Dosimetric study of pediatric PET/CT scan using different phantoms

Abstract

PET/CT tests are becoming increasingly important imaging tools in the noninvasive evaluation and children monitoring with known or suspected malignant diseases. This equipment allows the functional images overlapping obtained from the radiopharmaceuticals administration and anatomical images generated by X-ray beam attenuation. Although the immediate benefit to the individual patient can be substantial, the relatively high radiation doses associated with PET/CT compared with conventional exams have raised health care. This is especially concerning for children, who are more sensitive to radiation-induced carcinogenesis and have many remaining years to develop cancer. The aim of this study is evaluating and compare the doses generated by the CT scan and incorporated by the radionuclide 18F-FDG administration for 2 and 10-years old phantoms. To evaluate the CT dose, radiochromic film strips were positioned into two body phantoms, built by PMMA volumes. Two CT protocols were performed, one only for anatomical mapping and another for diagnosis. The Effective Dose from 18F-FDG was evaluated using the biokinetic model proposed by ICRP 106. The effective doses averages from CT were approximately double for 2-year phantom. The CT diagnostic protocol provides absorbed doses on average five times as high as the anatomical mapping protocol. The diagnostic CT scan is responsible for almost 60% of the effective dose in the PET/CT test, hence the importance of the tomographic protocol optimization, reducing the dose values to the minimum achievable. It is important to emphasize the importance of using the specific size of the patient when estimating the exposure dose for 18F-FDG PET/CT.