You need a lateral view. Is it better to rotate the image intensifier toward you or away from you? Why is fluoro time a poor indicator of radiation exposure ? How many Grays of radiation puts the patient at risk for skin injury? A 5-second DSA run uses how much more radiation than 5 seconds of fluoro? A typical embolization procedure exposes the patient to how many CXRs worth of radiation? What is the increased cancer risk of such a procedure? What is the cancer risk to the operator if he does 1 embo procedure per working day for 30 years?
Radiation exposure Radiation effects Minimizing radiation to the patient Minimizing radiation to you
X-rays are produced by accelerating electrons through high voltage (50- 150 kVp) applied to a tungsten target in an X-ray tube Amount of X-rays produced are determined by tube current (mA) and the tube voltage (kVp)
Dose is not administered uniformly throughout the patient’s body Radiation field is moved, angled, collimated Both fluoro and DSA are used Four metrics are used to estimate patient radiation dose Fluoro time Peak skin dose (not yet measured by equipment) Reference dose (air kerma) Dose-area product (DAP)
Also called “cumulative dose” The Air Kerma for the entire procedure, measured in Gy at a fixed reference point near the isocenter of the tube Does not account that the radiation field is moved to different areas of the patient during the procedure Conservative, generally overstates risk Measurement is likely accurate to within +/- 50%
Measure of total X-ray energy absorbed by the patient Basically the air kerma (dose) multiplied by the area of body exposed (area)
Fluoro time is only a very rough indicator of radiation dose, affected by: Patient size Beam location Beam angle Normal vs. high dose rate Distance of tube from the patient These can all add up to 10-fold difference in dose for the same fluoro time!
DOSE-AREA PRODUCT (DAP) CUMULATIVE AIR KERMA Product of the air kerma and the Air kerma = Kinetic Energy exposed area (in cm2) Released per unit Mass of Air; basically, how much radiation dose Good measure of stochastic risk is being delivered at a specific (cancer risk) because it estimates point (about where the patient’s total radiation energy delivered to skin is) a patient Also known as reference dose or Poor estimator of skin dose and cumulative dose deterministic effects large dose over small area or small Easy to measure, expressed in Gy dose over large area? Absorbed dose in tissue will be Unit of measurement (Gy-cm2) about equal to the air kerma at does not translate into standard that point units of dose (hard to use) Notification threshold = 3 Gy
Patients and staff are exposed to radiation, but only a portion is absorbed into the body Absorbed dose is measured in Gray or rads 1 Gray = 100 rads Approximate radiation doses: Fluoro = 2-10 rads/min CXR = 0.02 rads CT abdomen = about 2-10 rads Natural background radiation = 0.3 rads/year
Different forms of radiation (X-rays, alpha particles, etc) produce different biologic effects for same absorbed dose Dose equivalent (rem or Sievert) is used to measure biologic “harmfulness” of a radiation dose For diagnostic X-rays, 1 rem = 1 rad and 1 Gy = 1 Sv
Effective dose is the dose equivalent to the whole body caused by irradiating just a localized area This is calculated by multiplying the dose to each irradiated organ by a weighting factor based on the radiosensitivity of that organ Example effective doses: CXR = ~0.1 mSv PTA = 10-20 msV Biliary drainage = 40 mSv Transcatheter embolization or TIPS = 50-100 mSv Additional cancer risk = ~5%/Sv So, a long embolization procedure in a 30 year old increases risk of developing a fatal cancer by about 0.5%
Fluoro machines operate in automatic brightness control When brightness of picture is inadequate, the ABC automatically increases mA or kVp (or both) to increase X-ray penetration Large patients = more dose than small patients (up to 4-10x higher!) Abdominal fluoro = more dose than chest fluoro Oblique fluoro = more dose than AP fluoro
Direct exposure rate refers to entrance skin exposure where the X-ray beam enters the patient 2-10 rads/min for fluoro ~50 rads/min for DSA 30 mins of fluoro = 60-300 rads = 0.6-3 Gy
Indirect exposure rate refers to exposure to the staff from scattered radiation from the patient ~1/1000 of the skin entrance exposure rate at a distance of 1 meter Large patients increase scatter radiation Larger field (not collimated) increases scatter Scatter much higher on the X-ray tube side of the patient ▪ For lateral view, stand next to II, not next to tube!
Radiation effects with a threshold dose; effect is not observed unless threshold is exceeded
Early erythema – 3 Gy – 1-2 days – sunburn Epilation – 3-7 Gy – 3 weeks – hair loss Main erythema – 10 Gy - onset 1-4 weeks – burning, itching If >14 Gy, progresses to dry desquamation 1 week later If >18 Gy, progresses to moist desquamation (blistering, sloughing) 1 week later Ulceration – 24 Gy – 2-12 months
No threshold Any dose increases the chance of the effect, with higher doses increasing the chances Radiation-induced cancer
Approximate additional risk of fatal cancer for an adult for an examination: Extremity X-ray: <1/1,000,000 CXR: 1/100,000 to 1/1,000,000 Chest CT: 1/10,000 to 1/1,000 Multiphase abdominal CT: 1/1,000 to 1/500 These risks are additive to the ~25% background risk of dying of cancer
Very small (<10 kg) or very large (>135 kg) patients Age (3x risk for newborns, 1x risk at age 25, 0.2x risk for patients in 60s) Pregnant patients Prior radiation exposure within last 2 months Diabetes, autoimmune diseases, connective tissue diseases increase risk of skin effects
Ultrasound instead of fluoro when possible (biliary, arterial access) Patient should be as far from tube, and as close to II, as possible (good to be tall!) Don’t step on the pedal Pulse fluoro mode (7.5 or 15 frames/sec instead of 30/sec) View and save images with “last image hold” Exclude bone from the image
Collimate to smallest field of view possible Avoid exposure to eyes, thyroid and gonads Position and collimate without fluoro 5-8% of radiation exposure is delivered during preparation for imaging, positioning the table and adjusting collimators Avoid magnification ABC uses more radiation to brighten and sharpen the image in mag view Avoid high-dose or detail modes Use higher kVp (but can reduce contrast) Minimize overlap of fields and repeated acquisitions
Less time on the pedal Use last image hold Pulsed fluoro Low dose fluoro
Inverse square law Double distance from patient = ¼ the radiation dose from scatter radiation Nonessential personnel should be outside a 6-foot radius from the X-ray source Step out of room for DSA runs
Lead apron (0.5 mm Pb equivalent) blocks about 95% of scatter radiation Thyroid shield, leaded glasses are essential Most radiosensitive organs Lead drapes and clear leaded glass barriers
Record dose in the medical record If dose exceeded deterministic thresholds Discuss possible effects and management with patient Have patient or family member notify IR if deterministic effects occur Institute a clinical follow-up plan for the patient
Necessary when large radiation dose was used Telephone call at 2 weeks or so Redness? Blistering? Hair loss? Location of radiation field May need follow up for >1 year
You need a lateral view. Is it better to rotate the image intensifier toward you or away from you?
You need a lateral view. Is it better to rotate the image intensifier toward you or away from you? Toward you! Keep the beam away from you, because most of the scatter occurs at the point the beam enters the patient
Why is fluoro time a poor indicator of radiation exposure ?
Why is fluoro time a poor indicator of radiation exposure? Does not include DSA runs Dose varies greatly for the same fluoro time Thin or obese patient AP or oblique views Magnification Distance from X-ray source
How many Grays of radiation puts the patient at risk for skin injury?
How many Grays of radiation puts the patient at risk for skin injury? 3 Grays!
A 5-second DSA run uses how much more radiation than 5 seconds of fluoro?
A 5-second DSA run uses how much more radiation than 5 seconds of fluoro? About 10x more radiation for DSA!
A typical embolization procedure exposes the patient to how many CXRs worth of radiation? What is the increased cancer risk of such a procedure? What is the cancer risk to the operator if he does 1 embo procedure per working day for 30 years?
A typical embolization procedure exposes the patient to how many CXRs worth of radiation? About 1000! What is the increased cancer risk of such a procedure? About 0.5% for a 30 year old! What is the cancer risk to the operator if he does 1 embo procedure per working day for 25 years? 100 mSv (patient equivalent dose) x 1/250 (scatter fraction at 18 inches) x 1/20 (fraction of radiation that gets through the lead) x 5000 (# of procedures) = 100 mSv A career in IR is probably equivalent to having an embolization procedure done on yourself (0.5% additional cancer risk)
Mitchell E and Furey P. Prevention of radiation injury from medical imaging. J Vasc Surg 2011; 53:22S-27S. Miller D, et al. Clinical radiation management for fluoroscopically guided interventional procedures. Radiology 2010;257:321-332. Cousins C and Sharp C. Medical interventional procedures – reducing the radiation risks. Clin Radiol 2004;59:468-473. Wagner L. Angiography radiation dose – limiting dose to the patient while maintaining effective image quality. http://www.uth.tmc.edu/radiology/RSNA/2008/RSNA_wa gner_2008.pdf