User manual

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Appendix A
Calibration Protocol for Radiochromic Film
I. PURPOSE
To define an efficient protocol for calibration of radiochromic dosimetry film.
II. SCOPE
The calibration protocol applies to Gafchromic
™
EBT2 and EBT3 films at doses up to
about 10 Gy. The resulting calibration is intended for use with a radiochromic film
dosimetry protocol. The calibration protocol requires a minimum time to elapse
between exposure of the films and scanning. The time is shortest and the protocol is
most efficient when the calibration films are exposed within a narrow time window.
An explanation is given in Appendix C. The calibration exposures may be done on a
single film or multiple films. In either case it is assumed that the doses delivered in
the film plane are known. Note: The calibration is only valid when applied to
application films from the same production lot as the calibration films.
III. INTRODUCTION
The efficiency of this protocol stems from the use of fitting functions that behave
similarly to film. For example, consider the rational function X(D,n) = a + b/(D-c)
where X(D,n) is the scanner response in the nth color channel measured for film
exposed to dose D and a, b and c are constants. Figure 1 shows an example for
calibration data (seven dose points) from EBT3 film fit to this function. The function
behaves as film is expected to behave, i.e. as dose increases the response values
decrease because the film gets darker. The values asymptote to almost constant
values at very high dose.