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Title: Calibration of Film for Accurate Megavoltage Photon Dosimetry


An accurate method of converting film density to dose is presented. For films oriented parallel to the beam’s central axis, calibration curves were produced at several depths using Kodak XV-2 film for cobalt-60, 4 MV, and 18 MV beams. Then the appropriate curve was employed to convert the film density to dose at a specific depth. It is hypothesized that the change in film response with depth is due to changes in the photon spectra at depth in a phantom.

 [1]; ;  [2]
  1. Queen’s University, Department of Physics, Kingston, Ontario, Canada, K7L 3N6 (Canada)
  2. Kingston Regional Cancer Centre, 25 King Street West, Kingston, Ontario, Canada, K7L 5P9 (Canada)
Publication Date:
OSTI Identifier:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Dosimetry; Journal Volume: 19; Journal Issue: 1; Other Information: Copyright (c) 1994 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States

Citation Formats

Hale, J.I., Kerr, A.T., and Shragge, P.C.. Calibration of Film for Accurate Megavoltage Photon Dosimetry. United States: N. p., 2015. Web. doi:10.1016/0958-3947(94)90032-9.
Hale, J.I., Kerr, A.T., & Shragge, P.C.. Calibration of Film for Accurate Megavoltage Photon Dosimetry. United States. doi:10.1016/0958-3947(94)90032-9.
Hale, J.I., Kerr, A.T., and Shragge, P.C.. 2015. "Calibration of Film for Accurate Megavoltage Photon Dosimetry". United States. doi:10.1016/0958-3947(94)90032-9.
title = {Calibration of Film for Accurate Megavoltage Photon Dosimetry},
author = {Hale, J.I. and Kerr, A.T. and Shragge, P.C.},
abstractNote = {An accurate method of converting film density to dose is presented. For films oriented parallel to the beam’s central axis, calibration curves were produced at several depths using Kodak XV-2 film for cobalt-60, 4 MV, and 18 MV beams. Then the appropriate curve was employed to convert the film density to dose at a specific depth. It is hypothesized that the change in film response with depth is due to changes in the photon spectra at depth in a phantom.},
doi = {10.1016/0958-3947(94)90032-9},
journal = {Medical Dosimetry},
number = 1,
volume = 19,
place = {United States},
year = 2015,
month = 1
  • The central problems of photon beam film dosimetry are the dependence of film response upon photon energy, processing conditions, and film plane orientation. Researchers have overcome these problems by accurately fitting the depth-dependent sensitometric curve of Kodak XV-2 film to the equation OD(D,d) = OHs(1 - exp (- ..cap alpha.. 0(1 + ..beta..(d-dm))D)) where OD(D,d) is the optical density for dose D at depth d. ODs, ..cap alpha.. 0, and ..beta.. are constants characteristic of the film and beam energy but are independent of field size. Only central axis depth dose data for a single field are required to determinemore » their values. A computer program based upon this equation has been written which successfully generates single field isodose curves from film data for a variety of field sizes with an accuracy of +/- 3%. Data are presented for 60Co, and 4 and 10 MV x rays.« less
  • Purpose: Three-dimensional (3D) dosimeters are particularly useful for verifying the commissioning of treatment planning and delivery systems, especially with the ever-increasing implementation of complex and conformal radiotherapy techniques such as volumetric modulated arc therapy. However, currently available 3D dosimeters require extensive experience to prepare and analyze, and are subject to large measurement uncertainties. This work aims to provide a more readily implementable 3D dosimeter with the development and characterization of a radiochromic film stack dosimeter for megavoltage photon beam dosimetry. Methods: A film stack dosimeter was developed using Gafchromic{sup ®} EBT2 films. The dosimeter consists of 22 films separated bymore » 1 mm-thick spacers. A Virtual Water™ phantom was created that maintains the radial film alignment within a maximum uncertainty of 0.3 mm. The film stack dosimeter was characterized using simulations and measurements of 6 MV fields. The absorbed-dose energy dependence and orientation dependence of the film stack dosimeter were investigated using Monte Carlo simulations. The water equivalence of the dosimeter was determined by comparing percentage-depth-dose (PDD) profiles measured with the film stack dosimeter and simulated using Monte Carlo methods. Film stack dosimeter measurements were verified with thermoluminescent dosimeter (TLD) microcube measurements. The film stack dosimeter was also used to verify the delivery of an intensity-modulated radiation therapy (IMRT) procedure. Results: The absorbed-dose energy response of EBT2 film differs less than 1.5% between the calibration and film stack dosimeter geometries for a 6 MV spectrum. Over a series of beam angles ranging from normal incidence to parallel incidence, the overall variation in the response of the film stack dosimeter is within a range of 2.5%. Relative to the response to a normally incident beam, the film stack dosimeter exhibits a 1% under-response when the beam axis is parallel to the film planes. Measured and simulated PDD profiles agree within a root-mean-square difference of 1.3%. In-field film stack dosimeter and TLD measurements agree within 5%, and measurements in the field penumbra agree within 0.5 mm. Film stack dosimeter and TLD measurements have expanded (k = 2) overall measurement uncertainties of 6.2% and 5.8%, respectively. Film stack dosimeter measurements of an IMRT dose distribution have 98% agreement with the treatment planning system dose calculation, using gamma criteria of 3% and 2 mm. Conclusions: The film stack dosimeter is capable of high-resolution, low-uncertainty 3D dose measurements, and can be readily incorporated into an existing film dosimetry program.« less
  • Film dosimetry is an attractive tool for dose distribution verification in intensity modulated radiotherapy (IMRT). A critical aspect of radiochromic film dosimetry is the scanner used for the readout of the film: the output needs to be calibrated in dose response and corrected for pixel value and spatial dependent nonuniformity caused by light scattering; these procedures can take a long time. A method for a fast and accurate calibration and uniformity correction for radiochromic film dosimetry is presented: a single film exposure is used to do both calibration and correction. Gafchromic EBT films were read with two flatbed charge coupledmore » device scanners (Epson V750 and 1680Pro). The accuracy of the method is investigated with specific dose patterns and an IMRT beam. The comparisons with a two-dimensional array of ionization chambers using a 18x18 cm{sup 2} open field and an inverse pyramid dose pattern show an increment in the percentage of points which pass the gamma analysis (tolerance parameters of 3% and 3 mm), passing from 55% and 64% for the 1680Pro and V750 scanners, respectively, to 94% for both scanners for the 18x18 open field, and from 76% and 75% to 91% for the inverse pyramid pattern. Application to an IMRT beam also shows better gamma index results, passing from 88% and 86% for the two scanners, respectively, to 94% for both. The number of points and dose range considered for correction and calibration appears to be appropriate for use in IMRT verification. The method showed to be fast and to correct properly the nonuniformity and has been adopted for routine clinical IMRT dose verification.« less
  • This paper focuses on the accuracy, in absolute dose measurements, with GafChromic EBT film achievable in water for a 6 MV photon beam up to a dose of 2.3 Gy. Motivation is to get an absolute dose detection system to measure up dose distributions in a (water) phantom, to check dose calculations. An Epson 1680 color (red green blue) transmission flatbed scanner has been used as film scanning system, where the response in the red color channel has been extracted and used for the analyses. The influence of the flatbed film scanner on the film based dose detection process wasmore » investigated. The scan procedure has been optimized; i.e. for instance a lateral correction curve was derived to correct the scan value, up to 10%, as a function of optical density and lateral position. Sensitometric curves of different film batches were evaluated in portrait and landscape scan mode. Between various batches important variations in sensitometric curve were observed. Energy dependence of the film is negligible, while a slight variation in dose response is observed for very large angles between film surface and incident photon beam. Improved accuracy in absolute dose detection can be obtained by repetition of a film measurement to tackle at least the inherent presence of film inhomogeneous construction. We state that the overall uncertainty is random in absolute EBT film dose detection and of the order of 1.3% (1 SD) under the condition that the film is scanned in a limited centered area on the scanner and at least two films have been applied. At last we advise to check a new film batch on its characteristics compared to available information, before using that batch for absolute dose measurements.« less
  • Computed radiography (CR) systems have been gaining adoption as digital replacements for film for diagnostic and therapy imaging. As a result, film processors are being removed from service, leaving a void for the medical physicists who use film and processors for two-dimensional megavoltage beam dosimetry. This is the first report to evaluate the ability of a commercial CR reader and storage phosphor plate system to accurately quantitate absolute dose and dose distributions from a 6 MV photon beam. There are potential advantages and disadvantages of current CR systems compared to film systems. CR systems inherently produce a linear dose-response overmore » several logs of dose. However, the barium in the storage phosphor has a higher atomic number than the silver in film, resulting in significant energy sensitivity. The purpose of this work is to fully characterize the impact of these and other features of this CR system relevant to dosimetry. The tests performed and reported on in this study include uniformity of readout across a uniform field, geometrical accuracy, intra- and interday reproducibility, signal decay with time and with light exposure, dose-to-signal calibration, high dose effects, obliquity effects, perpendicular and parallel calibration results, field size and depth of measurement effects and the use of lead filters to minimize them, and intensity modulated radiation therapy quality assurance test results compared to that for film. Practical techniques are provided to optimize the accuracy of the system as a dosimetric replacement for film.« less