A new approach to film dosimetry for high energy photon beams: Lateral scatter filtering

Burch, Sandra E.; Kearfott, Kimberlee J.; Trueblood, Jon H.; Sheils, W. Chris; Yeo, Jason Inhwan; Wang, C. K. Chris

doi:10.1118/1.597999

Cited by 74 publications

(78 citation statements)

References 5 publications

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“…Due to the much smaller grain size, used in the EDR2 film structure, it is a very slow speed film and nearly energy independent for dose values of less than 5 Gy 13, [16][17][18][19][20][21] . Dose values obtained from EDR2 film measurements have been reported to agree with ion chamber measurements within 1-2% [11][12][13] .…”

Section: Methodsmentioning

confidence: 99%

Comparison of two-dimensional transmitted dose maps: evaluation of existing algorithms

Mohammadi

Bezak

Reich

2006

Australas. Phys. Eng. Sci. Med.

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Composite analysis and the gamma function are often used to assess the agreement between a reference and an evaluated two-dimensional dose maps. The intent of the study is to compare advantages, disadvantages and limitations of dose evaluation tools reported in the literature. In addition, in order to improve the gamma function output, a "Signed Matrix" was introduced using the ratio of relative dose difference maps. Transmitted dose maps were acquired for a range of homogeneous phantoms using Extended Dose Range (EDR2) films and a Scanning Liquid Ionization Chamber Electronic Portal Imaging Device (SLIC-EPID). For inhomogeneous case, the transmitted dose maps were obtained from EDR2 films measurement and a Treatment Planning System (TPS). The corresponding dose maps were compared based on composite and gamma function algorithms. The results showed that the agreement between reference and evaluated dose maps for the composite analysis were generally greater than those obtained using the gamma function. For homogeneous phantom comparison, the difference between the agreeing fractions calculated using composite analysis and gamma function increases with the increase of phantom thickness for deltaD = 0.5% and 1%. For inhomogeneous cases, a significant difference (approximately 5% for deltaD = 1.5%) was observed between the percentage agreement as calculated by composite and gamma function techniques. The concept of the composite model is closer than gamma function to the idea of the two-dimensional dose verification protocol proposed originally by van Dyk. However, the composite model results only display the passed or failed regions in the dose maps. On the other hand, the gamma function provides continuos information by distinguishing the points within each region. The overdosed/underdosed regions (the ratio of reference and evaluated doses at a given point) and the direction of the misalignment can be recognized with the enhanced gamma map convolved with a "Signed Matrix".

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Section: Methodsmentioning

confidence: 99%

Comparison of two-dimensional transmitted dose maps: evaluation of existing algorithms

Mohammadi

Bezak

Reich

2006

Australas. Phys. Eng. Sci. Med.

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“…21,24,25 The above field size and depth dependence measurements were repeated with two 0.3 mm thick lead foils sandwiching the dosimeters, separated by 6 mm solid water material upstream and 3 mm downstream.…”

Section: Iic6 Field Size and Depth Dependence With Lowenergy Photomentioning

confidence: 99%

Quantitative megavoltage radiation therapy dosimetry using the storage phosphor KCl:Eu2+

et al. 2009

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This work, for the first time, reports the use of europium doped potassium chloride ͑KCl: Eu 2+ ͒ storage phosphor for quantitative megavoltage radiation therapy dosimetry. In principle, KCl: Eu 2+ functions using the same photostimulatated luminescence ͑PSL͒ mechanism as commercially available BaFBr 0.85 I 0.15 :Eu 2+ material that is used for computed radiography ͑CR͒ but features a significantly smaller effective atomic number-18 versus 49-making it a potentially useful material for nearly tissue-equivalent radiation dosimetry. Cylindrical KCl: Eu 2+ dosimeters, 7 mm in diameter and 1 mm thick, were fabricated in-house. Dosimetric properties, including radiation hardness, response linearity, signal fading, dose rate sensitivity, and energy dependence, were studied with a laboratory optical reader after irradiation by a linear accelerator. The overall experimental uncertainty was estimated to be within Ϯ2.5%. The findings were ͑1͒ KCl: Eu 2+ showed satisfactory radiation hardness. There was no significant change in the stimulation spectra after irradiation up to 200 Gy when compared to a fresh dosimeter, indicating that this material could be reused at least 100 times if 2 Gy per use was assumed, e.g., for patient-specific IMRT QA. ͑2͒ KCl: Eu 2+ exhibited supralinear response to dose after irradiation from 0 to 800 cGy. ͑3͒ After x ray irradiation, the PSL signal faded with time and eventually reached a fading rate of about 0.1% / h after 12 h. ͑4͒ The sensitivity of the dosimeter was independent of the dose rate ranging from 15 to 1000 cGy/ min. ͑5͒ The sensitivity showed no beam energy dependence for either open x ray or megavoltage electron fields. ͑6͒ Over-response to low-energy scattered photons was comparable to radiographic film, e.g., Kodak EDR2 film. By sandwiching dosimeters between low-energy photon filters ͑0.3 mm thick lead foils͒ during irradiation, the over-response was reduced. The authors have demonstrated that KCl: Eu 2+ dosimeters have many desirable dosimetric characteristics that make the material conducive to radiation therapy dosimetry. In the future, a large-area KCl: Eu 2+ -based CR plate with a thickness of the order of a few microns, created using modern thin film techniques, could provide a reusable, quantitative, high-resolution two-dimensional dosimeter with minimal energy dependence.

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“…( 4 , 5 ) Scatter filtering does attenuate the low‐energy photons but also attenuates a fraction of the high‐energy photons and creates an additional unwanted scatter component. An alternative approach is to minimize error by matching scatter conditions for the calibration to the experiment as closely as possible while keeping the film development and analysis process consistent.…”

Section: Introductionmentioning

confidence: 99%

Accuracy of rapid radiographic film calibration for intensity‐modulated radiation therapy verification

Kulasekere

Moran

Fraass

et al. 2006

J Applied Clin Med Phys

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A single calibration film method was evaluated for use with intensity‐modulated radiation therapy film quality assurance measurements. The single‐film method has the potential advantages of exposure simplicity, less media consumption, and improved processor quality control. Potential disadvantages include cross contamination of film exposure, implementation effort to document delivered dose, and added complication of film response analysis. Film response differences were measured between standard and single‐film calibration methods. Additional measurements were performed to help trace causes for the observed discrepancies. Kodak X‐OmatV (XV) film was found to have greater response variability than extended dose range (EDR) film. We found it advisable for XV film to relate the film response calibration for the single‐film method to a user‐defined optimal calibration geometry. Using a single calibration film exposed at the time of experiment, the total uncertainty of film response was estimated to be <2% (1%) for XV (EDR) film at 50 (100) cGy and higher, respectively.PACS numbers: 87.53.‐j, 87.53.Dq

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A new approach to film dosimetry for high energy photon beams: Lateral scatter filtering

Cited by 74 publications

References 5 publications

Comparison of two-dimensional transmitted dose maps: evaluation of existing algorithms

Comparison of two-dimensional transmitted dose maps: evaluation of existing algorithms

Quantitative megavoltage radiation therapy dosimetry using the storage phosphor KCl:Eu2+

Accuracy of rapid radiographic film calibration for intensity‐modulated radiation therapy verification

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