An assessment of patient doses from CT scanning

• Main Author: Hashemi Malayeri, Bijan
• Published: University of Edinburgh 1998
• Subjects: 615.84
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.652211

The most common CT dosimetry approaches are standard method, Monte Carlo (MC) method and direct method. In the standard method CTDI is assessed inside a head and a body perspex phantom giving an index of the CT dose efficiency. In the MC method the patient doses are estimated by applying this mathematical technique to simulate the interaction of CT generated radiation with matter inside a mathematical model of phantom. In the direct method, measurement of organ doses is carried out directly inside an anthropomorphic physical phantom. We have developed the direct method by assessing CT axial and longitudinal dose distribution in an anthropomorphic phantom. Measurement of these dose distribution for any scanner allows us to quickly measure organ doses and effective dose, and hence patient doses for any examination protocol with a limited number of TLDs. This work describes the underlying principles and assumption of the direct CT disometry method we have developed and implemented. In addition the review of CT dosimetry provides a comprehensive and critical analysis of the methods developed to date. All dosimetry related concepts for the developed direct technique are considered. Comprehensive dose measurements were carried out to estimate the level of error involved in the developed approach. The MC approach was also used to compare the results of our proposed direct method with this commonly used method in CT dosimetry for routine examinations of some scanners. The proposed direct CT dosimetry method has now been used for several scanner models. The developed dosimetry method has been successfully implemented to assess the radiation dose resulted from various examination protocols using the recent modern CT modalities, that could not easily be investigated by other dosimetry approaches. We believe that the developed direct CT dosimetry approach overcomes many limitations imposed by other common approaches. It also provides a reliable and practical method for the assessment of patient doses from CT practices for a wide range of scan protocols.