MV방사선 치료는 둘러싸여 있는 정상조직의 피폭선량을 최소화 하면서, target volume 내에 정확하게 선량을 전달하는데 있어 중요한 요인이다. 본 연구에서는 방사선 치료의 높은 정확성을 유지하기 위하여 megavoltage X-ray imaging (MVI)에서 edge block 을 사용한 digital radiography (DR) system 검출기의 modulation transfer function (MTF: 변조전달함수), the noise power spectrum (NPS: 잡음전력스펙트럼) and the detective quantum efficiency (DQE: 양자검출효율)를 측정하고자 한다. 우리는 텅스텐으로 구성된 19 (thickness) ${\times}$ 10 (length) ${\times}$ 1 (width) $cm^3$의 edge block을 사용하였으며, 다음과 같은 setting들로 pre-sampling modulation transfer function (MTF)를 계산하였다: 6-megavolt (MV) energy를 사용하고, 다양한 Radiotherapy장비인 TrueBeamTM (Varian), BEAMVIEWPLUS (Siemens), iViewGT (Elekta), ClinacR iX (Varian) 를 사용하였다. MTF결과에서 Varian TrueBeamTM flattening filter free가 MTF의 50% ($mm^{-1}$)에서 0.46, 10% ($mm^{-1}$) 에서 1.40로 가장 highest value를 보였다. Noise 분포는 Elekta iViewGT가 가장 낮은 분포를 보였다. DQE에서는 E lekt a iViewGT가 peak DQE에서 0.0026 그리고 $1mm^{-1}$ DQE 에서 0.00014로 가장 높았다. 본 연구는 Edge method를 이용하여 MTF와 DQE산출을 재현하였으며, 현재 임상에서 사용되는 DR 시스템 측정의 높은 정확성을 유지할 수 있었으며 이러한 연구는 전통적인 QA 영상화뿐만 아니라 검출기 개발 연구에 있어서 정량적인 MTF, NPS, DQE 측정에 더욱 더 효율적으로 사용될 수 있다는 것을 알 수 있다.
MV방사선 치료는 둘러싸여 있는 정상조직의 피폭선량을 최소화 하면서, target volume 내에 정확하게 선량을 전달하는데 있어 중요한 요인이다. 본 연구에서는 방사선 치료의 높은 정확성을 유지하기 위하여 megavoltage X-ray imaging (MVI)에서 edge block 을 사용한 digital radiography (DR) system 검출기의 modulation transfer function (MTF: 변조전달함수), the noise power spectrum (NPS: 잡음전력스펙트럼) and the detective quantum efficiency (DQE: 양자검출효율)를 측정하고자 한다. 우리는 텅스텐으로 구성된 19 (thickness) ${\times}$ 10 (length) ${\times}$ 1 (width) $cm^3$의 edge block을 사용하였으며, 다음과 같은 setting들로 pre-sampling modulation transfer function (MTF)를 계산하였다: 6-megavolt (MV) energy를 사용하고, 다양한 Radiotherapy장비인 TrueBeamTM (Varian), BEAMVIEWPLUS (Siemens), iViewGT (Elekta), ClinacR iX (Varian) 를 사용하였다. MTF결과에서 Varian TrueBeamTM flattening filter free가 MTF의 50% ($mm^{-1}$)에서 0.46, 10% ($mm^{-1}$) 에서 1.40로 가장 highest value를 보였다. Noise 분포는 Elekta iViewGT가 가장 낮은 분포를 보였다. DQE에서는 E lekt a iViewGT가 peak DQE에서 0.0026 그리고 $1mm^{-1}$ DQE 에서 0.00014로 가장 높았다. 본 연구는 Edge method를 이용하여 MTF와 DQE산출을 재현하였으며, 현재 임상에서 사용되는 DR 시스템 측정의 높은 정확성을 유지할 수 있었으며 이러한 연구는 전통적인 QA 영상화뿐만 아니라 검출기 개발 연구에 있어서 정량적인 MTF, NPS, DQE 측정에 더욱 더 효율적으로 사용될 수 있다는 것을 알 수 있다.
In megavoltage (MV) radiotherapy, delivering the dose to the target volume is important while protecting the surrounding normal tissue. The purpose of this study was to evaluate the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE) using a...
In megavoltage (MV) radiotherapy, delivering the dose to the target volume is important while protecting the surrounding normal tissue. The purpose of this study was to evaluate the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE) using an edge block in megavoltage X-ray imaging (MVI). We used an edge block, which consists of tungsten with dimensions of 19 (thickness) ${\times}$ 10 (length) ${\times}$ 1 (width) $cm^3$ and measured the pre-sampling MTF at 6 MV energy. Various radiation therapy (RT) devices such as TrueBeam$^{TM}$ (Varian), BEAMVIEW$^{PLUS}$ (Siemens), iViewGT (Elekta) and Clinac$^{(R)}$iX (Varian) were used. As for MTF results, TrueBeam$^{TM}$(Varian) flattening filter free(FFF) showed the highest values of $0.46mm^{-1}$ and $1.40mm^{-1}$ for MTF 0.5 and 0.1. In NPS, iViewGT (Elekta) showed the lowest noise distribution. In DQE, iViewGT (Elekta) showed the best efficiency at a peak DQE and $1mm^{-1}DQE$ of 0.0026 and 0.00014, respectively. This study could be used not only for traditional QA imaging but also for quantitative MTF, NPS, and DQE measurement for development of an electronic portal imaging device (EPID).
In megavoltage (MV) radiotherapy, delivering the dose to the target volume is important while protecting the surrounding normal tissue. The purpose of this study was to evaluate the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE) using an edge block in megavoltage X-ray imaging (MVI). We used an edge block, which consists of tungsten with dimensions of 19 (thickness) ${\times}$ 10 (length) ${\times}$ 1 (width) $cm^3$ and measured the pre-sampling MTF at 6 MV energy. Various radiation therapy (RT) devices such as TrueBeam$^{TM}$ (Varian), BEAMVIEW$^{PLUS}$ (Siemens), iViewGT (Elekta) and Clinac$^{(R)}$iX (Varian) were used. As for MTF results, TrueBeam$^{TM}$(Varian) flattening filter free(FFF) showed the highest values of $0.46mm^{-1}$ and $1.40mm^{-1}$ for MTF 0.5 and 0.1. In NPS, iViewGT (Elekta) showed the lowest noise distribution. In DQE, iViewGT (Elekta) showed the best efficiency at a peak DQE and $1mm^{-1}DQE$ of 0.0026 and 0.00014, respectively. This study could be used not only for traditional QA imaging but also for quantitative MTF, NPS, and DQE measurement for development of an electronic portal imaging device (EPID).
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문제 정의
Thus, NPS is a very important element to describe the penumbra in the field of methodological MVI and noise properties of flatness in medical image systems. Thus, this study demonstrated the measurement of the NPS in the MVI field. Image processing is important to acquire an optimum radiation image.
제안 방법
This study evaluated the MTF, NPS and DQE using edge block in MVI to maintain a high accuracy in delivering dose. In order to maintain such a high accuracy, we evaluated the performance of four DR systems which were used in clinic. Our results were approximately 1.
The MTF was computed by performing a fast Fourier t ransfer (FFT) of the LSF and normalizing its value to unity at a zero spatial f requency. The one-dimensional NPS was expressed by averaging the axis direction from the bandwidth of the two dimensional NPS space, and the accumulation correction was calculated by extracted the ROI from the whole image size. The DQE was evaluated from the measured MTF and NPS
The purpose of this study was to evaluate the MTF, the NPS, and the DQE using an edge block in electronic portal imaging device (EPID) and meet the requirements concerning the position and the dose verification at the same time.
This study evaluated the MTF, NPS and DQE using edge block in MVI to maintain a high accuracy in delivering dose. In order to maintain such a high accuracy, we evaluated the performance of four DR systems which were used in clinic.
Then, 1024 × 512 2D white images were used and each NPS data was calculated. We applied two-dimensional FFTs in order to obtain ROI images and we performed a scale revision using the average ROI extracted from the whole image. The matrix size was 1024 × 512 pixels, the pixel size was 0.
대상 데이터
The DR detectors we used are Varian TrueBeamTM, Siemens BEAMVIEWPLUS, Elekta iViewGT and Varian Clinac® iX aS1000.
The DR systems used in study were Siemens BEAMVIEWPLUS, Elekta iViewGT, Varian TrueBeamTM and Varian Clinac® iX aS1000, which are a-Si flat panel detectors.
The performance evaluation of Varian TrueBeamTM was performed as flattening filter and flattening filter free. The SDD of the four DR devices are 132 cm. In all MVI units, a change is caused by magnification because the edge block is projected to be close to the minimum iso-center.
The imaging panel (IDU 20) includes a 1-mm Cu build up plate, a Gd2O2S:Tb scintillating phosphor layer, and a 1024 ×768 array of photodiodes switched by thin-film transistors deposited on a glass substrate.
이론/모형
The MTF measurement was performed using the pre-sampled MTF method described by Fujita et al.12,20-22). The MTF describes t he r esolution of the detector.
However, noise hardly affects the measurements because noise is included in all detectors23). Therefore, the penumbra and the flatness were measured using the IEC 62220-1 RQA5 methodologies of the NPS and the normalized noise power spectrum (NNPS) was measured with the 2D FFT methods by using the white images. Thus, NPS is a very important element to describe the penumbra in the field of methodological MVI and noise properties of flatness in medical image systems.
성능/효과
In the results, although Varian Clinac® iX aS1000 and Varian TrueBeamTM were made by the same manufacturer, Varian TrueBeamTM had a higher resolution and efficiency than Varian Clinac® iX aS1000.
0 mm−1 according to the increase in the spatial frequency, which is comparable to the values reported in the literature. The data indicated that the systems assessed in the current study by a common methodology achieved similar performances with respect to the DQE when compared against values common a MVI EPID.
후속연구
T he p erf ormance evaluation, such a s MTF, NPS, and DQE, is important not only clinically but also as for the detector improvement. Therefore, this study could be incorporated into used in clinical QA requiring performance and EPID development research.
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