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Patient dose in CT scanning

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Frank Ascoli

on 8 February 2013

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Transcript of Patient dose in CT scanning

Patient Dose in CT Scanning Frank Ascoli, MS, FACR
Chief Physicist Risks Benefits 62 millions CT scans per year
4 million scans per year on children
Atomic bomb data and nuclear industry data used to predict cancer risks
1.5%-2% of cancers seen today may be attributable to radiation dose Risk estimates are not hypothetical
1.5%-2% of all cancers today may be radiation induced
CT has a favorable benefit-risk ratio
Many CT’s are repeated due to lack of communication
Use automatic exposure controls
Replace CT with ultrasound and MRI when practical
About 1/3 of all CT not justified by medical need Hall’s conclusions Patient presents to ER ?? aortic dissection Small increase in the
probability of developing
childhood cancer, dwarfed
by the danger of failing
to get the exam What will
happen to
my baby? US death rate from cancer is 20%
Out of 10,000 people, 2,000 will die of cancer
10,000 people exposed to 1 rem (10 mGy) whole body
There is a RISK of 8 extra cases. 2008 instead of 2000 deaths, maybe..
Radiation induced cancer indistinguishable Cancer risk from radiation Risk estimates are not hypothetical
1.5%-2% of all cancers today may be radiation induced
CT has a favorable benefit-risk ratio
Many CT’s are repeated due to lack of communication
Use automatic exposure controls
Replace CT with ultrasound and MRI when practical
About 1/3 of all CT not justified by medical need Hall’s conclusions This bill would, commencing July 1, 2012, require hospitals and clinics, as specified, that use computed tomography (CT) X-ray systems for human use to record, if the CT systems are capable, the dose of radiation on every CT study produced during the administration of a CT examination, as specified.
  California CT dose law 2010 first year with a recorded 1.7% decrease in CT utilization

CT reduced in every setting except emergency medicine Small stochastic risk of a fatal car accident
Keep a record of all commutes, time, weather, road conditions
Does the log affect your decision to drive again?
Of course not!
The benefit outweighs the risk each time you get into the car
Prior commutes are irrelevant Radiation risk is like driving I'm worried about repeat screening We adjusted our
protocols, it's now
half the dose American College of Chest Physicians call for CT screening of individuals 55-74 with smoking history of 30 pack-years or more

Lower risk individuals will not benefit


JAMA 2012 CT colonography
CT lung for current and former smokers
CT cardiac screening
CT whole-body screening CT screening programs May underestimate volume of nodules
13% - 15% smaller on low dose unenhanced CT scans for volumes less than 200 mm3
No difference in larger nodules Low dose CT scans Lancet reports on 180,000 children scanned between 1985-2002
74 diagnosed with leukemia and 135 had brain tumors at end the end of follow-up, 2009
Risks are increased with multiple scans
ACR responds that CT saves lives when used appropriately and done with the lowest dose possible
Data shows an association but not necessarily cause and effect CT scans during childhood Children and young adults were scanned between 1985-2002
When natural incidence of cancer accounted for, relative risk is small
0.023 per extra mGy brain, or one case per 30,000 patients
0.036 per extra mGy leukemia, or 1 case per 10,000 patients
1 in 25,000 children are diagnosed with leukemia yearly
Remember, lifetime risk of developing cancer is 1 in 3 CT scans during childhood - 2 Do you know
the CTDI for
this scan? ACR accreditation diagnostic reference levels
75 mGy adult head
25 mGy adult body
20 mGy pedi body CTDI displays ACR accreditation diagnostic reference levels
75 mGy adult head
25 mGy adult body
20 mGy pedi body CTDI displays What can you
do to lower
my dose? 100 kVp 120 kVp 120 kVp 100 kVp Renal stone protocol in a patient with previous gastric bypass and a body mass index of 39 kg/m2. The left image, at 120 kVp with low-dose automatic dose modulation, with a dose-length product (DLP) of 1,060 mGy · cm and a dose of 15.9 mSv, shows the left lower pole renal calculus and left-sided hydronephrosis. The center image (follow-up CT examination), at 100 kVp and 50 mAs, with a DLP of 160 mGy · cm and a dose of 2.4 mSv, shows the left lower pole calculus with increased image noise. The right image, using SafeCT postprocessing, shows a substantial reduction in image noise. 3 million CT scans in 1980
62 million scans each year currently
4 million per year on children
0.7% - 2% future cancers, maybe..
Youth at higher risk
Develop smart CT protocols customized to each patient
Image Gently pledge! ACR website
Peak kV single most important tool to reduce dose
Use AEC
If BMI is <25 kg/m2 use 100 kVp for abdominal scan
Limit DLP
Use iterative reconstruction
Pitch > 1 Summary Long latency for stochastic effects
0% - 15% excess relative risk per Sievert, age dependent
Consider the risk of NOT performing the study
Compare to background radiation
Chest x-ray: 2 days
Mammography: 1.5 months
Head CT: 8 months
Body CT: 2.5 years
Hi res chest CT: 5 years AAPM 2012
Non-detectable risk for effective dose below 100 mSv
CT scan typically 10 mSv Image wisely www.imagewisely.org
Image gently www.imagegently.org
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