Population and Sample:
In small countries with less than 50 facilities literature recommends inclusion of at least 30-50% of these facilites for the purpose of DRL establishment [5].
A stratifeid,
random sample of 12 clinical sites was generated for the current study,
representing 54% of the Irish hospitals that carry a moderate to high paediatric caseload.
This sample included two large dedicated paediatric centres,
seven large general hospitals and three small general hospitals to reflect the nature of the Irish national paediatric imaging service.
Dose Quantities and Projections
Dose Area Product (DAP) is a recognised measure of paediatric patient dose for deriving DRLs [4],
and is readily available on NIMIS. DAP dose data were collected for paediatric antero-posterior (AP)/ postero-anterior (PA) chest,
AP abdomen,
AP pelvis,
AP and lateral cervical spine and AP and lateral lumbar spine.
These paediatric examinations are amongst the most common in paediatric projection radiography and contribute the highest potential doses to radiosensitive organs [1,4].
Patient groups
Weight is considered an optimal method of representing groups of children that addresses the considerable size range of paediatric patients [5].
Literature reports patient age groupings are routinely used when weight is not available.
Weight information is not available in NIMIS but patient date of birth and hence patient age can be identified. Age groups of <1,
1<5,
5<10 and 10<16 are recommended in literature and were applied in the current study.
These groups are reported in DRL studies conducted in Ireland [1] and Portugal [6].
DRLs arising from the current study can therefore be directly compared with previous survey data.
Data Collection
Access to NIMIS was granted by each clinical site.
Data retrieval aimed for 30 DAP doses per age group for each projection,
but for less frequently performed examinations,
10 DAP doses was taken as the absolute minimum for inclusion in the study,
as per published advice [5,4].
Data retrieval was limited to one retrospective year to maintain currency and relevance.
Equipment details including tube filtration,
quality assurance procedures,
receptor type and vendor information were also collected from each hospital since equipment can influence DAP dose distributions [7].
DRL Calculation
For each projection,
the DAP doses for each age group in each individual hospital were ranked and the median DAP was calculated.
Median is recommended as the measure of central DAP tendency as it is less affected by outliers in the rank [5].
For each projection and age group,
the 12 median values from the 12 hospitals were then ranked.
The 75th centile of the ranked median values is recommended for DRL calculation,
and thus this value is proposed as the national DRL for each age group for chest,
abdomen pelvis and spine examinations [5].