Full-beam PET monitoring in particle therapy with the INSIDE scanner: first measurements

May 3, 2016, 3:00 PM
20m

Speaker

P. Cerello, INFN Torino (INFN Torino (IT))

Description

In-beam PET is one of the options for real-time monitoring of the Bragg peak
depth in hadron-therapy sessions, which would allow hypofractionation and
the treatment of multiple lesions.
The INSIDE collaboration has recently completed the building of a PET
scanner, featuring two 10x25 cm2 planar heads at a default distance of 25 cm
from the iso-centre, that will soon be complemented by a tracker for prompt
charged particles and will operate at the CNAO synchrotron facility (Pavia,
Italy).
Testing with monoenergetic proton beams of 68, 72, 77 and 105 MeV
targeted to PMMA phantoms placed inside the FOV was performed at the
CNAO synchrotron, in order to fine-tune the detector performance in
controlled conditions.
Data acquisition was successful in both in-spill (1s) and inter-spill (4s)
modality, with a Coincidence Time Resolution (CTR), measured without a fine
time calibration, of about 480 ps.
The inter-spill image profiles along the beam axis for the 68 and 72 MeV
beams show the characteristic distal activity fall-off, with a measured proton
range difference in PMMA (3.6+-0.3 mm) that is compatible with the expected
value (3.64 mm) within few hundred microns. Similarly, for 77 and 105 MeV
beams delivered sequentially on the same phantom, the measured distance is
(30.2+-0.3) mm, to be compared to an expected value of 31.2 mm. Submillimetric
bias induced by disuniformity in the detector efficiency, geometrical
acceptance or reconstruction software the are being investigated with
simulated data.
When comparing inter-spill and in-spill data, it is observed that the fall-off
slope is steeper (as expected) and shorter (about 2 mm) for inter-spill data,.
The effect, likely caused by pair production far from the target followed by
annihilation, is being investigated, since its contribution is relevant when an
absolute measurement is required. In order to reject the neutron-induced
contribution, a filter that exploits the 700 μs bunch structure during the beam
delivery was developed.
Data acquisition with carbon beam on PMMA was successfully tested at the
beginning of April 2016.
Standard proton-based treatment plans were also delivered on PMMA
phantoms, reconstructed and successfully compared to previously simulated
data.
In order to start testing with patients, the integration of CT and PET data is
being completed, so as to be able to generate simulated profiles, which will be
compared to data in real-time, during the treatment delivery.

Primary author

P. Cerello, INFN Torino (INFN Torino (IT))

Presentation materials