Dual-slice spiral scanner: Doses delivered during thoracic and abdominal examinations

A new dual-slice spiral scanner (PICKER-ELSCINT CT-Twin) is dedicated to thoracic and abdominal examinations being implanted in our hospital. A dosimetric study was performed in order to evaluate the dose delivered to different body parts (skin, mid-thickness, lungs, etc) as a function of the CT parameters used for the most current protocols (determined by a statistical study including 250 patients). The aim was to establish a simple method allowing a quick estimation of the dose delivered to the patients knowing CT parameters used (kV, mAs/slice, pitch, slice thickness). Dosimetric measurements were performed using an Alderson anthropomorphic phantom and Li2B4O7:Cu TL powder (chosen because of its flat energy response in the studied energy range). Results obtained (precision: ± 5%) have shown that doses are dependent on the number of scans, mAs/slice and kV but very little dependent on slice thicknesses. For instance, doses at the abdomen center of patients irradiated at 120 kV vary from 0.7 to 1.7 cGy for mAs varying from 133 to 333 with a variation less than 10% when one passes from 'pitch 0.7- thickness 8 mm' to 'pitch 2- thickness 13 mm'. Other charts and tables deduced from experimental results will be presented. They show that doses delivered by helical computed tomography being relatively high, the number of procedures and section per procedures should be carefully adapted to the age of patients and the underlying pathology. (author)