In-beam Positron Emission Tomography Research Articles

Biological washout effect in in-beam PET: animal studies

Positron emission tomography (PET) is a practical tool for range verification of hadron therapy. As well, the quantitative washout of the positron emitters has a potential usefulness as a diagnostic index, but the modelling for this has not been established. In this study, we measured washout rates of rabbit brain and performed kinetic analysis to explore the washout mechanism. Six rabbit brains were irradiated by 11C and 15O ion beams, and dynamic PET scan was performed using our original depth of interest (DOI)-PET prototype. The washout rate was obtained based on the two-compartment model, where efflux from tissue to blood (k2), influx (k3) and efflux (k4) from the first to second compartments in tissue were evaluated. The observed k2, k3 and k4 of 11C were 0.086, 0.137 and 0.007 min−1, and those of 15O were 0.502, 0.360 and 0.007 min−1, respectively. It was suggested permeability of a molecule containing 11C atoms might be regulated by a transporter. The k2 of 15O was comparable with 15O-water. This study provides basic data for modelling of the washout effect.

Feasibility study of patient-specific dose verification in proton therapy utilizing positron emission tomography (PET) and generative adversarial network (GAN).

Online dose verification based on proton-induced positron emitters is a promising strategy for quality assurance in proton therapy. Because of the nonlinear correlation between dose and the activity distributions, a machine learning-based approach was developed to establish their relationship. Simulations were carried out using a pencil beam scanning system and a computed tomography (CT) image-based phantom. A DiscoGAN model was developed to perform dose verification for both central and off-center lines. Besides the activity as input, HU information from CT images and stopping power (SP) prior were incorporated as auxiliary features for the model. The performance was quantitatively studied in terms of mean absolute error (MAE) and mean relative error (MRE), under different signal-to-noise ratios (SNRs). In addition to a dataset comprising monoenergetic beams, two additional datasets were generated to evaluate the model's generalization capability: five reconstructed PET images based on an in-beam PET system and a dataset comprising spread-out Bragg peaks (SOBPs). The feasibility of dose verification was successfully demonstrated for all three datasets. For the monoenergetic case (i.e., raw activity of positron emitters), the MRE is found to be <1% for the central lines and 5% for the off-center lines, respectively. The range uncertainty is found to be less than 1mm. The prediction based on five PET images, which take into account the detection of 511-keV photons and image reconstruction, yields slightly inferior performance. For the SOBP case, the MRE of the center lines is found to be <3% and the range uncertainty is <1mm. The inclusion of anatomical information (HU and SP) improves both accuracy and generalization of the DiscoGAN model. The combination of proton-induced positron emitters, in-beam PET, and machine learning may become a useful tool allowing for patient-specific online dose verification in proton therapy.

Influence of momentum acceptance on range monitoring of 11C and 15O ion beams using in-beam PET

In heavy-ion therapy, the stopping position of primary ions in tumours needs to be monitored for effective treatment and to prevent overdose exposure to normal tissues. Positron-emitting ion beams, such as 11C and 15O, have been suggested for range verification in heavy-ion therapy using in-beam positron emission tomography (PET) imaging, which offers the capability of visualizing the ion stopping position with a high signal-to-noise ratio. We have previously demonstrated the feasibility of in-beam PET imaging for the range verification of 11C and 15O ion beams and observed a slight shift between the beam stopping position and the dose peak position in simulations, depending on the initial beam energy spread. In this study, we focused on the experimental confirmation of the shift between the Bragg peak position and the position of the maximum detected positron-emitting fragments via a PET system for positron-emitting ion beams of 11C (210 MeV u−1) and 15O (312 MeV u−1) with momentum acceptances of 5% and 0.5%. For this purpose, we measured the depth doses and performed in-beam PET imaging using a polymethyl methacrylate (PMMA) phantom for both beams with different momentum acceptances. The shifts between the Bragg peak position and the PET peak position in an irradiated PMMA phantom for the 15O ion beams were 1.8 mm and 0.3 mm for momentum acceptances of 5% and 0.5%, respectively. The shifts between the positions of two peaks for the 11C ion beam were 2.1 mm and 0.1 mm for momentum acceptances of 5% and 0.5%, respectively. We observed larger shifts between the Bragg peak and the PET peak positions for a momentum acceptance of 5% for both beams, which is consistent with the simulation results reported in our previous study. The biological doses were also estimated from the calculated relative biological effectiveness (RBE) values using a modified microdosimetric kinetic model (mMKM) and Monte Carlo simulation. Beams with a momentum acceptance of 5% should be used with caution for therapeutic applications to avoid extra dose to normal tissues beyond the tumour when the dose distal fall-off is located beyond the treatment volume.

Biological washout modelling for in-beam PET: rabbit brain irradiation by 11C and 15O ion beams

Positron emission tomography (PET) has been used for dose verification in charged particle therapy. The causes of washout of positron emitters by physiological functions should be clarified for accurate dose verification. In this study, we visualized the distribution of irradiated radioactive beams, 11C and 15O beams, in the rabbit whole-body using our original depth-of-interaction (DOI)-PET prototype to add basic data for biological washout effect correction. Time activity curves of the irradiated field and organs were measured immediately after the irradiations. All data were corrected for physical decay before further analysis. We also collected expired gas of the rabbit during beam irradiation and the energy spectrum was measured with a germanium detector. Irradiated radioactive beams into the brain were distributed to the whole body due to the biological washout process, and the implanted 11C and 15O ions were concentrated in the regions which had high blood volume. The 11C-labelled 11CO2 was detected in expired gas under the 11C beam irradiation, while no significant signal was detected under the 15O beam irradiation as a form of C15O2. Results suggested that the implanted 11C ions form molecules that diffuse out to the whole body by undergoing perfusion, then, they are incorporated into the blood-gas exchange in the respiratory system. This study provides basic data for modelling of the biological washout effect.

Evaluation of In-Beam PET Treatment Verification in Proton Therapy With Different Reconstruction Methods

In-beam positron emission tomography (PET) monitoring can provide early treatment assessment in proton therapy. However, open ring configurations and low positron emitter production yields degrade image quality, hampering the assessment accuracy. To achieve the highest precision for range monitoring, it is compulsory to mitigate image noise and compensate for data truncation. The goal of this article is to study the performance of state-of-the-art algorithms for in-beam PET image reconstruction, by evaluating the impact of the system response model and assessing the accuracy of range measurements. The approaches investigated here were maximum- a-posteriori algorithms combined with total-variation and median-root priors. Maximum-likelihood-expectation-maximization was used as reference. To compute the system matrix, different models were compared: a precise Monte Carlo model, and single-ray tracing with and without Gaussian blurring in image space. The proposed methods were tested on simulations of spread-out-bragg-peaks delivered on phantoms. The in-beam PET innovative imaging scanner geometry was used as a case study. After image post-processing, the explored methods delivered similar results. This article demonstrates the feasibility and reliability of using a simple and fast reconstruction method to perform range evaluations, given the correct image post-processing.

Range verification of radioactive ion beams of 11C and 15O using in-beam PET imaging

In advanced ion therapy, the visualization of the range of incident ions in a patient’s body is important for exploiting the advantages of this type of therapy. It is ideal to use radioactive ion beams for in-beam positron emission tomography (PET) imaging in particle therapy due to the high quality of PET images caused by the high signal-to-noise ratio. We have shown the feasibility of this idea through an in-beam PET study for 11C and 15O ion beams using the dedicated OpenPET system. In this work, we investigate the potential difference between the Bragg peak position and the position of the maximum detected positron-emitting fragments by a PET system for the radioactive beams of 11C and 15O. For this purpose, we measured the depth dose in a water phantom and performed PET scans of an irradiated PMMA phantom for the available beams of 11C and 15O at the Heavy Ion Medical Accelerator in Chiba (HIMAC). Then, we simulated the depth dose profiles in the water phantom and the yield of the positron-emitting fragments in a PMMA phantom for both available beams using the Monte Carlo code PHITS. The positions of the Bragg peak and maximum positron-emitting fragments from the measurements were well reproduced by simulation. The effect of beam energy broadening on the positional differences between two peaks was studied by simulating an irradiated PMMA phantom. The differences in position between the Bragg peak and the maximum positron-emitting fragments increased when the beam energy spread was broadened, although the differences were zero for the ideal mono-energetic beams. Greater differences were observed for 11C ion beams compared to 15O ion beams, although both beams had the same range in water, and the higher energy corresponded to a larger difference. For the known energy spread of the beams, the predicted differences between two peaks from the simulation were consistent with the measured data within submillimetre agreement.

Double-Field Hadrontherapy Treatment Monitoring With the INSIDE In-Beam PET Scanner: Proof of Concept

Positron emission tomography (PET) is a well established imaging technique for range monitoring in hadrontherapy. Multiple fields are standard protocol in treatments, but because of washout and residual activity background from previous irradiation plans, to this date quantitative verification of the particle range for each beam field is still an open issue. In this paper, a new method for the evaluation with a PET detector of the activity range of the second field of a treatment is discussed. Two treatment plans with two parallel-opposed beam fields, one using protons and one using carbon ions, were delivered on PMMA phantoms. In both cases, the second beam field was extracted from the first irradiation residual activity and compared with a reference image, obtained from the experimental acquisition of the second field alone. Results demonstrate good agreement between the extracted second field and the reference image, with average difference in the activity range along the preferential direction of the beam less than 0.5 mm for protons, and 1.5 mm for carbon ions. Without taking into account any preferential direction, differences within 0.5 mm were found for both cases. The method will soon be tested with nonhomogeneous phantoms and, subsequently, with in-vivo clinical data.

Evaluation of Median Root Prior for Robust In-Beam PET Reconstruction

Dose delivery verification in proton beam radiotherapy is used to ensure the delivery of the dose to the correct location. A positron emission tomography (PET) scanner can be used to detect the secondary radiation during the treatment, so-called in-beam PET. This is a challenging application for PET due to the low counts and limited angular coverage. We propose a maximum a posteriori (MAP) reconstruction with median root prior (MRP) for the reconstruction of in-beam PET data. The proposed method was compared against MAP with total variation (TV) prior and maximum likelihood expectation maximization (MLEM), which have previously been used for this application. The effects of different ring configurations and time-of-flight information were tested with simulations of a geometrical phantom and a realistic patient treatment plan. The results indicate that both MAP methods produced sharper edges than MLEM, allowing more accurate edge localization in the reconstructed images. Even for the partial ring configurations, no elongation was observed with MAP methods. MAP-MRP successfully reduced the noise, whereas MAP-TV resulted in checkerboard artifacts. MAP-MRP was also more stable against the selection of the reconstruction parameters. In conclusion, MAP-MRP offers a simple and robust alternative for the reconstruction of in-beam PET data.

OA054] Short-lived positron emitters for in-beam positron emission tomography (PET) verification of helium therapy

Purpose Radiotherapy with helium ions is receiving considerable interest because helium ions combine advantages of both protons and carbon ions. Like other ions, range uncertainties limit the accuracy of dose delivery, thus demanding in vivo verification techniques. Previous studies [1] , [2] show the feasibility of in-beam PET monitoring of proton therapy using very short-lived positron emitters such as 12N ( T 1 / 2 = 11 ms). The extension of this approach to helium ions requires information on the production yield of these positron emitters. Given the absence of such information, we investigated the production of positron emitters for monitoring of helium therapy. Methods The cyclotron at KVI-CART was used to bombard water, graphite and calcium phosphate targets with 3He and 4He beams having a range in water of 22 mm (E = 59 and 50 MeV/u respectively). Nuclide production was assessed via the detection of the 511 keV annihilation gammas using a sodium iodide detector (NaI). The beam was delivered in beam-on/beam-off pulses to identify the PET nuclides via half-life analysis. Results The production of short-lived PET nuclides was observed in all irradiated targets. The irradiation of water and graphite targets shows a decay with a half-life of about 10 ms, indicating the production of 12N and/or 13O. The production of this short-lived component is 8.3 × 10 - 4 per 4He and 1.2 × 10 - 3 per 3He. On the water target also 18Ne ( T 1 / 2 = 1.67 s) and 19Ne ( T 1 / 2 = 17.2 s) were observed with 4He beam, whereas only 18Ne is seen with 3He. With the 4He beam on calcium phosphate target, a half-life contribution of 0.898 ± 0.039 s was observed. Since several short-lived nuclides, including 43Ti, 42Sc and 18Ne are expected, the contribution may result from one or more of these nuclides. Conclusions More detailed quantification of the production per helium ion will be given during the presentation. The large production of a 10 ms component, about 50% higher than for protons1; is promising for real-time verification of helium therapy.

Carbon ions beam therapy monitoring with the INSIDE in-beam PET

In vivo range monitoring techniques are necessary in order to fully take advantage of the high dose gradients deliverable in hadrontherapy treatments. Positron emission tomography (PET) scanners can be used to monitor beam-induced activation in tissues and hence measure the range. The INSIDE (Innovative Solutions for In-beam DosimEtry in Hadrontherapy) in-beam PET scanner, installed at the Italian National Center of Oncological Hadrontherapy (CNAO, Pavia, Italy) synchrotron facility, has already been successfully tested in vivo during a proton therapy treatment.We discuss here the system performance evaluation with carbon ion beams, in view of future in vivo tests. The work is focused on the analysis of activity images obtained with therapeutic treatments delivered to polymethyl methacrylate (PMMA) phantoms, as well as on the test of an innovative and robust Monte Carlo simulation technique for the production of reliable prior activity maps.Images are reconstructed using different integration intervals, so as to monitor the activity evolution during and after the treatment. Three procedures to compare activity images are presented, namely Pearson correlation coefficient, Beam’s eye view and overall view. Images of repeated irradiations of the same treatments are compared to assess the integration time necessary to provide reproducible images. The range agreement between simulated and experimental images is also evaluated, so as to validate the simulation capability to provide sound prior information.The results indicate that at treatment end, or at most 20 s afterwards, the range measurement is reliable within 1–2 mm, when comparing both different experimental sessions and data with simulations.In conclusion, this work shows that the INSIDE in-beam PET scanner performance is promising towards its in vivo test with carbon ions.

Mid-range probing—towards range-guided particle therapy

Particle therapy can achieve excellent dose localization but is sensitive to range uncertainty. Therefore, online in vivo range verification before treatment is critical for treatment safety and quality assurance. We introduce a novel range-probing technique that uses mid-range treatment spots selected from the treatment plan as probing beams to be delivered before other treatment spots in pencil beam scanning. The probing spot signal can be acquired by an in-beam positron emission tomography (PET) scanner, and the reconstructed spot positions are compared with pre-calculated positions to measure the range shift. Mid-range probing ensures that the Bragg peaks stay inside the tumor even with significant range variation from the plan. Single-layered spots enable easier spot detection than multi-layered spots without cross-layered spot smearing. With therapeutic dose, the probing beam offers higher positron activities and range detectability than the low-dose imaging beam by up to two orders of magnitude, without exposing patients to extra radiation. Higher positron activities allow sufficient signal statistics in shorter acquisition time, therefore reducing metabolic washout of positron emitters. Thus, range shifts from the plan can be measured easily. We also describe two online range-compensated plan modification methods. We apply correction, if the range shift is above a certain tolerance.We studied feasibility using simulated particle treatment plans with online anatomical changes. For illustration, we demonstrate range shift measurement using simulated probing dose. The proposed range probing and correction effectively handled range shifts in the simulated cases. Both range-compensated adaptation and optimization accounted for online changes so that the delivered dose matched the planned dose.With a dedicated online in-beam PET scanner and phantom and clinical studies, which are currently being developed, this novel strategy may open up a range-guided particle therapy paradigm.

Online proton therapy monitoring: clinical test of a Silicon-photodetector-based in-beam PET

Particle therapy exploits the energy deposition pattern of hadron beams. The narrow Bragg Peak at the end of range is a major advantage but range uncertainties can cause severe damage and require online verification to maximise the effectiveness in clinics. In-beam Positron Emission Tomography (PET) is a non-invasive, promising in-vivo technique, which consists in the measurement of the β+ activity induced by beam-tissue interactions during treatment, and presents the highest correlation of the measured activity distribution with the deposited dose, since it is not much influenced by biological washout. Here we report the first clinical results obtained with a state-of-the-art in-beam PET scanner, with on-the-fly reconstruction of the activity distribution during irradiation. An automated time-resolved quantitative analysis was tested on a lacrimal gland carcinoma case, monitored during two consecutive treatment sessions. The 3D activity map was reconstructed every 10 s, with an average delay between beam delivery and image availability of about 6 s. The correlation coefficient of 3D activity maps for the two sessions (above 0.9 after 120 s) and the range agreement (within 1 mm) prove the suitability of in-beam PET for online range verification during treatment, a crucial step towards adaptive strategies in particle therapy.

Washout effect in rabbit brain: in-beam PET measurements using 10C, 11C and 15O ion beams

In particle therapy, in-beam positron emission tomography (PET) is expected to enable in situ noninvasive confirmation of the treatment delivery. For accurate range and dose verification or three-dimensional (3D) volume imaging, however, correction of the biological washout effect in a living body is necessary. In this study, we measured the washout rate in a rabbit brain using the recently developed technology for oxygen beam radiation as well as carbon ion beam radiation. To measure components of washout, three radionuclides, 10C, 11C and 15O, which were generated as secondary beams in the Heavy Ion Medical Accelerator in Chiba (HIMAC), were irradiated on the rabbit brain under two conditions, live and dead. In-beam data were acquired by our whole body dual-ring OpenPET, which enables 3D in-beam imaging. Regions of interests (ROIs) were set as a 3D positron distribution and the time activity curves (TACs) of the irradiated field were acquired. We obtained the washout rate for those conditions based on multiple component model analysis. A difference between washout speed in 11C ions and the 15O ions was observed. The observed medium and slow biological decay rates of 11C ions in rabbit brain were 0.30 min−1 and 0.004 min−1, respectively. Those values were consistent with the previous rabbit study results acquired by other imaging modalities, such as the pair of positron cameras or our single-ring small animal OpenPET prototype. The observed medium and slow biological decay rates of 15O ions were 0.72 min−1 and 0.024 min−1, respectively, which were faster than those of the 11C ion. Also, the medium biological decay rate of 15O ions was close to the washout rate in cerebral blood flow (CBF) measurements by dynamic PET with 15O-labeled water. These results should help to establish an accurate washout correction model.

In-Beam PET Imaging in Carbon Therapy for Dose Verification

Carbon particle therapy has shown great advantages in radiation therapy owing to its high relative biological effectiveness. In-beam positron emission tomography (PET) is an effective method for monitoring and measuring the position and dose of a carbon ion beam. In this paper, we use Geant4 application for emission tomography software to simulate carbon therapy and in-beam PET imaging processes. One hundred pulses of 12C with 100, 200, and 300 AMeV were impacted on a PMMA target. The distributions of positron-emitting nuclides and the radiation dose were calculated. The coincidence data of annihilation photons from positrons were measured via a small animal PET protocol, which uses the same detector size and ring radius as the MicroPET Focus 220. Finally, we reconstructed the 3-D PET image for the distribution of generated positron-emitting nuclides by using a filtered back projection algorithm, and the PET image was used to determine the position of maximum dose deposition. Thus, we demonstrate a comprehensive method to accurately identify the position of maximum dose deposition by using the reconstructed in-beam PET image.

Abstract ID: 183 Advances in the FLUKA PET tools

In this work the new developments of FLUKA [1] , [2] Positron Emission Tomography (PET) tools [3] are presented. FLUKA is a fully integrated Monte Carlo (MC) particle transport code, widely used for an extended range of applications, including medical physics. Recently FLUKA has provided the medical community with dedicated simulation tools for clinical applications, such as DICOM to voxel or PET simulation packages. PET is a well-established imaging technique in nuclear medicine and a promising method for clinical in vivo treatment verification in hadrontherapy. The application of clinically settled PET scanners to new irradiation environments such as hadrontherapy requires further experimental and theoretical research to which MC simulations could be applied. The FLUKA PET tools, besides including existing models from PET scanner manufacturers in its library, allows the configuration of new PET prototypes, thanks to its geometry framework supported by FLUKA GUI – Flair. Both the beam time structure and acquisition time can be specified by the user, allowing the correct reproduction of PET monitoring. Furthermore, different scoring routines allow an analysis on single and coincident events, as well as identification of parent isotopes generating annihilation events. Two image reconstruction codes are currently supported: the Filtered Back-Projection and the Maximum-Likelihood Expectation Maximization. Compatibility with other reconstruction frameworks is also possible. The FLUKA PET tools have been successfully tested for different detectors and scenarios, including conventional PET Quality Assurance and in-beam PET, either using as a source radioisotopes density maps, or simulating hadron beams interacting with complex targets, accounting for the various nuclear reactions. Finally, the results obtained so far confirm that the FLUKA PET tools are suitable to perform PET simulation studies in clinical environment.

Mid-range Probing—Towards Range-Guided Particle Therapy

Particle therapy can achieve excellent dose localization but is sensitive to range uncertainty. Therefore, online in vivo range verification before treatment is critical for treatment safety and quality assurance. We introduce a novel range-probing technique that uses mid-range treatment spots selected from the treatment plan as probing beams to be delivered before other treatment spots in pencil beam scanning. The probing spot signal can be acquired by an in-beam positron emission tomography (PET) scanner, and the reconstructed spot positions are compared with pre-calculated positions to measure the range shift. Mid-range probing ensures that the Bragg peaks stay inside the tumor even with significant range variation from the plan. Single-layered spots enable easier spot detection than multi-layered spots without cross-layered spot smearing. With therapeutic dose, the probing beam offers higher positron activities and range detectability than the low-dose imaging beam by up to two orders of magnitude, without exposing patients to extra radiation. Higher positron activities allow sufficient signal statistics in shorter acquisition time, therefore reducing metabolic washout of positron emitters. Thus, range shifts from the plan can be measured easily. We also describe two online range-compensated plan modification methods. We apply correction, if the range shift is above a certain tolerance. We studied feasibility using simulated particle treatment plans with online anatomical changes. For illustration, we demonstrate range shift measurement using simulated probing dose. The proposed range probing and correction effectively handled range shifts in the simulated cases. Both range-compensated adaptation and optimization accounted for online changes so that the delivered dose matched the planned dose. With a dedicated online in-beam PET scanner and phantom and clinical studies, which are currently being developed, this novel strategy may open up a range-guided particle therapy1 paradigm.

Development of a Whole-Body Dual Ring OpenPET for in-Beam PET

For in-beam positron emission tomography (PET), which is an in situ monitoring method for charged particle therapy, we developed the world’s first open-type PET system “OpenPET.” Following our previous studies for small prototypes, in this paper, we finally developed a whole-body dual ring OpenPET (WBDROP). This scanner has two separated rings. Each ring has two detector rings of 40 detector blocks, each of which has the capability of 4-layer depth-of-interaction identification. The ring diameter is 66 cm, and the adjustable open gap is fixed as 9 cm. We found that the system sensitivity was 4.4%. The average spatial resolution, which was measured through filtered back projection, was about 3.5 mm. For in-beam PET, imaging performance was confirmed through phantom experiments. Phantom study results with 11C beam and 10C beam irradiations of about 3 Gy showed that the beam stopping position in the target could be measured with a precision of better than 2 mm. The developed WBDROP promises high performance for in-beam PET imaging.

Development of Compact, Cost-effective, FPGA-Based Data Acquisition System for the iPET System

Positron emission tomography (PET) is a nuclear medicine imaging technology used to analyze physiological processes. An in-beam PET is used to verify the delivered dose during ion-beam therapy. Our group investigates the prototype C-shaped PET system, which is called the iPET system. In this study, we develop an expendability-enhanced field-programmable gate array (FPGA)-based data acquisition system for the iPET. We organize this data acquisition (DAQ) system using only one DAQ board, to ensure a compact and cost-effective DAQ system. We design the FPGA using modular functions, which include synchronization, deserialization, pulse height analysis, and data packaging functions. As a result, energy spectra and well-separated 9 × 9 flood images of the entire detector module are achieved. We obtain reconstructed PET images of point source (4 mm diameter), three cylindrical phantoms (3 cm diameter), and four sphere phantoms (3.0, 2.2, 1.3 and 1.0 cm diameter). We achieve approximately 300 kcps of maximum single count rate. The obtained results prove the compactness and cost-effectiveness of the proposed DAQ system.

In Beam PET Acquisition on 75 MeV. $\text {u}^{-1}$ Carbon Beam Using Sampling-Based Read-Out Electronics

Positron Emission Tomography (PET) dedicated to the ion range verification in the context of hadrontherapy treatments, requires a very selective experimental device able to discriminate the two gammas from ${\beta ^{+}}$ decay from prompt particles due to the interactions of the beam with the matter. Prompt particles are a background noise in the context of induced ${\beta ^{+}}$ activity measurement. A significant part of this background noise is produced by the ${\gamma }$ prompt emitted during beam spill. Therefore a precise knowledge of beam time structure is crucial to control the quality of data of in-beam PET acquisitions. In other words, beam time structure determines the number of primary ions per bunch and the nuclear induced background. An experiment was performed at the National Large Heavy Ion Accelerator (GANIL) in Caen (France) using a 75 A.MeV carbon beam in order to test the use of sampling-based read-out electronics to provide a very accurate time stamping of the detected particles. The experimental set-up is constituted by a small acceptance dual head detector positioned on each side of the beam centered on target. For this cyclotron beam, the cycle is 12 MHz with a beam spill of 10 ns. If acquisition takes into account only events occurring outside the spill, we demonstrate that the energy spectrum of events is equivalent to target radiative decay spectrum obtained just after stopping the beam. For this experiment, the technique of sampling signal was chosen, allowing to provide an accurate time measurement to adjust optimal time and energy cuts on the recorded data. With the time structure of the beam spill at GANIL, taking into account all the events, including those acquired during the spill, the measured background-to-signal event ratio is 10%.

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

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.