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Definitions:
•
T = gantry rotation time: 10-60 s
•
w = longitudinal field width: 1, 2.5, 5 cm
•
pitch, p = (couch displacement in T)/w
e.g., p = 0.2
→
each point “sees” 5 rotations
•
projection: each rotation is divided in 51 projections (‘fields’), 1 every 7
°
•
for each projection 64 binary MLC leaves can be moved IN or OUT
with a 0 – 100% intensity modulation
•
modulation factor, MF= ratio between maximum intensity in a
projection and the mean of the non-zero intensities
w
p=0.5
Helical Tomotherapy - treatment planning