Ryota Kohara

Study on the use of electron-tracking Compton gamma-ray camera to monitor the therapeutic proton dose distribution in real time

Radiation therapy with proton and heavy-ion beams has been better established lately and the patient throughput is increasing. Although the therapy beam is controlled with high accuracy, it is difficult to know the location of distal dose falloff in the body. If real-time monitoring of the location is realized, the treatment quality would be improved. We have developed an electron-tracking Compton camera (ETCC) for real-time monitoring on the proton therapy. Our ETCC has a wide energy dynamic range of 200-1300 keV and a wide field of view. Therefore, ETCC has a potential as a quality assurance tool for proton therapy. We simulated and conducted an experiment with a 155 MeV proton beam and a water phantom. We succeeded in imaging a Bragg peak with prompt gamma rays.

Advanced Compton Camera with the ability in electron tracking based on Micro Pixel Gas Detector for Medical Imaging

We have developed the electron tracking Compton camera (ETCC) with reconstructing the 3-D tracks of the scattered electron in Compton process in the range from sub-MeV to several MeV for both gamma-ray astronomy and medical imaging [Bhattacharya, D, et al., 2004; Kanbach, G, et al., 2004]. By measuring both the directions and energies of a recoil gamma ray and a scattered electron, the direction of the incident gamma ray is determined for each individual photon. Furthermore, a residual measured angle between the recoil electron and scattered gamma ray is powerful for the kinematical background-rejection. For the 3-D tracking of the electrons, the micro time projection chamber (mu-TPC) was developed, which consists of a new type of the micro pattern gas detector, or a micro pixel gas chamber (mu-PIC) [Kanbach, G, et al., 2004; Ochi, A, et al., 2001; Nagayoshi, T, et al., 2005]. The ETCC consists of this mu-TPC (10 cm cube) and the 6 times 6 times 3mm GSO crystal pixel arrays with a flat panel photo-multiplier surrounding the base and side of the mu-TPC for detecting the recoil gamma rays. The ETCC provided the gamma ray images of point sources between 120 keV and ~1 MeV with the angular esolution of 6 degree and 5 degree (FWHM) at 364 keV of 131iodine and 511 keV of 18F ion, respectively. Also the angle of the scattered electron was measured with the resolution of ~80 degree, by which most backgrounds were removed by the kinematical constraint. A mobile ETCC for medical imaging, which is fabricated in a 1 m cubic box, has been tested since October 2005. Here we present the imaging performances using both a phantom and a rat.

Simultaneous imaging of multi nuclides using the Electron Tracking Compton gamma-ray camera based on small animal and phantom experiments

Compton Camera has a potential for nuclear medicine. Because energy dynamic range and field of view is wide. Electron Tracking Compton Camera (ETCC) which we have developed consists of two detectors micro Time Projection Chamber (μTPC) and Pixel Scintillator Array (PSA). We have developed two type of ETCC small and large, and we have evaluated these cameras and have imaged phantom and small animal.

Diagnostic approach of using an electron tracking compton gamma-ray camera based on small animal and phantom experiments

A conventional Compton camera reconstructs initial gamma-rays direction as circle. A Compton gamma-ray camera which we have developed can detect electron tracks. So our camera can reconstruct the initial gamma-rays as arc. It makes getting the low noise of image. In this paper, we report the results of three version of electron tracking camera. One is 10 x 10 x 10 cm³ Time Projection Chamber (TPC) as a scatter detector and 15 x 15 cm² GSO pixel scintillator array (PSA) as an absorber. Second is a 10 x 10 x 10 cm³ TPC and a 10 x 10 cm2 LaBr₃ PSA. The energy resolution of LaBr₃ scintillator is about 2 times better than GSO scintillator. Third is a 30 x 30 x 15 cm³ TPC and a 30 x 30 cm² GSO pixel PSA. The efficiency of this system is better than 10 cm³ cube Compton gammra-ray camera.

Advanced Compton camera system for nuclear medicine: Prototype system study

A gamma-ray imager called Compton camera is expected as a new medical instrument for nuclear medicine. It has several advantages over the conventional techniques such as positron emission tomography and single photon emission tomography. Especially, the Compton camera can expand the range of diagnosis and therapy because various gamma-ray energies can be measured without changing system configuration. Many studies have been made on the Compton camera, however, its medical application is still challenging because in clinical environments it is very difficult to image targets due to large background activities. We will establish the imaging techniques and demonstrate the imaging capabilities of the advanced Compton camera. We constructed the prototype system with the gaseous chamber and the scintillation counter. We performed phantom experiments with a 131I gamma-ray source, assuming clinical environments. We evaluated the contrast resolution and found the limitations on the concentration ratio and the magnitude of statistics for imaging hotspots in the large background activity. We performed the Compton tomography in the only three-direction scan and obtained an axial image. We also demonstrated the fusion image with X-ray CT for clinical application.

Development of a Electron Tracking Compton Gamma-Ray Camera Using a Gas Micro-Tracking Device for Nuclear Medicine

the electron tracking compton gamma-ray camera is consisted of two detectors which are a scatter detector and absorb detector. The scatter detector is a Time Projection Chamber which spatial resolution is 0.4 mm and energy resolution is 25% at 22 keV. This system can take the recoiled electron track and energy. The absorb detector which catches the position and energy of a scattered gamma-ray. This detector is consisted of GSO scintillator and multianode photomultiplier tube. A position resolution is 6 mm and the energy resolution is 11% at 662 keV. A spatial resolution of this whole system is 3 cm at 10 cm distance from detector and the efficiency is 10-5 sec-1 m-2. And, we report the various kinds of images.

Development of Electron tracking Compton Camera based on micro pixel gas detector and its application for medical imaging

We have developed the Electron tracking Compton Camera (ETCC) with reconstructing the 3-D tracks of the scattered electron in Compton process for both gamma-ray astronomy and medical imaging [1–3]. By measuring both the directions and energies of a recoil gamma ray and a scattered electron, the direction of the incident gamma ray is determined for an individual photon. Furthermore, a residual measured angle between the recoil electron and scattered gamma ray is powerful for the kinematical background-rejection. For the 3-D tracking of the electrons, the Micro Time Projection Chamber (μ-TPC) was developed, which consists of a new type of the micro pattern gas detector, or a Micro Pixel Gas Chamber (μ-PIC). The ETCC consists of this μ-TPC and the GSO crystal pixel arrays below the μ̃TPC for detecting the recoil gamma rays. The ETCC provided the gamma ray images of point sources between 120keV and ∼1 MeV with the angular resolution of 6 degree (FWHM) at 511keV of 18F ion, respectively. Also the angle of the scattered electron was measured with the resolution of ∼80 degree. Two mobile ETCCs with 10cm-cube TPC for small animal and 30cm-cube TPC for human body, are now being operated for Medical Imaging test. We have studied the imaging performances using both phantoms and small animals (rats and mice) for conventional radioisotopes of 131I and 18F-FDG. In particular, new ETCC with LaBr3 pixel scintillator provides good images similar to SPECT for 131I and human PET for 511keV, respectively, where a clear concentration to tumors in a mouse is observed The 30cm-cube ETCC can get an image for 1m-size length objects in one measurement. Thus, we have carried out several comparisons of our images with those of SPECT and PET. Multi-tracer image using I-131 and FDG for small animal and the image for higher energy gamma ray above 511keV for plants using 54Mn have been carried out successfully. Also several new biomarkers and new radio nuclides were examined to verify the merits of ETCC for medical imaging.

Multi head compton camera system for nuclear medicine: Simulation study

PET (Positron Emission Tomography) and SPECT (Single Photon Emission Computed Tomography) systems are expected to improve the accuracy in identifying disease targets through molecular imaging. However, both systems suffer from some disadvantages. PET is restricted to use of few radionuclide. The gamma-ray detection efficiency in SPECT system is very low due to its collimator. We have developed a new gamma-ray camera system called CPT(ComPton Tomography) camera system using ETCC(Electron Tracking Compton Camera) to overcome these limitations while still preserving the advantages of molecular imaging[1]-[6]. This system needs no mechanical collimator, and can adapt to radionuclide with various gamma- ray energies. We have already reported our new image reconstruction technique suitable for this system in 2006 IEEE NSS and MIC [5]. In this paper, we estimate the visibility of hotspots in background with GEANT4 simulation. Furthermore, we confirm that the hotspot visibility is improved using new image correction technique.