M.A. Piliero

INSIDE in-beam positron emission tomography system for particle range monitoring in hadrontherapy

Abstract. The quality assurance of particle therapy treatment is a fundamental issue that can be addressed by developing reliable monitoring techniques and indicators of the treatment plan correctness. Among the available imaging techniques, positron emission tomography (PET) has long been investigated and then clinically applied to proton and carbon beams. In 2013, the Innovative Solutions for Dosimetry in Hadrontherapy (INSIDE) collaboration proposed an innovative bimodal imaging concept that combines an in-beam PET scanner with a tracking system for charged particle imaging. This paper presents the general architecture of the INSIDE project but focuses on the in-beam PET scanner that has been designed to reconstruct the particles range with millimetric resolution within a fraction of the dose delivered in a treatment of head and neck tumors. The in-beam PET scanner has been recently installed at the Italian National Center of Oncologic Hadrontherapy (CNAO) in Pavia, Italy, and the commissioning phase has just started. The results of the first beam test with clinical proton beams on phantoms clearly show the capability of the in-beam PET to operate during the irradiation delivery and to reconstruct on-line the beam-induced activity map. The accuracy in the activity distal fall-off determination is millimetric for therapeutic doses.

Full-beam performances of a PET detector with synchrotron therapeutic proton beams

Treatment quality assessment is a crucial feature for both present and next-generation ion therapy facilities. Several approaches are being explored, based on prompt radiation emission or on PET signals by [Formula: see text]-decaying isotopes generated by beam interactions with the body. In-beam PET monitoring at synchrotron-based ion therapy facilities has already been performed, either based on inter-spill data only, to avoid the influence of the prompt radiation, or including both in-spill and inter-spill data. However, the PET images either suffer of poor statistics (inter-spill) or are more influenced by the background induced by prompt radiation (in-spill). Both those problems are expected to worsen for accelerators with improved duty cycle where the inter-spill interval is reduced to shorten the treatment time. With the aim of assessing the detector performance and developing techniques for background reduction, a test of an in-beam PET detector prototype was performed at the CNAO synchrotron-based ion therapy facility in full-beam acquisition modality. Data taken with proton beams impinging on PMMA phantoms showed the system acquisition capability and the resulting activity distribution, separately reconstructed for the in-spill and the inter-spill data. The coincidence time resolution for in-spill and inter-spill data shows a good agreement, with a slight deterioration during the spill. The data selection technique allows the identification and rejection of most of the background originated during the beam delivery. The activity range difference between two different proton beam energies (68 and 72 MeV) was measured and found to be in sub-millimeter agreement with the expected result. However, a slightly longer (2 mm) absolute profile length is obtained for in-spill data when compared to inter-spill data.

First results of the INSIDE in-beam PET scanner for the on-line monitoring of particle therapy treatments

Quality assessment of particle therapy treatments by means of PET systems has been carried out since late `90 and it is one of the most promising in-vivo non invasive monitoring techniques employed clinically. It can be performed with a diagnostic PET scanners installed outside the treatment room (off-line monitoring) or inside the treatment room (in-room monitoring). However the most efficient way is by integrating a PET scanner with the treatment delivery system (on-line monitoring) so that the biological wash out and the patient repositioning errors are minimized. In this work we present the performance of the in-beam PET scanner developed within the INSIDE project. The INSIDE PET scanner is made of two planar heads, 10 cm wide (transaxially) and 25 cm long (axially), composed of pixellated LFS crystals coupled to Hamamatsu MPPCs. Custom designed Front-End Electronics (FE) and Data AcQuisition (DAQ) systems allow an on-line reconstruction of PET images from separated in-spill and inter-spill data sets. The INSIDE PET scanner has been recently delivered at the CNAO (Pavia, Italy) hadrontherapy facility and the first experimental measurements have been carried out. Homogeneous PMMA phantoms and PMMA phantoms with small air and bone inserts were irradiated with monoenergetic clinical proton beams. The activity range was evaluated at various benchmark positions within the field of view to assess the homogeneity of response of the PET system. Repeated irradiations of PMMA phantoms with clinical spread out Bragg peak proton beams were performed to evaluate the reproducibility of the PET signal. The results found in this work show that the response of the INSIDE PET scanner is independent of the position within the radiation field. Results also show the capability of the INSIDE PET scanner to distinguish variations of the activity range due to small tissue inhomogeneities. Finally, the reproducibility of the activity range measurement was within 1 mm.

A detector module composed of pixellated crystals coupled to SiPM strips

A detector based on a pixellated scintillator crystal coupled on two opposite sides to Silicon Photomultiplier (SiPM) strips is presented. In one direction the width of the SiPM strips matches the crystal pitch, while in the other direction the strip length is equal to the crystal pitch times the number of pixels in a row. The SiPM strips on one side are orthogonal to the strips on the other side. The crystal position can be identified using a row-column coding method. As a proof of concept, a small prototype using an array of 8 × 8 LYSO crystals, each one 1.5 mm × 1.5 mm × 10 mm in dimensions, has been built. The crystal is coupled on both sides to monolithic matrices composed of 8 SiPM strips, each one 1.5 mm wide (pitch) and 12 mm long by means of silicon grease. SiPMs strips have been obtained connecting in parallel single pixels belonging to a monolithic matrix, where each pixel has the same pitch of the scintillating crystal coupled to it. This arrangement allows a reduction from N2 to 2N of the number of analog channels needed to read-out the entire crystal array. Furthermore, this method provides the information about the Depth of Interaction of the primary particles impinging on the detector. The results of the prototype characterization in terms of energy and Depth Of Interaction resolution capabilities are presented here.

PV-0562: Hadron-therapy monitoring with in-beam PET: measurements and simulations of the INSIDE PET scanner

Hadrontherapy monitoring goal: Provide to clinicians information about the conformity between the dose distribution planned in TPS and the actual one [1-3]. In-beam PET: exploit the beta+ activation induced in the patients body by the hadrontherapy (HT) particle beam to perform treatment monitoring and dose-delivery accuracy assessment. INSIDE collaboration: build an in-beam PET and tracker combined device for on-line HT monitoring [4-5]. METHODS

A four-dimensional photon detector for PET application

We analyzed a photon detector for positron emission tomography with high spatial resolution and depth of interaction capability. The detector is composed of a monolithic LYSO scintillator crystal coupled on top and bottom sides to two custom SiPM arrays. We investigated the ability to reconstruct the DOI of the 511 keV photon comparing the number of triggered SiPMs on the two sides of the module. Acquisitions were performed scanning the lateral surface of the crystal with a collimated 511 keV photon beam at different incident positions. A standard deviation of 1.5 mm in depth of interaction was obtained at the center of the module.

A silicon pixel detector system as an imaging tool for proton beam characterization

High energy protons represent a very promising alternative in the tumor irradiation, as respect the photon and electron beams. In Italy, the first and at present the only proton-therapy facility, CATANA (Centro di AdroTerapia e Applicazioni Nucleari Avanzate), was built in Catania, at the Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali del Sud (INFN-LNS). Here a 62 MeV proton beam, produced by a Superconducting Cyclotron (SC), is used for the treatment of shallow tumors like those of the ocular region. A beam monitoring system, based on ion chambers for dose monitoring and on silicon diodes scanning the beam cross section for the beam quality control. Moreover, gaf-chromic films are used to measure the geometric features of the beams. Even though these systems are stable and reliable, nevertheless they are time consuming and, in the gas-chromic film case, they require an off-line analysis. In this paper we present a feasibility study for using a silicon pixel detector as device for proton beams imaging and characterization. We present the performance of such a device exposed to the CATANA proton beam in terms of dose, dose rate and exposure time response.