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Takehiro Tomitani

Bio: Takehiro Tomitani is an academic researcher from National Institute of Radiological Sciences. The author has contributed to research in topics: Detector & Beam (structure). The author has an hindex of 19, co-authored 64 publications receiving 1571 citations.


Papers
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Journal ArticleDOI
TL;DR: In this article, a reconstruction algorithm for TOF-positron computed tomography (PCT) based on the back-projection with 1-dimensional weight and 2-dimensional filtering is presented.
Abstract: In positron CT, the path difference of annhilation pair gamma rays can be measured by time-of-flight (TOF) difference of pair gamma rays. This TOF information gives us rough position information along a projection line and will reduce noise propagation in the reconstruction process. A reconstruction algorithm for TOF-positron computed tomography (PCT) based on the back-projection with 1-dimensional weight and 2-dimensional filtering is presented. Also a formula to evaluate the variance of the reconstructed image and the optimal back-projection function are presented. The advantage of TOF-PCT over conventional PCT was investigated in view of noise figure. An example of such noise figure evaluations for CsF and liquid Xenon scintillators is given.

170 citations

Journal ArticleDOI
TL;DR: The result shows the possibility of practical realization of moving target irradiation with pencil beam scanning, and the present status of the raster scanning system for the HIMAC new treatment facility is described.
Abstract: A project to construct a new treatment facility as an extension of the existing heavy-ion medical accelerator in chiba (HIMAC) facility has been initiated for further development of carbon-ion therapy. The greatest challenge of this project is to realize treatment of a moving target by scanning irradiation. For this purpose, we decided to combine the rescanning technique and the gated irradiation method. To determine how to avoid hot and/or cold spots by the relatively large number of rescannings within an acceptable irradiation time, we have studied the scanning strategy, scanning magnets and their control, and beam intensity dynamic control. We have designed a raster scanning system and carried out a simulation of irradiating moving targets. The result shows the possibility of practical realization of moving target irradiation with pencil beam scanning. We describe the present status of our design study of the raster scanning system for the HIMAC new treatment facility.

144 citations

Journal ArticleDOI
TL;DR: The washout effect must be taken into account for the verification of treatment plans by means of positron camera measurements and time-activity curves of both brain and thigh muscle were clearly explained by the three-component model analysis.
Abstract: Washout of 10C and 11C implanted by radioactive beams in brain and thigh muscle of rabbits was studied. The biological washout effect in a living body is important in the range verification system or three-dimensional volume imaging in heavy ion therapy. Positron emitter beams were implanted in the rabbit and the annihilation gamma-rays were measured by an in situ positron camera which consisted of a pair of scintillation cameras set on either side of the target. The ROI (region of interest) was set as a two-dimensional position distribution and the time–activity curve of the ROI was measured. Experiments were done under two conditions: live and dead. By comparing the two sets of measurement data, it was deduced that there are at least three components in the washout process. Time–activity curves of both brain and thigh muscle were clearly explained by the three-component model analysis. The three components ratios (and washout half-lives) were 35% (2.0 s), 30% (140 s) and 35% (10 191 s) for brain and 30% (10 s), 19% (195 s) and 52% (3175 s) for thigh muscle. The washout effect must be taken into account for the verification of treatment plans by means of positron camera measurements.

109 citations

Journal ArticleDOI
TL;DR: In this article, a positron camera, consisting of a pair of Anger-type scintillation detectors, was developed to verify ranges by using positron emitter beams, and a linear response of a 0.3 mm standard deviation within a ±200 mm region were obtained.
Abstract: A positron camera, consisting of a pair of Anger-type scintillation detectors, has been developed to verify ranges by using positron emitter beams. Each detector head is equipped with a NaI(Tl) crystal (diameter: 600 mm , thickness: 30 mm ) for high detection efficiency. To get a low counting rate for this application, the electric circuit was designed for flexibility in measurement and analysis by software. The energy and position were calibrated for high measurement accuracy. A spatial resolution of 8.6 mm in FWHM within a ±50 mm region (field of view) and a linear response of a 0.3 mm standard deviation within a ±200 mm region were obtained. The camera was designed so as to measure the ranges within an accuracy of 1 mm under a dose limitation (about 100 mGyE ) to reduce the safety margin for the irradiation field, and it met the required characteristics.

105 citations

Journal ArticleDOI
TL;DR: The washout rate of 11C activity implanted by injecting energetic 11C beams into thigh muscle of a rear leg of a rabbit is presented and it is found that about one third of the implanted beta+ activity can be used for imaging and the rest was washed out of the target area.
Abstract: Heavy ion therapy has two definite advantages: good dose localization and higher biological effect. Range calculation of the heavy ions is an important factor in treatment planning. X-ray CT numbers are used to estimate the heavy ion range by looking up values in a conversion table which relates empirically photon attenuation in tissues to particle stopping power; this is one source of uncertainty in the treatment planning. Use of positron emitting radioactive beams along with a positron emission tomograph or a positron camera gives range information and may be used as a means of checking in heavy ion treatment planning. However, the metabolism of the implanted positron emitters in a living object is unpredictable because the chemical forms of these emitters are unknown and the metabolism is dependent on the organ species and may be influenced by many factors such as blood flow rate and fluid components present. In this paper, the washout rate of 11C activity implanted by injecting energetic 11C beams into thigh muscle of a rear leg of a rabbit is presented. The washout was found to consist of two components, the shorter one was about 4.2 ± 1.1 min and the longer one ranged from 91 to 124 min. About one third of the implanted β+ activity can be used for imaging and the rest was washed out of the target area.

92 citations


Cited by
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Journal ArticleDOI
TL;DR: This paper intends to balance the capabilities of the two major molecular imaging modalities used in nuclear medicine, namely positron emission tomography and single photon emission computed tomography (SPECT).
Abstract: The recent introduction of high-resolution molecular imaging technology is considered by many experts as a major breakthrough that will potentially lead to a revolutionary paradigm shift in health care and revolutionize clinical practice. This paper intends to balance the capabilities of the two major molecular imaging modalities used in nuclear medicine, namely positron emission tomography (PET) and single photon emission computed tomography (SPECT). The motivations are many-fold: (1) to gain a better understanding of the strengths and limitations of the two imaging modalities in the context of recent and ongoing developments in hardware and software design; (2) to emphasize that certain issues, historically and commonly thought as limitations of one technology, may now instead be viewed as challenges that can be addressed; (3) to point out that current state of the art PET and SPECT scanners can (greatly) benefit from improvements in innovative image reconstruction algorithms; and (4) to identify important areas of research in PET and SPECT imaging that will be instrumental to further improvements in the two modalities. Both technologies are poised to advance molecular imaging and have a direct impact on clinical and research practice to influence the future of molecular medicine.

742 citations

Journal Article
TL;DR: The Gemini TF whole-body scanner represents the first commercially available fully 3-dimensional PET scanner that achieves time-of-flight capability as well as conventional imaging capabilities.
Abstract: Results from a new PET/CT scanner using lutetium-yttrium oxyorthosilicate (LYSO) crystals for the PET component are presented. This scanner, which operates in a fully 3-dimensional mode, has a diameter of 90 cm and an axial field of view of 18 cm. It uses 4 × 4 × 22 mm3 LYSO crystals arranged in a pixelated Anger-logic detector design. This scanner was designed to perform as a high-performance conventional PET scanner as well as provide good timing resolution to operate as a time-of-flight (TOF) PET scanner. Methods: Performance measurements on the scanner were made using the National Electrical Manufacturers Association (NEMA) NU2-2001 procedures to benchmark its conventional imaging capabilities. The scatter fraction and noise equivalent count (NEC) measurements with the NEMA cylinder (20-cm diameter) were repeated for 2 larger cylinders (27-cm and 35-cm diameter), which better represent average and heavy patients. New measurements were designed to characterize its intrinsic timing resolution capability, which defines its TOF performance. Additional measurements to study the impact of pulse pileup at high counting rates on timing, as well as energy and spatial, resolution were also performed. Finally, to characterize the effect of TOF reconstruction on lesion contrast and noise, the standard NEMA/International Electrotechnical Commission torso phantom as well as a large 35-cm-diameter phantom with both hot and cold spheres were imaged for varying scan times. Results: The transverse and axial resolution near the center is 4.8 mm. The absolute sensitivity of this scanner measured with a 70-cm-long line source is 6.6 cps/kBq, whereas scatter fraction is 27% measured with a 70-cm-long line source in a 20-cm-diameter cylinder. For the same line source cylinder, the peak NEC rate is measured to be 125 kcps at an activity concentration of 17.4 kBq/mL (0.47 μCi/mL). The 2 larger cylinders showed a decrease in the peak NEC due to increased attenuation, scatter, and random coincidences, and the peak occurs at lower activity concentrations. The system coincidence timing resolution was measured to be 585 ps. The timing resolution changes as a function of the singles rate due to pulse pileup and could impact TOF image reconstruction. Image-quality measurements with the torso phantom show that very high quality images can be obtained with short scan times (1–2 min per bed position). However, the benefit of TOF is more apparent with the large 35-cm-diameter phantom, where small spheres are detectable only with TOF information for short scan times. Conclusion: The Gemini TF whole-body scanner represents the first commercially available fully 3-dimensional PET scanner that achieves TOF capability as well as conventional imaging capabilities. The timing resolution is also stable over a long duration, indicating the practicality of this device. Excellent image quality is achieved for whole-body studies in 10–30 min, depending on patient size. The most significant improvement with TOF is seen for the heaviest patients.

630 citations

Journal ArticleDOI
TL;DR: Results of clinical phase I-II trials provide evidence that carbon-ion radiotherapy might be beneficial in several tumor entities, and the progress in heavy-ion therapy is reviewed, including physical and technical developments, radiobiological studiesmore and models, as well as radiooncological studies.
Abstract: High-energy beams of charged nuclear particles (protons and heavier ions) offer significant advantages for the treatment of deep-seated local tumors in comparison to conventional megavolt photon therapy. Their physical depth-dose distribution in tissue is characterized by a small entrance dose and a distinct maximum (Bragg peak) near the end of range with a sharp fall-off at the distal edge. Taking full advantage of the well-defined range and the small lateral beam spread, modern scanning beam systems allow delivery of the dose with millimeter precision. In addition, projectiles heavier than protons such as carbon ions exhibit an enhanced biological effectiveness in the Bragg peak region caused by the dense ionization of individual particle tracks resulting in reduced cellular repair. This makes them particularly attractive for the treatment of radio-resistant tumors localized near organs at risk. While tumor therapy with protons is a well-established treatment modality with more than 60 000 patients treated worldwide, the application of heavy ions is so far restricted to a few facilities only. Nevertheless, results of clinical phase I-II trials provide evidence that carbon-ion radiotherapy might be beneficial in several tumor entities. This article reviews the progress in heavy-ion therapy, including physical and technical developments, radiobiological studiesmore » and models, as well as radiooncological studies. As a result of the promising clinical results obtained with carbon-ion beams in the past ten years at the Heavy Ion Medical Accelerator facility (Japan) and in a pilot project at GSI Darmstadt (Germany), the plans for new clinical centers for heavy-ion or combined proton and heavy-ion therapy have recently received a substantial boost.« less

619 citations

Journal ArticleDOI
TL;DR: ToF leads to a better contrast-versus-noise trade-off than non-TOF but one that is difficult to quantify in terms of a simple sensitivity gain improvement.
Abstract: Significant improvements have made it possible to add the technology of time-of-flight (TOF) to improve PET, particularly for oncology applications. The goals of this work were to investigate the benefits of TOF in experimental phantoms and to determine how these benefits translate into improved performance for patient imaging. Methods: In this study we used a fully 3-dimensional scanner with the scintillator lutetium-yttrium oxyorthosilicate and a system timing resolution of ;600 ps. The data are acquired in list-mode and reconstructed with a maximum-likelihood expectation maximization algorithm; the system model includes the TOF kernel and corrections for attenuation, detector normalization, randoms, and scatter. The scatter correction is an extension of the model-based singlescatter simulation to include the time domain. Phantom measurements to study the benefit of TOF include 27-cm- and 35-cm-diameter distributions with spheres ranging in size from 10to37mm.ToassessthebenefitofTOFPETforclinicalimaging, patient studies are quantitatively analyzed. Results: The lesion phantom studies demonstrate the improved contrast of the smallest spheres with TOF compared with non-TOF and also confirm the faster convergence of contrast with TOF. These gains are evident from visual inspection of the images as well as a quantitative evaluation of contrast recovery of the spheres and noise in the background. The gains with TOF are higher for larger objects. These results correlate with patient studies in which lesions are seen more clearly and with higher uptake at comparable noise for TOF than with non-TOF. Conclusion: TOF leads to a better contrast-versus-noise trade-off than non-TOF but one that is difficult to quantify in terms of a simple sensitivity gain improvement: A single gain factor for TOF improvement does not include the increased rate of convergence with TOF nor does it consider that TOF may converge to a different contrast than non-TOF. The experimental phantom results agree with those of prior simulations and help explain the improved image quality with TOF for patient oncology studies.

547 citations

Journal ArticleDOI
TL;DR: In this review, state-of-the art in vivo proton range verification methods currently being proposed, developed or clinically implemented are described and compared.
Abstract: Protons are an interesting modality for radiotherapy because of their well defined range and favourable depth dose characteristics. On the other hand, these same characteristics lead to added uncertainties in their delivery. This is particularly the case at the distal end of proton dose distributions, where the dose gradient can be extremely steep. In practice however, this gradient is rarely used to spare critical normal tissues due to such worries about its exact position in the patient. Reasons for this uncertainty are inaccuracies and non-uniqueness of the calibration from CT Hounsfield units to proton stopping powers, imaging artefacts (e.g. due to metal implants) and anatomical changes of the patient during treatment. In order to improve the precision of proton therapy therefore, it would be extremely desirable to verify proton range in vivo, either prior to, during, or after therapy. In this review, we describe and compare state-of-the art in vivo proton range verification methods currently being proposed, developed or clinically implemented.

442 citations