Re: Angiogram Dose

[VRST17A@prodigy.com (MS DIANE M BOISVERT)]

Dear Jim:

This is in response to your inquiry about the estimated dose to a patient
from an angiogram.  It is almost impossible to estimate the dose without
having specific information about the machine, the procedure, and the
patient such as the actual beam-on time, the energy (kVp), the beam quality
and the patient size.   The fluoroscopic exposures vary significantly
between machines and depend greatly on the exposure factors employed for
the procedure.  This was noted in the recent AAPM Scientific Report "A
survey of fluoroscopic exposure rates.  Report of AAPM Diagnostic X-ray
Imaging Committee Task Group No. 11" (May/June 1995 issue of Medical
Physics).  Although it sounds (from the title) like this is precisely the
information you are looking for, the report was conducted to evaluate
fluoroscopic exposure rates at the entrant surface of the x-ray image
intensifier (so that medical physicists can compare their measurements with
typical values).   The measurements were not done with patient equivalent
phantoms and the results do not imply typical patient exposures.  However,
in the paper's discussion it is indicated that there is an effort underway
by the Center for Devices and Radiological Health in cooperation with the
Conference of Radiation Control Program  Directors (CRCPD) via the
Nationwide Exposure Trends (NEXT) program to survey on a large scale
entrance exposure rates to the patient.

If you are truly interested in calculating the dose equivalent, the
hospital radiology department should be able to supply you with average
patient entrance skin exposure (in mR/min) information specific to the
machine, the energy and typical beam quality that their angiogram protocol
requires (as measured during the annual medical physics survey).   You
could get an estimated entrance skin exposure if you know the beam on time.
To convert that to a dose equivalent is not straight-forward and would
require consideration of a f-factor to convert R to Rad or Gray, a
backscatter factor, etc.

If you would like additional information, you may contact me at VRST17A@PRODIGY.COM.

Regards,

Diane M. Boisvert