Physics Bucharest 2017

Delivery uncertainties - IMRT

H&N

Prostate

how intensity modulation is achieved?

Dosimetric effects of delivery uncertainties in dose rate , gantry angle , and MLC leaf positions for RapidArc vs sliding window IMRT plans • sliding window → larger number of overlapping segments and MU • RapidArc → rotation → larger apertures and less MU 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.

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