이 연구의 목적은 소조사면 선량계측을 위하여 엣지검출기의 성능을 평가하기 위함이다. 다양한 소조사면과 깊이에서 엣지검출기(Model 1118 Edge)를 이용하여 6 MV 광자선의 선량 직선성, 선량률 의존도, 출력 계수, 선량 측면도 및 심부선량 백분율을 따라 측정하였으며, 이를 표준용적의 이온전리함(CC13)과 광자선 다이오드 검출기(PFD)와 비교하였다. 선량 직선성을 일차 선형 맞춤 함수와 비교하였을 때, 세 검출기 모두 1% 미만의 차이를 나타냈으며, 엣지검출기는 -0.08~0.08%의 가장 낮은 차이를 보였다. 선량율의 변화(100~600 MU/min)에 따라 PFD와 엣지검출기의 정규화된 반응비는 1% 미만의 일정한 값을 보였으나, CC13은 100 MU/min에서 약 -5%의 변화를 나타냈다. 조사면의 크기($4{\times}4\;cm^2{\sim}10{\times}10\;cm^2$)에 따른 출력계수는 세 검출기 모두 거의 같은 값을 보였으나, $4{\times}4\;cm^2$ 이하의 소조사면에서는 엣지검출기와 PFD의 출력 계수가 CC13과 최대 21%의 차이보였다. 각 조사면에서 20~80%의 반음영 폭을 측정하였을 때, 평균적으로 CC13은 엣지검출기보다 2배, PFD는 약 30% 정도 더 넓게 나타났다. 또한 10~90%의 반음영의 경우, CC13과 PFD가 각각 55%와 19% 정도 더 넓은 폭을 나타냈다. 엣지검출기는 선량 측면도의 반치폭이 조사면의 크기와 거의 일치하였으나, 다른 두 검출기는 조사면의 크기보다 약 8~10% 더 크게 나타났으며, 심부선량백분율은 각 조사면에서 세 검출기 모두 거의 일치하였다. 엣지검출기의 성능평가를 위한 선량특성을 분석한 결과, $4{\times}4\;cm^2$ 이하의 소조사면에서 가장 적합한 특성을 나타냈으며, CC13과 PFD와 같은 검출기는 조사면이 작을수록 상당한 오차를 나타낼 수 있음을 알 수 있었다.
이 연구의 목적은 소조사면 선량계측을 위하여 엣지검출기의 성능을 평가하기 위함이다. 다양한 소조사면과 깊이에서 엣지검출기(Model 1118 Edge)를 이용하여 6 MV 광자선의 선량 직선성, 선량률 의존도, 출력 계수, 선량 측면도 및 심부선량 백분율을 따라 측정하였으며, 이를 표준용적의 이온전리함(CC13)과 광자선 다이오드 검출기(PFD)와 비교하였다. 선량 직선성을 일차 선형 맞춤 함수와 비교하였을 때, 세 검출기 모두 1% 미만의 차이를 나타냈으며, 엣지검출기는 -0.08~0.08%의 가장 낮은 차이를 보였다. 선량율의 변화(100~600 MU/min)에 따라 PFD와 엣지검출기의 정규화된 반응비는 1% 미만의 일정한 값을 보였으나, CC13은 100 MU/min에서 약 -5%의 변화를 나타냈다. 조사면의 크기($4{\times}4\;cm^2{\sim}10{\times}10\;cm^2$)에 따른 출력계수는 세 검출기 모두 거의 같은 값을 보였으나, $4{\times}4\;cm^2$ 이하의 소조사면에서는 엣지검출기와 PFD의 출력 계수가 CC13과 최대 21%의 차이보였다. 각 조사면에서 20~80%의 반음영 폭을 측정하였을 때, 평균적으로 CC13은 엣지검출기보다 2배, PFD는 약 30% 정도 더 넓게 나타났다. 또한 10~90%의 반음영의 경우, CC13과 PFD가 각각 55%와 19% 정도 더 넓은 폭을 나타냈다. 엣지검출기는 선량 측면도의 반치폭이 조사면의 크기와 거의 일치하였으나, 다른 두 검출기는 조사면의 크기보다 약 8~10% 더 크게 나타났으며, 심부선량백분율은 각 조사면에서 세 검출기 모두 거의 일치하였다. 엣지검출기의 성능평가를 위한 선량특성을 분석한 결과, $4{\times}4\;cm^2$ 이하의 소조사면에서 가장 적합한 특성을 나타냈으며, CC13과 PFD와 같은 검출기는 조사면이 작을수록 상당한 오차를 나타낼 수 있음을 알 수 있었다.
In this study, we evaluated an edge detector for small-beam dosimetry. We measured the dose linearity, dose rate dependence, output factor, beam profiles, and percentage depth dose using an edge detector (Model 1118 Edge) for 6-MV photon beams at different field sizes and depths. The obtained values...
In this study, we evaluated an edge detector for small-beam dosimetry. We measured the dose linearity, dose rate dependence, output factor, beam profiles, and percentage depth dose using an edge detector (Model 1118 Edge) for 6-MV photon beams at different field sizes and depths. The obtained values were compared with those obtained using a standard volume ionization chamber (CC13) and photon diode detector (PFD). The dose linearity results for the three detectors showed good agreement within 1%. The edge detector had the best linearity of ${\pm}0.08%$. The edge detector and PFD showed little dose rate dependency throughout the range of 100~600 MU/min, while CC13 showed a significant discrepancy of approximately -5% at 100 MU/min. The output factors of the three detectors showed good agreement within 1% for the tested field sizes. However, the output factor of CC13 compared to the other two detectors had a maximum difference of 21% for small field sizes (${\sim}4{\times}4\;cm^2$). When analyzing the 20~80% penumbra, the penumbra measured using CC13 was approximately two times wider than that using the edge detector for all field sizes. The width measured using PFD was approximately 30% wider for all field sizes. Compared to the edge detector, the 10~90% penumbras measured using the CC13 and PFD were approximately 55% and 19% wider, respectively. The full width at half maximum (FWHM) of the edge detector was close to the real field size, while the other two detectors measured values that were 8~10% greater for all field sizes. Percentage depth doses measured by the three detectors corresponded to each other for small beams. Based on the results, we consider the edge detector as an appropriate small-beam detector, while CC13 and PFD can lead to some errors when used for small beam fields under $4{\times}4\;cm^2$.
In this study, we evaluated an edge detector for small-beam dosimetry. We measured the dose linearity, dose rate dependence, output factor, beam profiles, and percentage depth dose using an edge detector (Model 1118 Edge) for 6-MV photon beams at different field sizes and depths. The obtained values were compared with those obtained using a standard volume ionization chamber (CC13) and photon diode detector (PFD). The dose linearity results for the three detectors showed good agreement within 1%. The edge detector had the best linearity of ${\pm}0.08%$. The edge detector and PFD showed little dose rate dependency throughout the range of 100~600 MU/min, while CC13 showed a significant discrepancy of approximately -5% at 100 MU/min. The output factors of the three detectors showed good agreement within 1% for the tested field sizes. However, the output factor of CC13 compared to the other two detectors had a maximum difference of 21% for small field sizes (${\sim}4{\times}4\;cm^2$). When analyzing the 20~80% penumbra, the penumbra measured using CC13 was approximately two times wider than that using the edge detector for all field sizes. The width measured using PFD was approximately 30% wider for all field sizes. Compared to the edge detector, the 10~90% penumbras measured using the CC13 and PFD were approximately 55% and 19% wider, respectively. The full width at half maximum (FWHM) of the edge detector was close to the real field size, while the other two detectors measured values that were 8~10% greater for all field sizes. Percentage depth doses measured by the three detectors corresponded to each other for small beams. Based on the results, we consider the edge detector as an appropriate small-beam detector, while CC13 and PFD can lead to some errors when used for small beam fields under $4{\times}4\;cm^2$.
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문제 정의
5 cm depth in the water phantom. This test was to measure the dependence on the field size and collecting volume for the different detector systems. The measurements were carried out for 1×1, 2×2, 4×4, 6×6, 8×8, and 10×10 cm2 field sizes; these were combined with multileaf collimator (MLC) square fields with square independent jaws.
가설 설정
1) Dose linearity: For the three detectors, dose linearity was measured to see if the detector signal was linearly proportional to the dose. The test was carried out for a field size of 10×10 cm2 at a depth of 5 cm in the water phantom.
제안 방법
All measurements were performed in an automatic water scanning phantom (Blue phantom, Scanditronix-Wellhofer, IBA, Germany) with a volume of 48×48×48 cm3.
Comparison of penumbra widths (10∼90%, 20∼80%) and FWHM (50%) of the beam profile at 10 cm depth evaluated by three dosimeters.
In this study, we evaluated the suitability and performanc of the edge detector for small photon beams. We also confirmed several dosimetric characteristics of the three detectors for various specific field sizes and depths.
The test was carried out for a field size of 10×10 cm2 at a depth of 5 cm in the water phantom. Measurements were conducted by delivering 10, 50, 100, 200, 400, and 600 monitor units (MU) for a 6 MV photon beam. The response signal was converted to dose (cGy) using the PDD value at the depth of 5 cm.
The measurements were carried out for 1×1, 2×2, 4×4, 6×6, 8×8, and 10×10 cm2 field sizes; these were combined with multileaf collimator (MLC) square fields with square independent jaws.
This work aims to evaluate the edge detector for small beam dosimetry in terms of basic dosimetric parameters such as dose linearity, dose rate dependence, output factor, beam profiles, and PDD. The edge detector was compared with a standard volume ionization chamber and a photon diode detector, which are the most commonly used detectors for beam data commissioning of medical linear accelerators.
To compare the effectiveness of the edge detector against other detector systems for small beam measurements, we analyzed the penumbra widths (10∼90% and 20∼80%) and full width at half-maximum (FWHM) for various field sizes.
대상 데이터
5 mm. The detector housing wall thickness is 0.13 mm, and the wall material is brass. A zero voltage bias was applied to the electrometer.
8 mm2 and 32 nC/Gy, respectively. The diode die is located 0.3 mm from the top, 4.3 mm from the end, and 2.7 mm from the side, with the cross marked on the top surface. The water equivalent depth is 0.
Unlike the edge detector, a 300 V bias was applied to the electrometer. The photon field detector (PFD, S/N: DEB012-3438, Scanditronix-Wellhofer, IBA, Uppsala, Sweden) is a highly doped p-type silicon detector with a diameter of 2 mm and thickness of 0.06 mm for the active area, which forms a circle. It is specially designed for measuring small photon beams.
The test was carried out for a field size of 10×10 cm2 at a depth of 5 cm in the water phantom.
13 cm3. The wall and central electrode material is C552, and the wall thickness is 0.070 g/cm2. Unlike the edge detector, a 300 V bias was applied to the electrometer.
성능/효과
The linear fit function results all showed excellent linearity, with the discrepancy within 1% for all three detectors; the best results were produced by the edge detector, which ranged within ±0.08% (not shown).
후속연구
We did not evaluate the stereotactic diode detector and diamond detectors, which are commonly used for small field dosimetry. Although some of the advantages and disadvantages are known for semiconductor detectors, which have a very small sensitive volume and very high resolution,10-12) further studies should be performed to evaluate stereotactic and diamond detectors as compared to the edge detector for small beam dosimetry.
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