Answer to Question #8455 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment/Shielding — Shielding

The following question was answered by an expert in the appropriate field:

  1. Which modality has the highest leakage radiation—fluoroscopy at 2.58 × 10-5 coulomb per kilogram per hour (C h kg-1) at 1 meter (m) or computed tomography (CT)?
  2. Is CT dose measured by CT dose index (CTDI), CTDI volume (CTDIvol), or effective dose?
  1. All x-ray tubes are restricted to a leakage radiation limit of < 2.58 × 10-5 C h kg-1 at 1 m from the tube housing.
  2. With the advent of multidetector CT (MDCT), adding table translation into the equation, we now have to consider "pitch" as a contributing factor to dose, either overscanning (pitch <1) or underscanning (pitch >1). Without pitch, the CT dose is the weighted CTDI or (CTDIw), which is just [(2 × peripheral exposure)/3] + (central exposure/3). But with helical scanning the CT dose is CTDIw/pitch.

Kishor M. Patel, PhD, DABR

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 18 August 2009. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.