Conventional and spiral CT dose indices in Yazd general hospitals, Iran

  ABSTRACT   Background: While the benefits of Computed Tomography (CT) are well known in accurate diagnosis, those benefits are not risk free. CT is a device with higher patient dose in comparison with other conventional radiological procedures. Is the reduction of exposures by requiring optimization of CT procedures [a principle concern in radiological protection]? In this study, the radiation dose of conventional and spiral CT were investigated and compared with European Commission Reference Dose Levels (EC RDLs).   Materials and Methods: The dosimetric quantities proposed in the European Guidelines (EG) for CT are Weighted Computed Tomography Dose Index (CTDIW) for a single slice for axial scanning or per rotation for helical scanning and Dose-Length Product (DLP) for a complete examination. The patient-related data were collected for brain, neck, chest, abdomen and pelvis examination s in each scanner. For each type of examination, 10 typical patients were randomly included. CTDI with an active length of 10cm was measured in two CT scanners by using UNFORS (Mult-O-Meter 601) in head and body phantom (PMMA) with 16 cm and 32 cm in diameter respectively. Mean values of CTDIW , DLP and Effective Dose(ED) were estimated for those examinations .   Results: CTDIW had a range of 15.8-24.7 mGy for brain, 16.1-30.6mGy for neck, 6.8-9.2 mGy for chest, 6.8-9.8 mGy for abdomen and pelvis. DLP had a range of 246.4-397.7 mGy.cm for brain, 104.6-262.2 mGy.cm for neck, 135-248.4 mGy.cm for chest, 187-298.9 mGy.cm for abdomen and 197.2-319.4 mGy.cm for pelvis. The mean values of effective dose were 0.74 mSv for brain, 0.9 mSv for neck, 3.1 mSv for chest, 3.7 mSv for abdomen and 5 mSv for pelvis.   Conclusion: The obtained results in this study have shown that CTDIW and DLP are lower than EC RDLs and other studies, in other words , the performance of all scanners has been satisfactory as far as CTDIw and DLP are concerned. The CTDIW and DLP in the conventional CT are higher than the spiral CT values . With regard to ALARA principle, for the establishment of reference dose levels, the radiation dose with spiral CT scanners should be taken into account.