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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 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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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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Aluminum , Kinetics , Magnesium , Ultraviolet Rays , United NationsABSTRACT
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.