User manual

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analysis in the following ways. As the slit becomes narrower more monitor
units may be required to obtain the same darkening of the film. Widening
the slit may reduce the accuracy and precision of the analysis because the
lines will be less sharp. Note: For the couch star shot no build-up slab is
used on top of the film. In the absence of the build-up material the effect of
scattered radiation will be reduced and exposed lines will be sharper. The
lack of a build-up layer will also reduce the dose/MU by a factor >2
depending on the beam energy.
5. Set the gantry and collimator at zero degrees and using a 6MV photon
beam (or other beam at the discretion of the physicist) expose the film with
300 MU. Then rotate the couch in increments of 30° covering couch
angles from -90° to +60° and expose the film with 300 MU at each
position. Note that each exposure should be the same with an ideal dose
to the film of 100–200 cGy each time. Adjustment of MU should be made
to achieve this aim.
6. Remove the film from the slab and proceed to Scanning and Star shot
Image Analysis, Step D1. Note: The couch star shot should look similar to
Figure 2. As no build-up layer the dose/MU is lower than for the gantry
star shot and the darkening on the film is less.
D. Scanning and Star shot Image Analysis
1. Connect an Epson 10000XL scanner to the computer, turn on the scanner
and activate the FilmQA
™
Pro software. The FilmQA
™
Pro screen has
three windows. The Case Data Selector Window is to the left, the Image
Window in the center and Analysis Window to the right. Under the line
“Case Object Management” at the bottom of the Case tree in the left
hand window click “Add new case object” – see Figure 3