# Establishment of local diagnostic reference levels for CT colonography at a tertiary hospital

## TL;DR

This study sets local radiation dose benchmarks for CT colonography at a South African hospital and finds significant variation between scanners.

## Contribution

The paper establishes the first local diagnostic reference levels for CT colonography in a South African tertiary hospital.

## Key findings

- The Philips Ingenuity scanner exceeded UK DRLs by 82% for CTDIvol and 214% for DLP.
- The Siemens Somatom scanner achieved CTDIvol and DLP values 45% and 19% below UK DRLs.
- Local DRLs of 6 mGy (CTDIvol) and 557 mGy*cm (DLP) were established for CT colonography.

## Abstract

Diagnostic reference levels (DRLs) are an important metric in identifying abnormally high radiation doses in diagnostic examinations. National DRLs for CT colonography do not currently exist in South Africa, but there are efforts to collect data for a national DRL project.

This study investigated radiation doses for CT colonography in adult patients at a large tertiary hospital in South Africa with the aim of setting local DRLs.

Patient data from two CT scanners (Philips Ingenuity and Siemens Somatom go.Top) in the period March 2020 – March 2023 were obtained from the hospital’s picture archiving and communication system (PACS) (n = 115). Analysis involved determining the median computed tomography dose index-volume (CTDIvol) and dose-length product (DLP) values. The findings were compared with DRLs established internationally.

Ingenuity median CTDIvol was 20 mGy and DLP was 2169 mGy*cm; Somatom median CTDIvol was 6 mGy and DLP was 557 mGy*cm. Ingenuity exceeded the United Kingdom’s (UK) recommended DRLs by 82% and 214%, respectively. Somatom median CTDIvol and DLP were 45% and 19% lower than UK NDRLs.

Somatom’s tin filter and other dose reduction features provided significant dose reduction. These data were used to set DRLs for CT colonography at the hospital; CTDIvol: 6 mGy and DLP: 557 mGy*cm.

In addition to informing radiation protection practices at the level of the institution, the established local DRLs contribute towards implementing regional and national DRLs.