Patient doses from CT in New Zealand and a simple method for estimating effective dose

Area of Science:

• Medical Physics
• Radiological Protection
• Diagnostic Imaging

Background:

• Computed tomography (CT) scanning is a significant contributor to patient radiation exposure in medical imaging.
• A 1992 survey in New Zealand indicated CT accounts for 81 microSv per capita annually, comprising 17% of the total medical irradiation dose.
• Routine surveys of CT scanners now include patient dose estimations by the National Radiation Laboratory (NRL).

Purpose of the Study:

• To assess patient radiation doses from CT scanning in New Zealand.
• To establish methods for estimating effective dose from CT scanners, particularly when normalized organ dose data are unavailable.
• To enable the formulation of reference dose levels for CT scanners.

Main Methods:

• Utilizing normalized organ dose data from Monte Carlo studies for specific CT scanner models.
• Employing the computed tomography dose index (CTDI), measured at 1 cm depth in Perspex phantoms and normalized for mAs, to estimate effective dose for scanners lacking normalized data.
• Comparing individual scanner doses against derived reference dose levels.

Main Results:

• CT scanning represents a substantial portion of medical radiation dose.
• CTDI can serve as a reliable proxy for estimating effective dose when direct data are absent.
• The developed methods allow for the establishment of comparative dose benchmarks.

Conclusions:

• Effective dose estimation from CTDI is a viable approach for radiological protection.
• Reference dose levels derived from CTDI estimates can guide quality assurance and dose reduction strategies.
• Continued monitoring and dose assessment are crucial for optimizing patient safety in CT examinations.