Absorbed doses from spiral CT and conventional spiral tomography: a phantom vs. cadaver study

For several radiological examinations, a clinician can select between conve ntional and spiral computed tomography. Using both techniques, this study a imed at evaluating the difference in absorbed doses when examining a single lateral jaw segment in a human cadaver head and Rando phantom. The present study involved the placement of thermoluminescent dosimeter (TLD) chips (G R-200) in the thyroid gland, and bilaterally, in the parotid and submandibu lar glands and the lenses of the eyes in both a human cadaver and a Rando p hantom at corresponding locations. Consecutive conventional spiral tomograp hic examinations were carried out in both the left upper and lower premolar area, using a Cranex TOME(R) multifunctional unit. Each examination consis ted of 4 slices with a 2 mm slice thickness and exposure parameters of 57 k V, 56 seconds and 1.6-2.0 mA. Regarding spiral computed tomography (CT), a Somatom Plus S(R) scanner (Siemens, Erlangen, Germany), with a slice thickn ess of 1 mm with settings at 120 kV and 165 mA, was used on both phantoms a nd separately in the upper and lower jaw. With conventional tomography, the findings of the present study showed that the parotid and submandibular gl ands on the side near the X-ray tube received the highest dose, both for th e cadaver head (doses ranging from 0.5 to 1.3 mGy) and the phantom (doses r anging from 0.6 to 2.6 mGy). For CT of the upper jaw, the highest doses wer e delivered to the parotid glands with an average absorbed dose of 9.2 and 10.6 mGy for the cadaver head and phantom, respectively. The submandibular glands received the highest doses during CT examination of the lower jaw wi th an average of 7.8 and 12.9 mGy for the cadaver head and phantom, respect ively. It appears from the present investigation that if small edentulous r egions are examined, radiation doses during conventional tomography remain much lower than during CT imaging. However, when multiple tomographic cuts are required, a spiral CT examination can replace a series of conventional examinations, especially in cases such as the rehabilitation of an edentulo us upper jaw or a more complex surgery.