The Specialists

Health Education

Are X-rays safe?

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