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Background Little is known about the risk of ischemic heart disease (IHD) in tuberculosis (TB) survivors. Methods We performed a population-based retrospective cohort study using the Korean National Health Insurance Service database. TB survivors (n = 60 602) and their 1:1 age- and sex-matched controls (n = 60 602) were enrolled. Eligible participants were followed up from 1 year after their TB diagnosis to the date of an IHD event, date of death, or the end of the study period (31 December 2018), whichever came first. The risk of IHD was estimated using a Cox proportional hazards regression, and stratified analyses were performed for related factors. Among IHD events, we additionally analyzed for myocardial infarction (MI). Results During a median of 3.9 years of follow-up, 2.7% of TB survivors (1633/60 602) and 2.0% of the matched controls (1228/60 602) developed IHD, and 0.6% of TB patients (341/60 602) and 0.4% of the matched controls (223/60 602) developed MI. The overall risk of developing IHD and MI was higher in TB patients (adjusted hazard ratio [aHR] 1.21, 95% confidence interval [CI]: 1.12–1.32 for IHD and aHR 1.48, 95% CI: 1.23–1.78 for MI) than in the matched controls. Stratified analyses showed that TB survivors have an increased risk of IHD and MI regardless of income, place of residence, smoking status, alcohol consumption, physical activity, body mass index, and Charlson comorbidity index. Conclusions TB survivors have a higher risk of IHD than matched controls. Strategies are needed to reduce the burden of IHD in TB survivors.

Background: The effect of serial change in alcohol consumption on stroke risk has been limitedly evaluated. We investigated the association of change in alcohol consumption with risk of stroke. Methods: This study is a population-based retrospective cohort study from National Health Insurance Service database of all Koreans. Four lakh five hundred thirteen thousand seven hundred forty-six participants aged ≥40 years who underwent 2 subsequent national health examinations in both 2009 and 2011. Alcohol consumption was assessed by average alcohol intake (g/day) based on self-questionnaires and categorized into non-, mild, moderate, and heavy drinking. Change in alcohol consumption was defined by shift of category from baseline. Cox proportional hazards model was used with adjustment for age, sex, smoking status, regular exercise, socioeconomic information, and comorbidities, Charlson Comorbidity Index, systolic blood pressure, and laboratory results. Subgroup analysis among those with the third examination was conducted to reflect further change in alcohol consumption. Results: During 28 424 497 person-years of follow-up, 74 923 ischemic stroke events were identified. Sustained mild drinking was associated with a decreased risk of ischemic stroke (adjusted hazard ratio, 0.88 [95% CI, 0.86–0.90]) compared with sustained nondrinking, whereas sustained heavy drinking was associated with an increased risk of ischemic stroke (adjusted hazard ratio, 1.06 [95% CI, 1.02–1.10]). Increasing alcohol consumption was associated with an increased risk of ischemic stroke (adjusted hazard ratio, 1.11 [95% CI, 1.06–1.17] from mild to moderate; adjusted hazard ratio, 1.28 [95% CI, 1.19–1.38] from mild to heavy) compared with sustained mild drinkers. Reduction of alcohol consumption from heavy to mild level was associated with 17% decreased risk of ischemic stroke through 3× of examinations. Conclusions: Light-to-moderate alcohol consumption is associated with a decreased risk of ischemic stroke, although it might be not causal and could be impacted by sick people abstaining from drinking. Reduction of alcohol consumption from heavy drinking is associated with a decreased risk of ischemic stroke.

Background: Conflicting results exist regarding the risk of ischemic stroke in tuberculosis survivors. We aimed to estimate the risk of ischemic stroke using a nationwide population-based retrospective cohort. Methods: We gathered data from the Korean National Health Insurance Service on tuberculosis survivors and 1:1 age- and sex-matched non-tuberculosis cases. Eligible participants were followed up from 1 year after tuberculosis diagnosis to the date of ischemic stroke event, date of death, or until the end of the study period (December 31, 2018), whichever came first. Cox proportional hazard regression and stratified analyses were performed to identify any related factors. Results: During follow-up periods of 3.8 years for patients with tuberculosis and matched non-tuberculosis cases, 1.3% of patients with tuberculosis (941/72 863) and 1.0% of matched non-tuberculosis cases (707/72 863) developed ischemic stroke. The overall risk of ischemic stroke was higher in tuberculosis patients (adjusted hazard ratio: 1.22 [95% CI, 1.10–1.36]) compared with the matched non-tuberculosis cases. A stratified analysis showed that patients with tuberculosis had increased risk of ischemic stroke regardless of age, sex, smoking status, alcohol consumption, physical activity, body mass index, and Charlson Comorbidity Index score. Conclusions: Tuberculosis survivors had a higher risk of ischemic stroke than their matched non-tuberculosis cases. The results of this study suggest that tuberculosis is a crucial infectious factor associated with increased incidence of ischemic stroke.

Nowadays, Neutron Transmutation Doping (NTD) of silicon ingots is successfully used to produce the n-type semiconductor. NTD’s main advantage, which is to say its uniform resistivity distribution, leads to semiconductor materials with fewer defects and, accordingly, better performance. Radial uniformity usually is achieved by rotating the ingot during irradiation. However, due to neutron attenuation, the neutron reaction rate in the ingot’s center region generally is lower than in the outer region. Such radial non-uniformity becomes severe when the diameter of the ingot is larger, or when materials with a high-neutron-reaction cross-section are used. In this study, a slit method to selectively shield neutrons that react with the ingot’s outer region and increase radial uniformity thereby was devised and herein is proposed. Dark matter (DM), graphite, stainless steel (SS) and borated stainless steel (BSS) were considered as shielding materials in a Monte Carlo-simulation-based evaluation of the radial uniformity of a Silicon Carbide (SiC) ingot. In the case of DM, the relative reaction rate at the center region of the ingot was increased; graphite did not enhance the radial uniformity; for both SS and BSS, the radial uniformity was under 1% with the optimized slot size. Therefore, it is expected that if the NTD technique is used in concert with the proposed slit method, semiconductors of exceedingly uniform dopant distribution can be produced.

Nowadays, evaluation of amounts and distributions of radioactive waste is an important preparatory step in the process of nuclear reactor decommissioning. For tentative estimation of radioactive waste, a cell-based rigorous 2 step (R2S) method usually is used; however, a poor resolution caused by the averaged flux and spectrum in a cell is still a great challenge because of leading to underestimated or overestimated results. To overcome the poor resolution, several systems were introduced. Neither system, however, provides any function for evaluation of radioactive waste amount and distribution. Thus, it is additionally required to classify radioactive waste based on the results of activation calculation. In this study, the advanced R2S (AR2S) system was developed. To verify the performance of the system, its results for a verification problem were compared with those of the cell-based R2S method. The results showed good agreement, which is to say, within 2.0% relative error. Also, several characteristics of fine/coarse mesh were analyzed. To demonstrate the performance of the AR2S system, the radioactive waste from the Japan Power Demonstration Reactor (JPDR) was estimated, and the result indicated a high-resolution distribution. Therefore, it is expected that the AR2S system will prove useful for precise evaluation of radioactive waste.

Although both obesity and menopause are associated with increased risk of diabetes mellitus (DM), the association between obesity and DM according to menopausal status remains uncertain. Therefore, we conducted a study to examine the relationship between obesity and incidence of diabetes mellitus (DM) in premenopausal and postmenopausal women. Total of 926,196 premenopausal and 1,193,881 postmenopausal women who underwent health examinations from 2009 to 2014 were identified using the database of the Korean National Health Insurance Service. We compared the incidence and risk of DM according to body mass index (BMI) and waist circumference (WC) in the two groups of women. Cox proportional hazards analyses were performed to evaluate the association between the presence of obesity and risk of DM according to menopausal state. During the 7.8-year follow-up period, 37,736 (4.1%) premenopausal women and 121,102 (10.1%) postmenopausal women were diagnosed with DM. Compared to the reference group (BMI 18.5–23), a stronger association between obesity and risk of DM was observed in both pre- and postmenopausal women: multivariable-adjusted hazard ratios and 95% confidence intervals for BMI subgroups &lt, 18.5, 23–25, 25–30, and &gt, 30 were 0.62 (0.54, 0.70), 1.91 (1.85, 1.97), 3.38 (3.28, 3.47), and 6.25 (6.02, 6.48), respectively (p trend &lt, 0.001) in premenopausal women and 0.87 (0.82, 0.92), 1.44 (1.41, 1.46), 2.00 (1.97, 2.03), and 2.96 (2.89, 3.02) in postmenopausal women (p trend &lt, 0.001, p-interaction &lt, 0.001). A similar trend was observed for WC. Subgroup analyses of women aged 45 to 55 also showed a stronger association with DM in premenopausal than in postmenopausal women. In conclusion, the association between obesity and DM was stronger in premenopausal women than in postmenopausal women. As estrogens are synthesized in adipose tissue by aromatization of androgens after menopause, increased estrogen levels in obese postmenopausal might have a protective effect against DM.

Background The association between nonalcoholic fatty liver disease (NAFLD) and Parkinson's disease (PD) remains uncertain. This study sought to assess the sex-specific association between NAFLD and PD risk considering that sex is an important factor in both conditions. Methods We included 2,651,169 men and 2,998,904 women (≥40 years of age) who underwent health examinations in 2009 using database of the Korean National Health Insurance Service. To define NAFLD, the Fatty Liver Index (FLI) was used and a score of at least 60 points was regarded as suggesting the presence of NAFLD. Cox proportional hazards analyses were performed to evaluate the association between the presence of NAFLD/each component of FLI and the risk of PD. All analyses were stratified by sex. Results The median follow-up duration was 7.3 years in both men and women. Of the total study population, 23,233 patients with PD (10,578 men and 12,655 women) were identified. Among men, a decreased risk of PD was observed in those with NAFLD [adjusted hazard ratio (aHR): 0.86, 95% confidence interval (CI): 0.82–0.91]. In contrast, among women, an increased risk of PD was observed in those with NAFLD (aHR: 1.09, 95% CI: 1.02–1.16). This different association according to sex was more prominent among younger participants but was not significant in the old age group. Conclusions NAFLD defined by FLI is differently associated with the risk of PD by sex (i.e., low risk of PD in men with NAFLD vs. high risk of PD in women with NAFLD).

In this research, a multi-slit prompt-gamma camera was developed to locate the distal dose falloff of the proton beam spots in spot scanning proton therapy. To see the performance of the developed camera, therapeutic proton beams were delivered to a solid plate phantom and then the prompt gammas from the phantom were measured using the camera. Our results show that the camera locates the 90% distal dose falloff (= d90%), within about 2–3 mm of error for the spots which are composed 3.8 × 108 protons or more. The measured location of d90% is not very sensitive to the irradiation depth of the proton beam (i.e., the depth of proton beam from the phantom surface toward which the camera is located). Considering the number of protons per spot for the most distal spots in typical treatment cases (i.e., 2 Gy dose divided in 2 fields), the camera can locate d90% only for a fraction of the spots depending on the treatment cases. However, the information of those spots is still valuable in that, in the multi-slit prompt-gamma camera, the distal dose falloff of the spots is located solely based on prompt gamma measurement, i.e., not referring to Monte Carlo simulation. Keywords: Proton therapy, Prompt gamma, Beam range verification, Distal dose falloff

This study aimed to verify whether neutron energy and flux could be simultaneously measured by a new technique that used array-type threshold detectors. Neutrons generated by nuclear reactions between 26-MeV protons and beryllium targets in the KIRAMS MC50 cyclotron were measured using array-type threshold detectors fabricated by superimposing four array-type activation foils composed of Au, Ag, In, and Cu. The measurement results were compared to the simulation results obtained using MCNPX and FISPACT codes. The study results showed that the spatial distribution of high-speed neutrons was mostly concentrated at the center of the beam whereas that of thermal neutrons was relatively sparse at the center of the beam.

A novel method to fabricate neutron activation foil arrays using a semiconductor printing technique is proposed; it allows higher resolutions, and fast and convenient fabrication. A validation irradiation test is performed, using a traditional array and the proposed printed array. The latter exhibited higher resolution and avoided the spatial distortion of the traditional foil array which can reach several tens of percent. Furthermore, it can be easily bent and made to use small individual foils (1 mm or less), making it suitable to measure neutron spatial distributions at the curved surfaces of pipes or the inner surface of irradiation passages.

We present a simulation method that can create accurate virtual models of hand with arbitrarily curved surfaces and perform distortion-free MCNPX simulations. Generally, MCNPX simulations of objects with arbitrarily curved surfaces are performed through voxelization. In this study, a polygon model is tetrahedralized by TetGen for the construction of the MCNPX geometry to be distortion-free. Then, dose estimation was successfully performed after converting the virtual model into an MCNPX input. A voxelized model was constructed for comparison purposes. The dose estimation functions of the two models were found to be similar, showing a similar amount of computing time by using the mesh tally option with 2e7 histories.

This paper describes an experimental setup developed to measure the beta-ray energy spectrum as well as a Geant4 simulation study conducted to characterize the properties of a beta-spectrometer. The beta-spectrometer comprises a multi-wire chamber to generate signals to indicate the incidence of beta rays and a plastic scintillation detector to measure its energy. The coincidence method of the detector signals was used to remove high gamma-ray interference. To evaluate the performance of the developed spectrometer, the energy spectra were measured with the radionuclide sources ( 137Cs and 207Bi) emitting internal conversion electrons and gamma rays. The gamma-ray interference removal rate of the spectrometer using the coincidence method was 99.12 ± 0.09%. To reconstruct the beta spectrum from the measured spectrum, Monte Carlo simulations using the Geant4 toolkit were performed to calculate the coefficient related to the effect of gamma rays. The obtained spectrum confirmed that the energy resolution and intrinsic internal conversion peak detection efficiency of the beta-spectrometer were 10.2% at 1 MeV and 91.6%, respectively.

In proton therapy, for both therapeutic effectiveness and patient safety, it is very important to accurately measure the proton dose distribution, especially the range of the proton beam. For this purpose, recently we proposed a new imaging method named gamma electron vertex imaging (GEVI), in which the prompt gammas emitting from the nuclear reactions of the proton beam in the patient are converted to electrons, and then the converted electrons are tracked to determine the vertices of the prompt gammas, thereby producing a 2D image of the vertices. In the present study, we developed a prototype GEVI system, including dedicated signal processing and data acquisition systems, which consists of a beryllium plate (= electron converter) to convert the prompt gammas to electrons, two double-sided silicon strip detectors (= hodoscopes) to determine the trajectories of those converted electrons, and a plastic scintillation detector (= calorimeter) to measure their kinetic energies. The system uses triple coincidence logic and multiple energy windows to select only the events from prompt gammas. The detectors of the prototype GEVI system were evaluated for electronic noise level, energy resolution, and time resolution. Finally, the imaging capability of the GEVI system was tested by imaging a 90 Sr beta source, a 60 Co gamma source, and a 45-MeV proton beam in a PMMA phantom. The overall results of the present study generally show that the prototype GEVI system can image the vertices of the prompt gammas produced by the proton nuclear interactions.

The Korea Atomic Energy Research Institute (KAERI) has constructed a test-bed facility, named PRIDE (PyRoprocess Integrated inactive DEmonstration), for demonstration of pyroprocessing technology. Even though the PRIDE facility utilizes depleted uranium, instead of actual spent fuel, as process material, it will play an important role not only from the process perspective, but also from the safeguards standpoint. In the present study, a Compton imaging system based on pixelated GAGG:Ce scintillation detectors was constructed and tested to determine its utility for accurate imaging of nuclear material locations and, thus, its applicability as a safeguards monitoring system at the PRIDE facility. In a lab-scale performance evaluation, when the dose rate induced by a 137Cs point-like source was ∼0.1 μSv/h, the source location was imaged within 5 min. The image resolutions were 22° and 7.6° for real-time monitoring using a back-projection algorithm and for near-real-time monitoring using a statistical...

We developed neutron detectors for detecting thermal and fast neutrons. The sensing element of the neutron detector uses a high-purity chemical-vapor-deposited (CVD) diamond plate, with a size of 3 mm × 3 mm × 0.5 mm, and the o5 mm detector is sealed for use in the reactor as a small tube by using laser micro welding. The electrodes of the fast and thermal neutron detectors are made up of Ag and Gd with approximately 100-nm and 5 μm thicknesses, respectively. The deposition method of the electrode uses the RF plasma sputtering system. The developed neutron detectors were tested on a 30-MeV cyclotron, which generates fast neutrons and gamma rays. High-density polyethylene plates, Cd plates, and Pb bricks were used for the moderator and shielding. The Ag electrode detector measured the current generated by fast neutrons and gamma rays. Although the sensitivity of the Gd electrode detector is smaller than that of the Ag electrode detector, it measured the current generated by thermal neutrons as well as fast neutrons and gamma rays.

In proton therapy, accurate monitoring of the in-vivo proton dose distribution is essential in order to deliver the planned dose to the tumor volume within a minimal safety margin. Recently, a strong correlation between the distributions of the proton dose and the prompt gammas was found, and various prompt-gamma distribution-measurement systems, including collimation-based systems, Compton cameras, knife-edge imaging systems, and ion vertex imaging systems, have been proposed. In the present study, the feasibility of proton dose distribution monitoring was tested using a two-dimensional measurement system for prompt gammas. The measurement system, developed in the present study, incorporates a vertically-aligned one-dimensional array of gamma sensors, a parallel multi-hole collimator, a precision movement system, and a digitizer- and LabVIEW-based automatic data acquisition system. A 45-MeV proton beam of 0.5 nA was delivered to a polymethyl methacrylate (PMMA) phantom, and the two-dimensional prompt-gamma distribution was measured using the developed system. The proton beam range could be quantitatively determined to within a 1.6-mm error by sigmoidal curve-fitting with the Boltzmann equation. A comparison of the prompt-gamma distribution as measured by our detection system with the proton dose distribution as measured independently by using Gafchromic EBT films positioned inside the PMMA phantom showed good agreement. Both results imply that it is, indeed, possible to confirm the patient’s proton dose distribution by using two-dimensional prompt-gamma measurements.

To verify in-vivo proton dose distribution, a 2-dimensional (2D) prompt-gamma measurement system, comprised of a multi-hole collimation system, a 2D array of CsI(Tl) scintillators, and a position-sensitive photomultiplier tube (PS-PMT), is under development. In the present study, to determine the optimal dimension of the measurement system, we employed a series of Monte Carlo simulations with the MCNPX code. To effectively measure the high-energy prompt gammas while minimizing background gammas, we determined the collimator hole size, collimator thickness, and scintillator length to be 0.4 × 0.4 cm2, 15 cm, and 5 cm, respectively. Thereafter, the performance of the optimized measurement system was estimated for monoenergetic proton pencil beams. The peak locations of the prompt-gamma distributions for 80- and 150-MeV proton beams were clearly distinguished, and the correlation between the beam range and the peak location was confirmed by using the measurement system. For a 200-MeV proton beam, however, the peak location could not be determined due to the dominance of background gammas and the lateral dispersion of the proton beam at the end of the beam range. Based on these simulation results, a prototype 2D prompt-gamma measurement system currently is under construction and, upon completion, will be tested with therapeutic proton beams.

Purpose: In vivo range verification is one of the most important parts of proton therapy to fully utilize its benefits delivering high radiationdose to tumor, while sparing the normal tissue with the so-called Bragg peak. Currently, however, range verification method is not used in clinics. The purpose of the present study is to optimize and evaluate the configuration of an array-type prompt gamma measurement system on determining distal dose edge for in vivo range verification of proton therapy. Methods: To effectively measure the prompt gammas against the background gammas, the Monte Carlo simulations with the MCNPX code were employed in optimizing the configuration of the measurement system, and the Monte Carlo method was also used to understand the effect of the background gammas, mainly neutron capture gammas, in the measured gamma distribution. To reduce the effect of the background gammas, the optimized energy window of 4–10 MeV in measuring the prompt gammas was employed. A parameterized source was used to maximize computation speed in the optimization study. A simplified test measurement system, using only one detector moving from one measurement location to the next, was constructed and applied to therapeuticproton beams of 80–220 MeV. For accurate determination of the distal dose edge, the sigmoidal curve-fitting method was applied to the measured distributions of the prompt gammas, and then, the location of the half-value between the maximum and minimum value in the curve-fitting was determined as the distal dose edge and compared with the beam range assessed by the protondose distribution. Results: The parameterized source term employed in optimization process improved the calculation speed by up to ∼300 times. The optimization study indicates that an array-type measurement system with 3, 2, 2, and 150 mm for scintillator thickness, slit width, septal thickness, and slit length, respectively, can effectively measure the prompt gamma distributions minimizing the contribution of background gammas. The present results show that a few hundred counts of prompt gammas can be easily obtained by measuring 10 s at each measurement location for proton beams of ∼4 nA. The distal dose edges determined by the prompt gamma distribution are 5.45, 14.73, and 27.74 cm for proton beams of 5.17 (80 MeV), 14.99 (150 MeV), and 27.38 (220 MeV) cm, respectively. Conclusions: The results show that the array-type measurement system can measure prompt gamma distributions from a therapeuticproton beam within a short measurement time, and that the distal dose edge can be determined within a few millimeters of error without using any sophisticated analysis.

Purpose: This paper describes a new gamma-ray imaging method, “gamma electron vertex imaging (GEVI),” which can be used for precise beam range verification in proton therapy. Methods: In GEVI imaging, the high-energy gammas from a source or nuclear interactions are first converted, by Compton scattering, to electrons, which subsequently are traced by hodoscopes to determine the location of the gamma source or the vertices of the nuclear interactions. The performance of GEVI imaging for use in-beam range verification was evaluated by Monte Carlo simulations employinggeant4 equipped with the QGSP_BIC_HP physics package. Results: Our simulation results show that GEVI imaging can determine the proton beam range very accurately, within 2–3 mm of error, even without any sophisticated analysis. The results were obtained under simplified conditions of monoenergetic pencil beams stopped in a homogeneous phantom and on the basis of the obtained results it is expected to achieve submillimeter accuracy in proton beam range measurement. Conclusions: If future experimental work confirms the simulated results presented in this paper, the use of GEVI imaging is expected to have a great potential in increasing the accuracy of proton beam range verification in a patient, resulting in significant improvement of treatment effectiveness by enabling tight conformation of radiationdose to the tumor volume and patient safety.

In proton therapy, accurate verification of in vivo dose distribution is necessary to ensure not only the safety of the patient but also the success of the treatment itself. It has been shown, both...

Proton therapy, thanks to the dose characteristics of the Bragg peak, according to which most of the radiation energy is delivered at the end of the beam with a very high dose gradient at the distal edge, can deliver a highly conformal radiation dose to the treatment volume. Currently, however, the benefit of this high dose gradient is not fully utilized in clinical practice due mainly to the dose-distribution uncertainty in the beam direction (i.e., the uncertainty of the beam range in the patient). In this paper, we present an imaging system based on gamma electron vertex imaging (GEVI), which is suitable for high-energy (1–30 MeV) gammas, and test its performance for therapeutic proton beams. GEVI images prompt gamma vertices, which are closely correlated with the dose distribution at the distal edge, by converting prompt gammas to electrons via Compton scattering and then tracking the recoiled electrons. Our experimental results show that the GEVI system can image the 2D vertices of the prompt gammas and, thus, can be utilized for the measurement of proton-beam ranges in patients. We believe, indeed, that GEVI makes possible real-time monitoring of in-vivo proton-beam ranges, whose utility significantly improves treatment effectiveness and enhances patient safety. We also expect that the GEVI system will find applications in other fields (e.g., gamma-ray astronomy, nuclear engineering, and high-energy physics) requiring high-energy-gamma (1–30 MeV) imaging.

The close relationship between the proton dose distribution and the distribution of prompt gammas generated by proton-induced nuclear interactions along the path of protons in a water phantom was demonstrated by means of both Monte Carlo simulations and limited experiments. In order to test the clinical applicability of the method for determining the distal dose edge in a human body, a human voxel model, constructed based on a body-composition-approximated physical phantom, was used, after which the MCNPX code was used to analyze the energy spectra and the prompt gamma yields from the major elements composing the human voxel model; finally, the prompt gamma distribution, generated from the voxel model and measured by using an array-type prompt gamma detection system, was calculated and compared with the proton dose distribution. According to the results, eective prompt gammas were produced mainly by oxygen, and the specific energy of the prompt gammas, allowing for selective measurement, was found to be 4.44 MeV. The results also show that the distal dose edge in the human phantom, despite the heterogeneous composition and the complicated shape, can be determined by measuring the prompt gamma distribution with an array-type detection system.

This research was supported by ETRI R&D program (Development of particle beam range verification technology based on prompt gamma-ray measurements, 15ZC1810), by National Nuclear R&D Program through the National Research Foundation of Korea (NRF) funded by Ministry of Education, Science and Technology (No. 2012-K001146, 2015M2A2A6A01045241), and by the Nuclear Safety Research Program through the Korea Foundation Of Nuclear Safety (KOFONS), granted financial resource from the Nuclear Safety and Security Commission(NSSC), Republic of Korea (No. 1403012).

This paper describes a new gamma-ray imaging method, "gamma electron vertex imaging (GEVI)," which can be used for precise beam range verification in proton therapy.In GEVI imaging, the high-energy gammas from a source or nuclear interactions are first converted, by Compton scattering, to electrons, which subsequently are traced by hodoscopes to determine the location of the gamma source or the vertices of the nuclear interactions. The performance of GEVI imaging for use in-beam range verification was evaluated by Monte Carlo simulations employing geant4 equipped with the QGSP_BIC_HP physics package.Our simulation results show that GEVI imaging can determine the proton beam range very accurately, within 2-3 mm of error, even without any sophisticated analysis. The results were obtained under simplified conditions of monoenergetic pencil beams stopped in a homogeneous phantom and on the basis of the obtained results it is expected to achieve submillimeter accuracy in proton beam range measurement.If future experimental work confirms the simulated results presented in this paper, the use of GEVI imaging is expected to have a great potential in increasing the accuracy of proton beam range verification in a patient, resulting in significant improvement of treatment effectiveness by enabling tight conformation of radiation dose to the tumor volume and patient safety.

양성자 치료 시 양성자 빔을 사용하여 정밀한 치료를 수행하고 환자의 안전을 제고하기 위해서는 인체 내 양성자 빔의 선량 분포를 확인하는 것이 중요하다. 이를 위해 본 연구팀은 이전 연구에서 1차원 배열형 검출기를 종형으로 배치하여 빔 진행방향으로 이동시켜가면서 2차원적인 즉발감마선 분포를 측정하여 양성자 선량 분포와 유사한 분포를 갖는 것을 확인하였다. 본 연구에서는 이를 바탕으로 즉발감마선 이차원분포를 실시간으로 측정하기 위해 이차원 평행다공형 집속 장치, 이차원 배열의 NaI(Tl) 섬광체와 MA-PMT로 이루어진 즉발감마선 이차원분포 측정 장치를 개발하였다. 개발한 즉 발감마선 이차원분포 측정 장치의 성능을 평가한 결과 $^{22}Na$ 감마선원의 에너지 분해능은 $10.9%{\pm}0.23p%$ (0.511 MeV)와 $6.4%{\pm}0.24p%$ (1.275 MeV)로 평가되었으며, $^{137}Cs$ 은 $9.8%{\pm}0.18p%$ (0.662 MeV)로 평가되었다. 고에너지 Am-Be 선원의 double escape 피크인 3.416 MeV의 에너지 분해능은 $11.4%{\pm}3.6p%$ 로 평가되었다. 본 측정 장치를 이용하여 45 MeV 양성자 빔을 PMMA에 조사하여 발생한 즉발감마선 이차원분포를 측정한 결과 0.5 nA의 세기의 양성자 빔에서 $9{\times}10^9$ 양성자 조사 시 양성자 선량 분포와 유사한 즉발감마선 이차원분포를 측정할 수 있음을 확인하였다. 추가로 측정한 즉발감마선 이차원분포의 프로파일 분포를 이용하여 양성자 빔의 비정을 평가해 본 결과 $17.0{\pm}0.4mm$ 로 평가되었고, 실제 비정인 17.4 mm과 굉장히 밀접한 관련이 있음을 확인하였다. 【In proton therapy, verification of proton dose distribution is important to treat cancer precisely and to enhance patients' safety. To verify proton dose distribution, in a previous study, our team incorporated a vertically-aligned one-dimensional array detection system. We measured 2D prompt-gamma distribution moving the developed detection system in the longitudinal direction and verified similarity between 2D prompt-gamma distribution and 2D proton dose distribution. In the present, we have developed two-dimension prompt-gamma measurement system consisted of a 2D parallel-hole collimator, 2D array-type NaI(Tl) scintillators, and multi-anode PMT (MA-PMT) to measure 2D prompt-gamma distribution in real time. The developed measurement system was tested with $^{22}Na$ (0.511 and 1.275 MeV) and $^{137}Cs$ (0.662 MeV) gamma sources, and the energy resolutions of 0.511, 0.662 and 1.275 MeV were $10.9%{\pm}0.23p%$ , $9.8%{\pm}0.18p%$ and $6.4%{\pm}0.24p%$ , respectively. Further, the energy resolution of the high gamma energy (3.416 MeV) of double escape peak from Am-Be source was $11.4%{\pm}3.6p%$ . To estimate the performance of the developed measurement system, we measured 2D prompt-gamma distribution generated by PMMA phantom irradiated with 45 MeV proton beam of 0.5 nA. As a result of comparing a EBT film result, 2D prompt-gamma distribution measured for $9{\times}10^9$ protons is similar to 2D proton dose distribution. In addition, the 45 MeV estimated beam range by profile distribution of 2D prompt gamma distribution was $17.0{\pm}0.4mm$ and was intimately related with the proton beam range of 17.4 mm.】

Chan Hyeong Kim, Jin Hyung Park, Hee Seo, and Han Rim Lee Citation: Medical Physics 39, 6523 (2012); doi: 10.1118/1.4749930 View online: http://dx.doi.org/10.1118/1.4749930 View Table of Contents: http://scitation.aip.org/content/aapm/journal/medphys/39/10?ver=pdfcov Published by the American Association of Physicists in Medicine Articles you may be interested in Erratum: “Dynamically accumulated dose and 4D accumulated dose for moving tumors” [Med. Phys.39(12),7359–7367 (2012)] Med. Phys. 40, 047201 (2013); 10.1118/1.4794486 Response to “Comment on ‘It is not appropriate to “deform” dose along with deformable image registration inadaptive radiotherapy’” [Med. Phys.39, 6531–6533 (2012)] Med. Phys. 40, 017102 (2013); 10.1118/1.4771963 Erratum: “Relationship between electron density and effective densities of body tissues for stopping, scattering,and nuclear interactions of proton and ion beams” [Med. Phys.39, 1016–1020 (2012)] Med. Phys. 40, 017202 (2013); 10.1118/1.4769415 Reply to “Comment on ‘Correspondence factor for Nucletron surface applicators’” [Med. Phys.39, 2947–2948(2012)] Med. Phys. 39, 2310 (2012); 10.1118/1.3694512 Gamma electron vertex imaging and application to beam range verification in proton therapy Med. Phys. 39, 1001 (2012); 10.1118/1.3662890