Uncertainties in effective dose estimation for CT transmission scan in total body PET-CT imaging with Auto mA3D tube current modulation

Background: positron emission tomography-computed tomography (pet-ct) is auseful hybrid imaging modality in the diagnosis of various malignancies. thismodality imposes almost 20 msv radiation dose to the patient. the purpose of thepresent study was to evaluate the uncertainties in calculated ct effective dose intube current modulation-activated scans by impact-dose software. materialsand methods: sixty total body dicom (30 male and 30 female) whole body pet-ctimages were selected. volume ct dose index (ctdivol) was recorded for each ofthe procedures. the image was divided into 5 regions of head & neck, chest,abdomen, pelvis and lower limbs according to special anatomical markers. effectivedoses for total body and separate organs were calculated by means of impact-dosesoftware once with global ctdivol and once with a summation of doses calculatedby 5 regional ctdivol and related scan ranges. results: the difference amongeffective doses for some organs and total body were considerable. the meanand standard deviation (sd) of the coefficient of variations (cv%) for totalbody, breast, gonads, liver, lung, red bone marrow (rbm), thyroid, kidneys,and uterus were 12.56, 11.61, 9.44, 8.1, 11.31, 5.93, 8.61, 6.03 and 12.49,respectively. uncertainties were higher for smaller patients by 19 noiseindexes while these changes were higher for bigger patients and 22 noiseindexes. conclusion: the tube current variation depends on the acquisition andpatient parameters. for measuring and reporting the total body and organs’effective doses in order to estimate the risks of ct’s radiation for total body pet-ctprocedures, the tube current variations must be considered.