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@#<b>Objective</b> To study whether the disinfection methods for thermoluminescence dosimeters used by major hospitals during the COVID-19 pandemic had an impact on monitoring personal dose of external irradiation, and to screen for the disinfection procedures suitable for use during the pandemic. <b>Methods</b> Hospitals with fever clinics during the epidemic in Shandong Province were selected from March to October 2020, we investigated the disinfection methods as well as the types and frequency of use of disinfection supplies used for thermoluminescence dosimeters during the pandemic in hospitals. Simulations were performed in experimental and control groups. <b>Results</b> The average doses measured by the disc dosimeter with different disinfection methods and the control group were 0.92-0.99 mSv and 0.98 mSv, respectively, and the deviation was ≤ 6%. The average doses measured by the glass tube dosimeter with different disinfection methods and the control group were 0.20-0.22 and 0.21, respectively, and the deviation was ≤ 5%. <b>Conclusion</b> The results showed that the commonly used disinfection methods had no influence on personal dose monitoring, but some disinfection measures were not suitable for dosimeters.
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Objective To explore the feasibility of quartz glass for radiotherapy dosimetry through the experimental study of the thermoluminescence characteristics of synthetic quartz glass. Methods The thermoluminescence glow curves of quartz glass under different annealing conditions were analyzed, the thermoluminescence characteristics of quartz glass were studied, and the measurement parameters were optimized. Using the Co-60 reference radiation field in the National Secondary Standard Dosimetry Laboratory, the quartz glass samples under different annealing conditions were irradiated following the dose levels of radiotherapy, i.e., 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, and 10.0 Gy, respectively. According to the relationship between the absorbed dose of quartz glass and the relative thermoluminescence signal intensity, the linearity and dispersion of the dose response of quartz glass were obtained, and the feasibility of quartz glass for radiotherapy dosimetry was analyzed. Results The linear correlation coefficient of dose response of quartz glass under annealing condition of 430℃ for 10 min was 0.9984, and the dose response dispersion was 0.97% at the absorbed dose of 2 Gy. The linear correlation coefficient of dose response of quartz glass under annealing condition of 600℃ for 1 h was 0.9911, and the dose response dispersion was 1.4% at the absorbed dose of 2 Gy. Conclusion Preliminary results suggest that quartz glass with annealing condition of 430℃ for 10 min has the potential to be used for radiotherapy dosimetry.
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@#<b>Objective</b> To monitor the cumulative terrestrial γ radiation dose around Shidaowan nuclear power plant, Shandong, China before operation, to analyze the dose levels and influencing factors, and to estimate the annual effective dose to local residents. <b>Methods</b> Fifty-six monitoring sites were selected within 30 km around the nuclear power plant. The environmental γ radiation dose was measured by the thermoluminescence dosimeter monitoring method. The γ radiation dose levels were investigated for 369 days in four monitoring periods (January 16 to April 14, April 15 to July 20, July 21 to October 21, 2021, and October 22, 2021 to January 20, 2022 for periods I to IV, respectively). Relations between γ radiation and monitoring time, altitude, distance from the nuclear power plant were analyzed, and the annual effective dose of terrestrial γ radiation to residents was estimated to reflect the background terrestrial γ radiation level in the area. <b>Results</b> The average values of terrestrial γ radiation dose rate in the four monitoring periods in the area were (76.196 ± 3.366), (81.773 ± 6.144), (93.554 ± 7.449), and (97.604 ± 9.396) nGy/h, respectively, and the terrestrial γ radiation dose rate in the whole year was (87.282 ± 6.589) nGy/h. The effective dose to residents was 0.428 mSv. The terrestrial γ radiation level was high from July 2021 to January 2022. There was no significant difference in the γ radiation dose rate at the monitoring sites with different distance from the nuclear power plant. No impact upon the terrestrial γ radiation dose by the altitude was observed in this study. <b>Conclusion</b> The terrestrial γ radiation level around Shidaowan nuclear power plant in 2021 was at the background level.
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Synthesis and characterization of halosulphate-based phosphors is important for thermoluminescence dosimetry (TLD), radiophotoluminescence dosimetry (RPL) and scintillator materials. The enhancement of luminescence output in halosulphate-based phosphors and it may be useful for lamp, solid-state lamp and radiation. Dosimetry by activator as well as sensitizer are well known properties. The combustion technique is not applicable for the synthesis of TLD phosphors due to very fine particles, which show less TL intensity, while sol-gel, solid-state diffusion, melt method and precipitation methods are applicable for TLD phosphors. Two halosulphates namely Na21( SO4 ) 7 F6 Cl and 2K3Ca2(SO4)3F were prepared and doped with Dy and Tm for different concentration .Halosulphate , Na21( SO4 ) 7 F6 Cl was prepared by wet chemical method and Halosulphate , 2K3Ca2(SO4)3F was prepared by solid state diffusion method . The characterization was done by X - ray diffraction ( XRD ) , Thermo luminescence (TL) was also studied . For Dy doped Na21( SO4) 7 F6 Cl , The peak was observed at 1200 C and shoulder at 1750C for 0.2 % molar concentration of Dy. and for 2K3Ca2(SO4)3F doped with Tm the shoulder peak was observed at 240 0 C and at 150 0C for 0.7 % molar concentration of Tm.
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Objective To investigate the effect of gaseous effluent from the six generator sets on the radiation level of the surrounding terrestrial environment in Daya Bay Nuclear Power Base after the operation of Ling’ao Nuclear Power plant. Methods The radiation level in the peripheral environment of the Base was monitored using the thermoluminescence dosimeter （TLD）. Twenty-five monitoring sites were set around the Base to investigate the variation of radiation level over a long period of time by collecting the TLDs every three months. Results From 2011 to 2020, the annual γ dose rate of the 25 sites ranged from 76.7 to 207.1 nGy/h, with an average value of (123.3 ± 5.7) nGy/h and a relative deviation of 2%-12%. The TLD monitoring and instantaneous measuring results of γ dose rate were consistent with the survey of the State Environmental Protection Administration in the 20th century and the baseline level prior to the operation of the nuclear power plant. Conclusion There are great differences in natural environmental radiation level across the TLD monitoring sites. The overall environmental γ radiation level within 50 km of the nuclear power base remains unchanged. The emission of gaseous effluent from the operation of the nuclear power plant does not have a cumulative impact on the radiation level of surrounding environment.
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Objective:To investigate the application of therapeutic grade ionization chamber to rapid measurement of short pulsed and high-dose-rate X-ray.Methods:The half-value layer of pulsed X-ray caused by an electron accelerator was measured by interpolation method and its equivalent energy was estimated. The cumulative doses from a certain amount of pulsed radiation at different distances in the same direction around the equipment were compared using the therapeutic grade ionization chamber and thermoluminescence measurement method . The relationship between the measurement result by using ionization chamber dosimeter and the distances away from source was analyzed. The cumulative doses from a certain amount of pulsed radiation at the same location at different frequencies were compared.Results:In working condition, 100 pulses of radiation were received accumulatively at 1 to 12 meters away from the outer wall of the equipment. The range of air Kerma was 0.08-9.65 mGy measured by using thermoluminescence dometers and 0.08 - 9.85 mGy using the ionization chamber dosimeters, respectively. The difference between both is within 10%. At different frequencies (1-10 Hz), there was no significant difference in X-ray air Kerma from 100 pulses measured by ionization chamber dosimeter at 2 m away from the front of the equipment ( P>0.05). Conclusions:The therapeutic grade ionization chamber dosimeter can be used for the rapid measurement of short pulsed X-ray radiation dose in the range of dose rates and pulse frequencies involved in the experimental accelerator device.
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Resumen Introducción: en la búsqueda de nuevos materiales útiles como dosímetros termoluminiscentes (TL) la alúmina (α-Al2O3) ha adquirido gran atención. La α-Al2O3 posee una sensibilidad TL que es perceptible a las concentraciones de impurezas y a las condiciones térmicas del crecimiento de sus cristales, por lo que encontrar nuevas variaciones del material permitirá aumentar su respuesta TL. Objetivo: analizar las curvas de brillo de matrices de alúmina pura sinterizadas bajo diferentes condiciones de calcinación y dopadas con cerio a concentración 0.1 % p/p (Al2O3:Ce), usando la función asimétrica logística, para calcular sus parámetros cinéticos termoluminiscentes y explicar el comportamiento del material. Materiales y métodos: polvo de alúmina bohemita fue utilizado para preparar muestras puras sintetizadas de bajo diferentes condiciones de calcinación (NALO y ALO). El cerio se introdujo mediante impregnación húmeda utilizando nitrato de cerio hexa-hidratado. El análisis estructural de las matrices se realizó mediante Difracción de Rayos X. La lectura TL se realizó en un TLD 4500. Resultados: la deconvolución obtenida en las curvas de brillo para los grupos ALO y NALO evidencia la presencia de tres y cuatro señales TL respectivamente, y de seis señales TL en la muestra Al2O3:Ce. Conclusión: los tratamientos térmicos aplicados introdujeron un cambio sustancial en la curva de brillo del material y en su cinética TL, en términos del número de trampas y de la cantidad inicial de portadores de carga atrapados. La introducción de impurezas de cerio produjo una modificación fundamental en la curva de brillo de las matrices de alúmina.
Abstract Introduction: in the search for new materials useful as thermoluminescent dosimeters (TL) alumina (α-Al2O3) has acquired great attention. The α-Al2O3 has a sensitivity TL that is perceptível to the concentrations of impurities and to the thermal conditions of the growth of its crystals, so finding new variations of the material will allow to increase its TL response. Objective: analyze the brightness curves of pure alumina matrices sintered under different calcination conditions and doped with cerium at a concentration of 0.1 % p/p (Al2O3:Ce), using the asymmetric logistic function, to calculate its thermoluminescent kinetic parameters and explain the behavior of the material. Materials and methods: boehmite alumina powder was used to prepare pure sintered samples of under different calcination conditions (NALO and ALO). The cerium was introduced by wet impregnation using cerium hexahydrate nitrate. The structural analysis of the matrices was carried out by X-ray diffraction. The TL reading was performed in a TLD 4500. Results: the deconvolution obtained in the brightness curves for the ALO and NALO groups evidences the presence of three and four TL signals respectively, and of six TL signals in the sample Al2O3:Ce. Conclusion: the applied heat treatments introduced a substantial change in the brightness curve of the material and its TL kinetics, in terms of the number of traps and the initial amount of charge carriers trapped. The introduction of cerium impurities produced a fundamental modification in the brightness curve of the alumina matrices.
Resumo Introdução: na busca por novos materiais úteis como dosímetros termoluminescentes (TL), a alumina (α-Al2O3) tem adquirido grande atenção. O α-Al2O3 possui uma sensibilidade TL que é perceptível às concentrações de impurezas e às condições térmicas do crescimento de seus cristais, portanto, encontrar novas variações do material permitirá aumentar sua resposta TL. Objetivo: analisar as curvas de brilho de matrizes de alumina pura sinterizadas sob diferentes condições de calcinação e dopadas com cério na concentração de 0,1 % p/p (Al2O3:Ce), utilizando a função logística assimétrica, para calcular seus parâmetros cinéticos termoluminescentes e explicar a comportamento do material. Materiais e métodos: o pó de alumina boehmite foi usado para preparar amostras de puro sinterizado sob diferentes condições de calcinação (NALO e ALO). O cério foi introduzido por impregnação a úmido com nitrato de cério hexaidratado. A análise estrutural das matrizes foi realizada por difração de raios X. A leitura TL foi realizada em um TLD 4500. Resultados: a deconvolução obtida nas curvas de brilho para os grupos ALO e NALO mostra a presença de três e quatro sinais TL respectivamente, e de seis sinais TL na amostra Al2O3: Ce. Conclusão: os tratamentos térmicos aplicados introduziram uma mudança substancial na curva de brilho do material e sua cinética de TL, em termos do número de armadilhas e da quantidade inicial de portadores de carga aprisionados. A introdução de impurezas de cério produziu uma modificação fundamental na curva de brilho das matrizes de alumina.
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Objective To explore the feasibility of application of the Monte Carlo method to simulate the whole body dose distribution in patients with total body X (γ) ray irradiation by comparing the actual measurement results.Methods A Monte Carlo model of a 6 MV Elekta Synergy Clinical linear accelerator was established by MCNPX.According to the relationship between the CT value and the density of the material,the CT of the ATOM physical phantom was converted into a voxel phantom for MCNPX calculation.The dose distribution of the whole body was simulated in the total body X (γ) ray irradiation.The simulated results were compared with the measurement values of the thermoluminescence dosimetry at different positions in the ATOM physical phantom to analyze the differences.Results The difference between the depth dose curve and the off-axis dose curve and the actual measurement values calculated by the 6 MV accelerator treatment head model in the water tank was less than 2％,with the maximum dose depth of approximately 1.5 cm and field size of 10 cm× 10 cm,which were consistent with the actual measurement values.The maximum difference between the simulated results at different locations in the body and the thermoluminescence dosimeter was approximately 4％,and the simulated results of MCNPX were almost in good agreement with the results of thermoluminescence.Conclusions The whole body dose distribution in patient with total body X (γ) ray irradiation can be accurately simulated by MCNPX.Monte Carlo simulation makes it possible to optimize the uniformity of the total body dose during the total body irradiation process.
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Objective To estimate the hand dose of occupational staff in five procedures of interventional radiology.Methods The thermoluminescence ring dosimeter(TLD,LiF:Mg,Ti)calibrated in dose equivalent Hp(0.07) was used to monitor the radiation dose to the both hands in five procedures of interventional radiology in four hospitals.Meanwhile,the tube voltage and current and the fluoroscopy time,accumulated doses,DAPs (Dosed-Area Product) and photographic frames were also recorded for statistical analysis(SPSS 18.0).Results In this study,five interventional procedures were monitored in 119 cases.The doses to the left and right hands of occupational personnel in the five interventional procedures were analyzed,and the difference was statistically significant (t =1.99,P＜ 0.05).The differences in the dose to the left hand and the right hand of the first operator with different interventional procedures were statistically significant (F =455.83,116.45,P＜0.01).Tube voltage,current,fluoroscopy time,and photographic frames in influence factor analysis were statistically significant (r =0.570,0.712,0.564,0.711,P＜ 0.05),indicating that four factors might affect the operator's hand doses.In addition,increasing these four factors directly led to increase in the operator's hand doses.The variables with statistical significance in the above single factor analysis were introduced into the multiple linear regression equation and the stepwise regression method was used to fit the equation.The fitting equation was y=225.763+ 1.862x1-98.125x2 (F=22.726,P＜0.05).Where,x1 was the fluoroscopy time and x2 was the photographic frames which showed that they were the main factors affecting the hand dose.Conclusions The dose to the hands of the primary operator was the highest,followed by the second operator,the assistant or nurses.The order of average doses to the hands of the primary operator was PM＞RFA＞CA＞ PTCA+PCI ＞ ITCA in the five procedures.The annual equivalent dose to primary operator's hands may exceed the dose limit for hands in practicing large amount of the PM procedures.
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Objective To evaluate the reliability of HARSHAW-3500 thermoluminescence dosimetry system by testing its performances.Methods HARSHAW-3500 thermoluminescence dosimetry system had its performances tested and evaluated according to Verification regulation of thermoluminescence dosimetry systems used in persontal and environmental monitoring forXandgammaradiation(JJG 593-2006),Testingcriteriaofpersonneldosimetryperformanceforexternalexposure (GBZ 207-2016),Specifications for individual monitoring of occupational external exposure (GBZ 128-2016) and Thermoluminescence dosimetry systems for personal and environmental monitoring (GB/T 10264-2014),such as batch homogeneity,repeatability,linearity,incidence angle response,stability,energy response and scale factor,quantity inspection,residual dose,detection limit and etc.Results Testing results of various performance indicators proved to be within the limits according to national and industrial standards.Conclusion HARSHAW-3500 thermoluminescence dosimetry system conforms to the requirements for radiation dose measurement.It is beneficial to the improvement of quality and performance of thermoluminescence dosimetry by performances analysis and evaluation.
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Objective To evaluate the reliability of HARSHAW-3500 thermoluminescence dosimetry system by testing its performances.Methods HARSHAW-3500 thermoluminescence dosimetry system had its performances tested and evaluated according to Verification regulation of thermoluminescence dosimetry systems used in persontal and environmental monitoring forXandgammaradiation(JJG 593-2006),Testingcriteriaofpersonneldosimetryperformanceforexternalexposure (GBZ 207-2016),Specifications for individual monitoring of occupational external exposure (GBZ 128-2016) and Thermoluminescence dosimetry systems for personal and environmental monitoring (GB/T 10264-2014),such as batch homogeneity,repeatability,linearity,incidence angle response,stability,energy response and scale factor,quantity inspection,residual dose,detection limit and etc.Results Testing results of various performance indicators proved to be within the limits according to national and industrial standards.Conclusion HARSHAW-3500 thermoluminescence dosimetry system conforms to the requirements for radiation dose measurement.It is beneficial to the improvement of quality and performance of thermoluminescence dosimetry by performances analysis and evaluation.
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Objective To establish the methods for measuring the dose to occupational staff's eye lens in interventional procedures with direct-reading dosimeters,and to realize the real-time monitoring of eye lens dose and warning for high dose rate,thus providing the scientific basis of the staff radiological protection in interventional procedures.Methods Direct-reading dosimeters were calibrated with personal dose equivalent HP (3).The eye lens doses for occupational staff in different kinds of interventional procedures were measured by the devices with both single-and double X-ray tubes.The data obtained fromthe direct-reading dosimeters was compared to those obtained from TLDs.Results Direct-reading dosimeters showed good linear fitting with the calibration of HP (3),and the coefficients of variation were lower than 5％.The average eye lens HP (3) for the main operator in coronary arteriography and stent implantation in brain obtained by direct-reading dosimeters were 12.0 and 24.5 μSv,respectively,whereas those obtained by TLDs were 11.9 and 22.7 μSv,respectively.The direct-reading dosimeters gave similar t~nds as TLDs do so.The direct-reading dosimeters were able to provide eye lens HP (3) in each individual interventional procedure,and to monitor the real-time dose rate as well.Conclusions The calibration of HP (3) and the data gained by direct-reading dosimeters are reliable.Therefore,the methods for real-time measurement of eye lens dose for occupational staff in interventional procedures are successfully established.
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Objective: To evaluate the level of ambient radiation in a PET/CT center. Materials and Methods: Previously selected and calibrated TLD-100H thermoluminescent dosimeters were utilized to measure room radiation levels. During 32 days, the detectors were placed in several strategically selected points inside the PET/CT center and in adjacent buildings. After the exposure period the dosimeters were collected and processed to determine the radiation level. Results: In none of the points selected for measurements the values exceeded the radiation dose threshold for controlled area (5 mSv/year) or free area (0.5 mSv/year) as recommended by the Brazilian regulations. Conclusion: In the present study the authors demonstrated that the whole shielding system is appropriate and, consequently, the workers are exposed to doses below the threshold established by Brazilian standards, provided the radiation protection standards are followed. .
Objetivo: Avaliar o nível de radiação no ambiente de um serviço de PET/CT. Materiais e Métodos: Para a determinação dos níveis de radiação no ambiente foram utilizados dosímetros termoluminescentes TLD-100H previamente selecionados e calibrados. Estes detectores foram expostos durante 32 dias em diversos pontos estrategicamente escolhidos nas dependências do serviço e nos prédios adjacentes. Após o período de exposição, os dosímetros foram recolhidos e processados. Resultados: Em nenhum dos pontos avaliados os valores medidos ultrapassaram os limites de restrição de dose para área controlada (5 mSv/ano) ou para área livre (0,5 mSv/ano) recomendados pelas normas brasileiras. Conclusão: Com este trabalho foi possível demonstrar que todas as blindagens do serviço estão adequadas e que, consequentemente, os trabalhadores, desde que seguindo as normas de radioproteção, receberão doses abaixo da dose de restrição indicada no Brasil. .
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Objective To measure and calculate the dose distribution (tissue absorbed dose) of mouth floor area while using 125I to treat sublingual gland carcinoma.Methods Phantom of head and neck was used to place the 125I radioactive seeds to simulate the sublingual gland carcinoma treatment.125I radioactive seeds of 29.6 and 25.9 MBq per seed were used as two groups,with 31 seeds in each group,and prescribed dose (peripheral matched dose) was 120 Gy.Thermoluminescence dosimetry (TLD) was used to measure the absorbed dose value in the simulated target and adjacent area.Gafchromic Eriochrome Black T (EBT) film was used to draw the dose distribution curve.Results Dose absorbed in the target area,target area center and the adjacent area one centimeter away from target reached 160 Gy,390-500 Gy,and 90-170 Gy,respectively.Dose of the skin ranged from 25 to 81 Gy,dose of mandible ranged from 7.9 to 67 Gy.No radiation cold spot was found.Conclusions 125I seeds could achieve an effective therapeutic dose distribution of the target area for sublingual gland carcinoma.Dose absorbed in the adjacent tissue is under safety limit.The radiation dose at mandible is lower,reducing the possibility of radiation damage to the bone.
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Objective To analyze the dose of radiation to medical staff during 125I seeds loading Methods The radiation dose at different distances was measured by using thermoluminescence dosimeters (TLD),and the safe range for medical person was calculated.The doses and annual accumualive doses to the medical staff were estimated.Results The dose attenuation rates were 77.61％,98.04％,98.79％,99.30％,99.71％ and 100％ at distance of 10,20,30,40,50 and 100 cm from seeds tank,respectively.The dose to fingertips,chest,lens and thyroid of doctor were 51.08,35.50,34.73 and 33.78 μGy,and the annual dose reached 12.77,8.88,8.68 and 8.45 mGy when the number of annual operations was 250.The attenuation rate was 79.60％ and 28.36％ of inside and outside lead glass,respectively.Conclusions The radiation is undetectable at 100 cm away from seeds tank in the process of loading of 125I seeds,and lead glass is necessary for radiation protection.
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Objective To investigate influence on dose distribution due to cavity and inhomogeneous structures using thermoluminescence dosimeters (TLD) and Chengdu phantoms.Methods A cavity 4 cm × 4 cm × 3 cm was made by a head and neck phantom and a lung phantom was cut into slices which were got a CT scanning and setup in a digital simulator.The TLD were pasted on edge and in the center of cavity structure and inhomogeneous structures.Treatment plans of different radiotherapy technologies were made generated and delivered on a linear accelerator.Then the TLD were read and analyzed.Results There were remarkable cavity effects of conventional single field,opposite fields and IMRT plans with 7 fields for head and neck phantom.There is similar effect in lung phantom.The more complexity the radiotherapy technology was the less cavity effect.Conclusions It is necessary to consider using more advanced radiotherapy technology or applying more fields to make treatment plans in order to decrease the cavity effect or similar effect when there are inhomogeneous structures.
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Three-dimensional thermoluminescence (TL) spectra from MgAl2O4 irradiated with UV light were measured over 300~600 K and 300~800 nm. The peak positions of TL glow curves were shifted to lower temperature with increasing the exposure time of UV light. The 476 K TL glow curve is due to the second kinetics and its activation energy and escape frequency factor are calculated to be 0.85 eV and 1.92x10(6) sec(-1), respectively. The TL spectra were split into 530 nm and 700 nm emission bands which were associated with V(2+) and Cr(2+), respectively. The linearity range of 700 nm emission band is smaller than that of 530 nm emission band, but the saturation time of 700 nm emission band is longer than that of 530 nm emission band.
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Aluminio , Cinética , Magnesio , Rayos Ultravioleta , Naciones UnidasRESUMEN
PURPOSE: Although many studies have investigated the dosimetric aspects of stereotactic radiosurgery in terms of target volume, the absorbed doses at extracranial sites; especially the lens or thyroid - which are sensitive to radiation for deterministic or stochastic effect -have infrequently been reported. The aim of this study is to evaluate what effects the parameters of radiosurgery have on the absorbed doses of the lens and thyroid in patients treated by stereotactic radiosurgery, using a systematic plan in a humanoid phantom. MATERIAL AND METHODS: Six isocenters were selected and radiosurgery was planned using the stereotactic radiosurgery system which the Department of Therapeutic Radiology at Seoul National University College of Medicine developed. The experimental radiosurgery plan consisted of 6 arc planes per one isocenter, 100 degrees for each arc range and an accessory collimator diameter size of 2 cm. After 250 cGy of irradiation from each arc, the doses absorbed at the lens and thyroid were measured by thermoluminescence dosimetry. RESULTS: The lens dose was 0.23+/-0.08% of the maximum dose for each isocenter when the exit beam did not pass through the lens and was 0.76 +/- 0.12 % of the maximum dose for each isocenter when the exit beam passed through the lens. The thyroid dose was 0.18 +/- 0.05% of the maximum dose for each isocenter when the exit beam did not pass through the thyroid and was 0.41 +/- 0.04% of the maximum dose for each isocenter when the exit beam passed through the thyroid. The passing of the exit beam is the most significant factor of organ dose and the absorbed dose by an arc crossing organ decides 80% of the total dose. The absorbed doses of the lens and thyroid were larger as the isocenter sites and arc planes were closer to each organ. There were no differences in the doses at the surface and 5 mm depth from the surface in the eyelid and thyroid areas. CONCLUSION: As the isocenter and arc plane were placed closer to the lens and thyroid, the doses increased. Whether the exit beams passed through the lens or thyroid greatly influenced the lens and thyroid dose. The surface dose of the lens and thyroid consistently represent the tissue dose. Even when the exit beam passes through the lens and thyroid, the doses are less than 1% of the maximum dose and therefore, are too low to evoke late complications, but nevertheless, we should try to minimize the thyroid dose in children, whenever possible.