AbstractID: 6731 Title: IMRT Optimization Based on Deliverable Intensities
Intensity modulated radiation therapy (IMRT) treatment planning typically considers beam optimization
and beam delivery as separate tasks. Following optimization, a multileaf collimator (MLC) or other beam
delivery device is used to generate fluence patterns for patient treatment delivery. Due to limitations and
characteristics of the MLC, the deliverable intensity distributions often differ from those produced by the
optimizer, leading to differences between the delivered and the optimized dose. A method has been
developed to incorporate the MLC restrictions into the optimization process. Our in-house IMRT system
has been modified to include the calculation of the deliverable intensity into the optimizer. In this process,
prior to dose calculation, intensities are converted to dynamic MLC sequences, which are then converted
into deliverable intensities. All other optimization steps remain the same. To evaluate the effectiveness of
deliverable optimization, two representative sites have been studied: Head & Neck and Prostate. The
comparisons for the head and neck case show that the DVH’s for the MLC based optimization are
considerably better (up to 15 % dose reduction to critical structures) than the DVH’s for the optimization
with a final conversion. The isodose distributions also show a clear improvement for the deliverable
optimization method. MLC based optimization results are very close to the original non-deliverable
optimization results, suggesting that IMRT can overcome the MLC limitations by adjusting individual
beamlets.