Surface dose measurement for helical tomotherapy

Snir, Jonatan; Mosalaei, H; Jordan, Kevin; Yartsev, Slav

doi:10.1118/1.3592021

Cited by 8 publications

(9 citation statements)

References 12 publications

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“…212 The submillimeter thickness of the thin layer configuration of RCF makes it a strong candidate for dosimetry at surface and buildup regions both in phantom and in vivo. 18,212 RCF can be used for MV photon beam dosimetry at a phantom surface with an air interface for static and/or IMRT fields, 18,98,[212][213][214][215][216][217][218][219][220][221][222][223][224] as well as PDD 173,212 and dose profiles 212 in the shallow buildup region. For such measurements, RCF (a single piece or a stack of several pieces) is positioned parallel to the surface and perpendicular to the beam axis.…”

Section: Conventional Field Sizesmentioning

confidence: 99%

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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Section: Conventional Field Sizesmentioning

confidence: 99%

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

et al. 2020

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“…Due to its sensitivity to visible light, the active area of the detector is encapsulated in a

1 \times 1 \times 0.185 {cm}^{3}

protective plastic box with a mass density of 1.03 g/cm 3 , having an effective point of measurement (EPM), which is the water‐equivalent depth from surface to half active layer, of 0.8 mm. Similar to TLDs, in order to avoid a short‐term signal decay period, the OSLs were read with an InLight MicroStar reader at least 30 min after exposure 24 , 25 . All OSLs were preexposed to 1 kGy, as suggested by Jursinic (25) in order to better linearize further dose response.…”

Section: Methodsmentioning

confidence: 99%

“…Similar to TLDs, in order to avoid a short-term signal decay period, the OSLs were read with an InLight MicroStar reader at least 30 min after exposure. (24)(25) All OSLs were preexposed to 1 kGy, as suggested by Jursinic (25) in order to better linearize further dose response. After irradiation and readout, nanoDots were optically bleached in a light source.…”

Section: F Optically Stimulated Detectorsmentioning

confidence: 99%

Surface dose measurements with commonly used detectors: a consistent thickness correction method

Reynolds

Higgins

2015

J Applied Clin Med Phys

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The purpose of this study was to review application of a consistent correction method for the solid state detectors, such as thermoluminescent dosimeters (chips (cTLD) and powder (pTLD)), optically stimulated detectors (both closed (OSL) and open (eOSL)), and radiochromic (EBT2) and radiographic (EDR2) films. In addition, to compare measured surface dose using an extrapolation ionization chamber (PTW 30‐360) with other parallel plate chambers RMI‐449 (Attix), Capintec PS‐033, PTW 30‐329 (Markus) and Memorial. Measurements of surface dose for 6 MV photons with parallel plate chambers were used to establish a baseline. cTLD, OSLs, EDR2, and EBT2 measurements were corrected using a method which involved irradiation of three dosimeter stacks, followed by linear extrapolation of individual dosimeter measurements to zero thickness. We determined the magnitude of correction for each detector and compared our results against an alternative correction method based on effective thickness. All uncorrected surface dose measurements exhibited overresponse, compared with the extrapolation chamber data, except for the Attix chamber. The closest match was obtained with the Attix chamber (−0.1%), followed by pTLD (0.5%), Capintec (4.5%), Memorial (7.3%), Markus (10%), cTLD (11.8%), eOSL (12.8%), EBT2 (14%), EDR2 (14.8%), and OSL (26%). Application of published ionization chamber corrections brought all the parallel plate results to within 1% of the extrapolation chamber. The extrapolation method corrected all solid‐state detector results to within 2% of baseline, except the OSLs. Extrapolation of dose using a simple three‐detector stack has been demonstrated to provide thickness corrections for cTLD, eOSLs, EBT2, and EDR2 which can then be used for surface dose measurements. Standard OSLs are not recommended for surface dose measurement. The effective thickness method suffers from the subjectivity inherent in the inclusion of measured percentage depth‐dose curves and is not recommended for these types of measurements.PACS number: 87.56.‐v

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“…112 Others have made skin dose measurements with MOSFETS and diodes for multibeam treatments and have found each to be useful. 54,113 OSL detectors have also been used for skin dose measurements and have been found to be sufficiently accurate. 113,114…”

Section: B2 Detectors Used For Measurement Of Surface Dose and Bumentioning

confidence: 99%

“…54,113 OSL detectors have also been used for skin dose measurements and have been found to be sufficiently accurate. 113,114…”

Section: B2 Detectors Used For Measurement Of Surface Dose and Bumentioning

confidence: 99%

Dosimetric effects caused by couch tops and immobilization devices: Report of AAPM Task Group 176

et al. 2014

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The dosimetric impact from devices external to the patient is a complex combination of increased skin dose, reduced tumor dose, and altered dose distribution. Although small monitor unit or dose corrections are routinely made for blocking trays, ion chamber correction factors, e.g., accounting for temperature and pressure, or tissue inhomogeneities, the dose perturbation of the treatment couch top or immobilization devices is often overlooked. These devices also increase skin dose, an effect which is also often ignored or underestimated. These concerns have grown recently due to the increased use of monolithic carbon fiber couch tops which are optimal for imaging for patient position verification but cause attenuation and increased skin dose compared to the "tennis racket" style couch top they often replace. Also, arc delivery techniques have replaced stationary gantry techniques which cause a greater fraction of the dose to be delivered from posterior angles. A host of immobilization devices are available and used to increase patient positioning reproducibility, and these also have attenuation and skin dose implications which are often ignored. This report of Task Group 176 serves to present a survey of published data that illustrates the magnitude of the dosimetric effects of a wide range of devices external to the patient. The report also provides methods for modeling couch tops in treatment planning systems so the physicist can accurately compute the dosimetric effects for indexed patient treatments. Both photon and proton beams are considered. A discussion on avoidance of high density structures during beam planning is also provided. An important aspect of this report are the recommendations the authors make to clinical physicists, treatment planning system vendors, and device vendors on how to make measurements of surface dose and attenuation and how to report these values. For the vendors, an appeal is made to work together to provide accurate couch top models in planning systems.

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Surface dose measurement for helical tomotherapy

Cited by 8 publications

References 12 publications

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

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

Surface dose measurements with commonly used detectors: a consistent thickness correction method

Dosimetric effects caused by couch tops and immobilization devices: Report of AAPM Task Group 176

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