MEASUREMENT OF ENTRANCE SKIN DOSE AND ABSORBED DOSE TO DIFFERENT ORGANS IN DUAL-ENERGY X-RAY ABSORPTIOMETRY SCANS USING THERMOLUMINESCENCE DOSIMETRY.

Thermoluminescence dosimetry is considered as an effective method in estimating the absorbed doses to organs in different imaging modalities. The present study focuses on dosimetry in dual-energy X-ray absorptiometry scans, for patients, and phantoms in various imaging centres. The cubical LiF (Mg, Ti) thermoluminescence dosemeters were inserted inside the holes of the Rando phantom slabs, to measure the absorbed dose to different organs in the whole body and lumbar scans. According to the results the maximum entrance skin dose was found to be 202.06 µGy for Hologic discovery W, which uses the fan beam scanning mode. The Norland XR-800 device took the scans with a much lower dose, as it uses the pencil beam for scanning the patients. The results of the study show that the radiation beam type, patient thickness, imaging technique and scan time may affect the radiation dose received by patient.

VARIATION SIMULATION OF RADON CONCENTRATION IN THE TISSUES AND ORGANS OF THE BODY BY AN ELECTRICAL CIRCUIT.

In this study, a new model based on electric circuit theory has been introduced to simulate the dynamics of radioactive chemically inert gases in the human body. For this manner, it is assumed that inert gas is transported through the body to various organs via the blood stream. In this simulation, a voltage source is equivalent to gas generation in the atmosphere, the conductivity is equivalent to the cardiac output of the organ, the capacitor capacitance is equivalent to the volume of blood or tissue and voltage across a capacitor is equivalent to the gas concentration in air or blood or a tissue. This simulation can be used to study the dynamics of any inert gas whose partition coefficients are known. We use this simulation to study the dynamics of radon in human body. The physiologically based pharmacokinetic (PBPK) model that describes the fate of radon in systemic tissue has been used for this simulation. Using this simulation, the effective dose equivalent resulting from inhalation of radon has been estimated. The calculated values agree with the previously reported value. Also, using the model, it has been shown that after inhalation of radon gas, absorbed dose has been decreased in different tissues by increasing the inhalation rate without radon. So that, by doubling the inhalation rate and the rate of cardiac output, the value of the absorbed dose has been decreased 11.88% in the adipose tissue, 25.49% in the red marrow tissue and 20.3% in the liver organ.

Processing the spike- like radon anomaly exhalation from the soil surface by electrical model.

A model based on electric circuit theory has been developed to simulate the radon concentration in an accumulator chamber from the soil surface. This model simulates the radon generation on earth as a voltage source, diffusion to the earth's surface as an electrical conductor, the convection flux of radon as an electrical current source and radon concentration in a chamber as a voltage across a capacitor. We use this model for processing the spike like an anomaly of radon. This paper offers a radon anomaly spike like has a duration time less than several hours. It is shown that the time constant of a general setup is very large with compare the duration time of a spike like anomaly. In this condition the actual shape of radon flux in earth is different from radon measuring concentration in the chamber. With regard to this model it is shown that the rise time of measured radon concentration must be equal the duration time of a spike like anomaly and the fall time must have a constant time equal the five times of constant time of our setup and it is independent of the shape of the anomaly.