The response of the detector shows a strong dependence on the angle of incident radiation that needs to be corrected for. On the other hand, inter-pixel relative response variations in the 0.95-1.08 range have been found and corrected for. The application of the device for the verification of dose planes of several treatments has shown gamma passing rates above 97% for tolerances of 2% and 2 mm. The verification of other clinical fields, like small fields and irregular fields used in the commissioning of the TPS, also showed large passing rates. The verification of garden fence and tongue-and-groove fields was affected by volume-averaging effects. CONCLUSIONS The results show that the liquid filled ionization chamber prototype here presented is appropriate for the verification of radiotherapy treatments with high spatial resolution. Recombination effects do not affect very much the verification of relative dose distributions. However, verification of absolute dose distributions may require normalization to a radiation field which is representative of the dose rate of the treatment delivered.
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Affiliation(s)
- Luis Brualla-González
- Servicio de Radiofísica, ERESA, Hospital General Universitario de Valencia, Avd. Tres Cruces 2, 46014, Valencia, Spain
| | - Aurelio Vázquez-Luque
- Detection and Radiation Technologies (DART), Edificio Emprendia, 15782, Santiago de Compostela, Spain.,Departamento de Física de Partículas, Universidade de Santiago de Compostela, Campus Sur s/n, 15782, Santiago de Compostela, Spain
| | - Martín Zapata
- Servizo de Radiofísica e Protección Radiolóxica, Complexo Hospitalario Universitario de Santiago, Travesía da Choupana s/n, 15706, Santiago de Compostela, Spain
| | - Diego Miguel González-Castaño
- Laboratorio de Radiofísica, RIAIDT, Universidade de Santiago de Compostela, 15782, Santiago de Compostela, Spain.,Grupo de Imaxe Molecular, Instituto de Investigación Sanitaria (IDIS), Complexo Hospitalario Universitario de Santiago, Travesía da Choupana s/n, 15706, Santiago de Compostela, Spain
| | - Víctor Luna-Vega
- Servizo de Radiofísica e Protección Radiolóxica, Complexo Hospitalario Universitario de Santiago, Travesía da Choupana s/n, 15706, Santiago de Compostela, Spain
| | - Jacobo Guiu-Souto
- Servizo de Radiofísica e Protección Radiolóxica, Complexo Hospitalario Universitario de Santiago, Travesía da Choupana s/n, 15706, Santiago de Compostela, Spain
| | - Juan Prieto-Pena
- Departamento de Física de Partículas, Universidade de Santiago de Compostela, Campus Sur s/n, 15782, Santiago de Compostela, Spain
| | - Trinitat García
- Servicio de Radiofísica, ERESA, Hospital General Universitario de Valencia, Avd. Tres Cruces 2, 46014, Valencia, Spain
| | - Domingo Granero
- Servicio de Radiofísica, ERESA, Hospital General Universitario de Valencia, Avd. Tres Cruces 2, 46014, Valencia, Spain
| | - Aurora Vicedo
- Servicio de Radiofísica, ERESA, Hospital General Universitario de Valencia, Avd. Tres Cruces 2, 46014, Valencia, Spain
| | - Joan Rosellò
- Servicio de Radiofísica, ERESA, Hospital General Universitario de Valencia, Avd. Tres Cruces 2, 46014, Valencia, Spain
| | - Miguel Pombar
- Servizo de Radiofísica e Protección Radiolóxica, Complexo Hospitalario Universitario de Santiago, Travesía da Choupana s/n, 15706, Santiago de Compostela, Spain.,Grupo de Imaxe Molecular, Instituto de Investigación Sanitaria (IDIS), Complexo Hospitalario Universitario de Santiago, Travesía da Choupana s/n, 15706, Santiago de Compostela, Spain
| | - Faustino Gómez
- Departamento de Física de Partículas, Universidade de Santiago de Compostela, Campus Sur s/n, 15782, Santiago de Compostela, Spain.,Grupo de Imaxe Molecular, Instituto de Investigación Sanitaria (IDIS), Complexo Hospitalario Universitario de Santiago, Travesía da Choupana s/n, 15706, Santiago de Compostela, Spain
| | - Juan Pardo-Montero
- Servizo de Radiofísica e Protección Radiolóxica, Complexo Hospitalario Universitario de Santiago, Travesía da Choupana s/n, 15706, Santiago de Compostela, Spain.,Grupo de Imaxe Molecular, Instituto de Investigación Sanitaria (IDIS), Complexo Hospitalario Universitario de Santiago, Travesía da Choupana s/n, 15706, Santiago de Compostela, Spain
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Brualla-González L, Aguiar P, González-Castaño DM, Gómez F, Roselló J, Pombar M, Pardo-Montero J. Recombination in liquid-filled ionization chambers beyond the Boag limit. Med Phys 2016; 43:4142. [PMID: 27370134 DOI: 10.1118/1.4953452] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE The high mass density and low mobilities of charge carriers can cause important recombination in liquid-filled ionization chambers (LICs). Saturation correction methods have been proposed for LICs. Correction methods for pulsed irradiation are based on Boag equation. However, Boag equation assumes that the charge ionized by one pulse is fully collected before the arrival of the next pulse. This condition does not hold in many clinical beams where the pulse repetition period may be shorter than the charge collection time, causing overlapping between charge carriers ionized by different pulses, and Boag equation is not applicable there. In this work, the authors present an experimental and numerical characterization of collection efficiencies in LICs beyond the Boag limit, with overlapping between charge carriers ionized by different pulses. METHODS The authors have studied recombination in a LIC array for different dose-per-pulse, pulse repetition frequency, and polarization voltage values. Measurements were performed in a Truebeam Linac using FF and FFF modalities. Dose-per-pulse and pulse repetition frequency have been obtained by monitoring the target current with an oscilloscope. Experimental collection efficiencies have been obtained by using a combination of the two-dose-rate method and ratios to the readout of a reference chamber (CC13, IBA). The authors have also used numerical simulation to complement the experimental data. RESULTS The authors have found that overlap significantly increases recombination in LICs, as expected. However, the functional dependence of collection efficiencies on the dose-per-pulse does not change (a linear dependence has been observed in the near-saturation region for different degrees of overlapping, the same dependence observed in the nonoverlapping scenario). On the other hand, the dependence of collection efficiencies on the polarization voltage changes in the overlapping scenario and does not follow that of Boag equation, the reason being that changing the polarization voltage also affects the charge collection time, thus changing the amount of overlapping. CONCLUSIONS These results have important consequences for saturation correction methods for LICs. On one hand, the two-dose-rate method, which relies on the functional dependence of the collection efficiencies on dose-per-pulse, can also be used in the overlapping situation, provided that the two measurements needed to feed the method are performed at the same pulse repetition frequency (monitor unit rate). This result opens the door to computing collection efficiencies in LICs in many clinical setups where charge overlap in the LIC exists. On the other hand, correction methods based on the voltage-dependence of Boag equation like the three-voltage method or the modified two-voltage method will not work in the overlapping scenario due to the different functional dependence of collection efficiencies on the polarization voltage.
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Affiliation(s)
- L Brualla-González
- Servicio de Radiofísica, ERESA, Hospital General Universitario de Valencia, Valencia 46014, Spain
| | - P Aguiar
- Grupo de Imaxe Molecular, Instituto de Investigación Sanitaria (IDIS), Santiago de Compostela 15702, Spain and Departamento de Psiquiatría, Radioloxía e Saúde Pública, Facultade de Medicina, Universidade de Santiago de Compostela, Santiago de Compostela 15782, Spain
| | - D M González-Castaño
- Grupo de Imaxe Molecular, Instituto de Investigación Sanitaria (IDIS), Santiago de Compostela 15702, Spain and Laboratorio de Radiofísica, RIAIDT, Universidade de Santiago de Compostela, Santiago de Compostela 15782, Spain
| | - F Gómez
- Grupo de Imaxe Molecular, Instituto de Investigación Sanitaria (IDIS), Santiago de Compostela 15702, Spain and Departamento de Física de Partículas, Universidade de Santiago de Compostela, Santiago de Compostela 15782, Spain
| | - J Roselló
- Servicio de Radiofísica, ERESA, Hospital General Universitario de Valencia, Valencia 46014, Spain
| | - M Pombar
- Grupo de Imaxe Molecular, Instituto de Investigación Sanitaria (IDIS), Santiago de Compostela 15702, Spain and Servizo de Radiofísica e Protección Radiolóxica, Complexo Hospitalario Universitario de Santiago de Compostela, Santiago de Compostela 15706, Spain
| | - J Pardo-Montero
- Grupo de Imaxe Molecular, Instituto de Investigación Sanitaria (IDIS), Santiago de Compostela 15702, Spain and Servizo de Radiofísica e Protección Radiolóxica, Complexo Hospitalario Universitario de Santiago de Compostela, Santiago de Compostela 15706, Spain
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Sukumar P, McCallum C, Hounsell AR, McGarry CK. Characterisation of a two-dimensional liquid-filled ion chamber detector array using flattened and unflattened beams for small fields, small MUs and high dose-rates. Biomed Phys Eng Express 2016. [DOI: 10.1088/2057-1976/2/2/025007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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A numerical model of initial recombination for high-LET irradiation: Application to liquid-filled ionization chambers. Radiat Phys Chem Oxf Engl 1993 2016. [DOI: 10.1016/j.radphyschem.2015.10.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Aguiar P, González-Castaño D, Gómez F, Pardo-Montero J. Recombination in liquid filled ionisation chambers with multiple charge carrier species: Theoretical and numerical results. Radiat Phys Chem Oxf Engl 1993 2014. [DOI: 10.1016/j.radphyschem.2014.05.058] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Gómez F, González-Castaño D, Díaz-Botana P, Pardo-Montero J. Study of the PTW microLion chamber temperature dependence. Phys Med Biol 2014; 59:2705-12. [PMID: 24787030 DOI: 10.1088/0031-9155/59/11/2705] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The use of liquid ionization chambers in radiotherapy has grown during the past few years. While for air ionization chambers the k(TP) correction for air mass density due to pressure and temperature variations is well known, less work has been done on the case of liquid ionization chambers, where there is still the need to take into account the influence of temperature in the free ion yield. We have measured the PTW microLion isooctane-filled ionization chamber temperature dependence in a ~ ±10 °C interval around the standard 20 °C room temperature for three operation voltages, including the manufacturer recommended voltage, and two beam qualities, (60)Co and 50 kV x-rays. Within the measured temperature range, the microLion signal exhibits a positive linear dependence, which is around 0.24% K(-1) at 800 V with (60)Co irradiation. This effect is of the same order of magnitude as the T dependence found in air ionization chambers, but its nature is completely different and its sign opposite to that of an air chamber. Onsager theory has been used to model the results and is consistent with this linear behaviour. However, some inconsistencies in the modelling of the 50 kV x-ray results have been found that are attributed to the failure of Onsager's isolated pair assumption for such radiation quality.
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Affiliation(s)
- F Gómez
- Departamento de Física de Partículas, Universidade de Santiago de Compostela, E-15782-Santiago de Compostela, Spain. Radiation Physics Laboratory, Universidade de Santiago de Compostela, E-15782-Santiago de Compostela, Spain
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Benítez E, Casado F, García-Pareja S, Martín-Viera J, Moreno C, Parra V. Evaluation of a liquid ionization chamber for relative dosimetry in small and large fields of radiotherapy photon beams. RADIAT MEAS 2013. [DOI: 10.1016/j.radmeas.2013.08.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Poppe B, Stelljes TS, Looe HK, Chofor N, Harder D, Willborn K. Performance parameters of a liquid filled ionization chamber array. Med Phys 2013; 40:082106. [PMID: 23927343 DOI: 10.1118/1.4816298] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Affiliation(s)
- B Poppe
- Clinic for Radiation Therapy, Pius-Hospital, Oldenburg 26121, Germany.
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Andersson J, Kaiser FJ, Gómez F, Jäkel O, Pardo-Montero J, Tölli H. A comparison of different experimental methods for general recombination correction for liquid ionization chambers. Phys Med Biol 2012; 57:7161-75. [DOI: 10.1088/0031-9155/57/21/7161] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Brualla-González L, Gómez F, Vicedo A, González-Castaño DM, Gago-Arias A, Pazos A, Zapata M, Roselló JV, Pardo-Montero J. A two-dimensional liquid-filled ionization chamber array prototype for small-field verification: characterization and first clinical tests. Phys Med Biol 2012; 57:5221-34. [DOI: 10.1088/0031-9155/57/16/5221] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Andersson J, Johansson E, Tölli H. On the property of measurements with the PTW microLion chamber in continuous beams. Med Phys 2012; 39:4775-87. [DOI: 10.1118/1.4736804] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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González-Castaño D, Gómez F, Brualla L, Roselló J, Planes D, Sánchez M, Pombar M. A liquid-filled ionization chamber for high precision relative dosimetry. Phys Med 2011; 27:89-96. [DOI: 10.1016/j.ejmp.2010.04.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/25/2009] [Revised: 03/31/2010] [Accepted: 04/28/2010] [Indexed: 10/19/2022] Open
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Low DA, Moran JM, Dempsey JF, Dong L, Oldham M. Dosimetry tools and techniques for IMRT. Med Phys 2011; 38:1313-38. [DOI: 10.1118/1.3514120] [Citation(s) in RCA: 298] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
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Pardo-Montero J, Gómez F. Determining charge collection efficiency in parallel-plate liquid ionization chambers. Phys Med Biol 2009; 54:3677-89. [DOI: 10.1088/0031-9155/54/12/005] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Kavuma A, Glegg M, Currie G, Elliott A. Assessment of dosimetrical performance in 11 Varian a-Si500 electronic portal imaging devices. Phys Med Biol 2008; 53:6893-909. [DOI: 10.1088/0031-9155/53/23/016] [Citation(s) in RCA: 24] [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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Pardo J, Roselló JV, Sánchez-Doblado F, Gómez F. Verification of intensity modulated profiles using a pixel segmented liquid-filled linear array. Phys Med Biol 2006; 51:N211-9. [PMID: 16723758 DOI: 10.1088/0031-9155/51/11/n01] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
A liquid isooctane (C8H18) filled ionization chamber linear array developed for radiotherapy quality assurance, consisting of 128 pixels (each of them with a 1.7 mm pitch), has been used to acquire profiles of several intensity modulated fields. The results were compared with film measurements using the gamma test. The comparisons show a very good matching, even in high gradient dose regions. The volume-averaging effect of the pixels is negligible and the spatial resolution is enough to verify these regions. However, some mismatches between the detectors have been found in regions where low-energy scattered photons significantly contribute to the total dose. These differences are not very important (in fact, the measurements of both detectors are in agreement using the gamma test with tolerances of 3% and 3 mm in most of those regions), and may be associated with the film energy dependence. In addition, the linear array repeatability (0.27% one standard deviation) is much better than the film one ( approximately 3%). The good repeatability, small pixel size and high spatial resolution make the detector ideal for the real time profile verification of high gradient beam profiles like those present in intensity modulated radiation therapy and radiosurgery.
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Affiliation(s)
- J Pardo
- Departamento de Física de Partículas, Facultade de Física, Universidade de Santiago de Compostela, Spain.
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