Compton Cones Research Articles

High-contrast Compton camera: Challenges to high-quality and broadband imaging

In the field of nuclear medicine, various radiopharmaceuticals require wideband x-ray/gamma-ray imaging devices for clinical and treatment monitoring. Compton cameras, which perform imaging using high-energy gamma rays, have the potential to significantly increase the variety of radioactive nuclides that can be imaged. However, artifacts caused by the so-called “Compton cone” have hindered their clinical use. Therefore, we propose the use of a collimator to improve the contrast of images obtained using Compton cameras. In this study, we developed a high-contrast Compton camera by attaching a tungsten collimator to its front surface. The contrast is improved by applying weighting to the signals based on the distance that the high-energy gamma rays penetrated the collimator walls. As a demonstration, we visualized 198Au plates that emit 412-keV gamma rays with and without the collimator. In addition, low-energy (<200 keV) x-ray/gamma-ray imaging, which is difficult for conventional Compton cameras, was achieved by performing single-photon emission computed tomography (SPECT) using the collimator and scatterer of the Compton camera. We demonstrated broadband gamma-ray imaging by visualizing a 133Ba standard source using 81-keV and 356-keV gamma rays based on the principles of SPECT and Compton cameras, respectively.

Tracking a moving point source using triple gamma imaging

Abstract With positron emission tomography (PET), the positron of a β + emitter radioisotope annihilates with a nearby electron producing a pair of back-to-back 511 keV gamma rays that can be detected in a scanner surrounding the point source. The position of the point source is somewhere along the Line of Response (LOR) that passes through the positions where the 511 keV gammas are detected. In standard PET, an image reconstruction algorithm is used to combine these LORs into a final image. This paper presents a new tomographic imaging technique to locate the position of a β + emitting point source without using a standard PET image reconstruction algorithm. The data were collected with a Proof-of-Concept (PoC) PET scanner which has high spatial and energy resolutions. The imaging technique presented in this paper uses events where a gamma undergoes Compton scattering. The positions and energies deposited by the Compton scattered gamma define the surface of a Compton cone (CC) which is the locus of all possible positions of the point source, allowed by the Compton kinematics. The position of the same point source is also located somewhere on the LOR. Therefore, the position of the point source is defined by the 3 gammas and is given by the intersection point of the LOR and the Compton cone inside the Field of View (FOV) of the scanner. We refer to this method as CC×LOR. This new technique can locate the point source with an uncertainty of about 1 mm, after collecting a minimum of 200 CC×LOR events.

Improvement of double photon emission Compton imaging using angular and polarization correlations in cascade photons

A Compton camera is a gamma ray imaging system that produces images by superposing Compton cones calculated from Compton kinematics. However, the reconstructed images exhibit a high background. In this study, the angular correlation and polarization correlation were used to decrease the background. 111In, which emits 171 keV and 245 keV cascade gamma rays, was imaged using Compton camera modules in the ring structure. The 3D list-mode ordered subset expectation maximization method was used to reconstruct the images. Probability modeling of events reflecting angular and polarization correlations was applied to the image-reconstruction algorithm. The results were compared with those of a typical Compton camera method using only 245 keV Compton cones. The sensitivity of the proposed method was 1.03% of that of the typical method. However, compared to the typical method, the application of angular and polarization correlations improved the signal-to-background ratio. The proposed method is expected to be useful in capturing low-background images wherein a ring-type Compton camera and cascade photon-emitting nuclides can be used.

Component characterization and commissioning of a gamma-PET prototype detector system

Hybrid imaging systems, comprising PET and Compton camera modules, have recently gained in interest, due to their capability to simultaneously detect positron annihilation photons and γ-rays from single-photon emitting sources as also used in SPECT. A unique feature of such systems, however, is the capability to also be operated in a so called γ-PET mode. Here, specific β+- emitting radioisotopes (such as 44Sc, 1°C or 14O) are used to detect triple-coincidences between two annihilation γ-rays (in PET imaging) and a third, prompt photon (in Compton imaging), that is emitted by the deexcitation of the decay’s daughter nucleus. Consequently, an intersection between the line-of-response (LOR) and the Compton cone can be determined, which (in principle) allows to localize the photons’ emission vertices on a single decay basis. In practice, however, a few tens of events are required to localize a point source, which still results in a considerable sensitivity improvement compared to conventional PET imaging.For a proof-of-principle study, we used a pixelated GAGG crystal array (16 × 16 crystals; 1.45 × 1.45 × 6 mm3 crystal volume; 25 μm SPAD SiPMs as readout) as Compton camera scatterer and PET detectors, and a three-layered LYSO crystal array (1.2 × 1.2 × 6.66 mm3 crystal volume; 50 μm SPAD SiPMs as readout) as Compton camera absorber. We characterized the individual detector components with regard to their energy resolution and the capability to identify the various scintillator array’s individual crystals. Our first γ-PET prototype was tested in PET-only and Compton-only imaging mode, in which spatial resolutions of 3.2–3.5 mm FWHM (PET-only mode) and 14.4–19.3 mm FWHM (Compton-only mode at 1,274 keV) were achieved, respectively, using a22Na point source and 10 iterations of an ML-EM reconstruction algorithm. By using triple-coincidences in a γ-PET mode (event-wise intersection of the LOR and the Compton cone), we could demonstrate the capability of the prototype to perform a full 3D point source reconstruction using only 77 events.

Feasibility study of imaging with tissue-scattered triple-γ coincidence events in Compton-PET

The objective of the present work is to study Compton-PET imaging with single scattered (in tissue) data using a non-pure beta emitter (44Sc). Such radioisotopes are advantageous because of the extra gamma radiation to be used in triple-γ coincidences. Utilizing the single scattered events in conjunction with an additional gamma (1157 keV) emitted from 44Sc, provided us with an opportunity to obtain the direct images of the source activity distribution. The idea presented here is unique because there is hardly any imaging research with tissue-scattered data in the literature, especially for a Compton-PET system using a non-pure beta emitter. Initially, we described the locus of tissue-scattered point as a prolate spheroid surface or spindle toroid, which became two intersection points after using Compton cones from both ends of 511 keV photon detections. We considered a human-sized Compton-PET system of two types — (i) ideal and (ii) state-of-art scanner — depending on the energy and timing resolutions of detectors. The list-mode data were generated via GATE simulations. The appropriate trigger logic was applied using the two-window method to separate the events corresponding to single tissue-scattered and true (unscattered) coincidences. The imaging involves estimating the annihilation point for each triple-coincidence event using Compton cone of 1157 keV gamma and time-of-flight information for the 511 keV. Thus, we directly obtained images of the activity distribution without using any reconstruction algorithm. They turned out indeed meaningful, establishing our feasibility study. For quality assessment, we compared the full-width-half-maximum (FWHM) of the intensity profiles of various images. For ideal scanner, for instance, the FWHM for the tissue-scattered image was almost double of that for the unscattered one. Although the image quality was not all that good, but we expected it because of physics-based uncertainties involved in the tissue-scattered imaging. Nonetheless, separate assessments of the underlying activity from two independent data sets — one from single tissue-scattered, another from the usual true coincidences — could certainly improve image interpretation in medical diagnosis.

A Pseudo-TOF Image Reconstruction Approach for Three-Gamma Small Animal Imaging

In this article, we propose a novel image reconstruction technique for three-gamma (3- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ {\gamma }$ </tex-math></inline-formula> ) imaging systems that aims at reaching high image quality with a low statistics. The proposed approach is based on the utilization of a ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ {\beta +}$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\gamma }$ </tex-math></inline-formula> ) emitter and a liquid xenon (LXe) camera, the Xenon Medical Imaging System 2 (XEMIS2), that is currently being manufactured. The third gamma emitted is more energetic than the two 511-keV photons and interacts mostly through Compton scattering in LXE; therefore, we utilize the interactions’ position and the deposited energy to define a Compton cone that gives the direction from where the third gamma was emitted. The intersection point between the cone and the two coincidence photons’ lines of response (LOR) is the center of the probability distribution function (PDF), a resolution model similar to that of time-of-flight (TOF)-positron emission tomography (PET). The third gamma’s information is used to narrow the LOR portion employed during reconstruction. In this article, we show reconstruction results from simulation using highly realistic Geant4 Application for Emission Tomography (GATE) Monte Carlo simulation of the imaging device and a NEMA-like phantom.

Whole gamma imaging: a new concept of PET combined with Compton imaging

We proposed a concept of whole gamma imaging (WGI) that utilizes all detectable gamma rays for imaging. An additional detector ring, which is used as the scatterer, is inserted in the field-of-view of a PET ring so that single gamma rays can be detected by the Compton imaging method. In particular, for the non-pure positron emitters which emit an additional gamma ray almost at the same time, triple gamma imaging will be enabled; localization on each line-of-response (LOR) is possible by using the Compton cone of the additional gamma ray. We developed a prototype to show a proof of the WGI concept. The diameters of scatterer ring and PET ring were set as 20 cm and 66 cm, respectively. For Compton imaging of the 662-keV gamma ray from a 137Cs point source, spatial resolution obtained by the list-mode OSEM algorithm was 4.4 mm FWHM at the 8 cm off-center position and 13.1 mm FWHM at the center position. For PET imaging of a 22Na point source, spatial resolution was about 2 mm FWHM at all positions. For the triple gamma imaging, 5.7 mm FWHM (center) and 4.8 mm FWHM (8 cm off-center) were obtained for the 22Na point source just by plotting the intersecting points between each LOR and each Compton cone of the 1275-keV gamma ray. No image reconstruction was applied. Scandium-44 was produced as a practical candidate of the non-pure positron emitters, and 6.6 mm FWHM (center) and 5.8 mm FWHM (8 cm off-center) were obtained in the same manner. This direct imaging approach which neither requires time-consuming event integration nor iterative image reconstruction may allow in vivo real-time tracking of a tiny amount of activity. Our initial results showed the feasibility of the WGI concept, which is a novel combination of PET and Compton imaging.

Simulation study on SOI based electron tracking Compton camera using deep learning method

Compton imaging is a promising method of sub MeV to a few MeV gamma-rays and expected to use in various application field, such as medical imaging, environmental monitoring and astrophysics. Several types of Compton camera has beed developed using different materials. One of the drawbacks in conventional Compton imaging is relatively low signal to background ratio caused by its projected Compton cones. Recoil electron tracking is one straight-forward way to improve the signal-to-background ratio, however, it is only realized in gaseous detectors. The realization of electron tracking in solid detectors is under investigation because of its short track in scatter materials. We demonstrated the capability of electron tracking in silicon-on-insulator (SOI) pixel detector with 30 μm pixels size. The extraction of ejected direction of recoil electrons in Compton scattering is an important problem. In this work, we investigated the use of deep learning for estimating the angle in plane and depth using Geant 4 Monte Carlo simulation. The effect of pixel size to the estimation accuracy and SPD is characterized for the application of actual silicon-on-insulator based SOI detectors. The imaging capability is also characterized using predicted recoil electron direction.

Building blocks of a multi-layer PET with time sequence photon interaction discrimination and double Compton camera

Current PET detectors have a very low sensitivity, of the order of a few percent. One of the reasons is the fact that Compton interactions are rejected. If an event involves multiple Compton scattering and the total deposited energy lays within the photoelectric peak, then an energy-weighted centroid is the given output for the coordinates of the reconstructed interaction point. This introduces distortion in the final reconstructed image. The aim of our work is to prove that Compton events are a very rich source of additional information as one can improve the resolution of the detector and implicitly the final reconstructed image. This could be a real breakthrough for PET detector technology as one should be able to obtain better results with less patient radiation. Using a PET as a double Compton camera, by means of Compton cone matching i.e., Compton cones coming from the same event should be compatible, is applied to discard randoms, patient scattered events and also, to perform a correct matching among events with multiple coincidences. In order to fully benefit experimentally from Compton events using monolithic scintillators a multi-layer configuration is needed and a good time-of-flight resolution.

Performance studies towards a TOF-PET sensor using Compton scattering at plastic scintillators

We have developed a sensor head for a time-of-flight (TOF) PET scanner using plastic scintillators that have a very fast timing property. Given the very small cross section of photoelectric absorption in plastic scintillators at 511 keV, we use Compton scattering in order to compensate for detection efficiency. The detector will consist of two layers of scatterers and absorbers which are made of plastic and inorganic scintillators such as GAGG:Ce, respectively. Signals are read by monolithic Multi Pixel Photon Counters, and with energy deposits and interaction time stamps are being acquired. The scintillators are built to be capable of resolving interaction position in three dimensions, so that our system has also a function of depth-of-interaction (DOI) PET scanners. TOF resolution of ∼ 200 ps (FWHM) is achieved in both cases of using the leading-edge discriminator and time-walk correction and using a configuration sensitive to DOI. Both the position resolution and spectroscopy are demonstrated using the prototype data acquisition system, with Compton scattering events subsequently being obtained. We also demonstrated that the background rejection technique using the Compton cone constraint could be valid with our system.

Improving PET sensitivity with a Compton algorithm

Current PET detectors have a very low sensitivity, of the order of a few percent. One of the reasons is that Compton events are being rejected. In this work we aim to prove that Compton events are a very rich source of additional information that can play a crucial role in the image reconstruction process. With this additional data, the detector sensitivity will be substantially improved and thus, the applied dose on the patient can also be reduced. This could be a really breaking point for PET detector technology as one should be able to obtain better image quality with less patient radiation. By means of Compton cone matching (the Compton cones coming from the same event should be compatible) one should be able to better recognize matching events and discard randoms and even events that have previously suffered scattering within the patient’s body.

Evaluation of double photon coincidence Compton imaging method with GEANT4 simulation

Compton imaging has been used for various applications including astronomical observations, radioactive waste management, and biomedical imaging. The positions of radioisotopes are determined in the intersections of multiple cone traces through a large number of events, which reduces signal to noise ratio (SNR) of the images. We have developed an advanced Compton imaging method to localize radioisotopes with high SNR by using information of the interactions of Compton scattering caused by two gamma rays at the same time, as the double photon coincidence Compton imaging method. The targeted radioisotopes of this imaging method are specific nuclides that emit several gamma rays at the same time such as 60Co, 134Cs, and 111In, etc. Since their locations are determined in the intersections of two Compton cones, the most of cone traces would disappear in the three-dimensional space, which enhances the SNR and angular resolution. In this paper, the comparison of the double photon coincidence Compton imaging method and the single photon Compton imaging method was conducted by using GEANT4 Monte Carlo simulation.

3$\gamma $ Medical Imaging with a Liquid Xenon Compton Camera and $^{44}$Sc Radionuclide

The development of a liquid xenon Compton camera called XEMIS2 (XEnon Medical Imaging System) is a step forward to a new type of medical imaging based on the use of 44Sc radionuclide emitting two annihilation rays and a third high energy ray simultaneously. The single phase TPC (Time Projection Chamber) under construction, containing nearly 200 kg of xenon, is designed to measure most of the Compton interactions in the active area with a sub-millimetre position resolution and a good energy resolution of 4% on 511 keV photopeak. The intersection of the Compton cone surface from the third ray with the line of response from the two annihilation rays allows to localize the radionuclide with a precision (FWHM) of about 1 cm along this line. The large field of view of such a liquid xenon camera combined with the 3 imaging technique will provide a good quality image while keeping the injected activity at a very low level. XEMIS2 will be installed in the Nantes University Hospital in order to demonstrate its capability to image small animals injected with a low activity of only 20 kBq in 20 mn acquisition time. To achieve this goal, a precise measurement of the ionization signal is provided by a pixelized anode, shielded by a Frisch Grid and read out by a low noise front-end electronics. In addition, new cryogenic and purification subsystems have been tested, allowing safe recovery of xenon in liquid phase at flow rates of about 1 ton per hour.

Electron Pattern Recognition using trigger mode SOI pixel sensor for Advanced Compton Imaging

Compton imaging is a useful method for localizing sub MeV to a few MeV gamma-rays and widely used for environmental and medical applications. The direction of recoiled electrons in Compton scattering process provides the additional information to limit the Compton cones and increases the sensitivity in the system. The capability of recoiled electron tracking using trigger-mode Silicon-On-Insulator (SOI) sensor is investigated with various radiation sources. The trigger-mode SOI sensor consists of 144 by 144 active pixels with 30 μm cells and the thickness of sensor is 500 μm. The sensor generates the digital output when it is hit by gamma-rays and 25 by 25 pixel pattern of surrounding the triggered pixel is readout to extract the recoiled electron track. The electron track is successfully observed for 60Co and 137Cs sources, which provides useful information for future electron tracking Compton camera.

Using triple gamma coincidences with a pixelated semiconductor Compton-PET scanner: a simulation study

The Voxel Imaging PET (VIP) Pathfinder project presents a novel design using pixelated semiconductor detectors for nuclear medicine applications to achieve the intrinsic image quality limits set by physics. The conceptual design can be extended to a Compton gamma camera. The use of a pixelated CdTe detector with voxel sizes of 1 × 1 × 2 mm3 guarantees optimal energy and spatial resolution. However, the limited time resolution of semiconductor detectors makes it impossible to use Time Of Flight (TOF) with VIP PET. TOF is used in order to improve the signal to noise ratio (SNR) by using only the most probable portion of the Line-Of-Response (LOR) instead of its entire length. To overcome the limitation of CdTe time resolution, we present in this article a simulation study using β+-γ emitting isotopes with a Compton-PET scanner. When the β+ annihilates with an electron it produces two gammas which produce a LOR in the PET scanner, while the additional gamma, when scattered in the scatter detector, provides a Compton cone that intersects with the aforementioned LOR. The intersection indicates, within a few mm of uncertainty along the LOR, the origin of the beta-gamma decay. Hence, one can limit the part of the LOR used by the image reconstruction algorithm.

Noise evaluation of Compton camera imaging for proton therapy

Compton Cameras emerged as an alternative for real-time dose monitoring techniques for Particle Therapy (PT), based on the detection of prompt-gammas. As a consequence of the Compton scattering process, the gamma origin point can be restricted onto the surface of a cone (Compton cone). Through image reconstruction techniques, the distribution of the gamma emitters can be estimated, using cone-surfaces backprojections of the Compton cones through the image space, along with more sophisticated statistical methods to improve the image quality. To calculate the Compton cone required for image reconstruction, either two interactions, the last being photoelectric absorption, or three scatter interactions are needed. Because of the high energy of the photons in PT the first option might not be adequate, as the photon is not absorbed in general. However, the second option is less efficient. That is the reason to resort to spectral reconstructions, where the incoming γ energy is considered as a variable in the reconstruction inverse problem. Jointly with prompt gamma, secondary neutrons and scattered photons, not strongly correlated with the dose map, can also reach the imaging detector and produce false events. These events deteriorate the image quality. Also, high intensity beams can produce particle accumulation in the camera, which lead to an increase of random coincidences, meaning events which gather measurements from different incoming particles. The noise scenario is expected to be different if double or triple events are used, and consequently, the reconstructed images can be affected differently by spurious data. The aim of the present work is to study the effect of false events in the reconstructed image, evaluating their impact in the determination of the beam particle ranges. A simulation study that includes misidentified events (neutrons and random coincidences) in the final image of a Compton Telescope for PT monitoring is presented. The complete chain of detection, from the beam particle entering a phantom to the event classification, is simulated using FLUKA. The range determination is later estimated from the reconstructed image obtained from a two and three-event algorithm based on Maximum Likelihood Expectation Maximization. The neutron background and random coincidences due to a therapeutic-like time structure are analyzed for mono-energetic proton beams. The time structure of the beam is included in the simulations, which will affect the rate of particles entering the detector.

Development of a Compton Camera for Online Range Monitoring of Laser-Accelerated Proton Beams via Prompt-Gamma Detection

Presently large efforts are conducted in Munich towards the development of proton beams for bio-medical applications, generated via the technique of particle acceleration from high-power, short-pulse lasers. While so far mostly offline diagnostics tools are used in this context, we aim at developing a reliable and accurate online range monitoring technique, based on the position-sensitive detection of prompt ? rays emitted from nuclear reactions between the proton beam and the biological sample. For this purpose, we develop a Compton camera, designed to be able to track not only the Compton scattering of the primary photon, but also to detect the secondary Compton electron, thus reducing the Compton cone to an arc segment and by this increasing the source reconstruction efficiency. Design specifications and the status of the protype system are discussed.

82 SUBMILLIMETER NUCLEAR MEDICAL IMAGING WITH A COMPTON CAMERA USING TRIPLE COINCIDENCES OF COLLINEAR BETA+− ANNIHILATION PHOTONS AND GAMMA RAYS

PET cameras had their breakthrough as an imaging instrument for clinical application studies due to the large variety of radioactively labeled tracer molecules [1]. These tracers carry an e emitting isotope to e.g. a tumor. Annihilation of the positron into two back-to-back 511 keV photons allows to restrict the source origin in 2 dimensions onto a line of response (LOR). Superimposing the LORs of different decay events locates the source distribution of the emitter in 3D. Modern PET systems reach a spatial resolution of 3-10 mm. A disadvantage of this technique is the diffusion of the positron before its decay with a typical range of ca. 1 mm (depending on its energy). This motion and Compton scattering of the 511 keV photons within the patient limit the performance of PET. We present a nuclear medical imaging technique, able to reach submillimeter spatial resolution in 3 dimensions with a reduced activity application compared to conventional PET. This ’gamma-PET’ technique draws on specific e sources simultaneously emitting an additional photon with the β decay. Exploiting the triple coincidence between the positron annihilation and the third photon, it is possible to separate the reconstructed ’true’ events from background [2,3]. Therefore the spatial uncertainty introduced by the motion of the e or by Compton scattering within the patient can be strongly reduced in the direction normal to the annihilation. Especially Sc is of interest, which β decays into Ca, emitting an 1157 keV photon. With its halflife of 3.9 h, Sc has to be produced from a Ti generator (t1/2 = 60.4 a) [4]. Presently this cannot be performed in clinically relevant quantities, however, this may change with the soon expected availability of highly brilliant gamma beams [2]. Sc has already been applied in patient studies [5]. We combined the Compton camera technique, i.e. the measurement of photon energies and positions of Compton scattering interactions, with a PET camera defining the LOR. Due to the Compton kinematics and subsequent photon absorption, a Compton camera can reconstruct the origin of a primary photon on the surface of a ’Compton cone’ [6]. Superimposing such cones from different events reduces

Reconstruction of electron trajectories in high-resolution Si devices for advanced Compton imaging

Compton imaging has been demonstrated to provide excellent detection and localization capabilities in the search and characterization of radiation sources. However, the currently achievable sensitivity is limited by the Compton cone, which is backprojected. By measuring the initial trajectory of the Compton electron, the cone may be reduced to a cone segment with a corresponding increase in sensitivity. We have demonstrated the ability to measure electron trajectories (tracks) in thick ( 650 μ m ), fully depleted silicon scientific CCDs, with a spatial resolution of 10 μ m in 2D. These measured tracks have been used to benchmark simulations of electron physics and detector response. We have developed an electron track algorithm to measure the initial electron direction in 3D from the CCD image, and utilized the modeled electron tracks to evaluate the angular resolution as a function of energy and initial direction for electrons up to ∼ 500 keV . For electrons above 150 keV and 30° out-of-plane, we have achieved an in-plane angular uncertainty of σ α ≲ 40 ∘ , and an out-of-plane uncertainty of σ β ≲ 30 ∘ in each hemisphere.

Design Guidelines for a Double Scattering Compton Camera for Prompt-$\gamma$ Imaging During Ion Beam Therapy: A Monte Carlo Simulation Study

In hadrontherapy in order to fully take advantage of the assets of the ion irradiation, the position of the Bragg peak has to be monitored accurately. Here, we investigate a monitoring method relying on the detection in real time of the prompt γ emitted quasi instantaneously during the nuclear fragmentation processes. Our detection system combines a beam hodoscope and a double scattering Compton camera. The prompt-γ emission points are reconstructed by intersecting the ion trajectories given by the hodoscope and the Compton cones reconstructed with the camera. We propose here to study in terms of point spread function and efficiency the theoretical feasibility of the emission points reconstruction with our set-up in the case of a photon point source in air. First we analyze the nature of all the interactions which are likely to produce an energy deposit in the three detectors of the camera. It is underlined that upper energy thresholds in both scatter detectors are required in order to select mainly Compton events (one Compton interaction in each scatter detector and one interaction in the absorber detector). Then, we study the influence of various parameters such as the photon energy and the inter-detector distances on the Compton camera response. These studies are carried out by means of Geant4 simulations. We use a source with a spectrum corresponding to the prompt-γ spectrum emitted during the carbon ion irradiation of a water phantom. In the current configuration, the spatial resolution of the Compton camera is about 6 mm (Full Width at Half Maximum) and the detection efficiency 10-5. Finally, provided the detection efficiency is increased, the clinical applicability of our system is considered.