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

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