Estimating the Absorbed Dose to Critical Organs During Dual X-ray Absorptiometry

OBJECTIVE: The purpose of this study is to estimate a patient's organ dose (effective dose) during performance of dual X-ray absorptiometry by using the correlations derived from the surface dose and the depth doses in an anthropomorphic phantom. MATERIALS AND METHODS: An anthropomorphic phantom was designed and TLDs (Thermoluminescent Dosimeters) were placed at the surface and these were also inserted at different depths of the thyroid and uterus of the anthropomorphic phantom. The absorbed doses were measured on the phantom for the spine and femur scan modes. The correlation coefficients and regression functions between the absorbed surface dose and the depth dose were determined. The derived correlation was then applied for 40 women patients to estimate the depth doses to the thyroid and uterus. RESULTS: There was a correlation between the surface dose and depth dose of the thyroid and uterus in both scan modes. For the women's dosimetry, the average surface doses of the thyroid and uterus were 1.88 (micro)Gy and 1.81 (micro)Gy, respectively. Also, the scan center dose in the women was 5.70 (micro)Gy. There was correlation between the thyroid and uterus surface doses, and the scan center dose. CONCLUSION: We concluded that the effective dose to the patient's critical organs during dual X-ray absorptiometry can be estimated by the correlation derived from phantom dosimetry.

[Estimation of absorbed dose of uterus and thyroid in women based on scan center dose in radiation with DEXA pencil-beam system]

Dual energy X-ray absorptiometery [DEXA] is presently considered as the standard technique for diagnosis of osteoporosis. Since there is still no evaluation based on the correlation between scan center dose and critical organs doses, in this study after measuring surface doses of thyroid and uterus as critical organs the correlation between scan center dose and thyroid and uterus surface doses were calculated in order to assess the rate of radiation doze to patients. In this study, 40 women underwent bone densitometry of Lunar DPX-MD system with pencil beam in two scan modes of AP spine and femur, simultaneously. Then surface doses of thyroid, uterus, scan center, and background were measured by placing 433 TLDs-400 at the surface of thyroid and uterus and also scan center. Then correlation between scan center dose and critical organs surface dose were analyzed and regression functions with significant level were determined. In AP spine and femoral scanning, average surface doses of thyroid [91 TLD-400] and uterus [84 TLD-400] were 1.88 +/- 1.36 and 1.81 +/- 1.03 micro Gy, respectively. Scan center dose in this scanning mode was 5.70 +/- 2.38 micro Gy. There was significant correlation between surface doses of thyroid and uterus and scan center dose. Therefore, regression functions and correlation coefficients were calculated. The observed significant correlation between critical organs surface dose and scan center dose showed that Lunar DPX-MD with pencil beam has very low radiation, similar to background doses