CT Users Group

Paul Charnock

IRS Ltd.

Abstract

There are a number of SPECT/CT units in the North-West England. Historically, Nuclear Medicine Physicists deal with these units in terms of treatment planning and QA with diagnostic physicists only involved in QA of the CT component. Recent discussions have highlighted the need to consider the effective dose contributed by the CT component, as the SPECT component is well established.

In order to attempt this, the displayed CTDI values were first confirmed to be accurate with use of the ImPACT CTDI phantom and a pencil ionisation chamber. With displayed CTDI values confirmed as correct, the CTDI values were converted first to DLP for a 20cm length and then to Effective Dose using factors from NRPB-W67.

Resultant Effective Doses were then compared between manufacturers and with typical doses for similar diagnostic examinations from NRPB-W67.

It is concluded that resultant Effective Doses can be used as baseline values for these units, however further work is required to establish accurate conversion factors for the clinical protocols before they can be combined with the SPECT effective dose to give an overall risk factor for a patient undergoing SPECT/CT.

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