Rationale for National and Local Dose Reference Levels and Collective Effective Dose in CT

Radiation Dose Associated With Over Scanning in Neck CT

The increasing utilization of computed tomography scans exposes patients to significant amounts of radiation. One of the factors that can result in unnecessary radiation dose is scanning beyond the clinically indicated anatomical region. This study aims to assess the optimization in overscan frequency, scan length, and radiation dose following targeted educational talks aimed to address a routinely over scanned protocol; the computed tomography Neck. A targeted radiation awareness talk regarding scan adherence as a method of radiation dose optimization was delivered to all medical imaging technologists employed at a large teaching hospital. An audit of the radiation dose associated with computed tomography Neck protocols was conducted in the month before, a month after and 1 year after the awareness talk. Results show that following the radiation awareness talks there was a 15% reduction in overscan frequency, an average over scan length reduction of 33% and a 20% reduction in overall radiation dose. The targeted nature of the talk, explicitly addressing scan range in the neck region, significantly reduced radiation dose to the patients. The results of this study are effective in illustrating the potential clinical radiation dose saving from strict adherence to scan range.

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.

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.