Assessment of skyshine photon dose rates from 9 and 18 MV medical linear accelerators

Background: skyshine describes the radiation scattered by the atmosphere above a LINAC facility to a point on the ground. The aim of this study was to measure the skyshine photon dose rates from two different [9 MV and 18 MV] medical linear accelerators

Materials and Methods: the photon beam was directed upward [180 degree gantry position], with a maximum photon field size [40 × 40 cm2] at the isocenter. Measurements were obtained around the external points selected outside the room facilities at a horizontal distance from the target by the calibrated RDS-110 survey meter at four points around the isocenter

Results: the measured values of the skyshine photon exposure rates at four points for 9 MV and 18 MV were 0.6, 0.5, 0.5, and 0.4 microSv/h, and 0.6, 0.4, 0.4, and 0.5 micro Sv/h, respectively. All the measured skyshine photon exposure rates were lower than the values recommended by NCRP 147

Conclusion: there is a poor agreement between the measured and the calculated values; therefore it seems that caution is needed while using the equations available in NCRP 147 or 151

[Evaluation of the natural gamma radiation level in residential zones and determination of annual effective exposure dose in the residents of Hamadan province, Iran, 2012]

Human is always exposed to natural background ionizing radiation which may have harmful effects; therefore, measurement of the natural background radiation is important. In this study, was measured the dose of effective natural background gamma radiation in indoor residential zones of Hamadan Province. In this cross-sectional study, we selected four stations along the main geographic directions and one in the center of city for measurement of the indoor dose rate in each of the cities in Hamadan Province. Based on the household numbers, some houses were selected randomly in every station and natural background indoor dose was measured by using RDS-110 survey meter. Then, using the results of our previous study about measuring the level of outdoor natural gamma radiation in this province, we determined the level of annual effective exposure dose from natural gamma radiation in Hamadan residents. In Hamadan province cities, maximum and minimum indoor natural background radiation [gamma ray] belonged to Razan City [1.41 +/- 0.079 mSv] and Asadabad City [0.955 +/- 0.044 mSv], respectively. Mean annual equivalent indoor dose in Hamadan Province was 1.20 +/- 0.070 mSv. Also the maximum indoor natural background radiation dose [gamma ray] in the buildings with the age of more and less than 25 years were 1.42 +/- 0.219 mSv and 1.44 +/- 0.149 mSv, respectively. According to the results of this study and our previous study about outdoor gamma natural background radiation, the annual effective dose in Hamadan Province residents was 0.83 mSv. According to the results of this study, it seems that annual effective equivalent dose due to indoor gamma radiation in Hamadan Province exceeded the mean external exposure amount reported by UNSCEAR [0.5 mSv]. Also the annual effective dose due to gamma background radiation in Hamadan Province residents is 0.83 mSv, which is higher than the global average [0.48 mSv] reported by UNSCEAR - 2000. Therefore epidemiological studies to assess the prevalence of chronic diseases associated with natural radiation exposure among Hamadan Province residents are recommended

[Evaluation of radiation dose received by operating room personnel during radiological procedures]

Utilization of ionizing radiation in some surgery operations [especially orthopedic operations] is inevitable. One of the main occupational hazards of physicians and other personnel could be radiation exposure risks. This study aimed to evaluate the exposure doses received by operating room personnel in such surgery operations. 30 personnel of operation room in university affiliated hospitals of Hamadan city [excluding physicians and nurses] were studied as they received radiation doses. 3 TLD [thermoluminescent dosimet ers] chips were fixed on the apron of each staff member. To estimate the high risk examinations, staff members also completed a questionnaire about the type and number of the radiological examinations that they had participated. Minimum and maximum level of doses received by the participants were between 0.24 and 0.56 mSv in a four month period. Therefore, amount of annual doses received by the personnel would be between 0.73 and 1.7 mSv, respectively [without reduction of background radiation]. As the accuracy of TL dosimeters is normally about 0.1 mSv; therefore, it can be claimed that the received doses by the personnel was very low and comparable with background radiation. The results indicated that the radiation doses received by operating room personnel were very low. They were less than maximum predicted doses reported by the International Commission of Radiation Protection. However, the use of dose recording systems for awareness about absorbed doses beyond permitted limits is necessary

[Comparison of absorbed skin dose received by patients in cone beam computed tomography, spiral and conventional computed tomography scanning]

The evaluation of absorbed dose received by patients could give useful information for radiation risk estimation. This study was performed to compare the entrance skin dose received by patients in cone beam computed tomography [CBCT], conventional and spiral computed tomography [CT]. In this experimental study, 81 calibrated TLD chips were used. The TLD chips were placed on facial, thyroid and end of sternum skin surface in patients referred for CT of the paranasal sinuses [3 TLD chips for each area] to estimate the absorbed dose received by central part of radiation field, thyroid and out of field areas, respectively. The data were analyzed using one-way ANOVA and Tukey tests. The dose delivered to the center of irradiated field was about 0.79 +/- 0.09 mGy in CBCT technique compared with 16.31 +/- 3.71 and 18.84 +/- 4.12 mGy for spiral and conventional CT, respectively. The received dose by the out of field areas was about 54 percent of central area dose. There was statistical significant relationship between the imaging modalities and absorbed dose received by patients [P=0.016]. The least absorbed dose was for CBCT and the greatest dose was for conventional CT imaging technique. The dose delivered to central area of irradiated field in conventional and spiral CT imaging modalities was about 24 times greater than of that in CBCT. Also, the highest received dose was for central areas of radiated field and the lowest dose was for the out of field areas

Comparison of Singh index accuracy and dual energy X-ray absorptiometry bone mineral density measurement for evaluating osteoporosis

The Singh index is an inexpensive simple method to evaluate bone density, commonly used to assess osteoporosis is based on the radiological appearance of the trabecular bone structure of the proximal femur on a plain antero-posterior [AP] radiograph. The purpose of this study was to compare between Singh index and bone mineral density measurement using dual energy X-ray absorptiometry [DXA]. Three orthopedists evaluated radiographs of 72 patients suspected with osteoporosis. The inter-observer agreements of the Singh index were obtained by using kappa statistics. The bone mineral density [BMD] of proximal femur was measured by DXA in all patients, and then the BMD results were compared with those of Singh index by using reference radiographic charts of the Singh index method. Dual-energy X-ray absorptiometry was used to measure bone mineral density. A Norland XR46 system was used for the investigations. The inter-observer agreement kappa values were 0.01, 0.07 and 0.09 [mean value: 0.05] and the strength of the observer agreements was negligible. The obtained osteoporosis prevalence among the studied patients was 38.9%.The inter-observer variation was large, there was no any correlation between the Singh index and bone densitometry. So, the index cannot be used; for evaluating and osteoporosis diagnosis, because of its low reliability

Assessment of bone mineral density with dual energy X-ray absorptiometry in pre- and post-menopausal women

Osteoporosis is a chronic disease that contributes substantially to decrease physical activity and decline in the quality of life. Osteoporosis can be diagnosed easily with the use of dual-energy X-ray absorptiometry [DXA] equipment. The aim of this study was to investigate the magnitude of bone loss on proximal femur and lumbar spine LS in pre- and post-menopausal women from Isfahan Osteoporosis Diagnosis Center [IODC] since 2005. Bone mineral density [BMD] measurements using DXA have been performed at IODC. 185 pre-menopausal and 174 early post-menopausal women were selected randomly. A Norland XR46 system was used for the investigations. The student t-test was done to find the difference between the T-scores of the femoral neck [FN] and lumbar spine [LS] in pre- and post-menopausal women. Mean BMDs for the FN and LS in pre-menopausal women were 0.859 +/- 0.136 and 1.012 +/- 0.161 and in post-menopausal women were 0.816 +/- 0.119 and 0.919 +/- 0.140, respectively. Long-term BMD CVs of 1.0% and 1.2% for the LS and FN were found, respectively. The differences between the FN and LS for pre- and post-menopausal women were t = - 9.02, p < 0.05 and t = -3.50, p < 0.05, respectively. In spite of, the reported lower BMD T-scores for the LS compared with the FN for women, we found that the FN had significantly lower T-score than LS for both pre- and post-menopausal women