Establishment of national diagnostic reference levels (NDRL) for computed tomographic (CT) procedures in Sri Lanka: first nation-wide dose survey.

The main purpose of this study was to establish the national diagnostic reference levels (NDRLs) for common CT procedures for the first time in Sri Lanka. Patient morphometric, exposure parameters, and dose data such as volume CT dose index (CTDIvol) and dose length product (DLP) were collected from 5666 patients who underwent 22 procedure types. The extreme dose values were filteblue before analysis to ensure that the data comes from standard size patients. The median of the dose distribution was calculated for each institution, and the third quartile value of the median distribution was consideblue as the NDRL. Based on the inclusion and exclusion criteria, 4592 patients data from 17 procedure types were consideblue for NDRL establishment covering 41\% of the country's total CT machines. The proposed NDRLs based on CTDIvol and DLP for non-contrast (NC) head:82.2 mGy/1556 mGy.cm, contrast-enhanced (CE) head: 82.2 mGy/1546 mGy.cm, chest-NC:7.4 mGy/350 mGy.cm, chest-CE:8.3 mGy/464 mGy.cm, abdomen NC:10.5 mGy/721 mGy.cm, abdomen arterial (A) phase:13.4 mGy/398 mGy.cm, abdomen venous (V) phase:10.8 mGy/460 mGy.cm, abdomen delay (D) phase:12.6 mGy/487 mGy.cm, sinus NC:30.2 mGy/452 mGy.cm, lumbar spine--NC:24.1 mGy/1123 mGy.cm, neck-NC:27.5 mGy/670 mGy.cm, high resolutions CT (HRCT) of chest:10.3 mGy/341 mGy.cm, kidney, ureter and bladder (KUB) NC:19.4 mGy/929 mGy.cm, chest to pelvis (CAP) NC:10.8 mGy/801 mGy.cm, CAP-A:10.4 mGy/384 mGy.cm, CAP-V:10.5 mGy/534 mGy.cm and CAP-D:16.8 mGy/652 mGy.cm. Although the proposed NDRLs are comparable with other countries, the observed broad dose distributions between the CT machines within the country indicate that dose optimisation strategies for Sri Lanka should be implemented for most of the CT facilities.