Range monitoring with the INSIDE PET scanner at CNAO

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 G. Battistoni, M.G. Bisogni, P. Cerello, V. Patera    31-01-2017     Leggi in PDF

Hadrontherapy is now a consolidated approach in cancer treatment, with a growing number of treatment facilities in the world. Still, there are some limitations that prevent its full exploitation: among them, range monitoring. A direct measurement of the dose or of the beam-induced activity distribution during or immediately after the treatment would improve the quality level and pave the way to more aggressive treatment plans. Some facilities implement this feature either "in-room" (few minutes after the end of the treatment session) or "offline" (several minutes after): the β+ activity induced by beam-tissue interactions is measured with Positron Emission Tomography (PET) scanners. An online measurement, however, is highly desirable, as it would minimise errors due to metabolic washout and maximise the statistics (the contribution of short-lived isotopes is missed by the "in-room" and "offline" approaches).

Range monitoring with the INSIDE PET scanner at CNAO

The INSIDE PET scanner in the CNAO treatment room, with a patient mask positioned on the bed (left); the INSIDE tracker (right).

These are the main goals of the INSIDE (Innovative Solution for Dosimetry in Hadrontherapy) research project, coordinated by the University of Pisa, in collaboration with the University of Turin, University of Rome "La Sapienza", the Polytechnic University of Bari, the National Institute of Nuclear Physics (INFN) along with the National Centre of Oncological Hadrontherapy (CNAO) of Pavia. The INSIDE collaboration has built and commissioned at the CNAO synchrotron facility (Pavia, Italy) an in-beam PET, that will soon be complemented by a tracker for prompt charged particles detection (shown in the first figure above). The PET scanner features two 10x25 cm2 planar heads, each made by 10 modules of LFS crystals coupled to Silicon PhotoMultipliers, positioned at a default distance of 60 cm from each other, above and below the patient bed.

Range monitoring with the INSIDE PET scanner at CNAO

A slice of the measured (left) and simulated (centre) activity map and the comparison between the two masks (right).

After the successful testing of the PET scanner on PMMA phantoms, in terms of spatial resolution, response uniformity and reproducibility, the first data taking during a treatment session to a patient took place on December 1st, 2016.

The treatment consisted in the delivery of 3.7x1010 protons in the 66.3 – 144.4 MeV energy range, in a 4 minutes time interval. After the end of the delivery, the PET acquisition continued for 30 seconds. The reconstructed 3D activity map (shown in the second figure above) was analysed and compared to an accurate simulation based on FLUKA Monte Carlo code. The difference between the measured and expected range values, was evaluated in every 1.6x1.6 mm2 region of the delivery surface. The observed level of agreement is very satisfactory in terms of spatial resolution (about 2 mm standard deviation), while the average value (about 1 mm) likely suffers from uncertainties in the positioning of the prototype. The reproducibility, evaluated by comparing two measurements taken in consecutive treatment sessions, gives a similar result, with no bias on the average value.

After upgrading the mechanical positioning system and integrating the charged particle tracker, testing with patients will continue during 2017, also for carbon ion treatments.

Homepage: From left: Veronica Ferrero (Università di Torino e INFN, Sezione di Torino), Matteo Morrocchi (Università di Pisa e INFN, Sezione di Pisa), Elisa Fiorino (INFN, Sezione di Torino), Francesco Pennazio (INFN, Sezione di Torino).