Answer to Question #1084 Submitted to "Ask the Experts"

Q

Last week I had a CT scan of my sinuses. How much radiation was I exposed to in this test? How does this compare to a chest x ray? Five years ago I had a full-head CT scan. Is a full-head CT scan more or less radiation than a sinus CT scan? In 1999 I had a bone densitometry. How much radiation is involved in this test? Finally—throughout my life I have had many x rays. I am concerned that I will get cancer from them. I know that the average person is exposed to only 360 mrem per year. Tests included: (1) Routine dental x rays (all life long) (2) Barium enema—1981 (3) 2 x rays of left hip—1983 (4) CT scan of head—1996 (5) 2 hand x rays—1998 (6) 2 hip x rays—2000 (7) CT scan of sinuses—2001 (8) 1 hand, 1 elbow, and 1 neck—1997 (9) 2 chest x rays—unknown date I am 35—have I gone over the limit into the high risk cancer "zone"?

A

In just a minute, I'll answer your questions one at a time. I'm going to use effective radiation dose in my answers so we can compare radiation doses from each of the exams and then you can add the doses together to look at risk of cancer. In our field, we use effective dose as a way to take radiation exposures to various parts of the body and convert them to an equivalent risk to the whole body. For example, during a chest x ray only the chest is exposed (the skin exposure is about 50 mR). We can "weight" the organs in the chest for their biological sensitivity to radiation and come up with a whole-body equivalent dose (about 6 mrem). This means that the dose to the chest from a chest x ray is an equivalent risk to the whole body receiving 6 mrem. It is also important to note that there are dose ranges to each of these exams depending on the equipment used, the radiographic technique, number of films, and size of the body part. You also might want to look at the answer to Question 708, under "Medical and Dental Procedures," which includes a table of effective doses for common exams. Now, for each of your questions: How much radiation was I exposed to for the CT sinus exam? The effective dose is around 100-200 mrem. How does this compare to a chest x ray? The effective dose from a single chest x ray is around 5-10 mrem. Is a full-head CT scan more or less radiation than a sinus CT scan? Depends on the radiographic technique and how many pictures are taken. The estimate for the sinus CT would also be applicable for a head CT. How much radiation is involved in a bone densitometry? It depends on the body part exposed. If the densitometry was of the wrist, the effective dose is zero. If it was of the lumbar spine, the effective dose is as much as 1-5 mrem. Routine dental x rays. The effective dose is between zero and 0.4 mrem, depending on how many x rays are taken and the type of exam. Barium enema. The effective dose is between 200 and 700 mrem, depending on the number of films and total fluoroscopy time. Hip x ray. The effective dose will be around 10-40 mrem. Hand x rays. The effective dose is zero. Neck x rays. The effective dose for a cervical spine series of x rays (typically 5-6 x rays) is about 25-30 mrem. The risk for lifetime fatal cancer due to radiation exposure is estimated to be 4 in one million per 1,000 mrem. This can be compared with the general lifetime fatal cancer estimate of 1 in 4 or 5 of dying of cancer; this translates to 200,000 per million. If you add the radiation risk estimate (if you received, say, 5,000 mrem in your lifetime) this would become 200,020 per million. It is important to note that these are statistically calculated estimates based on the best available information. Most of that information is from individuals who received more than 10,000 mrem—whether high doses to someone can actually predict what low doses will do is unknown. It is estimated that over 550,000 people will die of cancer this year; over 1.2 million will be diagnosed. Annual incidence rates are about 2,100 per million for women and 4,750 per million for men. References:

• Wall BF, Hart D. Revised radiation doses for typical x-ray examinations. The British Journal of Radiology, 70: 437-439; 1997. [5,000 patient dose measurements from 375 hospitals]
   
• United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and effects of ionizing radiation, Vol. 1: Sources. New York, NY: United Nations Publishing; 2000.
   
• International Commission on Radiation Protection. 1990 Recommendations of the International Commission on Radiological Protection. New York, NY: Pergamon Press; ICRP Publication 60; 1990.
   
• American Cancer Society website: http://www.cancer.org/. Accessed 30 July 2001.

Kelly Classic Certified Medical Health Physicist