The physics of radiochromic process: one calibration equation for all film types

Abstract

A: A unique calibration equation for all radiochromic film types is proposed. The determination of this equation comes from an analogy that the authors made between the radiochromic and photographic processes. Photography dynamics is ruled by a differential equation, the logistic equation, describing phenomena of growth versus competition. A solution of the logistic equation is the Green-Saunders equation which was used for the first time by the same authors in a previous referred work for the calibration of a set of EBT3 Gafchromic films. Since this equation has a fundamental physical interpretation, the fitting parameters also represent important physical quantities and two of them in particular fix the film dynamics; one being the contrast and the other the abscissa of the inflection point of the sensitometric curve. In order to show the validity of this approach for more than one radiochromic film type, two sets of radiochromic films, the B3 and HD-V2 Gafchromic films were exposed to several known doses and the Green-Saunders equation was found to perfectly fit the experimental data. A comparison with the same procedure used for EBT3 Gafchromic films is proposed. The findings of this work are an important step forward in the understanding of an interesting and widely used dosimetry technique.

Methodology for radiochromic film analysis using FilmQA Pro and ImageJ

“…These universal calibrations are valid since their parameters are related to the physical mechanism associated with film exposure, namely, the activation of the crystalline polydiacetylene molecules in the active layer. Similarly, Casolara et al [49,50] have shown parallels between the responses of radiochromic and photographic film and therefore the ability to describe the dynamic developing process of both through a general equation to create a universal calibration curve. As these universal calibration curves are described by parameters which depend on the response of the sensitive material in the film, and most films share the same active material, they are broadly applicable across various types of film.…”

Ultra-high dose rate dosimetry with miniaturized scintillation detectors coupled to optical fibers

“…This energy value results from the initial beam energy of (18.1±0.3) MeV (that was measured in previous studies 21,22 ) to which the energy loss (755 keV) in the extraction window is subtracted. The beam uniformity in the scintillators' position was evaluated to be <2% in horizontal and vertical directions by means of measurements with calibrated EBT-XD Gafchromic films 23,24 . The measurement runs were performed by delivering short beam shots of the duration of about 2 s to the GAGG, BaF 2 and PS scintillators in the range (12-626) Gy/s and to BaF 2 scintillator up to 10 kGy/s.…”

Radiochromic Films for the Two-Dimensional Dose Distribution Assessment

“…Santos et al have recently reviewed the most of the functional forms proposed so far for RCF calibration [18]. These include rational, power, polynomial, and logarithmic functions, as well as universal functions applicable for several RCF types and dose ranges [90,91]. It should be noted that the choice of the calibration equation depends on the dynamic range and sensitivity required by the measurement as well as on the physical quantity used to evaluate the RCF darkening (netOD, raw PV, etc.…”