48% of the total dose of ionizing radiation exposure for individuals in the United States has been attributed to medical tests and procedures(Prokop M).
Estimated CT scans may be associated with 1.5-2% of all cancers in the United States in the future (Brenner DJ et al).
Many CT examinations are done unnecessarily and dose reductions are possible without compromising diagnostic accuracy.
Natural background radiation, varies by geographic location, averages 3 mSv/y in the US.
Average radiation dose from medical imaging has increased 6 fold in the past 30 years.
Radiation induced risk occur at doses higher than 100 mSV.
Risk model on lifetime attributable cancer predicts that 1 in 1000, persons exposed to 10 mSV wiil develop cancer because of that single exposure.millisieverts
Medical imaging contributes about 50% of the overall radiation dose to the US population, compared with about with about 15% in 1980 (Mettler FA).
Estimated 29,000 future cancers could be related to radiation exposure from CT scans performed in the United States (Berrington de Gonzalez A et al).
It is estimated that 2% of cancers in United States will be attributed to radiation from CT and that 15% will be due to such scans performed in pediatric patients.
92-95% of patients are not informed of radiation risks prior to their CTscan (Lee CI et al).
Approximately 5% of all CT scans are done on children, 10% on individuals aged 20-30 years, and 5% of 20 year old undergo annual CT imaging (Smith-Bindman a et al).
Estimated 2% of future cancers will result from current imaging use, at present rates.
Estimated risk of developing cancer in a 20-year-old woman undergoing a CT scan of the chest is approximately one in 330, compared to one in 880 for 20-year-old male, an abdominal CT scan with contrast and a 40-year-old woman is associated with an estimated risk of developing cancer of approximately one in 870, compared with one in 942 for a 40-year-old male: risk decreases with lower dose, older age, and male sex ( Smith-Bindman R et al).
CT scan of chest typically delivers more than 100 times the radiation dose of a routine frontal and lateral chest X-ray.
Due to increased speed of image acquisition allowing vascular, cardiac, and multiphase exams of new CT scans are associated with higher radiation exposure.
The radiation exposure from myocardial perfusion imaging is twice that of a CT scan with the equivalent of approximately 700 chest x-rays.
The typical dose of radiation received during nuclear cardiac stress test procedure can range from 9.4 millisieverts to 40.7 millisieverts.
Abdominal and pelvic CT scan median effective dose suggested to be 8-10 mSv, yet the median dose found in a study was 66% higher and the median dose of a multiphase abomen and pelvic CT scan was nearly 4 fold higher (Smith-Bindman R et al).
Estimated risk of radiation-induced cancer from typical abdominal CT scan is approximately 1 in 300-1 in 2000 depending upon the dose, age, sex, and body part scanned.
A typical CT of the abdomen/pelvis exposes the fetus to 10 mGY-25 mGY which is below the 100 mGY associated with development of deficits for a fetus between 2-15 weeks geststational age.
At 15 weeks gestational age it is estimated that it takes more than 200 mGY to induce CNS defects in a fetus.
Brain dose from a head CT is approximately 50-60 mGy.
Colon dose from abdominal/pelvis CT scan is approximately 15-20 mGy.
There is an estimated 2% increased lifetime risk for a malignancy to develop for a fetus exposed to 50 mGY if exposed after 15 weeks.
Exposure of less than 50 mGY for a diagnostic test is not associated with fetal anomalies or fetal death.
Using risk projection models it was estimated that in the early 1990s 0.2% of incident cancers due to CT scan use in the UK (Berrington de Gonzalez A et al).
Presently CT scan use is estimated to be 10 times what is was in the UK in the 1990s the estimated in the US incident risk of cancer may be as high as 1.5-2.0% (Brenner DJ et al).
Average CT scan of the brain .06 Gy.
Absorbed dose quantifies energy deposited per unit mass, measured in grays (Gy).
1Gy is equivalent to the energy deposition of one J per kilogram of tissue.
Not all types of radiation produce the same biological effect and the dose equivalent is often substituted for the absorbed dose.
Dose equivalent is the product of the absorbed dose and a radiation weighting factor expressed in sieverts (Sv).
Effective doses are reported in units of millisieverts and compare radiation risk from different imaging examinations.
Effective doses from CT scans range from less than 1 to approximately 10 mSv.
A standard CT scan of the chest delivers a radiation dose of 8 to 10 millisieverts (mSv), which is the equivalent of 600 to 750 chest radiographs.
Low-dose CT, at 1.5 mSv, represents the equivalent of approximately 113 chest radiographs.
Low dose CT is recommended in at-risk individuals every year through age 80, this is quite a lot of radiation.
Abnormal results may require follow-up imaging, in which case diagnostic CT is utilized at the level of 10 mSv.
Average effective dose from naturally occurring background radiation, such as radon gas and cosmic rays is approximately 3 mSv/year.
Radiation weighting factor for x-rays and gamma rays is 1.0, and 1Gy is equivalent to 1 Sv in medical imaging.
Radiation doses in medical imaging typically are expressed as millisieverts (mSv).
Bilateral mammogram associated with mean dose 0.4 mSV.
Chest X-Ray 0.1 mean dose mSV.
The mean radiation dose to an adult from a chest radiograph is around 0.02 mSv (2 mrem) for a front view (PA or posterior-anterior) and 0.08 mSv (8 mrem) for a side view (LL or latero-lateral).
PET CT 24 mean dose mSV.
MUGA scan mean mSV 9.4.
Bone scan 6.3 mean mSV.
CT Brain 2.0 mean mSV.
CT neck 6.0 mean mSV.
CT chest 7.0 mean mSV.
CT chest/and/ pelvis mean 18.0 mSV.
CT and/pelvis 10.0 mean mSV.
CT pelvis 6.0 mean mSV.
Sentinel lymph node biopsy 0.4 mean dose mSV.
Stereotactic biopsy 0.2 mean mSV.O
In a retrospective study of 64,000 patients who received cumulative x-ray doses of 1.02 Sv distributed over approximately 92 exposures at 11 mSv per exposure in conjunction with pneumothorax treatment for tuberculosis revealed no increase in risk of lung cancer: concluding that the effect of radiation is not cumulative ( Einstein AJ et al).
In a study of 31,710 women receiving cumulative doses of radiation in similar repeated exposures for tuberculosis treatment significant increased risk for breast cancer for those patients receiving less than 70 cGy (Howe GR et al).
Average yearly background radiation dose is approximately 3 mSvc.
Estimated excess cancer mortality from radiation exposure is 1 death per 2000 scans, assuming an effective dose of 10 mSv per scan and a risk of 5% per sievert (Brenner DJ, Hall EJ).
Brain cancer is a concerned as the head is the most commonly examined part of pediatric patients.
WwThere is evidence that there is an increase brain tumors after pediatric CT examinations.
A chest x-ray delivers a radiation dose of 0.02 mSv.
A resting nuclear scan combined with a stress scan using the radioactive tracer technetium-99m sestamibi – averages 11.3 mSv. and is about 500 times the dose of a chest x-ray.
A rest-stress scan using the radioactive tracer technetium-99m tetrofosmin averages 9.3 mSv. and is about 500 times the dose that comes from a chest x-ray.
Doses are much higher for nuclear stress tests that use the radioactive tracer thallium-201 – about 22 mSv with a single injection of thallium.
Myocardial perfusion imaging is the most common imaging test for diagnosing coronary artery disease and accounts for 20% of the total annual medical radiation to which patients are exposed.
When thallium and technetium-99m sestamibi are combined, the radiation dose averages about 29.2 mSv.
In a study (Stopsack KH) of 54,447 adults, 48.4% underwent at least one CT scan in a ten-year period: 10 year radiation doses from CT scan were 0.12 9.9 mSV in 15.8% of the population, 10-24.9 mSv in 16.9%, 25-99.9 mSv in 13.8% and, and 100 mSv or greater in 1.9%.
Exposure to medical radiation from CT scans is associated with elevated risk of thyroid cancer and leukemia.
The elevated risk in thyroid cancer and leukemia in association with medical CT was stronger in females than males.
No significant association between the risk of cancer and CT scans was observed in overall patients with NHL, however, increased risks were found in patients ≤45 years of age.
Dose-response relationship is observed in patients ≤45 years of age for thyroid cancer, leukemia and lymphoma.
CT scans may be associated with an increased risk of thyroid cancer and leukemia and those diagnosed with NHL at a younger age.
The elevated risk in thyroid cancer and leukemia in association with medical CT is stronger in females than males.