Aw. Beavis et al., Optimization of the step-and-shoot leaf sequence for delivery of intensitymodulated radiation therapy using a variable division scheme, PHYS MED BI, 46(9), 2001, pp. 2457-2465
To deliver an intensity modulated radiation therapy (IMRT) plan by multilea
f collimator (MLC) it is necessary to convert beam profiles, generated from
the inverse treatment planning algorithm, into a series of instructions th
at the MLC control system can execute. An idealized IMRT beam profile can b
e regarded as a continuously varying two-dimensional function and is usuall
y represented by an intensity map, i.e., a discretized description in space
and in intensity of the beam profile. It is common to assume that the inte
nsity map be defined over a regular grid with N steps and equal increments
of intensity levels. In reality, this may not be the optimal representation
of the beam profile and may introduce unnecessary discrepancies between th
e intensity pattern delivered and that ideally required. We have implemente
d an algorithm capable of minimizing the difference between the two pattern
s on a beam specific basis. In other words, it can produce optimized intens
ity maps, individually produced to suit the (continuous function) intensity
profile they are intended to approximate. This enhancement in conformation
is achieved by allowing variable step size and unconstrained intensity lev
els in the final leaf sequence.