SU-E-I-47: Comparison of Risks for Two Medical Imaging Procedures

Radiologists may need to decide which type of image procedure is most appropriate for a particular patient. One factor relevant in making this decision is the relative risk of secondary cancers due to each relevant procedure. Differences in the risk posed by each method are not just due to the total radiation dose imparted by each procedure, but also the distribution of absorbed dose across various organs in the imaging procedure. Two imaging procedures with the same total radiation dose may pose different risks of differential sensitivity to radiation across organs.

New methods of radiation dosimetry enable us to estimate the dose distribution across organs in individual patients. We propose a measure of the relative risk of two medical imaging procedures derived from the hazard function of cancer incidence. The relative risk measure is shown to approximately equal to a weighted sum of the dose difference in each organ. The weights are proportional to organ specific incidence rates. The measure is also sensitive to factors such as the patient's age at exposure to radiation, the attained age and gender, as well as the incidence characteristics of the population to which the patient belongs. We propose to quantify the effects of these factors using information from publically available SEER database for US based patients as well as the LSS study of atomic bomb survivors. The method is illustrated by application to a study comparing chest and abdominal CT scans for a group of pediatric patients.

Fig. 1 shows higher absolute relative risk for those exposed at younger ages, with chest scans being riskier for females while abdominal scans were riskier for males. At higher ages, the relative risk is approximately equal.

Relative risks can quantify risks comparisons between imaging procedures.