engleski

Evaluation of organ doses and radiation risk for CT examination of thorax

The computed tomography examinations become very important tool in diagnosis, follow up and screening of different diseases. It is considered that CT exams contribute the most to the population radiation dose. Organ doses from CT examinations are considerably larger in comparison to corresponding conventional radiographs. According to the literature recurrence of CT scans increase the risk of cancer development as a late effect of the use of CT. The aim of our work is to measure and compare organ doses in the anthropomorphic Rando phantom and doses on the surface of the phantom during two different CT protocols of thorax ; standard CT protocol which implies 120 kV and 160 mA and low dose CT protocol using 120 kV and 30 mA. The measured doses were compared to the doses measured previously on 60 patients with lymphoproliferative disorders on the same positions as on phantom. For dosimetry measurements thermoluminescent dosimeters type LiF:Mg, Ti and radiophotoluminescent glass dosimeters type GD-352M were used. The results showed that low dose protocol yielded with the reduction of organ doses by the average factor of 5. The doses measured on the phantom were in a good agreement with average doses measured on patients for both protocols (on sternum average dose was 23 mGy and 5 mGy for standard and low dose protocol, respectively). Despite high-dose radiation, repeat CT exams in this group of patients during their lifetime are important for the diagnosis, and later for monitoring of the effectiveness of therapy. Only during therapy (1-2 years) 2-8 CT exams are needed. For these patients, which involve large number of younger and middle age patients, lifetime attributable risks (LAR) of cancer incidence for selected radiosensitive organs were calculated for both protocols. LAR is calculated using mean measured organ doses for five expositions in Rando phantom and BEIR VII risk factors which are gender and age dependent. For standard dose protocol, for 20 year old patient, organs with the highest LARs are breasts (437 cancers per 100 000 women), lungs (296 cases per 100 000 women and 127 cases per 100 000 men), thyroid (102 cases per 100 000 women), stomach (49 cases per 100 000 women and 37 cases per 100 000 men) and colon (30 cases per 100 000 men). Low dose protocol reduces LARs by the average factor of 5. Although CT exams today provide an excellent diagnostic tool they are not exempt from potential radiation risks therefore the use of low dose CT protocol as a standard are highly recommended.

computed tomography (CT); thermoluminescent dosimeters (TLD); radiphotoluminescent dosimeters (RPL); organ doses; radiation risk

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