2150-2151 / 3107
Delivery uncertainties - IMRT
H&N
Prostate
Dosimetric effects of delivery
uncertainties in
dose rate
,
gantry angle
, and
MLC leaf
how intensity modulation is achieved?
•
sliding window
→
larger number of
overlapping segments and MU
•
RapidArc
→
rotation
→
larger
apertures and less MU
2%-2 mm
g
for systematic MLC leaf bank shifts
of 0.5, 1, 1.5, and 2 mm. Points that failed in red.
Betzel GT et al, Med Phys 39(10) 2012
positions
for RapidArc vs sliding
window IMRT RT plans
The susceptibility to MLC leaf position
errors is inversely proportional to the
mean leaf gap width
Geometric errors in smaller apertures
→
larger impact on dosimetric errors.