AbstractID: 7591 Title: Integration of IMRT Dose Optimization and Leaf Sequencing in
a Common Algorithm
The doses delivered by IMRT differ from those produced by an optimized plan that does not account for changes to the intensity
profile caused by the leaf sequencing process. An integer model is proposed to match the process of planning to that of delivery in
order to identify and reduce the sources of discrepancy. An integer program was written to observe dose limits and accept restrictions
on monitor units and segments used per beam angle. Results are reported for a thoracic case, in which tumor came around the spinal
cord. Computations were made tractable by paring the number of dose points, and using a restricted number of contours.
Distributions were corrected for leaf perturbations by increasing the fluence through a beam component by a factor (3%) proportional
to the number of its open borders. Scatter corrections for dose were made with Gratis software. Comparisons were made to the
method of deriving an intensity map by considering beam components independently. The integrated process eliminated violations in
the cord dose limit. With prescriptions normalized to strictly meet the constraint, the integrated approach gave 7% higher target dose
and reduced monitor units by 31%. Strict homogeneity was satisfied only when the effects of leaf sequencing were ignored,
uncovering the need for more freedom in delivery. The dose distribution can be improved and expended monitor units reduced by
successfully matching the process of planning fluence profiles to the method of delivery with an integrated integer algorithm.
Supported by NSF and NIH