Establishment of national diagnostic reference levels (DRLs) for radiotherapy localisation computer tomography of the head and neck.

Aim: The aim of this research is to establish if variation exists in the dose delivered for head and neck (HN) localisation computed tomography (CT) imaging in radiation therapy (RT); to propose a national diagnostic reference levels (DRLs) for this procedure and to make a comparison between the national DRL and a DRL of a European sample.

Background: CT has become an indispensable tool in radiotherapy (RT) treatment planning. It is a requirement of legislation in many countries that doses of ionising radiation for medical exposures be kept 'As Low As Reasonably Achievable'. There are currently no dose guidelines for RT localisation CT of the HN.

Materials and methods: All RT departments in Ireland and a sample of European departments were surveyed. Dose data on CT dose length product (DLP); dose index volume (CTDIvol); current time product; tube voltage and scan length was acquired for ten average-sized HN patients from each department. DRLs were proposed for DLP and CTDIvol using the rounded 75th percentile of the distribution of the means.

Results: 42% of Irish departments and one European department completed the survey. Significant variation was found in the mean DLP, CTDIvol and scan lengths across the Irish departments. The proposed Irish DRL is 882 mGy cm and 21 mGy and the European department DRL is 816 mGy cm and 21 mGy, for DLP and CTDIvol, respectively.

Conclusions: Variation exists in doses used for HN RT localisation CT. DRLs have been proposed for comparison purposes with the aim of dose optimisation.