Radiation Reduction Strategies How Low Can You Go? Stewart Carlyle Bushong Baylor College of Medicine sbushong@bcm.edu
Objectives Review radiation units of measure Understand the issues of overutilization and inappropriate utilization Describe strategies to reduce radiation dose in CT and fluoroscopy Know how to use effective dose and radiation risk coefficients to estimate response
Radiation Measurement Radiation Exposure…. Gray (Gya) Tissue Dose…………...Gray (Gyt) Effective Dose.............Sievert (Sv)
Radiation Exposure Intensity of ionization in air Unit is Gray (Gya) 1 Gya = 1 J/kg
Gray (Gya)
10 mGya 30 sec of fluoro 50 PA CXRs 2 KUBs
10 mGya
Tissue Dose Measure of energy transferred to tissue per unit mass Does not reflect radiosensitivity of tissue or stochastic risk 1 gray is equal to the transfer of 1 joule per kilogram of irradiated tissue
Gray (Gyt)
10mGyt 30 sec of fluoro 50 PA CXRs 2 KUBs 4 screening mammograms 1/4 brain CT scan 1/2 body CT scan
Effective Dose Measure of radiation dose allowing for: some types of radiations are more damaging than others some parts of the body are more radiosensitive than others
Defined as sum over specified tissues as the products of the absorbed dose in a tissue and the weighting factor for that tissue Allows for comparison of stochastic risks
Sievert (Sv)
Effective Dose ď śTakes into account where the radiation is absorbed and attempts to reflect equivalent whole-body dose that results in a stochastic risk that is equivalent to the stochastic risk from the actual absorbed dose to those tissues in a non-uniform, partial-body irradiation such as CT
10 mSv 300 PA CXRs 2 brain CT scans 1 chest CT scans 1 body CT scans 1 cerebral angiogram 3 years of background radiation 500 transcontinental flights
Effective Dose E = ∑T (ω T •ωR •D T,R ) E = Effective Dose in mSv ωT = Tissue-Weighting Factor ωR = Radiation-Weighting Coefficient DT,R = Average Absorbed Dose in mGy
1990
2008
http://www.nrc.gov/reading-rm/doc-collections/commission/secys/2008/secy2008-0092/enclosure.pdf
Stochastic Biologic Effects Randomly occurring No dose threshold Cancer and genetic dose risk
Deterministic Biologic Effects Dose related dose severity Dose threshold
2 Gy
3 Gy
2 Gy acute
18 Gy
Stochastic Radiation Risk Incidence……. 8x10-2 Sv-1 Mortality………5x10-2Sv-1
ď ś42:100 cancer unrelated to radiation ď ś1:100 cancer from 100 mSv radiation exposure
Ubiquitous Background
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http://www.ncrponline.org/images/160_pie_charts/Fig3-19.pdf
Radiation Exposure from All Sources
http://www.ncrponline.org/images/160_pie_charts/Fig3-19.pdf
NATURAL 3 mSv
MEDICAL IMAGING 3.2 mSv 0.3 mSv
0.3 mSv
Background 50%
2.0 mSv
1.5 mSv
Medical Radiation 0.7 mSv 48%
0.4 mSv
0.6 mSv
TOTAL 6.2 mSv
1990
2006
vm S
Annual Effective Dose to Individual in US Population from Diagnostic Medical Radiation 3.5 3 2.5 2 1.5 1 0.5 0
3
0.53 1990
2006
Year
Thatâ&#x20AC;&#x2122;s 5.7X increase!
Medical Radiation Procedures in US
Percentage of Procedures
Percentage of Dose
Increased Pediatric CT in the Emergency Department
Broder et al. Emerg Radiol 2007; 14:227-32
It’s Complicated We drive use Industry drives use Non-radiologists drive use Media drives use Public drives use
Isnâ&#x20AC;&#x2122;t it easier to just get a CT?
Computed Tomography Dose Index (CTDIvol) Measure of the CT scanner radiation output taking into account specific imaging protocols, i.e. pitch, transverse vs. helical, FOV Not a measure of absorbed dose Very useful in comparing dose estimates when adjusting protocols Reported in mGy
Dose Length Product (DLP) DLP (mGy • cm) = CTDIvol (mGy) X length of scan (cm)
Effective dose can be estimated by DLP • k where k is body region specific
Effective Dose = DLP • k Region of Body Head Neck Chest Abdomen Pelvis
k (mSv • mGy-1 • cm-1) 0.0023 0.0054 0.017 0.014 0.019
Effective Dose = 1090.28 • 0.0023 = 2.5 mSv
Effective Dose = 646.09 • 0.0023 = 1.49 mSv
Effective Dose = 281.10 • 0.0023 = 0.64 mSv
Effective Dose = 89.31 • 0.0023 = 0.205 mSv
Factors Affecting Dose in CT kVp mAs Pitch Collimation Patient Size Noise Index
Patient Size patient size (peds) CT dose with all other factors remaining the same Select appropriate scan FOV to CT dose Utilize dose modulation
Dose Modulation Angular (X, Y)
Z-axis
340 mA
80 mA
340 mA
25% of mA
340 mA
75% of mA
Original 380 mA
Simulated 70 mA 18% of dose
130 mAs
40 mAs*
20mAs*
* Simulated, by adding noise
Conventional Radiography & Fluoroscopy Chest 44% UGI 24%
UGI 1%
Percentage of Procedures
Chest 13%
Percentage of Dose
ALARA At Last, Another Raise Already After Love in the Afternoon, Repeat Again As Long As Repeating is Allowed As Low As Reasonably Achievable
Itâ&#x20AC;&#x2122;s a trifecta baby!
e ra Re duc
to ose t n d ogis atio nol adi tech er duc st & Re iologi rad
dia pat tion d ien t os e t o
Medical Imaging Trifecta
High quality images yielding diagnosis &/or treatment
e ra Re duc
to ose t n d ogis atio nol adi tech er duc st & Re iologi rad
dia pat tion d ien t os e t o
Medical Imaging Trifecta
High quality images yielding diagnosis &/or treatment
Re duc
dia pat tion d ien t os e t o
e ra
Reduce Radiation Dose to Patient
Reduce Radiation Dose to Patient Appropriate study Reduce time Collimate Employ mag only when necessary Employ grid only when necessary Utilize dose reduction features
Pulsed fluoro Added filtration High kV low mA Last image grab
Appropriate Study
Reduce Time
Collimation
Co ll
im ato r
Collimate
Use Mag Only When Necessary
No ma g
2X ma 1.5 g Xm ag
3X ma g
Mag
Use Pulsed Fluoro
30 pulses/sec 6 pulses/sec 4 pulses/sec 2 pulses/sec
7.0 mGy/min 1.4 mGy/min 0.9 mGy/min 0.5 mGy/min
Use High kV and Low mA Use Added Filtration
Average setting 77 kV 1.6 mA 19 mGy/min Pediatric setting 83 kV 1.4 mA 10 mGy/min (0.1 mm Cu + 1.0 mm Al added filtration)
Use Last Image Grab
La st Im Gr age ab
S Ex pot po su re
Spot vs. Last Image Grab
0.6 mGy/spot
no additional radiation
Exposure Comparison - VCUG Team Diligent Dose
Team Asleep Dose at the Tower •1.5 minutes of continuous fluoro mGy •Average setting
• 1.5 minutes of pulsed fluoro 23 mGy • Pediatric setting (Added •Grid filtration) •5 spots • No grid 13.3 mGy X Grabs • 5 Last Image23
270
29 mGy
299 mGy
e ra Re duc
to ose t n d ogis atio nol adi tech er duc st & Re iologi rad
dia pat tion d ien t os e t o
Medical Imaging Trifecta
High quality images yielding diagnosis &/or treatment
e ra Re duc
to ose t n d ogis atio nol adi tech er duc st & Re iologi rad
dia pat tion d ien t os e t o
Medical Imaging Trifecta
High quality images yielding diagnosis &/or treatment
Reduce Radiation Dose to Radiologist & Technologist to ose t n d ogis atio nol adi tech er duc st & Re iologi rad
Reduce Radiation Dose to Radiologist & Technologist How many times have you… …put an unshielded hand in beam? …chosen expediency over personal safety? …turned an unshielded back to the x-ray source? …been unaware of the foot on the pedal? …operated fluoro without protective curtain? …stood too close to the fluoro tower?
Protection from Scatter In room only when necessary Distance Shielding Reduce patient radiation exposure
Reduce time Collimate Use pulsed fluoro Utilize last image grab
Distance Truth is ever to be found in simplicity.
Distance
BACK UP!
I1 (d2) :: 2 I2 (d1) 2
Shielding Control booth Portable barrier Pb aprons, gloves, Bucky slot cover Pb curtain
Take Home Points ď śAverage dose in US has increased from 3.6mSv to 6.2 mSv since 1990 ď śAlmost completely related to medical radiation mainly from CT
Take Home Ponits ď śChildren are especially sensitive to stochastic effects of radiation due to radiosensitivity and life expectancy
Take Home Point ď śBy using dose-reduction features in CT and fluoroscopy, radiation dose can be cut by an order of magnitude ď śWhen considering new or replacement CT & fluoroscopy equipment, purchasing dose-reduction features indicates your commitment to your patients and staff despite the higher cost
Dose Reduction Efforts Interventional Radiology New neuro IR room has all modern dose-reduction features
Nuclear Medicine Dose reduction across the board on radiotracers
Dose Reduction Efforts Mammography Digital mammo throughout system with lower dose than film-screen technique by about 30%
ď śBy following ALARA using dosereduction features, exposure can be minimized
How Low Can You Go?