User manual
91
noise is reduced by using relatively wider path widths with the provision not to
include areas beyond the length of the exposed beam lines nor encroach
upon the area of higher
exposure where the beams
cross near the isocenter.
Right-click the icon in the
bottom right corner of the
Image Window (see right) to
reveal a menu of analysis
options:
1. Number of regression points: To find the center of the beams the
analysis paths are split into a number of segments over which the
response maxima are sought. Default is 1½% (percent of the total
analysis path length). The optimum is unlikely to be outside the range
from 1-2%. Very short paths are unlikely to be helpful since they may
be shorter than the beam width. Very long paths are unlikely to be
helpful since they may cover two or more beams.
2. Analysis color channel: Follow the protocol and the red channel is all
you will need for radiochromic film. In an extreme case where the
response of radiochromic film is very high – say at doses >>10Gy – the
green channel response has a higher contrast and may be preferred.
The gray channel is available for non-radiochromic film images.
3. Star shot lines are darker than background: Follow the protocol and
this is always the case for radiochromic film. If you selected to scan as
a color negative in the Epson
®
Scan utility, you would need to change
the selection to “Star shot lines are brighter than background”.
4. Detection mode: the method used to detect the analysis path
extrema. Six detection choices are available: average all, closest to
found extremum point, search local extremum, most inner detected
point, refit detection range and center of extremum detection range.