User manual

CALIBRATION (Video: http://www.youtube.com/watch?v=AKqpsFKprf0)

The calibration process uses films irradiated with known doses to generate a calibration

table and calculate a set of calibration functions, one for each color channel. These

calibration functions correlate the dose values of the exposed films with the color values

in the scanned images. This section describes how to use FilmQA

™

Pro do a film

calibration. For demonstration purposes it uses files downloaded with the FilmQA

™

Pro

installation file and installed in Program Files/Ashland Advanced Materials or ISP

Advanced Materials

FilmQA

™

Pro uses simple, asymptotic, rational calibration functions that behave like

film, i.e. the response asymptotes to constant value at high dose just the way film

darkens with increasing dose. The simplest and most widely applicable of these rational

functions requires definition of three coefficients so the specific behavior of a batch of

radiochromic film could be defined with as few as three data points. In practice, we

recommend a minimum of four points since with this redundancy the application

provides some statistics that can show which of the calibration functions is best. In

general the dose points for a particular case should be

chosen in geometric progression – say 0, 75, 150 and

300 cGy - rather than in arithmetic progression. One or

two more points could be added if the dose range is

much larger – say 0 to 20 Gy – but there is no

advantage to the much large numbers of data points –

sometimes tens in number – that are frequently used.

Since relatively few calibration films are necessary, the

recommended way is to use the OneScan Protocol and

scan the calibration films all together in one image

rather than separately.