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Use of calculations to validate beam quality and relative dose measurements for a kilovoltage X-ray therapy unit. Phys Eng Sci Med 2022; 45:537-546. [PMID: 35381970 DOI: 10.1007/s13246-022-01120-8] [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: 11/25/2021] [Accepted: 03/16/2022] [Indexed: 10/18/2022]
Abstract
Relative dosimetry measurements are required to fully commission kilovoltage X-ray units for superficial and orthovoltage X-ray therapy. Validation of these relative dosimetry measurements with Monte Carlo methods is advantageous being independent of the measurement process. In this study use is made of the X-ray spectrum generating program SpekPy along with the EGSnrc Monte Carlo code to calculate depth doses and explore the dosimetry effect of changes in backscatter. These calculations are compared with previously reported measurements for the Pantak SXT 150 X-ray therapy unit. SpekPy can also be used to generate half value layer (HVL) values and these are also compared to previously reported HVL measurements for the same X-ray therapy unit. It was found that agreements of the order of 5% in HVL, 3% in depth dose and 1% in backscatter doses were found between Monte Carlo calculations and the previously published measured data. Exit doses in conditions of lack of full backscatter were explored with Monte Carlo calculations demonstrating reduced exit dose up to 20% in these conditions. It is concluded that SpekPy with Monte Carlo codes such as EGSnrc provides a straightforward approach to validating various relative dosimetry measurements in kilovoltage X-ray dosimetry.
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Niroomand‐Rad A, Chiu‐Tsao S, Grams MP, Lewis DF, Soares CG, Van Battum LJ, Das IJ, Trichter S, Kissick MW, Massillon‐JL G, Alvarez PE, Chan MF. Report of AAPM Task Group 235 Radiochromic Film Dosimetry: An Update to TG‐55. Med Phys 2020; 47:5986-6025. [DOI: 10.1002/mp.14497] [Citation(s) in RCA: 64] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 09/15/2020] [Accepted: 09/17/2020] [Indexed: 12/12/2022] Open
Affiliation(s)
| | | | | | | | | | | | - Indra J. Das
- Radiation Oncology Northwestern University Memorial Hospital Chicago IL USA
| | - Samuel Trichter
- New York‐Presbyterian HospitalWeill Cornell Medical Center New York NY USA
| | | | - Guerda Massillon‐JL
- Instituto de Fisica Universidad Nacional Autonoma de Mexico Mexico City Mexico
| | - Paola E. Alvarez
- Imaging and Radiation Oncology Core MD Anderson Cancer Center Houston TX USA
| | - Maria F. Chan
- Memorial Sloan Kettering Cancer Center Basking Ridge NJ USA
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Subiel A, Silvestre Patallo I, Palmans H, Barry M, Tulk A, Soultanidis G, Greenman J, Green VL, Cawthorne C, Schettino G. The influence of lack of reference conditions on dosimetry in pre-clinical radiotherapy with medium energy x-ray beams. Phys Med Biol 2020; 65:085016. [PMID: 32109893 DOI: 10.1088/1361-6560/ab7b30] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Despite well-established dosimetry in clinical radiotherapy, dose measurements in pre-clinical and radiobiology studies are frequently inadequate, thus undermining the reliability and reproducibility of published findings. The lack of suitable dosimetry protocols, coupled with the increasing complexity of pre-clinical irradiation platforms, undermines confidence in preclinical studies and represents a serious obstacle in the translation to clinical practice. To accurately measure output of a pre-clinical radiotherapy unit, appropriate Codes of Practice (CoP) for medium energy x-rays needs to be employed. However, determination of absorbed dose to water (Dw) relies on application of backscatter factor (Bw) employing in-air method or carrying out in-phantom measurement at the reference depth of 2 cm in a full backscatter (i.e. 30 × 30 × 30 cm3) condition. Both of these methods require thickness of at least 30 cm of underlying material, which are never fulfilled in typical pre-clinical irradiations. This work is focused on evaluation the effects of the lack of recommended reference conditions in dosimetry measurements for pre-clinical settings and is aimed at extending the recommendations of the current CoP to practical experimental conditions and highlighting the potential impact of the lack of correct backscatter considerations on radiobiological studies.
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Affiliation(s)
- Anna Subiel
- National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom. Author to whom any correspondence should be addressed
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Harwood JR, Nelli FE. A model-based algorithm to correct for the loss of backscatter in superficial X-ray radiation therapy. Phys Med 2019; 65:157-166. [PMID: 31494369 DOI: 10.1016/j.ejmp.2019.08.018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Revised: 05/29/2019] [Accepted: 08/23/2019] [Indexed: 10/26/2022] Open
Abstract
Dosimetry protocols for superficial X-rays prescribe the determination of kerma on the surface of a phantom through the use of a backscatter factor (Bw) that accounts for the effect of phantom scatter. Bw values corresponding to full-scatter phantoms are provided by these protocols. In practice, clinical situations arise wherein there is insufficient scattering material downstream, resulting in published Bw values that overestimate the amount of occurring scatter. To provide an accurate dose calculation the backscatter values need to be corrected for any reduction in scattered radiation. Estimating the change of Bw in situations with incomplete backscatter has previously been achieved by direct measurements or Monte Carlo modelling. For increasing the accuracy of clinical dosimetries, we developed a physical model to deduce an algorithm for calculating backscatter factors in situations with reduced downstream scattering medium. The predictions of the model were validated by comparison with published data, Monte Carlo simulations and film-based measurements for beams with a half-value layer of 0.8, 2 and 4 mm Al. Our algorithm accurately predicts the effect of partial scatter conditions with suitable precision. Its reliability, combined with the simplicity of calculation, makes this methodology suitable to be incorporated into routine clinical dosimetry. The algorithm's underlying physical model provides an intuitive understanding of the effects of field size and beam energy on backscatter reduction, permitting a rational management of this effect.
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Affiliation(s)
- Jeffrey R Harwood
- Andrew Love Cancer Centre, University Hospital Geelong, 70 Swanston St, Geelong, Vic 3220, Australia.
| | - Flavio E Nelli
- Andrew Love Cancer Centre, University Hospital Geelong, 70 Swanston St, Geelong, Vic 3220, Australia
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Chen Q, Molloy J, Izumi T, Sterpin E. Impact of backscatter material thickness on the depth dose of orthovoltage irradiators for radiobiology research. Phys Med Biol 2019; 64:055001. [PMID: 30673636 DOI: 10.1088/1361-6560/ab0120] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The orthovoltage x-ray energy frequently used in radiation research is prone to dosimetry errors due to insufficient backscatter conditions. In many radiobiology studies, especially for cell irradiations, precise dose calculation algorithms such as Convolution-Superposition or Monte Carlo are impractical and as such, less accurate hand calculation methods are used for dose estimation. These dose estimation methods typically assume full backscatter conditions. The purpose of this study is to demonstrate the magnitude of the dose error that results from insufficient backscatter, and to provide lookup tables to account this issue. The beam spectra of several widely used commercial systems (XRAD-225, XRAD-320, SARRP) were used in Monte Carlo (MC) simulations on a series of phantom setups to investigate the impact of varying backscatter conditions on dosimetry. The depth dose curves for different field sizes, water phantom thicknesses and beam qualities were generated. In addition, depth dependent backscatter factors for different field sizes and different beam qualities were calculated. It is demonstrated that as much as a 50% dose difference exists for different backscatter conditions at the beam qualities studied. The choice of cell dish size as well as other changes in the experiment setup can have more than 10% impact on the dose. The impact of backscatter is reduced with a decrease in field size. Further, the thickness needed to provide full backscatter can be approximated as being equal to the field size. It is imperative to ensure full backscatter conditions during system and dosimeter calibration, or to use the look-up table provided in this study.
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Affiliation(s)
- Quan Chen
- Department of Radiation Medicine, The University of Kentucky, Lexington, KY 40536, United States of America. Author to whom any correspondence should be addressed. Radiation Medicine, University of Kentucky, Markey Cancer Center, Rm CC063, 800 Rose St., Lexington, KY 40536-0293, United States of America
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Hill R, Healy B, Butler D, Odgers D, Gill S, Lye J, Gorjiara T, Pope D, Hill B. Australasian recommendations for quality assurance in kilovoltage radiation therapy from the Kilovoltage Dosimetry Working Group of the Australasian College of Physical Scientists and Engineers in Medicine. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2018; 41:781-808. [DOI: 10.1007/s13246-018-0692-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Hewson EA, Butson MJ, Hill R. Evaluating TOPAS for the calculation of backscatter factors for low energy x-ray beams. ACTA ACUST UNITED AC 2018; 63:195014. [DOI: 10.1088/1361-6560/aadf28] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Skin dose assessment with treatment planning system (TPS) and skin reaction evaluation of early breast cancer patients treated via an intraoperative radiation therapy (IORT) device. JOURNAL OF RADIOTHERAPY IN PRACTICE 2018. [DOI: 10.1017/s1460396918000237] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractPurposeTo assess skin dose and incidence of skin reactions in early breast cancer patients treated via Intrabeam™ intraoperative radiation therapy (IORT) device.Materials and methodsIn total, 250 breast cancer patients treated with a single fraction of 20 Gy using 50 kV photon were recruited. The applicator to skin distance (ASD) was measured before the initiation of the radiation and the skin dose in each patient was accordingly calculated based on the treatment planning system (TPS).ResultsThe average skin doses calculated were equal to 7·91, 5·83, 3·96 and 2·14 Gy for 6–10, 10–15, 15–20 and 20–30 mm ASD values, respectively. It is noticeable that the skin doses could be lower than the TPS measurements up to 45%, mostly due to lack of backscatter radiation in breast tissue compared with the full scatter condition in the Zeiss water phantom. Finally, only three patients showed low-grade skin reactions 1 week after IORT. A review of the related literature also revealed the incidence of lower skin complications among patients treated via Intrabeam™ compared with MammoSite™ machine.ConclusionsThe Intrabeam™ TPS did not seem to be very reliable for accurate skin dosimetry. However, breast cancer treatment using Intrabeam™ could result in fewer incidences of skin reactions than MammoSite™ machine.
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Effect of verification imaging on in vivo dosimetry results using Gafchromic EBT3 film. Phys Med 2016; 32:1461-1465. [DOI: 10.1016/j.ejmp.2016.10.020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Revised: 09/20/2016] [Accepted: 10/26/2016] [Indexed: 11/19/2022] Open
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de-Azevedo-Vaz SL, Peyneau PD, Ramirez-Sotelo LR, Vasconcelos KDF, Campos PSF, Haiter-Neto F. Efficacy of a cone beam computed tomography metal artifact reduction algorithm for the detection of peri-implant fenestrations and dehiscences. Oral Surg Oral Med Oral Pathol Oral Radiol 2016; 121:550-6. [PMID: 27068312 DOI: 10.1016/j.oooo.2016.01.013] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Revised: 12/06/2015] [Accepted: 01/18/2016] [Indexed: 10/22/2022]
Abstract
OBJECTIVE To determine whether the use of a metal artifact reduction (MAR) algorithm improves the detection of peri-implant fenestrations and dehiscences on cone beam computed tomography scans. STUDY DESIGN One hundred titanium fixtures were implanted into bovine ribs after the creation of defects simulating fenestrations and dehiscences. Images were acquired using four different protocols, namely, A2 (MAR on, voxel 0.2 mm), A3 (MAR on, voxel 0.3 mm), B2 (MAR off, voxel 0.2 mm), and B3 (MAR off, voxel 0.3 mm). For all protocols, receiver operating characteristic (ROC) curves were determined. Values for the areas under the ROC curves (Az) were subjected to analysis of variance. RESULTS Az values were not statistically different among protocols regardless of the defect type (P > .05). CONCLUSIONS The MAR algorithm tested by us did not improve the diagnosis of peri-implant fenestrations and dehiscences with use of either the 0.2 mm or the 0.3 mm voxel sizes.
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Affiliation(s)
- Sergio Lins de-Azevedo-Vaz
- Department of Clinical Dentistry, Faculty of Dentistry, Federal University of Espirito Santo, Vitoria, Espirito Santo, Brazil.
| | - Priscila Dias Peyneau
- Department of Oral Diagnosis, Division of Oral Radiology, Piracicaba Dental School, State University of Campinas, Piracicaba, Sao Paulo, Brazil
| | - Laura Ricardina Ramirez-Sotelo
- Department of Oral Diagnosis, Division of Oral Radiology, Piracicaba Dental School, State University of Campinas, Piracicaba, Sao Paulo, Brazil
| | - Karla de Faria Vasconcelos
- Department of Oral Diagnosis, Division of Oral Radiology, Piracicaba Dental School, State University of Campinas, Piracicaba, Sao Paulo, Brazil
| | - Paulo Sérgio Flores Campos
- Department of Oral Radiology, Division of Oral Radiology, School of Dentistry, Federal University of Bahia, Salvador, Bahia, Brazil
| | - Francisco Haiter-Neto
- Department of Oral Diagnosis, Division of Oral Radiology, Piracicaba Dental School, State University of Campinas, Piracicaba, Sao Paulo, Brazil
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The variation of HVL with focal spot to chamber distance as a function of beam quality for the Pantak Therapax 150 X-ray unit and the implications on dose to water determination using the IPEMB code of practice. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2014; 37:559-66. [DOI: 10.1007/s13246-014-0289-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2014] [Accepted: 07/12/2014] [Indexed: 11/25/2022]
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Hill R, Healy B, Holloway L, Kuncic Z, Thwaites D, Baldock C. Advances in kilovoltage x-ray beam dosimetry. Phys Med Biol 2014; 59:R183-231. [DOI: 10.1088/0031-9155/59/6/r183] [Citation(s) in RCA: 110] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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13
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A study on the use of Gafchromic™ EBT3 film for output factor measurements in kilovoltage X-ray beams. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2013; 36:465-71. [DOI: 10.1007/s13246-013-0226-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2013] [Accepted: 10/21/2013] [Indexed: 10/26/2022]
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14
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Eaton DJ, Doolan PJ. Review of backscatter measurement in kilovoltage radiotherapy using novel detectors and reduction from lack of underlying scattering material. J Appl Clin Med Phys 2013; 14:4358. [PMID: 24257277 PMCID: PMC5714622 DOI: 10.1120/jacmp.v14i6.4358] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Revised: 06/18/2013] [Accepted: 06/11/2013] [Indexed: 11/23/2022] Open
Abstract
Lack of underlying material can lead to dose reduction in kilovoltage radiotherapy treatments because of backscatter reduction. Conversely, the use of lead shielding can lead to large dose enhancement close to the lead interface. GAFCHROMIC film has been shown to be of use in verification of local backscatter factors compared to reference data in codes of practice, but careful handling and multiple readings are required to reduce systematic uncertainties to between 3% and 4%. Monte Carlo modeling of the specific treatment unit should be performed in cases which are found to differ from reference values before alternative values are adopted clinically, but these cases are expected to be few. GAFCHROMIC film may also be used to estimate backscatter reduction more readily than customized ionization chambers, for a range of beam qualities, applicator sizes and depth, with and without lead shielding. Differences were found between different studies, and it is not clear to what extent these are due to variation in equipment and/or technique. However, a layer of wax around lead shielding of 1 mm thickness should be sufficient to eliminate lead enhancement effects for all kilovoltage energies from 40 kV to 300 kV.
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Gorjiara T, Hill R, Bosi S, Kuncic Z, Baldock C. Water equivalence of NIPAM based polymer gel dosimeters with enhanced sensitivity for x-ray CT. Radiat Phys Chem Oxf Engl 1993 2013. [DOI: 10.1016/j.radphyschem.2013.05.018] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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16
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Reporting uncertainties in measurement: what approach should be followed? AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2013; 36:1-3. [DOI: 10.1007/s13246-013-0190-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Odgers D, Haque M. Near-catheter dosimetry of a HDR brachytherapy source using Gafchromic film. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2013; 36:159-66. [DOI: 10.1007/s13246-013-0186-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2012] [Accepted: 02/18/2013] [Indexed: 10/27/2022]
Affiliation(s)
- David Odgers
- Institute of Medical Physics, School of Physics, University of Sydney, Australia.
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Yu PKN, Butson MJ. Measurement of effects of nasal and facial shields on delivered radiation dose for superficial x-ray treatments. Phys Med Biol 2013; 58:N95-N102. [PMID: 23422253 DOI: 10.1088/0031-9155/58/5/n95] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Kilovoltage x-ray beams are used for the treatment of facial cancers when located on the patient's skin or subcutaneous tissue. This is of course due to the sharp depth dose characteristics of these beams delivering much lower doses at depth, than high energy x-ray beams. When treatment is performed, lead shields are often used within the nasal passage, or behind the lips and ears. These shields affect the backscattering patterns of the x-ray beams producing perturbations to upstream dose thus reducing delivered dose to the tumour. Experimental results using radiochromic films have shown that up to 10.5% ± 1.9% reduction in tumour dose can occur for field sizes less than 5 cm circle diameter for x-ray beams of 50 to 150 kVp. These results were confirmed using EGSnrc Monte Carlo techniques. Clinically more than 70% of treatments used fields of diameters less than 3 cm where the reductions were up to 6% ± 1.3%. Using a 1 cm diameter field, which can be used for skin cancer treatment on the nose, reductions up to 2.5% ± 1.3% were seen. Thus corrections need to be applied for dose calculations when underlying lead shields are used clinically in kilovoltage x-rays. The size of the reduction was also found to be dependent on the depth of the shield which will normally clinically vary from approximately 0.5 cm for nasal shields or behind eye lobes and up to approximately 1 cm for lips or cheek areas. We recommend that clinics utilize data for corrections to delivered dose in kilovoltage x-ray beams when lead shields are used in nasal passages, behind lips or behind ears for dose reduction. This can be easily and accurately measured with EBT2 Gafchromic film.
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Affiliation(s)
- Peter K N Yu
- Department of Physics and Materials Science, City University of Hong Kong, Kowloon Tong, Hong Kong
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Mesbahi A, Zakariaee SS. Effect of anode angle on photon beam spectra and depth dose characteristics for X-RAD320 orthovoltage unit. Rep Pract Oncol Radiother 2013; 18:148-52. [PMID: 24416546 DOI: 10.1016/j.rpor.2012.12.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2012] [Revised: 09/23/2012] [Accepted: 12/18/2012] [Indexed: 12/01/2022] Open
Abstract
BACKGROUND In radiation therapy with orthovoltage units, the tube design has a crucial effect on its dosimetric features. AIM In this study, the effect of anode angle on photon beam spectra, depth dose and photon fluence per initial electron was studied for a commercial orthovoltage unit of X-RAD320 biological irradiator. MATERIALS AND METHODS The MCNPX MC code was used for modeling in the current study. We used the Monte Carlo method to model the X-RAD320 X-ray unit based on the manufacturer provided information. The MC model was validated by comparing the MC calculated photon beam spectra with the results of SpekCalc software. The photon beam spectra were calculated for anode angles from 15 to 35 degrees. We also calculated the percentage depth doses for some angles to verify the impact of anode angle on depth dose. Additionally, the heel effect and its relation with anode angle were studied for X-RAD320 irradiator. RESULTS Our results showed that the photon beam spectra and their mean energy are changed significantly with anode angle and the optimum anode angle of 30 degrees was selected based on less heel effect and appropriate depth dose and photon fluence per initial electron. CONCLUSION It can be concluded that the anode angle of 30 degrees for X-RAD320 unit used by manufacturer has been selected properly considering the heel effect and dosimetric properties.
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Affiliation(s)
- Asghar Mesbahi
- Medical Physics Department, Medical School, Tabriz University of Medical Sciences, Tabriz, Iran ; Radiation Oncology Department, Imam Hospital, Tabriz, Iran
| | - Seyed-Salman Zakariaee
- Medical Physics Department, Medical School, Tabriz University of Medical Sciences, Tabriz, Iran
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The dosimetry of eye shields for kilovoltage X-ray beams. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2012. [DOI: 10.1007/s13246-012-0166-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Mart CJ, Elson HR, Lamba MAS. Measurement of low-energy backscatter factors using GAFCHROMIC film and OSLDs. J Appl Clin Med Phys 2012; 13:3832. [PMID: 23149776 PMCID: PMC5718537 DOI: 10.1120/jacmp.v13i6.3832] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Revised: 05/04/2012] [Accepted: 07/05/2012] [Indexed: 11/23/2022] Open
Abstract
Some of the lowest voltages used in radiotherapy are termed Grenz and superficial X‐rays of ~ 20 and ~ 100 kVp, respectively. Dosimetrically, the surface doses from these beams are calculated with the use of a free in‐air air kerma measurement combined with a backscatter factor and the appropriate ratio of mass energy absorption coefficients from the measurement material to water. Alternative tools to the standard ion chamber for measuring the BSF are GAFCHROMIC EBT2 film and optically stimulated luminescent dosimeter (OSLD) crystals made from Al2O3. The scope of this project included making three different backscatter measurements with an Xstrahl‐D3100 X‐ray unit on the Grenz ray and superficial settings. These measurements were with OSLDs, GAFCHROMIC EBT2 film, and a PTW ionization chamber. The varied measurement methods allowed for intercomparison to determine the accuracy of the results. The ion chamber measurement was the least accurate, as expected from previous experimental findings. GAFCHROMIC EBT2 film proved to be a useful tool which gave reasonable results, and Landauer OSLDs showed good results for smaller field sizes and an increasing overresponse with larger fields. The specific backscatter factors for this machine demonstrated values about 5% higher than the universal values suggested by the AAPM and IPEMB codes of practice for the 100 kVp setting. The 20 kvp measured data from both techniques showed general agreement with those found in the BJR Supplement No. 10, indicating that this unit's Grenz ray spectrum is similar to those used in previous experimental work. PACS number: 87.53.Bn
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Affiliation(s)
- Chris J Mart
- The Barrett Cancer Center, University of Cincinnati, Cincinnati, OH 45219, USA.
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Practical considerations for reporting surface dose in external beam radiotherapy: a 6 MV X-ray beam study. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2012; 35:271-82. [DOI: 10.1007/s13246-012-0145-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2011] [Accepted: 05/28/2012] [Indexed: 11/25/2022]
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Nakano M, Hill RF, Whitaker M, Kim JH, Kuncic Z. A study of surface dosimetry for breast cancer radiotherapy treatments using Gafchromic EBT2 film. J Appl Clin Med Phys 2012; 13:3727. [PMID: 22584169 PMCID: PMC5716557 DOI: 10.1120/jacmp.v13i3.3727] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2011] [Revised: 01/17/2012] [Accepted: 01/13/2012] [Indexed: 11/26/2022] Open
Abstract
The present study quantified surface doses on several rectangular phantom setups and on curved surface phantoms for a 6 MV photon field using the Attix parallel‐plate chamber and Gafchromic EBT2 film. For the rectangular phantom setups, the surface doses on a homogenous water equivalent phantom and a water equivalent phantom with 60 mm thick lung equivalent material were measured. The measurement on the homogenous phantom setup showed consistency in surface and near‐surface doses between an open field and enhanced dynamic wedge (EDW) fields, whereas physical wedged fields showed small differences. Surface dose measurements made using the EBT2 film showed good agreement with results of the Attix chamber and results obtained in previous studies which used other dosimeters within the measurement uncertainty of 3.3%. The surface dose measurements on the phantom setup with lung equivalent material showed a small increase without bolus and up to 6.9% increase with bolus simulating the increase of chest wall thickness. Surface doses on the cylindrical CT phantom and customized Perspex chest phantom were measured using the EBT2 film with and without bolus. The results indicate the important role of the presence of bolus if the clinical target volume (CTV) is quite close to the surface. Measurements on the cylindrical phantom suggest that surface doses at the oblique positions of 60° and 90° are mainly caused by the lateral scatter from the material inside the phantom. In the case of a single tangential irradiation onto Perspex chest phantom, the distribution of the surface dose with and without bolus materials showed opposing inclination patterns, whereas the dose distribution for two opposed tangential fields gave symmetric dose distribution. This study also demonstrates the suitability of Gafchromic EBT2 film for surface dose measurements in megavoltage photon beams. PACS number: 87.53.Bn
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Affiliation(s)
- Masahiro Nakano
- Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW 2006, Australia.
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Backscatter factor measurements for kilovoltage X-ray beams using thermoluminescent dosimeters (TLDs). RADIAT MEAS 2011. [DOI: 10.1016/j.radmeas.2011.08.019] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Benmakhlouf H, Bouchard H, Fransson A, Andreo P. Backscatter factors and mass energy-absorption coefficient ratios for diagnostic radiology dosimetry. Phys Med Biol 2011; 56:7179-204. [DOI: 10.1088/0031-9155/56/22/012] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Gorjiara T, Hill R, Kuncic Z, Bosi S, Davies JB, Baldock C. Radiological characterization and water equivalency of genipin gel for x-ray and electron beam dosimetry. Phys Med Biol 2011; 56:4685-99. [PMID: 21734335 DOI: 10.1088/0031-9155/56/15/004] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The genipin radiochromic gel offers enormous potential as a three-dimensional dosimeter in advanced radiotherapy techniques. We have used several methods (including Monte Carlo simulation), to investigate the water equivalency of genipin gel by characterizing its radiological properties, including mass and electron densities, photon interaction cross sections, mass energy absorption coefficient, effective atomic number, collisional, radiative and total mass stopping powers and electron mass scattering power. Depth doses were also calculated for clinical kilovoltage and megavoltage x-ray beams as well as megavoltage electron beams. The mass density, electron density and effective atomic number of genipin were found to differ from water by less than 2%. For energies below 150 keV, photoelectric absorption cross sections are more than 3% higher than water due to the strong dependence on atomic number. Compton scattering and pair production interaction cross sections for genipin gel differ from water by less than 1%. The mass energy absorption coefficient is approximately 3% higher than water for energies <60 keV due to the dominance of photoelectric absorption in this energy range. The electron mass stopping power and mass scattering power differ from water by approximately 0.3%. X-ray depth dose curves for genipin gel agree to within 1% with those for water. Our results demonstrate that genipin gel can be considered water equivalent for kilovoltage and megavoltage x-ray beam dosimetry. For megavoltage electron beam dosimetry, however, our results suggest that a correction factor may be needed to convert measured dose in genipin gel to that of water, since differences in some radiological properties of up to 3% compared to water are observed. Our results indicate that genipin gel exhibits greater water equivalency than polymer gels and PRESAGE formulations.
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Affiliation(s)
- Tina Gorjiara
- Institute of Medical Physics, School of Physics, University of Sydney, NSW 2006, Australia
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Smith L, Hill R, Nakano M, Kim J, Kuncic Z. The measurement of backscatter factors of kilovoltage X-ray beams using Gafchromic™ EBT2 film. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2011; 34:261-6. [DOI: 10.1007/s13246-011-0073-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2010] [Accepted: 04/05/2011] [Indexed: 10/18/2022]
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Yohannes I, Kolditz D, Kalender WA. Semiempirical analysis of materials' elemental composition to formulate tissue-equivalent materials: a preliminary study. Phys Med Biol 2011; 56:2963-77. [DOI: 10.1088/0031-9155/56/10/005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Gorjiara T, Hill R, Kuncic Z, Adamovics J, Bosi S, Kim JH, Baldock C. Investigation of radiological properties and water equivalency of PRESAGE®dosimeters. Med Phys 2011; 38:2265-74. [DOI: 10.1118/1.3561509] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Gorjiara T, Hill R, Kuncic Z, Bosi S, Baldock C. An evaluation of Genipin gel as a water equivalent dosimeter for megavoltage electron beams and kilovoltage x-ray beams. ACTA ACUST UNITED AC 2010. [DOI: 10.1088/1742-6596/250/1/012036] [Citation(s) in RCA: 4] [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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Hill R, Kuncic Z, Baldock C. The water equivalence of solid phantoms for low energy photon beams. Med Phys 2010; 37:4355-63. [DOI: 10.1118/1.3462558] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Hill R, Smith L, Kim J, Nakano M, Kuncic Z. SU-GG-T-365: Backscatter Factor Measurements Using Gafchromic EBT2 Film. Med Phys 2010. [DOI: 10.1118/1.3468762] [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
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