Orateur
Description
The PETITION PET detector, has been developed for in-beam use at Gantry 2 at PSI,
with an open ring design allowing for measurement of patient activation both during and
following proton therapy treatment. Tools for time resolved simulations of patient
treatments have been implemented using Gate. Intra-field imaging in the dead time
between delivery of each energy layer, approximately 100 ms, can be performed for
measurement of short-lived isotopes such as 12N (t1/2 = 11 ms). Following this inter-field
imaging of the produced isotopes, primarily 15O and 11C (t1/2 = 122 s and 20.3 min
respectively), can be performed between delivery of subsequent fields to generate 3D
images of the induced activity distribution. We also consider a scenario in which the PET
scanner is rotatable, moving the opening of the ring to allow for delivery of each new
treatment field. If coincidences are recorded while the scanner rotates, the loss of spatial
resolution due to the opening of the scanner may be compensated, allowing for possible
detection of anatomical changes in the patient. Imaging for approximately 30 seconds,
during the couch and gantry repositioning, provides sufficient counts for reconstruction of
the activity. The activity fall off of short lived isotopes produced during delivery of the first
treatment field is well correlated to the dose fall off (R2=0.947). Imaging
of the field while rotating the scanner leads to a reduction in the mean-absolute-error by
54-70% compared to imaging at a fixed angle for each field. Development of a new PET
reconstruction software for the purpose of inter-field imaging allows for fast reconstruction
times, and could potentially provide validation of treatments within clinically relevant time
frames. In beam measurements with phantoms are currently being performed, and
comparison with Gate simulations is ongoing.
