• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.3
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• pp.283-288
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• 2013

This paper describes development of a high speed Doppler OFDI system for non-invasive vascular imaging. Doppler OFDI (optical frequency domain imaging) is one of the phase-resolved second generation OCT (optical coherence tomography) techniques for high resolution imaging of moving elements in biological tissues. To achieve a phase-resolved imaging, two temporally separated measurements are required. In a conventional Doppler OCT, a pair of massively oversampled successive A-lines is used to minimize de-correlation noise at the expense of significant imaging speed reduction. To minimize a de-correlation noise between targeted two measurements without suffering from significant imaging speed reduction, several methods have been developed such as an optimized scanning pattern and polarization multiplexed dual beam scanning. This research represent novel imaging technique using frequency multiplexed dual beam illumination to measure exactly same position with aimed time interval. Developed system has been verified using a tissue phantom and mouse vessel imaging.

• Nuclear Engineering and Technology
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• v.54 no.6
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• pp.2204-2212
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• 2022

Recently, the demand for alpha imaging detectors for quantifying the distributions of alpha particles has increased in various fields. This study aims to reconstruct a high-resolution image from an alpha imaging detector by applying a super-spatial resolution method combined with the maximum-likelihood expectation maximization (MLEM) algorithm. To perform the super-spatial resolution method, several images are acquired while slightly moving the detector to predefined positions. Then, a forward model for imaging is established by the system matrix containing the mechanical shifts, subsampling, and measured point-spread function of the imaging system. Using the measured images and system matrix, the MLEM algorithm is implemented, which converges towards a high-resolution image. We evaluated the performance of the proposed method through the Monte Carlo simulations and phantom experiments. The results showed that the super-spatial resolution method was successfully applied to the alpha imaging detector. The spatial resolution of the resultant image was improved by approximately 12% using four images. Overall, the study's outcomes demonstrate the feasibility of the super-spatial resolution method for the alpha imaging detector. Possible applications of the proposed method include high-resolution imaging for alpha particles of in vitro sliced tissue and pre-clinical biologic assessments for targeted alpha therapy.

• Progress in Medical Physics
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• v.16 no.2
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• pp.89-96
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• 2005

In this study, we investigated the effect of time gating threshold on the delivered dose at a organ with internal motion by respiration. Generally, the internal organs have minimum motion at exhalation during normal breathing. Therefore to compare the dose distribution time gating threshold, in this paper, was determined as the moving region of target during 1 sec at the initial position of exhalation. The irradiated fields were then delivered under three conditions; 1) non-moving target 2) existence of the moving target in the region of threshold (1sec), 3) existence of the moving target region out of threshold (1.4 sec, 2 sec). And each of conditions was described by the moving phantom system. It was compared with the dose distributions of three conditions using film dosimetry. Although the treatment time increased when the dose distributions was obtained by the internal motion to consider the TGT, it could be obtained more exact dose distribution than in the treatment field that didn't consider the internal motion. And it could be reduced the unnecessary dose at the penumbra region. When we set up 1.4 sec of threshold, to reduce the treatment time, it could not be obtained less effective dose distribution than 1 sec of threshold. Namely, although the treatment time reduce, the much dose was distributed out of the treatment region. Actually when it is treated the moving organ, it would rather measure internal motion and external motion of the moving organ than mathematical method. If it could be analyzed the correlation of the internal and external motion, the treatment scores would be improved.

• Progress in Medical Physics
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• v.18 no.4
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• pp.221-225
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• 2007

Monte Carlo calculations were performed to demonstrate the dose modulation with dynamic magnetic fields in phantom. The goal of this study is to obtain the uniform dose distributions at a depth region as a target on the central axis of photon beam under moving transverse magnetic field. We have calculated the depth dose curves for two cases of moving magnetic field along a depth line, constant speed and optimal speed. We introduced step-by-step shift and time factor of the position of the electromagnet as an approximations of continuous moving. The optimal time factors as a function of magnetic field position were calculated by least square methods using depth dose data for static magnetic field. We have verified that the flat depth dose is produced by varying the speed of magnetic field as a function of position as a results of Monte Carlo calculations. For 3 T magnetic field, the dose enhancement was 10.1% in comparison to without magnetic field at the center of the target.

• The Journal of Korean Society for Radiation Therapy
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• v.19 no.1
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• pp.51-54
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• 2007

Purpose: Total body irradiation is used to kill the total malignant cell and for immunosuppression component of preparatory regimens for bone-marrow restitution of patients. Beam spoiler is used to increase the dose to the superficial tissues. This paper finds the property of the distance between beam spoiler and patient. Materials and Methods: Set-up conditions are 6 MV-Xray, 300 MU, SAD = 400 cm, field size = $40{\times}40cm^2$. The parallel plate chamber located in surface, midpoint and exit of solid water phantom. The surface dose is measured while the distance between beam spoiler and patient is altered. Because it should be found proper distance. The solid water phantom is fixer and beam spoiler is moving. Results: Central dose of phantom is 10.7 cGy and exit dose is 6.7 cGy. In case of distance of 50 cm to 60 cm between beam spoiler and solid water phantom, incidence dose is $14.58{\sim}14.92cGy$. Therefore, The surface dose was measured $99.4{\sim}101%$ with got near most to the prescription dose. Conclusion: In clinical case, distance between beam spoiler and patient affect surface dose. If once $50{\sim}60cm$ of distance between beam spoiler and patient, surface dose of patient got near prescription dose. It would be taken distance between beam spoiler and patient into account in clinical therapy.

• Progress in Medical Physics
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• v.24 no.4
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• pp.243-252
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• 2013

The aim of this study was to clarify the impacts of acquisition parameters on artifacts in four-dimensional computed tomography (4D CT) images, such as the partial volume effect (PVE), partial projection effect (PPE), and mis-matching of initial motion phases between adjacent beds (MMimph) in cine mode scanning. A thoracic phantom and two cylindrical phantoms (2 cm diameter and heights of 0.5 cm for No.1 and 10 cm for No.2) were scanned using 4D CT. For the thoracic phantom, acquisition was started automatically in the first scan with 5 sec and 8 sec of gantry rotation, thereby allowing a different phase at the initial projection of each bed. In the second scan, the initial projection at each bed was manually synchronized with the inhalation phase to minimize the MMimph. The third scan was intentionally un-synchronized with the inhalation phase. In the cylindrical phantom scan, one bed (2 cm) and three beds (6 cm) were used for 2 and 6 sec motion periods. Measured target volume to true volume ratios (MsTrueV) were computed. The relationships among MMimph, MsTrueV, and velocity were investigated. In the thoracic phantom, shorter gantry rotation provided more precise volume and was highly correlated with velocity when MMimph was minimal. MMimph reduced the correlation. For moving cylinder No. 1, MsTrueV was correlated with velocity, but the larger MMimph for 2 sec of motion removed the correlation. The volume of No. 2 was similar to the static volume due to the small PVE, PPE, and MMimph. Smaller target velocity and faster gantry rotation resulted in a more accurate volume description. The MMimph was the main parameter weakening the correlation between MsTrueV and velocity. Without reducing the MMimph, controlling target velocity and gantry rotation will not guarantee accurate image presentation given current 4D CT technology.

• Journal of radiological science and technology
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• v.39 no.4
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• pp.601-606
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• 2016

Because of non-coplanar therapy with couch rotation in respiratory gated radiation therapy, the recognition of marker movement due to the change in the distance between the infrared camera and the marker due to the rotation of the couch is called RPM (Real-time The purpose of this paper is to evaluate the accuracy of motion reflections (baseline changes) of 2D gating configuration (two dot marker block) and 3D gating configuration (six dot marker block). The motion was measured by varying the couch angle in the clockwise and counterclockwise directions by $10^{\circ}$ in the 2D gating configuration. In the 3D gating configuration, the couch angle was changed by $10^{\circ}$ in the clockwise direction and compared with the baseline at the reference $0^{\circ}$. The reference amplitude was 1.173 to 1.165, the couch angle at $20^{\circ}$ was 1.132, and the couch angle at $1.0^{\circ}$ was 1.083. At $350^{\circ}$ counterclockwise, the reference amplitude was 1.168 to 1.157, the couch angle at $340^{\circ}$ was 1.124, and the couch angle at $330^{\circ}$ was 1.079. In this study, the phantom is used to quantitatively evaluate the value of the amplitude according to couch change.

• Journal of radiological science and technology
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• v.42 no.3
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• pp.217-222
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• 2019

The purpose of this study is to evaluate the dose distribution by gantry rotation and MLC moving speed on treatment planning system(TPS) and linear accelerator. The dose analyzer phantom(Delta 4) was scanned by CT simulator for treatment planning. The planning target volumes(PTVs) of prostate and pancreas was prescribed 6,500 cGy, 5,000 cGy on VMAT(Volumetric Modulated Arc Therapy) by TPS while MLC speed changed. The analyzer phantom was irradiated linear accelerator using by planned parameters. Dose distribution of PTVs were evaluated by the homogeneity index, conformity index, dose volume histogram of organ at risk(rectum, bladder, spinal cord, kidney). And irradiated dose analysis were evaluated dose distribution and conformity by gamma index. The PTV dose of pancreas was 4,993 cGy during 0.1 cm/deg leaf and gantry that was the most closest prescribed dose(5,000 cGy). The dose of spinal cord, left kidney, and right kidney were accessed the lowest during 0.1 cm/deg, 1.5 cm/deg, 0.3 cm/deg. The PTV dose of prostate was 6,466 cGy during 0.1 cm/deg leaf and gantry that was the most closest prescribed dose(6,500 cGy). The dose of bladder and rectum were accessed the lowest during 0.3 cm/deg, 2.0 cm/deg. For gamma index, pancreas and prostate were analyzed the lowest error 100% at 0.8, 1.0 cm/deg and 99.6% at 0.3, 0.5 cm/deg. We should used the optimal leaf speed according to the gantry rotation if the treatment cases are performed VMAT.

• Progress in Medical Physics
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• v.18 no.2
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• pp.81-86
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• 2007

The cone-beam CT (CBCT) which is acquired using on-board imager (OBI) attached to a linear accelerator is widely used for the image guided radiation therapy. In this study, the effect of respiratory motion on the quality of CBCT image was evaluated. A phantom system was constructed in order to simulate respiratory motion. One part of the system is composed of a moving plate and a motor driving component which can control the motional cycle and motional range. The other part is solid water phantom containing a small cubic phantom ($2{\times}2{\times}2cm^3$) surrounded by air which simulate a small tumor volume in the lung air cavity CBCT images of the phantom were acquired in 20 different cases and compared with the image in the static status. The 20 different cases are constituted with 4 different motional ranges (0.7 cm, 1.6 cm, 2.4 cm, 3.1 cm) and 5 different motional cycles (2, 3, 4, 5, 6 sec). The difference of CT number in the coronal image was evaluated as a deformation degree of image quality. The relative average pixel intensity values as a compared CT number of static CBCT image were 71.07% at 0.7 cm motional range, 48.88% at 1.6 cm motional range, 30.60% at 2.4 cm motional range, 17.38% at 3.1 cm motional range The tumor phantom sizes which were defined as the length with different CT number compared with air were increased as the increase of motional range (2.1 cm: no motion, 2.66 cm: 0.7 cm motion, 3.06 cm: 1.6 cm motion, 3.62 cm: 2.4 cm motion, 4.04 cm: 3.1 cm motion). This study shows that respiratory motion in the region of inhomogeneous structures can degrade the image quality of CBCT and it must be considered in the process of setup error correction using CBCT images.

• The Journal of Korean Society for Radiation Therapy
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• v.26 no.1
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• pp.29-35
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• 2014

Purpose : This study has already started commercial Gated RapidArc automation equipment which was not previously in the Gated radiation therapy can be performed simultaneously with the VMAT Gated RapidArc radiation therapy to the accuracy of the analysis to evaluate the usability, Amplitude mode applied to the patient. Materials and Methods : The analysis of the distribution of radiation dose equivalent quality solid water phantom and GafChromic film was used Film QA film analysis program using the Gamma factor (3%, 3 mm). Three-dimensional dose distribution in order to check the accuracy of Matrixx dosimetry equipment and Compass was used for dose analysis program. Periodic breathing synchronized with solid phantom signals Phantom 4D Phantom and Varian RPM was created by breathing synchronized system, free breathing and breath holding at each of the dose distribution was analyzed. In order to apply to four patients from February 2013 to August 2013 with liver cancer targets enough to get a picture of 4DCT respiratory cycle and then patients are pratice to meet patient's breathing cycle phase mode using the patient eye goggles to see the pattern of the respiratory cycle to be able to follow exactly in a while 4DCT images were acquired. Gated RapidArc treatment Amplitude mode in order to create the breathing cycle breathing performed three times, and then at intervals of 40% to 60% 5-6 seconds and breathing exercises that can not stand (Fig. 5), 40% While they are treated 60% in the interval Beam On hold your breath when you press the button in a way that was treated with semi-automatic. Results : Non-respiratory and respiratory rotational intensity modulated radiation therapy technique absolute calculation dose of using computerized treatment plan were shown a difference of less than 1%, the difference between treatment technique was also less than 1%. Gamma (3%, 3 mm) and showed 99% agreement, each organ-specific dose difference were generally greater than 95% agreement. The rotational intensity modulated radiation therapy, respiratory synchronized to the respiratory cycle created Amplitude mode and the actual patient's breathing cycle could be seen that a good agreement. Conclusion : When you are treated Non-respiratory and respiratory method between volumetric intensity modulated radiation therapy rotation of the absolute dose and dose distribution showed a very good agreement. This breathing technique tuning volumetric intensity modulated radiation therapy using a rotary moving along the thoracic or abdominal breathing can be applied to the treatment of tumors is considered. The actual treatment of patients through the goggles of the respiratory cycle to create Amplitude mode Gated RapidArc treatment equipment that does not automatically apply to the results about 5-6 seconds stopped breathing in breathing synchronized rotary volumetric intensity modulated radiation therapy facilitate could see complement.