HT2  Status of Proton and Ion Transmission Imaging -Status of in vivo Dosimetry with Prompt Secondary Radiation

Sunday, Oct. 27  10:20-12:20  ASEM 201

Session Chair:  alberto del guerra, University Pisa, Italy; Taiga Yamaya, National Institute of Radiological Sciences, Japan; Reinhard Schulte, Department of Basic Sciences, Division of Radiation Research, Loma Linda University, United States

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(10:20) HT2-1, Status of the Clinical Head Scanner for Proton CT at LLUMC

R. Schulte

Loma Linda University Medical Center, Loma Linda, USA
We describe the current status of the clinical (Phase 2) head scanner presently developed for proton computed tomography (pCT) in support of proton therapy treatment planning and pre-treatment verification in patients treated with particle beam therapy after extensive preclinical testing. The Phase 2 pCT system consists of two silicon telescopes which track individual protons before and after the phantom/patient, and a novel multistage scintillator detector that measures a combination of the residual energy and range of the proton which is then converted to water equivalent path length (WEPL) of the protons in the scanned object. The multitude of WEPL values from protons directed at the object from all possible directions is processed by an interative parallelizable reconstruction algorithm that runs on modern GP-GPU hardware. We performed measurements and simulations on the system and find that the new pCT scanner will support low-intensity proton fluxes that are compatible with image acquisition in less than 10 minutes.

(10:35) HT2-2, Status of the Italian Proton Computed Tomography Project

M. Bruzzi1,2, M. Bucciolini3,2, M. Carpinelli4,5, C. Civinini2, G. Cuttone6, D. Lo Presti7,8, S. Pallotta3,2, C. Pugliatti8,7, N. Randazzo7, F. Romano6, V. Sipala4,5, M. Scaringella9, C. Stancampiano6, C. Talamonti2,3, M. Tesi9, E. Vanzi10, M. Zani2,3

1Dipartimento di Fisica ed Astronomia, Florence, Firenze, Italy
2INFN Sezione di Firenze, INFN FI, Firenze, Italy
3Dipartimento di Scienze biomediche, sperimentali e cliniche, BIO, Firenze, Italy
4INFN Sezione di Cagliari, INFN CA, Cagliari, Italy
5Dipartimento di Chimica e Farmaciay Department, Sassari, Firenze, Italy
6INFN Laboratori Nazionali del Sud, INFN LNS, Catania, Italy
7INFN Sezione di Catania, INFN CT, Catania, Italy
8Dipartimento di Fisica, CATANIA, Catania, Italy
9DIpartimento di Ingegneria Industriale, Firenze 2, Firenze, Italy
10SOD Fisica medica Azienda Ospedaliera Careggi, Careggi, Firenze, Italy
The Italian project PRIMA (Proton IMAging) funded by INFN CSN5 has developed a proton Computed Tomography (pCT) prototype based on single proton tracking. Approach to the pCT consists in the use of silicon microstrip detectors to reconstruct the individual proton trajectory before and after they traverse the phantom and a calorimeter for measuring particle residual energy. A small area apparatus has been already tested and an upgraded prototype, with larger active area (5x20cm2) and with improved data acquisition system (1 MHz readout frequency), is now under manufacturing in view to match requirements for pre-clinical tests.

(10:50) HT2-3, (Withdrawn), Front End and DAQ for a High Rate pCT Detector

P. Rubinov

Fermi National Accelerator Laboratory, Batavia, IL, USA

On behalf of the NIU-Fermilab-Delhi pCT collaboration
Abstract withdrawn

(11:05) HT2-4, Proton Beam Radiography set-up with a Timepix based TPC

J. Visser1, S. Brandenburg2, M. van Beuzekom1, A. Biegun2, M. J. van Goethem3, B. Huisman1, P. Tsopelas1, N. Ghazanfari2, P. Dendooven2

1Nikhef, Amsterdam, The Netherlands
2Kernfysisch Versneller Instituut, Groningen, The Netherlands
3department Radiation Oncology, University Medical Center Groningen, Groningen, The Netherlands
By using high energy protons instead of X-rays in radiotherapy the radiation dose in the healthy tissues surrounding the tumour can be strongly reduced, thereby reducing the occurrence of serious long-term complications. However, due to the finite range of the protons and the Bragg peak the quality of the dose distribution is very sensitive to the accuracy of the proton range prediction used in the treatment planning process. Currently, the proton range is deduced from X-ray CT imaging. As the physics of X-ray attenuation differs significantly from that of proton stopping, these predictions suffer from systematic errors. By using 2D proton imaging in combination with the X-ray CT data, the accuracy of the proton range prediction can be improved substantially. This will lead to a lower dose in the healthy tissue by reducing the margin in the treatment planning, thus enhancing the advantage of proton therapy over conventional radiotherapy. To achieve optimal imaging quality with protons both the energy loss of the protons in the patient body and their trajectories should be reconstructed with high resolution. This implies that the energy loss straggling and multiple scattering in the position sensitive detectors used for tracking should be minimized. We will present the design and first results of feasibility experiments of a proton imaging system in which the proton trajectories are measured in 3D by Timepix based time-projection-chambers with ≤0.1 mm and ≤1 mrad resolution, while the detector thickness is less than 100 mg/cm2, thus minimizing multiple scattering and energy loss straggling.

(11:20) HT2-5, Development of Prompt Gamma Based In-Vivo Range Verification Systems in Proton Radiotherapy.

J. C. Polf1, D. S. Mackin2, S. Beddar2

1Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, USA
2Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, TX, USA
The goal of radiation therapy is to ensure local tumor control by delivering a prescribed dose of radiation to cancerous tissues while minimizing radiation-induced side effects to surrounding healthy tissue. Proton radiotherapy is a highly conformal treatment method that provides the ability to precisely target dose delivery in the desired treatment volume, thus sparing dose to healthy tissues. However, the effectiveness of proton therapy, like all forms of external beam radiation therapy, remains limited by uncertainties due to patient set-up errors, changes in patient anatomy, and a lack in our fundamental understanding of the day-to-day response of tissue to proton beam irradiation. Fortunately, inherent to proton therapy is the emission of elemental prompt gamma rays (PG) due to proton-nucleus interactions in irradiated tissues. Since PG emission only occurs where the proton beam interacts with the patient, it is strongly correlated to delivered dose, making it a prime signal for beam range verification. Therefore many researchers have begun development on systems for PG measurement and PG imaging (PGI) that can provide information about the true in-vivo beam range within the patient during treatment delivery. However, to use PG emission for verification, it must be effectively measured and imaged. Due to the high energies of emitted PGs (up to 10 MeV), current medical gamma detectors cannot efficiently measure the energy and spatial information necessary to reconstruct images of PG emission during beam delivery. This has led to a large need and thus research effort to develop fast and efficient detectors for the measurement of PGs emitted from tissues irradiated during proton radiotherapy. In this presentation we discuss the clinical need for in-vivo range verification in proton therapy, and provide an overview of current research and development of PG based systems for measuring the in-vivo range of proton treatment beams.

(11:35) HT2-6, Prompt Gamma Imaging with a Slit Camera for Real-Time Range Control in Proton Therapy: First Experimental Results at Clinical Beam Currents

I. Perali1,2, A. Celani3, E. Baio1, C. Fiorini1,2, T. Frizzi3, E. Clementel4, S. Henrotin5, G. Janssens5, D. Prieels5, F. Roellinghoff5, J. Smeets5, F. Stichelbaut5

1Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milano, Italy
2Sezione di Milano, INFN, Milano, Italy
3XGLab, Milano, Italy
4iMagX Project, ICTEAM Institute, Universit Catholique de Louvain, Louvain-la-Neuve, Belgium
5Ion Beam Applications SA, Louvain-la-Neuve, Belgium
Treatments delivered by proton therapy are affected by uncertainties on the range of the beam within the patient. To reduce these margins and improve feedback on treatment delivery, different projects are investigating real-time range control by imaging prompt gammas emitted along the proton tracks in the patient. This study supports the development of a prompt gamma camera using a knife-edge slit collimator to produce a reversed 1-dimensional projection of the beam path on a scintillation detector for treatments delivered in pencil beam scanning mode. The ability of this camera design to detect modifications of the beam penetration depth in a PMMA target was already demonstrated down to 1 mm accuracy for doses compatible with single pencil beams at low proton beam currents thanks to the HiCam photodetection system. In order to fulfill the very demanding count rate capability required for prompt gamma imaging at clinical beam currents, a new, dedicated, cost-effective photodetection system was designed and will be presented, as well as experimental results. This ultra-fast, 1-dimensional, high-energy gamma imaging device relies on two rows of 20 LYSO crystal slabs, directly coupled to SiPMs arrays and readout by 40 independent acquisition channels in fast counting mode. A test board limited to 2 channels was implemented to benchmark the performances of various components and validate the adequate combination of crystal material, surface treatment, optical coupling and SiPMs. This prototype was tested during proton irradiation at the West German Proton Therapy Centre in Essen and was, to our knowledge, the very first to achieve successful acquisitions at clinical beam currents of several nA at nozzle exit. These performances were furthermore demonstrated in challenging conditions up to the maximum clinical beam energy of 230 MeV, laying a major milestone towards the development of a practical solution for online range control in proton therapy.

(11:50) HT2-7, Status Review of Ion Therapy Monitoring by Prompt Secondary Radiation.

D. Dauvergne, E. Testa

IPNL, CNRS/IN2P3 and Universit Lyon 1, Villeurbanne, France
Prompt radiation induced by nuclear fragmentation is expected to provide real-time in vivo control of ion therapy. Several projects worldwide aim at providing clinical imaging devices in a near future. We propose to make a review on these imaging modalities and on their technical aspects. - Prompt-gamma (or bremmstrahlung) monitoring has been proposed ten years ago, and is being intensively studied by many collaborations. Although no imaging device is clinically available yet, several solutions are envisaged: - collimated cameras offer the advantage of simplified reconstruction, at the expense of an efficiency and a spatial resolution limited by the collimation; - Compton cameras of various designs are also at the stage of reduced-size prototypes. Their increased efficiency is counterbalanced by a higher complexity to treat high fluxes of data, and by the reconstruction procedure that may delay considerably the control of the irradiation. - The influence of Time-of-Flight (TOF) will be discussed. TOF allows in any case a reduction of secondary radiations induced by neutrons. In the case of carbon therapy, it is mandatory to observe any correlation between ion range and prompt-gamma profile. Depending on the beam time-structure, a beam monitor may be necessary for tagging each incident ion or ion bunch. - secondary proton vertex imaging seems also very promising for carbon therapy, since secondary protons may escape the patient, which is much less probable in the case of proton therapy. Tracking telescopes are used. We will discuss these modalities in terms of counting rates, signal to background ratio, accuracy in ion range verification with and without heterogeneities in the beam path, and their applicability for real-time monitoring.

(12:05) HT2-8, Recent Developments in SiPM-Based Time-of-Flight Detectors and Their Potential for in-Situ PET and Prompt Gamma Imaging

D. R. Schaart

Delft university of Technology, Delft, The Netherlands
The use of time-of-flight (TOF) information in positron emission tomography (PET) has been shown to enable significant improvement in image noise properties, especially in larger patients. Silicon photomultipliers (SiPMs) are solid-state photosensors offering high internal gain while being compact, essentially transparent to gamma rays, and insensitive to magnetic fields. Since several years a number of manufacturers are offering reliable and practical devices. This has spurred many research groups to explore their potential use in scintillation detectors for PET, aiming at e.g. compactness, high spatial resolution, depth-of-interaction (DOI) correction, MRI-compatibility, and improved TOF performance. At the same time, SiPM technology itself is undergoing rapid development. For example, a fully digital implementation of the SiPM, the so-called digital photon counter or dSiPM, has been introduced recently. SiPMs and dSiPMs enable excellent timing resolution, with coincidence resolving times (CRTs) well below 200 ps FWHM having been demonstrated by several groups already. This paper presents an overview of recent developments in (d)SiPM-based PET detectors as well as an outlook on the potential impact of these results on in-situ PET and prompt gamma imaging for particle therapy treatment monitoring. It is discussed how the favorable properties of SiPMs and dSiPMs can be exploited to provide realistic solutions for in-vivo particle therapy monitoring concepts proposed by various groups in recent years. In particular, it is shown how the excellent timing performance of (d)SiPM based scintillation detectors can be used to improve sensitivity and to reduce artifacts of in-situ PET devices, as well as to reduce background noise in prompt gamma imaging.