Dose distribution in organs: patient-specific phantoms versus reference phantoms
2017
Introduction : The absorbed dose received by an exposed individual cannot be directly measured. Therefore, simulations are performed using Computational Exposure Models. The reference phantom recommended by International Commission on Radiological Protection (ICRP) are consistent with the information provided by ICRP 89 about the reference anatomical and physiological parameters for male/female human bodies. However, patients rarely fit to these parameters, which can lead to a disparity of the real dose received during the examination. This paper aims to compare distribution of dose in organs of male/female specific-phantoms and reference phantoms. Methods : The absorbed dose estimation was performed for brain, lungs, liver and kidneys using the EGSnrc Monte Carlo code and a parallel source algorithm. The choice of the number of stories more suitable to obtain satisfactory dosimetric results was based on the statistical uncertainty using the coefficient of variance function. In this work were used a patient-specific phantom for a man (1.73m / 70.3kg) and another for a woman (1.63m / 60.3kg) which are similar to the reference phantoms. The comparison of the absorbed dose from each phantom gender was performed using the relative error. Results : The results were expressed in terms of conversion coefficients to brain, lungs, liver and kidneys. The greatest absolute relative error between the organs of the patient-specific phantom and the reference phantom was 22.92% in the liver and 62.84% in the kidneys, respectively for man and woman. Conclusion : There are errors that cannot be disregarded. These differences occur since the reference phantoms are based on Western European and North American population, not including the diversity of the Brazilian population. This paper shows the need for a specific study for each patient or for the population of other countries, since there are different body types, which affects the distribution of the dose in their organs.
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