Depth dose of critical organs of phantom based on surface dose exposed with Dual X-ray absorptiometry: pencil beam using TLD dosimetry

Introduction: Dual X-ray absorptiometry (DXA) is one of the most widely used techniques for non-invasive assessment of bone status. Radiation dosimetry is well established technique for pencil beam and fan beam DXA system, for the assessment of the surface absorbed dose. No published assessment of the absorbed dose for the various depths of the critical organs such as the thyroid and uterus was found. Therefore, in this study, we measured the surface dose and depth dose of critical organs to determine the correlation between the depth dose and the surface dose. Materials and Methods: A Lunar DPX-MD (pencil beam) system was used in this study. An anthropomorphic phantom was designed. AP spine and femur scan modes were used to measure the surface and depth doses of the thyroid left and right lobes and uterus in various deeps and scan centers. TLDs-400 were placed at the surface, near the source and also inserted at different depths in thyroid and uterus of the anthropomorphic phantom. Absorbed doses were measured on the phantom for AP spine and femur scans. The correlation between the absorbed dose and the depth was found using the linear regression analysis. Results: There was no significant correlation between the depth dose and the scan center dose except in the femur scan. AP spine effective dose were calculated as 0.064, 0.059, 0.061 and 0.242 µSv for thyroid left, right lobes, uterus and ovary, respectively. Conclusion: It is concluded that there is significant correlation between the surface and the dose of various depths of the scanned sections.