Reference photon dosimetry data: A preliminary study of in-air off-axis factor, percentage depth dose, and output factor of the Siemens Primus linear accelerator

Cho, S. H.

doi:10.1120/1.1617191

Cited by 5 publications

(7 citation statements)

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“…All the in-air OAFs reported in this study were measured with farmer-type ionization chambers, at a source-toaxis distance (SAD) of 100 cm, with an appropriate plastic buildup cap for the 6 MV photon beam. 2 RFS: the reference field size (RFS is normally a 10 ϫ 10 cm 2 field for photon beams. ); other variables are as defined earlier.…”

Section: Definitions Of Variables and Dosimetric Quantitiesmentioning

confidence: 99%

“…Details about the RPC's measurement techniques and instrumentation can be found elsewhere. 2 The RPC has accumulated a sufficient number of data on the Varian Clinac 2100 series linear accelerators and, therefore, a statistical analysis on the data could reveal some similarity among photon dosimetry data. The RPC-measured FDD, OF, and in-air OAF data were extracted from the RPC database for a statistical analysis.…”

Section: The Rpc-measured Datamentioning

confidence: 99%

“…The modern computer-controlled linear accelerators for radiation therapy are becoming more reproducible, in terms of their structures and dosimetric characteristics, as long as the make and model of the machines are identical. 1,2 Consequently, dosimetry data commonly applicable for linear accelerators of the same make, model, and nominal energy may exist. The availability of such data will significantly benefit a wide range of radiation oncology and medical physics practices.…”

Section: Introductionmentioning

confidence: 99%

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Reference photon dosimetry data and reference phase space data for the photon beam from Varian Clinac 2100 series linear accelerators

et al. 2004

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The current study presents the reference photon dosimetry data (RPDD) and reference phase space data (RPSD) for the 6 MV photon beam from Varian 2100 series linear accelerators. The RPDD provide the basic photon dosimetry data, typically collected during the initial commissioning of a new linear accelerator, including output factors, depth dose data, and beam profile data in air and in water. The RPSD provide the full phase space information, such as position, direction, and energy for each particle generated inside the head of any particular linear accelerator in question. The dosimetric characteristics if the 6 MV photon beam from the majority of the aforementioned accelerators, which are unaltered from the manufacturer's original specifications, can be fully described with these two data sets within a clinically acceptable uncertainty (approximately +/-2 %). The current study also presents a detailed procedure to establish the RPDD and RPSD using measured data and Monte Carlo calculations. The RPDD were constructed by compiling our own measured data and the average data based on the analysis of more than 50 sets of measured data from the Radiological Physics Center (RPC) and 10 sets of clinical dosimetry data obtained from 10 different institutions participating in the RPC's quality assurance monitoring program. All the measured data from the RPC and the RPC-monitored institutions were found to be within a statistically tight range (i.e., 1sigma approximately 1% or less) for each dosimetric quantity. The manufacturer's standard data, except for in-air off-axis factors that are available only from the current study, were compared with the RPDD, showing that the manufacturer's standard data could also be used as the RPDD for the photon beam studied in this study. The RPSD were obtained from Monte Carlo calculations using the BEAMnrc/ DOSXYZnrc code system with 6.2 MeV (a spread of 3% full width at half maximum) and 1.0 mm full width at half maximum as the values of the energy and radial spread of a Gaussian electron pencil beam incident on the target, respectively. The RPSD were capable of generating Monte Carlo data that agreed with the RPDD within the acceptance criteria adopted in the current study (e.g., 1% or 1 mm for depth dose). A complete set of the RPDD and RPSD from the current study is available from the RPC website (http://rpc.mdanderson.org) or via mass storage media such as DVD or CD-ROM upon request.

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Section: Definitions Of Variables and Dosimetric Quantitiesmentioning

confidence: 99%

Section: The Rpc-measured Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Reference photon dosimetry data and reference phase space data for the photon beam from Varian Clinac 2100 series linear accelerators

et al. 2004

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“…(16) On the other hand, there are those who believe that, in the current age of computer design, linacs can be produce to very tight specifications and thus reference database are appropriate. (17,18) AAPM Task Group 106 cautions that careful evaluation is needed before using reference database in linacs' commissioning, but states that it is an excellent source of quality assurance for verifying commissioning results. (19) This was a recent point/counter point debate in the Medical Physics journal, where it was argued whether or not reference databases or vendor-provided databases are appropriate.…”

Section: Introductionmentioning

confidence: 99%

Enhanced dynamic wedge output factors for Varian 2300CD and the case for a reference database

Njeh¹

2015

J Applied Clin Med Phys

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Dose inhomogeneity in treatment planning can be compensated using physical wedges. Enhanced dynamic wedges (EDW) were introduced by Varian to overcome some of the shortcomings of physical wedges. The objectives of this study were to measure EDW output factors for 6 MV and 20 MV photon energies for a Varian 2300CD. Secondly, to review the literature in terms of published enhanced dynamic wedge output factors (EDWOF) for different Varian models and thereby add credence to the case of the validity of reference databases. The enhanced dynamic wedge output factors were measured for the Varian 2300CD for both 6 MV and 20 MV photon energies. Twelve papers with published EDWOF for different Varian linac models were found in the literature. Comparing our results with the published mean, we found an excellent agreement for 6 MV EDWOF, with the percentage differences ranging from 0.01% to 0.57%, with a mean of 0.03%. The coefficient of variation of published EDWOF ranged from 0.17% to 0.85% and 0.1% to 0.9% for the for 6 MV and 18 MV photon energies, respectively. This paper provides the first published EDWOF for 20 MV photon energy. In addition, we have provided the first compendium of EDWOFs for different Varian linac models. The consistency of value across models and institution provide further support that a standard dataset of basic photon and electron dosimetry could be established as a guide for future commissioning, beam modeling, and quality assurance purposes.PACS numbers: 87.50, 87.55

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“…Because of the consistency in output performance of today's modern linac, the specific source models produced from this data are expected to be broadly applicable to Varian 2100 series linacs. 23,[25][26][27][28][29][30][31][32][33][34][35] Measurements were made using a small volume (0.04 cm 3 , 4 mm diameter) ion chamber. To account for the volume effects of the ion chamber, which tend to smear the dose and exaggerate the dose penumbra, a Gaussian convolution was applied to the calculated dose data for all profile comparisons.…”

Section: C Validation Testingmentioning

confidence: 99%

Modification and validation of an analytical source model for external beam radiotherapy Monte Carlo dose calculations

et al. 2016

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Purpose: A dose calculation tool, which combines the accuracy of the dose planning method (DPM) Monte Carlo code and the versatility of a practical analytical multisource model, which was previously reported has been improved and validated for the Varian 6 and 10 MV linear accelerators (linacs). The calculation tool can be used to calculate doses in advanced clinical application studies. One shortcoming of current clinical trials that report dose from patient plans is the lack of a standardized dose calculation methodology. Because commercial treatment planning systems (TPSs) have their own dose calculation algorithms and the clinical trial participant who uses these systems is responsible for commissioning the beam model, variation exists in the reported calculated dose distributions. Today's modern linac is manufactured to tight specifications so that variability within a linac model is quite low. The expectation is that a single dose calculation tool for a specific linac model can be used to accurately recalculate dose from patient plans that have been submitted to the clinical trial community from any institution. The calculation tool would provide for a more meaningful outcome analysis. Methods: The analytical source model was described by a primary point source, a secondary extra-focal source, and a contaminant electron source. Off-axis energy softening and fluence effects were also included. The additions of hyperbolic functions have been incorporated into the model to correct for the changes in output and in electron contamination with field size. A multileaf collimator (MLC) model is included to facilitate phantom and patient dose calculations. An offset to the MLC leaf positions was used to correct for the rudimentary assumed primary point source.Results: Dose calculations of the depth dose and profiles for field sizes 4 × 4 to 40 × 40 cm agree with measurement within 2% of the maximum dose or 2 mm distance to agreement (DTA) for 95% of the data points tested. The model was capable of predicting the depth of the maximum dose within 1 mm. Anthropomorphic phantom benchmark testing of modulated and patterned MLCs treatment plans showed agreement to measurement within 3% in target regions using thermoluminescent dosimeters (TLD). Using radiochromic film normalized to TLD, a gamma criteria of 3% of maximum dose and 2 mm DTA was applied with a pass rate of least 85% in the high dose, high gradient, and low dose regions. Finally, recalculations of patient plans using DPM showed good agreement relative to a commercial TPS when comparing dose volume histograms and 2D dose distributions. Conclusions: A unique analytical source model coupled to the dose planning method Monte Carlo dose calculation code has been modified and validated using basic beam data and anthropomorphic phantom measurement. While this tool can be applied in general use for a particular linac model, specifically it was developed to provide a singular methodology to independently assess treatment

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Reference photon dosimetry data: A preliminary study of in-air off-axis factor, percentage depth dose, and output factor of the Siemens Primus linear accelerator

Cited by 5 publications

References 0 publications

Reference photon dosimetry data and reference phase space data for the photon beam from Varian Clinac 2100 series linear accelerators

Reference photon dosimetry data and reference phase space data for the photon beam from Varian Clinac 2100 series linear accelerators

Enhanced dynamic wedge output factors for Varian 2300CD and the case for a reference database

Modification and validation of an analytical source model for external beam radiotherapy Monte Carlo dose calculations

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