AbstractID: 7562 Title: Smoothing Intensity Modulated Radiotherapy Delivery under
Hardware Constraints
A method was developed to smooth intensity modulated beam delivery sequences while
considering hardware constraints. The method applied matrix operations to model the
MLC leaf motion and hardware constraints such as the interleaf digitization,
synchronization, intersegment field abutment, etc. It was implemented and tested for
simulated and clinical intensity modulated fields. The simulated cases included intensity
distributions from 3x3 to 30x30 in dimension with 5 to 1000 intensity levels. The clinical
cases included four IMRT treatments sites: prostate, head and neck, lung and esophagus
cancers. In particular, we studied the effects of increasing levels of the smoothing on the
dose-volume histograms of the IMRT treatments that were optimized through the inverse
planning process. The dose distributions were calculated using a finite pencil-beam
model implemented in a commercial treatment planning system. We found that dramatic
reductions (up to 90%) in the number of the leaf segments were achieved by applying the
smoothing operation that minimized the MLC leaf travel distance, the total beam-on time
and the number of the leaf segments. For all studied cases, the effects were significant
for the unconstrained delivery than for the constrained delivery. The effects were mostly
found to be more sensitive for the complex intensity distributions such as the head-andneck cases than for the less complex ones such as the prostate cases. Our results
indicated the importance of considering hardware constraints for individual treatment
sites when smoothing an intensity modulated treatment delivery.
Supported by Department of Army and Institutional Intramural Grants.