1221 / 1542
IMRT: What are the Potential Weak Links?
Many (small) field segments are made by the MLC for building a dose
distribution
Leaf positioning and travelling becomes important
Dose calculations are more complex due to leaf rounding effects,
tongue and groove effects, leaf transmission …
Small-field dosimetry (output factor and beam profiles) becomes
important
Beam stability (segmented IMRT)
Low MU fields lead to short beam-on times
Check output, flatness, and symmetry stability at start up and steady
state of the dose delivery
For > 2 MU dose output and beam profile stability should be within
±
2% (1 SD)
Ezzell G, Galvin JM, Low D, Palta JR, Rosen I, Sharpe MB, Xia P, Xiao Y, Xing L and Yu CX. Guidance document
on delivery, treatment planning, and clinical implementation of IMRT: Report of the IMRT subcommittee of
the AAPM Radiation Therapy Committee. Med. Phys. 30: 2090 – 2115, 2003