Simulation of proton therapy treatment verification via PET imaging of induced positron-emitters

Earlier works, including a recent one at BNL, demonstrated that PET is a promising technique to verify the dose distribution of proton therapy, which is increasingly used in radiation oncology because the dose conforms more tightly to the tumor than common x-ray radiation therapy. Proton therapy produces positron-emitting isotopes along the beam path, allowing the therapy dose distribution to be imaged by PET as a form of quality assurance of the treatment. This is especially important when treating inhomogeneous organs such as the lungs or the head-and-neck, where the calculation of the expected dose distribution for treatment planning is more difficult. In this paper, we present Monte Carlo simulations of the yield of positron emitters produced by proton beams up to 250 MeV, followed by statistically realistic Monte Carlo simulation of the images expected from a clinical PET scanner. The emphasis of this study is to accurately predict the positron emitter distribution and to determine the quality of the PET signal in the region near the Bragg peak which is critical to the success of PET imaging for verification of proton beam location and dosimetry. In this paper, we also demonstrate that the image results depend strongly on the available nuclear reaction cross section data. We determine quantitatively the differences in the calculated positron emitter yields resulting from four different sets of input nuclear reaction cross section data. They are compared to the simulated distributions of positron emitter productions and absorbed proton energies.