Room: AAPM ePoster Library
Purpose: At higher energies, protons traverse a patient volume relatively undeflected, with a cumulative multiple Coulomb scattering that scales as 1/ßp. This effect could be exploited at higher energies to treat patients volumetrically using a tightly constrained proton pencil beam, using methods more akin to photon-based volumetrically modulated arc therapies.
Methods: The MATLAB-based, open-source treatment planning software package, matRad, was used to simulate treatment plans using a 6-MV photon treatment, a Bragg peak proton treatment, and a hypothetical 800-MeV proton volumetric treatment. The dose deposition profile of the 800-MeV beam was modeled in Geant4, based on the parameters of the proton linac at the Los Alamos Neutron Science Center. A TG-119 phantom and a head and neck case were used to compare the three treatment methodologies.
Results: For the TG-119 case, the dose to the core and body was minimal with Bragg proton, while the highest dose conformity to the target region was delivered with the relativistic proton treatment. For the head and neck case, Bragg protons demonstrated the lowest treatment doses to the spinal cord and brainstem, while the relativistic case demonstrated the lowest dose profile to the parotid glands and larynx. The target dose conformity was highest with the relativistic proton case.
Conclusions: A volumetric proton treatment delivered at relativistic proton energies may show promise for certain patient geometries where the dose profiles could win out over photon or Bragg proton treatments. Further evaluation is needed across a broad range of potential cases in order to make that determination.