Towards establishment of the national reference dose levels from computed tomography examinations in Tanzania.

Without the knowledge of reference dose levels (RDLs) from computed tomography (CT) examinations, the optimal dose to patients undergoing CT examinations cannot be realised. The aim of this study was therefore to assess the radiation dose levels from CT examinations according to reference dose quantities proposed by the European Commission (EC) guidelines. The dosimetric quantities proposed in the EC for CT are weighted CT dose index (CTDI(w)) for a single slice and dose-length product (DLP) for a complete examination. The RDLs from five common CT examinations were obtained from eight hospitals. The RDLs in terms of CTDI(w) and DLP were estimated from measurements of CTDI in standard phantoms using typical exposure parameters. Mean values of CTDI(w) for head and lumbar spine had a range of 25-77 and 18-47 mGy, respectively, while those for chest, abdomen and pelvis had a range of about 11-25 mGy, respectively. Mean values of DLP for head, chest and abdomen had a range of 610-1684, 496-992 and 717-1428 mGy cm, respectively, while those for lumbar spine and pelvis had a range of 200-382 and 526-1302 mGy cm, respectively. Wide variations of mean CTDI(w) and DLP values among hospitals observed for similar CT examinations were mainly attributed to the variations of CT scanning protocols and scanner types. The mean CTDI(w) values per examination for almost all hospitals were below proposed RDLs, while the mean DLP values per examination were almost all above the proposed RDLs for all except one hospital. These were mainly influenced by the large scan length used in Tanzanian hospitals. In order to achieve the required level of dose for establishment of the national RDLs, it was concluded that further investigation of optimization of scanning protocols is needed.