Effective doses to patients undergoing thoracic computed tomography examinations

The purpose of this study was to investigate how x-ray technique factors an d effective doses vary with patient size in chest CT examinations. Techniqu e factors (kVp, mAs, section thickness, and number of sections) were record ed fur 44 patients who underwent a routine chest CT examination. Patient we ights were recorded together with dimensions and mean Hounsfield unit value s obtained from representative axial CT images. The total mass of directly irradiated patient was modeled as a cylinder of water to permit the computa tion of the mean patient dose and total energy imparted for each chest CT e xamination. Computed values of energy imparted during the chest CT examinat ion were converted into effective doses taking into account the patient wei ght. Patient weights ranged from 4.5 to 127 kg, and half the patients in th is study were children under 18 years of age, All scans were performed at 1 20 kVp with a 1 s scan time. The selected tube current showed no correlatio n with patient weight (r(2) = 0.06), indicating that chest CT examination p rotocols do not take into account for the size of the patient. Energy impar ted increased with increasing patient weight, with values of energy imparte d for 10 and 70 kg patients being 85 and 310 mJ, respectively. The effectiv e dose showed an inverse correlation with increasing patient weight, howeve r, with values of effective dose for 10 and 70 kg patients being 9.6 and 5. 4 mSv, respectively. Current CT technique factors (kVp/mAs) used to perform chest CT examinations result in relatively high patient doses, which could be reduced by adjusting technique factors based on patient size. (C) 2000 American Association of Physicists in Medicine.