Earticle

Background: This study aims to predict the midline dose based on the entrance and exit doses from optically stimulated luminescence detector (OSLD) measurements for total body irradiation (TBI). Materials and Methods: For TBI treatment, beam data sets were measured for 6 MV and 15 MV beams. To evaluate the tissue lateral effect of various thicknesses, the midline dose and peak dose were measured using a solid water phantom (SWP) and ion chamber. The entrance and exit doses were measured using OSLDs. OSLDs were attached onto the central beam axis at the entrance and exit surfaces of the phantom. The predicted midline dose was evaluated as the sum of the entrance and exit doses by OSLD measurement. The ratio of the entrance dose to the exit dose was evaluated at various thicknesses. Results and Discussion: The ratio of the peak dose to the midline dose was 1.12 for a 30 cm thick SWP at both energies. When the patient thickness is greater than 30 cm, the 15 MV should be used to ensure dose homogeneity. The ratio of the entrance dose to the exit dose was less than 1.0 for thicknesses of less than 30 cm and 40 cm at 6 MV and 15 MV, respectively. Therefore, the predicted midline dose can be underestimated for thinner body. At 15 MV, the ratios were approximately 1.06 for a thickness of 50 cm. In cases where adult patients are treated with the 15 MV photon beam, it is possible for the predicted midline dose to be overestimated for parts of the body with a thickness of 50 cm or greater. Conclusion: The predicted midline dose and OSLD-measured midline dose depend on the phantom thickness. For in-vivo dosimetry of TBI, the measurement dose should be corrected in order to accurately predict the midline dose.

본 연구의 목적은 의료용 LINAC에서 방사선 에너지를 이용하는 열형광선량계(TLD), 형광유리선량계(PLD) 및 광자 극발광선량계(OSLD)의 에너지 의존성과 방향 의존성을 분석하여 방사선 서비스의 질을 향상시키는 것이다. 각 선량계 에 대하여 의존도가 낮은 우수한 선량계를 식별하여 우수한 선량계를 새 선량계로 사용할 수 있는 기초 자료도 제시하고 자 한다. 이를 위해 실험계획을 수립하고, LINAC HECK를 이용하여 31일 동안 매일 재현성을 평가하였다. 에너지 의존성을 알아보기 위해 선량계를 RANDO 팬텀 형태의 복부 조사야 끝에서 10 ~ 40 cm 간격으로 10 cm 단위로 두 가지 조건으로 두었다. 100 MU/min 단위로 100 MU/min에서 400 MU/min까지, 선량률을 400 MU/min으로 고정하고 선량을 1 Gy 증분 단위로 1에서 5 Gy로 변경하여 결과를 도출하였다. 또한 방향 의존성 실험을 위해 선량은 2 Gy로 고정하고 RANDO 팬텀의 복부 조사야로부터 40 cm 거리에서 0°에서 90°까지 15° 간격으로 좌우 전방향을 측정하였다. 실험 전 재현성 평가에서 각각의 변동계수(CV)는 허용한계 2%(0.02) 내에서 좋은 일치성을 보였다. 민감도 는 최고선량과 최저선량의 차이가 가장 작은 PLD 민감도가 10 cm, 20 cm, 40 cm, 1 Gy에서 우수하였으며 선량률은 100 MU/min으로 증가하였다. 30 cm에서 TLD 민감도는 최고선량과 최저선량의 차이가 가장 작다는 점에서 우수하였 다. 에너지 의존도 측면에서 TLD 값은 10cm, 20cm 및 30cm에서 가장 좋았으며 고정 선량률은 400 MU/min이고 선량은 1 Gy 단위로 1 ~ 5 Gy입니다. 방향의존성은 TLD, PLD, OSLD가 표면선량 0° ~ 90°에서 각각 48%, 74%, 86%의 감소율을 보였다. 이는 방향 의존성이 TLD, PLD, OSLD 순으로 증가함을 의미한다. 전반적으로 PLD는 우수한 감도를 보인 반면 TLD는 우수한 에너지 의존성을 보였다. 또한 방향 의존성은 TLD, PLD, OSLD 순으로 증가하였다.

The aims of this study were to improve the quality of radiation services by analyzing the energy dependence and direction dependence of thermoluminescent dosimeters (TLDs), photoluminescent dosimeters (PLDs) and optically stimulated luminescence dosimeters (OSLDs) using radiation energy at a medical LINAC, comparing the results from statistical processing, and identifying an excellent dosimeter with a low dependence on the features above. This paper also presents basic data through which an excellent dosimeter can be used as a new one. To this end, an experimental plan was established, and the reproducibility was evaluated every day for 31 days using a LINACHECK. To examine the energy dependence, the dosimeter was placed at different distances from the end of the abdomen irradiation field of a RANDO phantom form 10 to 40 cm at 10 cm increments under two conditions: fixing the dose to 1 Gy and changing the dose rate from 100 MU/min to 400MU/min at 100 MU/min increments; and fixing the dose rate at 400 MU/min and changing the dose from 1 to 5 Gy at a of 1 Gy increments. In addition, for an experiment of direction dependence, the dose was fixed to 2 Gy, and the left and right omnidirections were measured at 15° intervals from 0° to 90° at a distance of 40 cm from the abdomen irradiation field of the RANDO phantom. In the reproducibility evaluation before the experiment, each coefficient of variation (CV) showed good coincidence within a tolerance limit of 2 % (0.02). In terms of the sensitivity, the PLD sensitivity, whose difference was the smallest between highest and lowest doses, were excellent at 10 cm, 20 cm and 40 cm, at 1 Gy with the dose rate increased at 100 MU/min. At 30 cm, the TLD sensitivity was excellent in that the difference was smallest between highest and lowest doses. In terms of energy dependence, the TLD values were best at 10 cm, 20 cm and 30 cm, at a fixed dose rate of 400 MU/min and a dose of 1 - 5 Gy in 1 Gy increments. In terms of the direction dependence, TLD, PLD and OSLD showed a reduction rate of 48 %, 74 % and 86 %, respectively, at a surface dose of 0° to 90°. This suggests that the direction dependence increases in the order of TLD, PLD and OSLD. Overall, the PLD showed excellent sensitivity, whereas the TLD showed excellent energy dependence. In addition, the direction dependence increased in the order of TLD, PLD and OSLD.

최근 개인선량계로 사용이 증가하고 있는 수동형 선량계인 OSLD와 능동형 선량계인 EPD의 상대 반응도(relative response), 측정 불확도(uncertainty of measurement)를 계산하여 방향의존성(angular dependence)을 비교, 분석하였다. OSLD는 수평, 수직방향의 $0^{\circ}{\sim}{\pm}90^{\circ}$ 범위에서 평균 상대 반응도는 0.97, 0.95의 작은 변화를 보였고 방향의존성에 대한 불확도는 0.65, 0.62로 전체 불확도에 미치는 영향은 미미한 것으로 판단되었다. EPD는 $0^{\circ}{\sim}{\pm}60^{\circ}$ 범위에서 수평, 수직방향 평균 상대 반응도는 0.94, 0.97로 확인되어 IEC 61526 규정을 만족하였다. 방향의존성에 대한 불확도는 수평, 수직방향에서 0.44, 0.40로 전체 불확도에 미치는 영향은 미미하였다. 그러나 수평방향에서 $+90^{\circ}$, $-90^{\circ}$ 방향의 상대 반응도는 0.60, 0.37이고 수직방향에서 $+90^{\circ}$ 방향의 반응도는 0.06으로 반응도의 큰 변화를 관찰할 수 있었다. OSLD의 방향 의존성은 $0^{\circ}{\sim}{\pm}90^{\circ}$ 범위까지 EPD에 비해 우수하였으며 EPD의 경우 구조적 특징으로 반응도가 급변하는 특정방향이 존재하였다. 따라서 수동형선량계와 보조선량계의 병행사용이 개인피폭선량측정의 정확도를 기할 수 있을 것으로 판단된다.

The angular dependence of active dosimeters, EPD, is analysed and compared with that of passive dosimeters, OSLD, after evaluating their relative response and uncertainty of measurement, where it is known that the personal use of them has been increased recently. There appeared a minor variation for average relative response of OSLD in the horizontal and vertical directions within the range $0^{\circ}{\sim}{\pm}90^{\circ}$, which are 0.97 and 0.95 respectively. The variations of angular dependence in the same situations with OSLD are 0.65 and 0.62, respectively, which also reveals a negligible effect on the overall uncertainty. EPDs within the interval $0^{\circ}{\sim}{\pm}60^{\circ}$ for horizontal and vertical directions are 0.94 and 0.97, respectively. These satisfy the requirements of IEC 61526. Uncertainties about the dependence of direction from horizontal and vertical directions are 0.44, 0.40, respectively. The impact of these uncertainties on the overall uncertainty was negligible. However, we observed a significant change in reactivity: the relative reactivities for $+90^{\circ}$ and $-90^{\circ}$ from the horizontal direction are 0.60, 0.37, while that form vertical direction is 0.06. The direction dependence of OSLD was superior to EPD in the range of $0^{\circ}{\sim}{\pm}90^{\circ}$. There appeared a rapidly changing structural features in EPD response for a certain direction. Therefore, we conclude that concurrent use of passive dosimeters and auxiliary dosimeter provides accurate data for personal dose measurements.

This study was conducted from July 1 to September 30, 2018 using Optically Stimulated Luminescence Dosimeter(OSLD) and photoluminescent glass dosimeter(PLD) to measure the 3-month exposure dose and the cumulative dose in the active working area of the nuclear medicine worker Respectively. As a result, the cumulative dose for three months in the worker and work area was measured as 1.97 mSv and 2.02 mSv in the PLD. The mean surface dose and the mean depth dose of the OSLD were measured to be 2.04 mSv. The difference in the total surface dose measured by the PLD and the OSLD was 0.66mSv and the total mean surface dose was 0.07mSv. The difference between the total depth dose and the total depth dose was 0.1mSv and 0.02mSv, respectively. It was found that the dose value of the OSLD was higher than that of the PLD. In addition, it was found that the maximum difference of 0.01mSv was observed between the PLD and the OSLD of the worker. For the dose measurement of the two dosimetry systems, there was no significant difference between the PLD and the OSLD in the surface dose of 0.239 (p>0.05). Also, the significance of PLD and OSLD in the deep dose was 0.109, which was not statistically significant (p>0.05).

뇌출혈 진단 방법 중 CT는 비침습적으로 피사체의 3차원 영상을 제공할 수 있다. 그래서 응급실에서 급성인 환자 상대로 많이 사용되고 중요한 역할을 담당하고 있다. 뇌혈관 CT는 다른 혈관 CT에 비해 비교적 촬영 빈도가 높으며 뇌혈관 CT 검사 시 적절한 SNR, 합리적인 유효선량으로 검사를 해야한다. 뇌혈관 CT 검사 시 이중에너지와 단일에너지를 이용하였을 때 실질적으로 어느 것이 유효선량이 적으며, SNR이 차이가 없는지 환자영상과 Phantom영상을 같이 비교하였다. SNR과 CNR의 P값이 0.05이상일 때 통계적으로 차이가 없다고 보았고, 유효선량은 0.05미만일 경우 통계적으로 차이가 있다고 보았다. 실험에서는 병원영상의 환자선량을 비교하였을 때 이중에너지의 유효선량이 53.53% 적게, Phantom의 OLSD 이중에너지 유효선량이 57.94% 적게, Phantom의 Dose Report의 이중에너지 유효선량이 56.04% 적었다. 그래서 뇌혈관조영 CT는 이중에너지를 권장한다.

Single source and dual source measurements using anthropomorphic phantoms in which the phantoms are lined up in human body equivalents use OSLD (Optically Stimulated Luminescence Dosimeter), so the effective dose is calculated using OSLD. For hospital images, SNR (Signal to Noise Ratio) and CNR (Contrast to Noise Ratio) were measured in MCA (Middle Cerebral Artery) for single source and dual source, and for phantom images, SNR and CNR were measured for brain parenchyma of single source and dual source. For hospital imaging, SNR and CNR were measured in MCA for both single-source and dual-source, and for phantom images, SNR and CNR were measured for brain parenchyma from single-source and dual-source. As a result of comparing the SNR and CNR of the hospital image and the phantom image, there was no statistical difference. Comparing patient doses in hospital images, the effective dose of the dual source was 53.53% less and the effective dose of the dual energy phantom was 57.94% less. The dose can be increased in other areas, but the cerebrovascular area is useful because the dose is small.