In-beam PET at clinical proton beams with pile-up rejection


In-beam PET at clinical proton beams with pile-up rejection

Helmbrecht, S.; Enghardt, W.; Fiedler, F.; Iltzsche, M.; Pausch, G.; Tintori, C.; Kormoll, T.

Positron emission tomography (PET) is a means of imaging the β+-activity produced by the radiation field in ion beam therapy and therefore for treatment verification. Prompt Γ-rays that are emitted during beam application challenge the detectors and electronics of PET systems, since those are designed for low and medium count rates. Typical PET detectors operated according a modified Anger principle suffer from multiple events at high rates. Therefore, in-beam PET systems using such detectors rely on a synchronization of beam status and measurement to reject deteriorated data.

In this work, a method for pile-up rejection is applied to conventional Anger logic block detectors. It allows for an in-beam data acquisition without further synchronization.

Though cyclotrons produce a continuous wave beam, the radiation field shaping technique introduces breaks in the application.
Time regimes mimicking synchrotrons as well as cyclotron based ones using double-scattering or pencil beam scanning field shaping at dose rates of 0.5, 1.0 and 2.0 Gy/min were investigated. Two types of inhomogeneous phantoms were imaged. The first one simulates cavity structures, the other one mimics a static lung irradiation.

It could be shown that, depending on the dose rate and the beam time structure, in-beam measurement including a few seconds decay time only, yield images which revealed all inhomogeneities in the phantoms. This technique can be the basis for the development of an in-beam PET system with traditional detectors and off-the-shelf electronics.

Keywords: Positron emission tomography; in-beam PET; Pile up; Proton therapy; Ion beam therapy

Permalink: https://www.hzdr.de/publications/Publ-23478
Publ.-Id: 23478