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Patient Safety: Balancing Risk Versus Benefit [continued]


ICACTL DIVISION NEWS \| Summer 2008	<<BACK \| 1 \| 2

The balance of medical necessity with potential risk is a crucial component to quality patient care and is therefore addressed and evaluated through several aspects of the ICACTL accreditation program. Participating laboratories should be particularly familiar with Section 2 of The ICACTL Standards, Part 2, CT Laboratory Operations - Computed Tomography Testing, where guidelines related to Quality Assurance are included. As detailed, a Quality Assurance Committee must be in place to provide oversight and be responsible for the development, implementation and evaluation of these processes and for incorporating corrective actions for improvement, where deficiencies are noted. The Quality Assurance Committee must take every precaution necessary to ensure that for patients who undergo CT imaging, the benefits outweigh the potential risk. The goal is to keep radiation doses to patients as low as reasonably achievable or the ALARA recommendations of the Radiological Society of North America. Within Section 4 of The ICACTL Standards, Part 1, CT Laboratory Operations - Organization, laboratory safety is addressed including guidelines for the measurement and assessment of patient dose in accordance with current professional standards and regulatory guidelines.

Specifically related to radiation safety issues, The ICACTL Standards require the following:

The identification of patients scheduled for
CT imaging is verified

Verification that the indication for the exam is appropriate and accurate

Identification of patients who may be pregnant, with counseling if necessary

The radiation exposure for CT acquisition is set at the lowest values that are consistent with satisfactory image quality for the study ordered

The establishment of separate pediatric protocols based on patient age or weight

Compliance of all protocols with
ALARA recommendations

Utilization of dose modulation or current reduction techniques, where appropriate

Justification of the use of higher than recommended radiation doses

Documentation of CTDI or DLP, if available on the system

Annual dose assessment by a qualified expert or medical physicist

Review of the dose assessment report by the Quality Assurance Committee

Communication to staff about occupational exposure

Definitions

Absorbed dose
The absorption of energy from radiation in units of mGy.

Effective dose
A single dose parameter that reflects a risk of a non-uniform exposure in terms of an equivalent whole-body exposure. In units of mSv.

Computed Tomography Dose Index (CTDI)
Primary dose measurement concept in CT; represents the average absorbed dose. The CTDI is always measured in the axial scan mode for a single rotation of the x-ray source.

CTDI vol
The representative dose for a specific scan protocol.

Dose Length Product (DLP)
The integrated absorbed dose per scan length. It is the product of CTDI volume and the scan length. Units are mGy per cm.

***

Unit conversion
1 Gy = 100 rads (old unit)
1 Sv = 100 rem

It is critical that both referring physicians and imaging professionals work in concert to balance the risk versus benefit to the patient when it comes to exposure to ionizing radiation. By implementing comprehensive policies and procedures that address radiation safety, as outlined in The ICACTL Standards, laboratories will be in a position to ensure that their patients receive appropriate and safe CT procedures.

METHODS TO REDUCE RADIATION IN CT

Clear indication to warrant the CT exam
Only scan region clinically indicated
Dose modulation
Automatic exposure control
Beam collimation
Beam filtration
Protocol based on size and weight of patient
Noise reduction techniques
Detector efficiency
Awareness of CTDI or DLP on system

Have a question? The ICACTL is here to help. Laboratories may direct questions about ICACTL accreditation to Mary Lally, RT(R)(MR), ICACTL Technical Manager, via email at lally@intersocietal.org.

REFERENCES

"Are Medical Tests A Hazard?", Ladies Home Journal, May 2008

EPA publication, May 2007, "Radiation Risks and Realities"
www.epa.gov/radiation/docs/402-k-07-006.pdf

AAPM Report 96, January 2008, Report of AAPM Task Group 23, "The Measurement, Reporting and Management of Radiation Dose in CT"
www.aapm.org/pubs/reports/RPT_96.pdf

Cember, H. Introduction to Health Physics, Pergamon Press, 2nd edition 1989.

"CT Dose Management." International Commission on Radiation Protection (ICRP); Publication 87.

"Pregnancy and Medical Radiation." International Commission on Radiation Protection (ICRP); Publication 84.

"Radiation Protection in Humans: Extending the Concept of As Low As Reasonably Achievable (ALARA) from Dose to Biological Damage." Prasad KN, Cole WC, Haase GM. Br J Radiol, 2004 Feb 7;914:97-9.

"Radiation Safety in Cardiology." Limacher MC, Douglas PS, Germano G, et al.; JACC 1998 Mar 15; 31(4):892-913.

"Reference Values for Diagnostic Radiology: Application and Impact." Gray JE, Archer BR, Hobbs BB, Mettler Fa, et al. Radiology, 2005;235:354-358.

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Definitions