SUBJECT: M.S. Thesis Presentation
BY: Scott Sample
TIME: Wednesday, March 14, 2007, 11:00 a.m.
PLACE: Neely Building, 118
TITLE: IMRT Beam Angle Optimization Using MCNP
COMMITTEE: Dr. Cassiano de Oliveira, Chair (NRE)
Dr. Tim Fox (MP)
Dr. Nolan Hertel (NRE)
Dr. Eric Elder (MP)


Equispaced beam arrangements are typically used for IMRT plans. This beam arrangement provides adequate dose coverage to the target while sparing dose to the other structures. However, an equispaced beam arrangement may not provide the “best” dose coverage to the target while sparing dose to the other structures. Beam angle optimization attempts optimize the beam directions to produce a “better” IMRT plan; this is achieved by increasing dose to the target while minimizing dose to the remaining structures. Most methods of beam angle optimization attempt to optimize the beam angles and the beam intensity profiles to find an optimal set of beam angles. This thesis attempts to optimize the beam angles without determining the beam intensity profiles. A MCNP simulation is run to score the beam directions; the simulation is run as an adjoint problem to reduce simulation time, with the target as the source and the detectors scoring the dose for the gantry angles of the beam. Then, an optimization algorithm is run to select a set of beam angles for an optimized IMRT plan. The optimized IMRT plan is compared to an equispaced IMRT on a commercial treatment planning system to determine if this method of beam angle optimization is “better” than using an equispaced beam arrangement. The results of this thesis indicate that the coupling of a MCNP simulation for scoring and an optimization algorithm to select beam angles will produce a “better” IMRT plan than an equispaced IMRT plan. Three different geometries were used and for all geometries, the optimized IMRT plan had a higher average dose to the target while maintaining or increasing dose sparing to the critical structure and normal tissue.