A prototype, glassless densitometer traceable to primary optical standards for quantitative radiochromic film dosimetry

Rosen, Benjamin; Soares, Christopher G.; Hammer, Clifford G.; Kunugi, Keith A.; DeWerd, Larry A.

doi:10.1118/1.4922134

Cited by 9 publications

(19 citation statements)

References 47 publications

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“…For all postirradiation analyses, film samples were scanned at least seven days following exposure to minimize change in film response due to small variations in development duration . Film was scanned postirradiation in the same numerical order as it was scanned prior to irradiation to mitigate any positional or temporal nonuniformities associated with the LDS scanner . In order to provide a calibrated optical density measurement, a series of NIST‐traceable calibrated reference materials (CRMs) bracketing the expected film OD range were included with every scan.…”

Section: Methodsmentioning

confidence: 99%

“…The film dosimeters were scanned using the UWMRRC Laser Densitometry System (LDS). 38 The LDS is a NIST-traceable laser densitometry system developed in-house that performs pointbased measurements of radiochromic film suspended in freespace using coherent light to mitigate common film scanning artifacts, such as positional scan dependence and high noise in low-dose regions. 39,40 The LDS uses a 635 nm diode laser light source and point photodiode detector.…”

Section: E Film Preparation and Preirradiation Scanningmentioning

confidence: 99%

“…39,40 The LDS uses a 635 nm diode laser light source and point photodiode detector. Rosen et al 38 demonstrated total elimination of the lateral response artifact (LRA) and minimal nonuniformity using the LDS. Thus, no corrections for LRA or scanner nonuniformity were made.…”

Section: E Film Preparation and Preirradiation Scanningmentioning

confidence: 99%

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Experimental investigation of GafChromic^® EBT3 intrinsic energy dependence with kilovoltage x rays, ¹³⁷Cs, and ⁶⁰Co

Hammer

Rosen

Fagerstrom³

et al. 2017

Medical Physics

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Purpose: To determine experimentally the intrinsic energy response, k bq , of EBT3 GafChromic â radiochromic film with kilovoltage x rays, 137 Cs, and 60 Co in therapeutic and diagnostic dose ranges through direct measurement with an accompanying mathematical approach to describe the physical processes involved. Methods: The EBT3 film was irradiated with known doses using 60 Co, 137 Cs, and 13 NIST-matched kilovoltage x-ray beams. Seven dose levels, ranging from 57 to 7002 mGy, were chosen for this work. Monte Carlo methods were used to convert air-kerma rates to dose rates to the film active layer for each energy. A total of 738 film dosimeters, each measuring (1.2 9 1.2) cm 2 , were cut from three film sheets out of the same lot of the latest version of EBT3 film, to allow for multiple dosimeters to be irradiated by each target dose and beam quality as well as unirradiated dosimeters to be used as controls. Net change in optical density in excess of the unirradiated controls was measured using the UWMRRC Laser Densitometry System (LDS). The dosimeter intrinsic energy response, k bq , for each dose level was determined relative to 60 Co, as the ratio of dosimeter response to each beam quality relative to the absorbed dose to the film active volume at the same dose level. A simplified, single-hit mathematical model was used to derive a single-free-parameter, b, which is a proportionality constant that is dependent on beam quality and describes the microdosimetric interactions within the active layer of film. The response of b for each beam quality relative to 60 Co was also determined. Results: k bq was determined for a wide range of doses and energies. The results show a unique variation of k bq as a function of energy, and agree well with results from other investigations. There was no measurable dose dependence for k bq within the 500-7002 mGy range outside of the expanded measurement uncertainty of 3.65% (k = 2). For doses less than 500 mGy, the signal-to-noise ratio was too low to determine k bq accurately. The single-free-parameter, b, fit calculations derived from the single-hit model show a correlation with k bq that suggests that b, at least in part, characterizes the microdosimetric interactions that determine k bq . Conclusions: For the beam qualities investigated, a single energy-dependent k bq correction can be used for doses between 500 and 7002 mGy. Using the single-hit model with the single-free-parameter fit to solve for b shows promise in the determination of the intrinsic energy response of film, with b being the mathematical analog of the measured k bq .

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Section: Methodsmentioning

confidence: 99%

Section: E Film Preparation and Preirradiation Scanningmentioning

confidence: 99%

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Experimental investigation of GafChromic^® EBT3 intrinsic energy dependence with kilovoltage x rays, ¹³⁷Cs, and ⁶⁰Co

Hammer

Rosen

Fagerstrom³

et al. 2017

Medical Physics

View full text Add to dashboard Cite

show abstract

“…An in-house laser densitometer was used as a readout system (Rosen et al , 2015). This laser densitometer operates by scanning a tray insert along a 2D plane using a 635 nm laser paired with a photodiode.…”

Section: Methodsmentioning

confidence: 99%

“…After the netOD was calculated for each dosimeter, the netOD of a control dosimeter from the same batch of dosimeters was subtracted from the result to account for any polymerization induced by the background. The uncertainty of each netOD measurement was calculated through the propagation of the standard deviations of the pre-irradiation OD, post- irradiation OD, and the uncertainty of the netOD of the control (Rosen et al , 2015). Each of these uncertainties arose from the propagation of the standard deviations of the voltage readouts from the densitometer and the standard deviation arising from the calibration of voltage readout to OD for the densitometer.…”

Section: Methodsmentioning

confidence: 99%

Initial characterization of a gel patch dosimeter forin vivodosimetry

et al. 2016

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In vivo dosimetry is a greatly underutilized tool for patient safety in clinical external beam radiotherapy treatments, despite being recommended by several national and international organizations (AAPM, ICRU, IAEA, NACP). The reasons for this underutilization mostly relate to the feasibility and cost of in vivo dosimetry methods. Due to the increase in the number of beam angles and dose per fraction in modern treatments, there is a compelling need for a novel dosimeter that is robust and affordable while able to operate properly in these complex conditions. This work presents a gel patch dosimeter as a novel method of in vivo dosimetry. DEFGEL, a 6%T normoxic polyacrylamide gel, was injected into 1-cm thick acrylic molds to create 1-cm thick small cylindrical patch dosimeters. To evaluate the change in optical density due to radiation induced polymerization, dosimeters were scanned before and after irradiation using an in-house developed laser densitometer. The dose-responses of three separate batches of gel were evaluated and compared to check for linearity and repeatability. The response development time was evaluated to ensure that the patch dosimeter could be high throughput. Additionally, the potential of this system to be used as an in vivo dosimeter was tested with a clinically relevant end-to-end in vivo phantom test. All irradiations were performed with a Varian Clinac 21EX at the University of Wisconsin Medical Radiation Research Center (UWMRRC). The dose response of all three batches of gel was found to be linear within the range of 2–20 Gy. At doses below 0.5 Gy the statistical uncertainties were prohibitively large to make quantitative assessments of the results. The three batches demonstrated good repeatability in the range of 2 Gy to up to 10 Gy, with only slight variations in response at higher doses. For low doses the dosimeter fully developed within an hour while at higher doses they fully developed within four hours. During the in vivo phantom test the predicted patch absorbed dose was 4.23 Gy while the readout dose was evaluated to be 4.37 Gy, which corresponds to a 3.2% discrepancy. The dosimeter and densitometer pairing shows promise as an in vivo dosimetry system, especially for hypofractionated or MRI-guided radiotherapy treatments where higher doses are prescribed.

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Report of AAPM Task Group 235 Radiochromic Film Dosimetry: An Update to TG‐55

et al. 2020

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The use of radiochromic film (RCF) dosimetry in radiation therapy is extensive due to its high level of achievable accuracy for a wide range of dose values and its suitability under a variety of measurement conditions. However, since the publication of the 1998 AAPM Task Group 55, Report No. 63 on RCF dosimetry, the chemistry, composition, and readout systems for RCFs have evolved steadily. There are several challenges in using the new RCFs, readout systems and validation of the results depending on their applications. Accurate RCF dosimetry requires understanding of RCF selection, handling and calibration methods, calibration curves, dose conversion methods, correction methodologies as well as selection, operation and quality assurance (QA) programs of the readout systems. Acquiring this level of knowledge is not straight forward, even for some experienced users. This Task Group report addresses these issues and provides a basic understanding of available RCF models, dosimetric characteristics and properties, advantages and limitations, configurations, and overall elemental compositions of the RCFs that have changed over the past 20 yr. In addition, this report provides specific guidelines for data processing and analysis schemes and correction methodologies for clinical applications in radiation therapy.

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A prototype, glassless densitometer traceable to primary optical standards for quantitative radiochromic film dosimetry

Cited by 9 publications

References 47 publications

Experimental investigation of GafChromic^® EBT3 intrinsic energy dependence with kilovoltage x rays, ¹³⁷Cs, and ⁶⁰Co

Experimental investigation of GafChromic^® EBT3 intrinsic energy dependence with kilovoltage x rays, ¹³⁷Cs, and ⁶⁰Co

Initial characterization of a gel patch dosimeter forin vivodosimetry

Report of AAPM Task Group 235 Radiochromic Film Dosimetry: An Update to TG‐55

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A prototype, glassless densitometer traceable to primary optical standards for quantitative radiochromic film dosimetry

Cited by 9 publications

References 47 publications

Experimental investigation of GafChromic® EBT3 intrinsic energy dependence with kilovoltage x rays, 137Cs, and 60Co

Experimental investigation of GafChromic® EBT3 intrinsic energy dependence with kilovoltage x rays, 137Cs, and 60Co

Initial characterization of a gel patch dosimeter forin vivodosimetry

Report of AAPM Task Group 235 Radiochromic Film Dosimetry: An Update to TG‐55

Contact Info

Product

Resources

About

Experimental investigation of GafChromic^® EBT3 intrinsic energy dependence with kilovoltage x rays, ¹³⁷Cs, and ⁶⁰Co

Experimental investigation of GafChromic^® EBT3 intrinsic energy dependence with kilovoltage x rays, ¹³⁷Cs, and ⁶⁰Co