SU-E-T-491: A FLUKA Monte Carlo Computational Model of a Scanning Proton Beam Therapy Nozzle at IU Proton Therapy Center.

Purpose: Charged particle therapy, especially proton therapy is a growing treatment modality worldwide. Monte Carlo (MC) simulation of the interactions of proton beam with equipment, devices and patient is a highly efficient tool that can substitute measurements for complex and unrealistic experiments. The purpose of this study is to design a MC model of a treatment nozzle to characterize the proton scanning beam and commissioning the model for the Indiana University Health Proton Therapy Center (IUHPTC.

Analytic estimates of secondary neutron dose in proton therapy.

Proton beam losses in various components of a treatment nozzle generate secondary neutrons, which bring unwanted out of field dose during treatments. The purpose of this study was to develop an analytic method for estimating neutron dose to a distant organ at risk during proton therapy. Based on radiation shielding calculation methods proposed by Sullivan, we developed an analytical model for converting the proton beam losses in the nozzle components and in the treatment volume into the secondary neutron dose at a point of interest.

Influence of beam efficiency through the patient-specific collimator on secondary neutron dose equivalent in double scattering and uniform scanning modes of proton therapy.

Purpose: Conventional proton therapy facilities use double scattering nozzles, which are optimized for delivery of a few fixed field sizes. Similarly, uniform scanning nozzles are commissioned for a limited number of field sizes. However, cases invariably occur where the treatment field is significantly different from these fixed field sizes.

Scan pattern optimization for uniform proton beam scanning.

Magnetic beam scanning allows one to spread proton beam over the desired radiation field area, improving beam utilization and conformity to the target area. This article discusses generic scan forms for generating uniform circular and rectangular fields and establishes criteria that can be applied to optimize selected scan patterns. During construction of the Midwest Proton Radiotherapy Institute (MPRI), Indiana University developed a magnetically scanned beam spreading system for the 3 m long gantry nozzle.

Energy spectrum control for modulated proton beams.

In proton therapy delivered with range modulated beams, the energy spectrum of protons entering the delivery nozzle can affect the dose uniformity within the target region and the dose gradient around its periphery. For a cyclotron with a fixed extraction energy, a rangeshifter is used to change the energy but this produces increasing energy spreads for decreasing energies. This study investigated the magnitude of the effects of different energy spreads on dose uniformity and distal edge dose gradient and determined the limits for controlling the incident spectrum.