High sensitivity radiochromic film dosimetry using an optical common‐mode rejection and a reflective‐mode flatbed color scanner

Abstract

A novel method that can greatly improve the dosimetric sensitivity limit of a radiochromic film (RCF) through use of a set of color components, e.g., red and green, outputs from a RGB color scanner has been developed. RCFs are known to have microscopic and macroscopic nonuniformities, which come from the thickness variations in the film's active radiochromic layer and coating. These variations in the response make the optical signal-to-noise ratio lower, resulting in lower film sensitivity. To mitigate the effects of RCF nonuniform response, an optical common-mode rejection (CMR) was developed. The CMR compensates nonuniform response by creating a ratio of the two signals where the factors common to both numerator and denominator cancel out. The CMR scheme was applied to the mathematical operation of creating a ratio using two components, red and green outputs from a scanner. The two light component lights are neighboring wavebands about 100 nm apart and suffer a common fate, with the exception of wavelength-dependent events, having passed together along common attenuation paths. Two types of dose-response curves as a function of delivered dose ranging from 3.7 mGy to 8.1 Gy for 100 kV x-ray beams were obtained with the optical CMR scheme and the conventional analysis method using red component, respectively. In the range of 3.7 mGy to 81 mGy, the optical densities obtained with the optical CMR showed a good consistency among eight measured samples and an improved consistency with a linear fit within 1 standard deviation of each measured optical densities, while those with the conventional analysis exhibited a large discrepancy among eight samples and did not show a consistency with a linear fit.

Contact lens‐type ocular in vivo dosimeter for radiotherapy

“…Ohuchi and Papaconstadopoulos et al reported that reflectance can be processed like transmittance because a radiochromic film's active layer is transparent. 29,30 The CLOD also used the active layer of the film. Therefore, the response to irradiation was quantified in terms of optical density (OD) values.…”

“…where Rf denotes the reflectance of the irradiated CLOD, Rf 0 denotes the reflectance of the nonirradiated CLOD, and Rf bg denotes the background reflectance without the CLOD. 29,31 In addition to these scanning protocols, the dependence of scanning orientation was investigated by rotating the CLOD above the scanner bed in intervals of 30°. The netOD value of the CLOD irradiated with 100 cGy was normalized to a 0°r eading.…”

Note: Calibration of EBT3 radiochromic film for measuring solar ultraviolet radiation

“…This definition was also employed by Butson et al 2 and a similar one was used by Ohuchi 15 for reflected optical density. The (UVA + UVB) irradiance (power per unit area, W m −2 ) and exposure (irradiance integrated over time, J cm −2 or J m −2 ) were measured.…”

Variations in dose distribution and optical properties of GafchromicTM EBT2 film according to scanning mode

“…This is borrowed from the tradition of radiographic film dosimetry, in which the degree of film darkening is quantified in terms of optical density and converted into applied dose. Even though dose assessment is traditionally carried out by transmission measurement, some authors 22,23 proposed the reflection mode for the reading of radiochromic film. A transparent film can be read in reflection mode by placing it upon a diffuse white surface, which is available in most flatbed scanners.…”