Journal des méthodes de diagnostic médical
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Patient Dose Audit in Computed Tomography at Cancer Institute of Guyana

Ramzee Small, Sayan Chakraborty and Petal Surujpaul

Objective: This study is the first investigation on computed tomography (CT) unit in Guyana at the Cancer Institute of Guyana (CIG), aimed at performing an audit on the radiation dose estimated by the GE LightSpeed QXi CT unit for common computed tomography examinations.

Method: A RaySafe X2 CT calibration detector were used to obtained measurements for common CT examinations (head, neck, chest, abdomen, pelvis, upper extremity and lower extremity) done in free air as the control (36 data) and also with patients (35 data). Patient’s measurement was limited to the head, chest, abdomen and pelvis CT examinations. Exposure/electro-technical parameters and dose metrics (CTDI_vol, DLP) were recorded and the k-coefficient conversion factor established by National Radiology Protection Board (NRPB) was used to calculate the effective dose associated with each examination.

Results: The results indicated that the CT unit overestimated the dose for patient measurements and underestimated the dose for measurements taken In-Air with the exception of the head protocol which showed overestimation with the patient measurements. Both over-and underestimation were documented for the neck protocol. Comparison of estimated dose between published data shows that there are variations in techniques and radiation dose across institution for similar examinations and that the protocols reported by CIG documented an overall higher effective dose.

Conclusion: The variation in estimated effective dose reported by CIG, is as a consequence of differences in CT scanner design and examination protocols.