Establishment of national diagnostic reference levels for breast cancer CT protocols in radiation therapy.

OBJECTIVE: To establish whether CT dose variation occurs in breast cancer localization procedures between radiation therapy (RT) centres in Ireland and to propose diagnostic reference levels (DRLs) for this procedure.

METHODS: All RT centres in Ireland were invited to participate in a dose audit survey, providing data on the CT dose index volume (CTDIvol), dose-length product (DLP), current-time product (mAs), tube potential, scan length, slice thickness, scanning margins, use of automated exposure control (AEC) and scanner technology for 10 patients with breast cancer who were average sized. DRLs were derived for each dose descriptor by calculation of the rounded 75th percentile of the distribution of mean doses.

RESULTS: Data were returned for 60 patients from 6 RT centres (50% response rate). Significant variation in mean CTDIvol and mean DLP was observed between centres (p < 0.0001). Mean scan lengths and mean mAs differed significantly between centres (p < 0.0001). Tube potential was 120 kV for all sequences across centres. AEC was employed in all but one centre. Proposed DRLs for breast localization are 26 mGy and 732 mGy cm for CTDIvol and DLP, respectively.

CONCLUSION: CT dose variation occurs between centres, establishing a need for optimization. DRLs for breast cancer localization have been proposed with the potential for reduction in CT dose.

ADVANCES IN KNOWLEDGE: This article provides the first reported DRL for breast cancer CT localization procedure in RT and can be used as a benchmark for comparison for other RT centres.