AbstractID: 7357 Title: A Preliminary Study of Reducing Dose Inhomogeneity in IMRT
Optimization
In intensity modulated radiation therapy (IMRT), a treatment plan is often generated
with an inverse planning system, optimized based on an objective function. A quadratic
objective function, which measures a mean dose deviation of the target and normal
structures, is often used in the current planning systems. A problem observed with these
systems, is that cold or hot dose spots often present in the target or critical structures,
although these cold or hot spots appear in a small volume. Such cold spots in the tumor
target and hot spots in sensitive structures may lead to substantial problems.. The purpose
of this study is to develop a new objective function to eliminate these cold and hot spots.
Pre-calculated pencil beams with a cylindrical phantom developed by University of
Wisconsin were adopted for this study. A Line search method from the MATLAB was
used for optimization. Objective functions with a higher power was tested and compared
with the quadratic objective function. It was found that objective functions with a higher
power were more effective in eliminating very hot or cold spots. Furthermore, a refine
procedure was introduced to combine the advantage of the high power and the low power
objective functions. This refine procedure took the result from the low power objective
function, and used the higher power objective function to eliminate the hot and clod spots
generated by the lower power objective function. The preliminary study showed that this
new optimization method generated a plan with better dose uniformity.