Re: Lung Cancer Screening

[Douglas Simpkin <dsimpkin@execpc.com>]

Robert E. Peterson wrote:
>I am looking for any information about lung cancer screening using a helical
>CT scanner. Are there any states where this type of screening is permitted,
>and what radiation dose is associated with this procedure.

I'm not sure about the screening legality; presently the patients seen here 
are "screened" filling a physician's prescription.

The dose to the patient chest midline is estimated to be about 90 mrad. 
This was determined from the following:
Helical CT, 140 kVp, 40 mA; acquire 10 mm thick slices at a pitch of 2, at 
1 sec per tube rotation; reconstruct slices 5 mm apart. CTDI at patient 
center for GE CT/i scanner is 1.1 rad per 340 mAs × 1.4 (at 140 kVp) = 4.5 
mrad/mAs.
Effective mAs for chest procedure is 40 mAs/2 pitch = 20 mAs, so center 
dose is 4.5 mrad/mAs × 20 mAs = 90 mrad.

By comparison, the dose to the center of the patient from PA and LAT chest 
radiography is about 15 mrad. This rough estimate assumes an entrance skin 
dose for the PA view of ~15 mrad, while from LAT view it’s ~45 mrad. 
Assuming roughly 2 HVLs of tissue attenuation to midline from each view, 
dose at midline is 15/4 + 45/4 = 15 mrad.

Doug

Douglas J. Simpkin, Ph.D., D.A.B.R.
St. Luke's Medical Center
2900 West Oklahoma Avenue
Milwaukee, WI 53215
phone: (414)649-6457
fax: (414)649-5118
email: dsimpkin@execpc.com

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