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Are X-rays safe?
Prepared by Dr Alex Ching
Version: 20170618
RADIATION IS NATURAL
The small dose of diagnostic irradiation is just a very minor addition to the underlying risks of having cancer in our lifetime. For all of us as adults, our risk of getting cancer in our lifetime is 1 out of 3-4 anyway, even we have never undergone any X-ray checking. Therefore, the theoretical increased risk should not be of major concern to us.
We obey ALARA (As Low As Reasonably Achievable) principle and we have been well- trained to use the appropriate amount of radiation necessary for a proper medical imaging examination. As with other medical procedures, X-rays are safe when used with care.
CONCEPT OF BERT (Background Equivalent Radiation Time)
|
Examination / Event |
Radiation dose (mSv*) |
Time required for the same dose of radiation to be released from our normal living environment |
No. of CXR with equivalent dosage |
|
Radiation in our normal living environment |
3 |
1 year |
40 |
|
8 hours continental flight (e.g. HK to Shanghai) |
0.08 |
1 week |
1 |
|
Intercontinental flight (e.g. HK to NY) |
1 |
4 months |
15 |
|
Smoking |
45** (one pack per day) |
15 year |
600 |
|
|
|
|
|
|
HEAD & NECK |
|||
|
Intraoral X-ray |
0.005 |
1 day |
<1 |
|
CT Brain |
2 |
8 months |
25 |
|
CT Brain plain & contrast |
4 |
1.5 year |
50 |
|
CT Neck |
6 |
2 years |
75 |
|
|
|
|
|
|
CHEST & HEART |
|
|
|
|
Chest X-ray |
0.08 |
1 week |
1 |
|
CT Thorax (low dose) |
1.5 |
6 months |
20 |
|
CT Thorax |
7 |
2.5 years |
90 |
|
CT Calcium Score |
3 |
1 year |
40 |
|
CT Coronary Angiogram |
12 |
4 years |
150 |
|
|
|
|
|
|
ABDOMEN AND PELVIS |
|||
|
Pelvic X-ray |
1 |
4 months |
15 |
|
IVU |
3 |
1 years |
40 |
|
Upper GI series |
4.5 |
1.5 year |
60 |
|
Lower GI series |
6 |
2 years |
75 |
|
CT Colon |
6 |
2 years |
75 |
|
CT Urogram |
5.2 |
2 years |
75 |
|
CT Abdomen and pelvis (plain) |
10 |
3.5 years |
125 |
|
Abdomen CTA |
20 |
7 years |
250 |
|
|
|
|
|
|
PET AND NUCLEAR MEDICINE |
|||
|
PET / CT |
25 |
8.5 years |
310 |
|
Bone Scan (Tc-99m MDP, 25 mCi) |
7.4 |
2.5 years |
90 |
|
Thyroid Scan (Tc-99m Pertechnetate, 5 mCi) |
2.4 |
10 months |
30 |
|
Renal Scan (Tc-99m MAG3, 8 mCi) |
1.2 |
5 months |
15 |
|
Cardiac Perfusion (Tc-99m Sestamibi, 35 mCi) |
11 |
4 years |
150 |
|
Myocardial Viability (TL-201 Chloride, 3 mCi) |
25.5 |
8.5 years |
320 |
|
|
|
|
|
|
BONE |
|||
|
DEXA (Bone Densitometry) |
0.001 |
3 hours |
<1 |
|
X-ray Spine |
1.5 |
6 months |
20 |
|
X-ray Extremity |
0.001 |
3 hours |
<1 |
|
CT Spine |
6 |
2 years |
75 |
|
|
|
|
|
|
WOMEN IMAGING |
|||
|
Mammogram |
0.4 |
7 weeks |
7 |
|
|
|
|
|
|
OTHERS |
|||
|
Cardiac catherization |
10 |
3.5 years |
125 |
|
Coronary angioplasty / stenting |
20 |
7 years |
250 |
Remarks: * scientific unit of measurement for radiation dose; ** projected estimation
Notes: This chart simplifies a highly complex topic for patient’s informational use. The effective doses are typical values for an average-sized adult. Doses for Paediatric patients vary in accordance with their body sizes. They are significantly different from those given to adults.
ACTIVITIES WITH 1 CHANCE IN 1,000,000 FATAL CONSEQUENCE
Smoking 1.4 cigarettes (lung cancer)
Eating 40 tablespoons of peanut butter (aflatoxin poisoning)
Eating 100 charcoal boiled BBQ goose (carcinogenic substances produced by grilling)
Spending 2 days in the main streets in Causeway Bay (air pollution)
Driving 40 miles in a car (automobile accident)
Flying 2,500 miles in a commercial jet (crash)
Padding a canoe for 6 miles (drowning)
Receiving 0.1 mSv radiation dose (cancer)
RADIATION DOSE AND GENERAL EFFECTS
|
Radiation Dose (mSv) |
General Effects |
|
10,000 |
Radiation sickness with death in several weeks |
|
1,000 |
Intermediate radiation sickness; Unlikely to cause death |
|
100-1,000 |
Dose-related risk of developing cancer |
|
50 |
Increased cancer risk according to statistics (Highest dose allowed annually for occupational exposure) |
|
20 |
Maximum dose allowed for radiation workers over a 5-years period |
|
1.5-3 |
Annual radiation dose from our normal living environment |
Further Reading:
- Lancet. 2004; 363; 345-351
- RadiologyInfo.org www.pedrad.org/associations/5364/ig/index.cfm.
- Society of Nuclear Medicine Procedure Guideline, USA.
- Radiation Dose to Adults from Common Imaging Examinations, The American College of Radiology, June 2017
