Radiation Safety Michael Shortsleeve, MD Thomas Osborne, MD MAH.

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Radiation Safety Michael Shortsleeve, MD Thomas Osborne, MD MAH

Transcript of Radiation Safety Michael Shortsleeve, MD Thomas Osborne, MD MAH.

Radiation Safety

Michael Shortsleeve, MD Thomas Osborne, MDMAH

Radiation Safetyoutline

• 1. Background radiation to the general public• 2. X ray production and terms• 3. X ray interaction• 4. The Fluoroscopy machine

-And specific related exposure concerns • 5. Radiation Biology• 6. Tips to decrease patient and operator exposure

Michael Shortsleeve, MD & Thomas Osborne, MD

-U.S. Nuclear Regulatory Commission

BackgroundX-ray Production

•An electrically heated filament within the X-ray tube generates electrons•Electrons are then accelerated from the filament to hit a tungsten target

–This is done with a high voltage potential in the tube

Michael Shortsleeve, MD & Thomas Osborne, MD

antonine-education.co.uk

BackgroundX-ray Production

•The quantity of electron flow, is the current–Described in units of milliamperes (mA)

•The maximum kinetic energy of the accelerated electrons

–Is defined in terms of kilovolts peak potential (kVp)

Michael Shortsleeve, MD & Thomas Osborne, MD

Energy = kVpAmount = ma

BackgroundX-ray Production

• Higher mA values = more electrons =more X-rays– The relationship is directly proportional

• Increasing kVp = an increase in the energy of the X-ray

–However, this relationship is not directly proportional

• The total number of X-rays produced at a set kVp depends directly on the product of the mA and exposure time and is described in terms of mA-s

Michael Shortsleeve, MD & Thomas Osborne, MD

Energy = kVpAmount = maTotal xrays = mAs

BackgroundDescription of Radiation Exposure Terms

•X-ray machine output is described in terms of Entrance Skin Exposure (ESE) "table-top dose."

–Amount of radiation delivered to the skin–Units of ESE are Roentgens per minute (R/min)

Michael Shortsleeve, MD & Thomas Osborne, MD

Wilhelm Conrad Röentgen

BackgroundDescription of Radiation Exposure Terms

•Patient radiation exposure is described in terms of radiation dose •Radiation dose is:

–The energy imparted per unit mass of tissue –And has the units of Rad –Rad is an acronym for Radiation Absorbed Dose–Immediate biological effects are described in terms of Rad

Michael Shortsleeve, MD & Thomas Osborne, MD

BackgroundDescription of Radiation Exposure Terms

•Occupational radiation exposure is also described in terms of radiation dose

–However, the unit used is called the Rem –Roentgen Equivalent Man

–Rems are synonymous with risk of latent Health effects–Dose equivalent was developed in an effort to incorporate biology into the physics of radiation exposure

For discussion: 1 Rad = 1 Rem

Michael Shortsleeve, MD & Thomas Osborne, MD1 chest X-ray = about 6 mrem1 CAT Scan = about 110 mrem

1 rem = 1,000 mrem

X ray interaction

X-rays have several fates:

•No interaction: X-ray passes completely through tissue–To the image recording device

•Complete absorption: X-ray energy is completely absorbed–No imaging information results

•Partial absorption with scatter: Scattering involves a partial transfer of energy to tissue, a different trajectory

–Degrade image quality–Primary source of radiation exposure to operator and staff

Michael Shortsleeve, MD & Thomas Osborne, MD

X ray interaction

•Probability of radiation interaction is a function of:–Tissue electron density –Tissue thickness–X-ray energy (kVp)

•Dense material attenuates more –Bone, barium, iodine

•The differential rate of attenuation provides the contrast necessary to form an image

Michael Shortsleeve, MD & Thomas Osborne, MD

X ray interaction Exposure

•The primary beam X-rays travel in straight but divergent directions as they exit the X-ray machine

•The degree of divergence increases with distance away from the X-ray origin (tungsten target)

Michael Shortsleeve, MD & Thomas Osborne, MD1 chest X-ray = about 6 mrem1 CAT Scan = about 110 mrem

• Consequently, the number of X-rays traveling through a unit area decreases with increasing distance•Therefore, radiation exposure decreases with increasing distance

–Exposure is directly proportional to the # of X-rays/unit area–The inverse square law

Michael Shortsleeve, MD & Thomas Osborne, MD1 chest X-ray = about 6 mrem1 CAT Scan = about 110 mrem

X ray interaction Exposure

ExposureThe Inverse Square Law

•XA = the radiation exposure rate at distance DA

•XB = the radiation exposure rate at distance DB

•Therefore doubling the distance from a radiation source decreases radiation exposure by a fourth

Michael Shortsleeve, MD & Thomas Osborne, MD1 chest X-ray = about 6 mrem1 CAT Scan = about 110 mrem

ExampleThe Inverse Square Law

•An operator normally stands 1 meter away–If the exposure rate at this point is 15 mrem/min–And if the total time is 2 min (= 30 mrem)

•What is the reduction at 1.2 meters away?

Michael Shortsleeve, MD & Thomas Osborne, MD1 chest X-ray = about 6 mrem1 CAT Scan = about 110 mrem

ExampleThe Inverse Square Law

•An operator normally stands 1 meter away.–The exposure rate at this point is 15 mrem/min–Total time is 2 min. (= 30 mrem)

•What is the reduction at 1.2 meters away?

Michael Shortsleeve, MD & Thomas Osborne, MD

A 31% percent reduction in radiation exposure is achieved in this example.

1 chest X-ray = about 6 mrem1 CAT Scan = about 110 mrem

Fluoroscopy

•X-ray tube (under table)•X-rays, captured by an Image Intensifier (above table)

–Which converts the X-ray energy into light. –Light output is then distributed to a closed-circuit video –Output can also be distributed to a spot film or cine.

•Although the output must be greater•10 – 20 x greater with cine•“Last Image Hold” option

Michael Shortsleeve, MD & Thomas Osborne, MD

Saint Luke’s Health System Fluoroscopy Users Manual

FluoroscopyScatter

•Radiation is scattered in all directions–However, radiation levels are significantly lower above the table than below because of tissue attenuation in the forward direction

Michael Shortsleeve, MD & Thomas Osborne, MD

•The scatter radiation profile tilts with the X-ray tube•Less exposure on the II side of the table when oblique angles are being imaged

–tissue attenuation

Michael Shortsleeve, MD & Thomas Osborne, MD

FluoroscopyScatter

•Larger field = more tissue irradiated•Larger field = increased scatter radiation

–Some of this scatter will degrade the resulting image –Some of this extra scatter will enter you

•Therefore, cone down the image

Michael Shortsleeve, MD & Thomas Osborne, MD

Fluoroscopy Field Size and Collimators

Fluoroscopy Automatic Brightness Control (ABC)

•ABC mode was developed to provide a consistent image quality during dynamic imaging•With ABC, output is adjusted automatically to bring the brightness to a constant, proper level

–Ex: when there is too much dark, the mA, kVp, or both, increase –The ABC compensates brightness loss caused by decreased xray reception by generating more X-rays–Therefore, a bigger patient or more dense material = more exposure

Michael Shortsleeve, MD & Thomas Osborne, MD

Fluoroscopy Magnification Modes

•Magnification by electronically manipulating a smaller radiation II input area over the same II output area •The ABC system compensates for the lower output brightness by increasing radiation production and subsequent exposure to patient and staff

Michael Shortsleeve, MD & Thomas Osborne, MD

(Field-Of-View) ESE (R/min) Increase Factor

Normal(9 inch) 1.2 1.0

Mag 1(6 inch) 2.9 2.4

Mag 2(4.5 inch) 5.2 4.3

Saint Luke’s Health System Fluoroscopy Users Manual

Fluoroscopy Magnification Modes

Michael Shortsleeve, MD & Thomas Osborne, MDSaint Luke’s Health System Fluoroscopy Users Manual

Radiation BiologyStochastic Effects

•Carcinogenesis •A non-threshold linear response to the dose-effect relationship•1 rem to 1 million persons would result in an increase in cancer deaths from 190,000 to 190,400

–increase of 0.2 %

Michael Shortsleeve, MD & Thomas Osborne, MD

National Council on Radiation Protection and Measurements. Recommendations on limits for exposure to ionizing radiation, NCRP Report No. 91, Bethesda, MD,1987.

•Effects that appear only above a threshold dose •The threshold may vary from person to person•The severity of these effects increases with increasing dose above the threshold•Most of these deterministic effects are seen within days or weeks after the exposure, but cataracts may appear a few years after exposure

Michael Shortsleeve, MD & Thomas Osborne, MD

Radiation BiologyDeterministic Effects

Radiation BiologyDeterministic Effects

Michael Shortsleeve, MD & Thomas Osborne, MD

Effect Threshold Hours of Fluoro Hours of Cine effect(rad) 5 R/min 30 R/min

Transient Erythema 200 0.7 0.1 24 hrEpilation 300 1 0.2 3 wkErythema 600 2 0.3 10 dayPericarditis 800 2.7 0.4 >10 wkDermal Necrosis 1800 6 1 >10 wk

Saint Luke’s Health System Fluoroscopy Users Manual

Symptomatic Skin Reactions

•Two case reports–Unfortunately, many more in the literature

Michael Shortsleeve, MD & Thomas Osborne, MD

Symptomatic Skin Reactions

•On March 29, 1990, a 40-year-old male underwent coronary angiography, coronary angioplasty…

–And a second angiography procedure (due to complications) followed by a coronary artery by-pass graft.

•Total fluoroscopy time estimated to be > 120 min

Michael Shortsleeve, MD & Thomas Osborne, MD

Case Report #1:

Thomas B. Shope, Ph.DScientific Exhibit 060PH at the 81st Scientific Asssembly and Annual Meeting of theSociety of North America, November 26 - December 1, 1995. Radiology Vol. 197(P) Supplement, P449

Symptomatic Skin Reactions

7 w following the procedures

Michael Shortsleeve, MD & Thomas Osborne, MD

Case Report #1:

Thomas B. Shope, Ph.DScientific Exhibit 060PH at the 81st Scientific Asssembly and Annual Meeting of theSociety of North America, November 26 - December 1, 1995. Radiology Vol. 197(P) Supplement, P449

Symptomatic Skin Reactions

21 M following the procedures

Michael Shortsleeve, MD & Thomas Osborne, MD

Case Report #1:

Thomas B. Shope, Ph.DScientific Exhibit 060PH at the 81st Scientific Asssembly and Annual Meeting of theSociety of North America, November 26 - December 1, 1995. Radiology Vol. 197(P) Supplement, P449

Symptomatic Skin Reactions

Following skin grafting procedure

Michael Shortsleeve, MD & Thomas Osborne, MD

Case Report #1:

Thomas B. Shope, Ph.DScientific Exhibit 060PH at the 81st Scientific Asssembly and Annual Meeting of theSociety of North America, November 26 - December 1, 1995. Radiology Vol. 197(P) Supplement, P449

Symptomatic Skin Reactions

•Pt had a 20 min cardiac catheter ablation –Prior to the procedure the separator cones were removed so that the fluoroscopic c-arms could be easily rotated around the patient –The separator cone is a spacer attached to the tube housing designed to keep the patient at a reasonable distance from the x-ray source–This is done specifically to avoid the high skin-dose rates that can be encountered near the tube port

Michael Shortsleeve, MD & Thomas Osborne, MD

Case Report #2:

Benjamin R. Archer Louis K. Wagner Protecting patients by training physicians in fluoroscopic radiation management, Journal of Applied Clinical Medical Physics, Vol.1, No.,1, Winter, 2000.

Symptomatic Skin Reactions

•During the procedure, the right arm moved into the field

•However, personnel were not aware of this change because sterile covers were draped over the patient

Michael Shortsleeve, MD & Thomas Osborne, MD

Case Report #2:

Benjamin R. Archer Louis K. Wagner Protecting patients by training physicians in fluoroscopic radiation management, Journal of Applied Clinical Medical Physics, Vol.1, No.,1, Winter, 2000.

Symptomatic Skin Reactions

•3 w s/p the procedure –Bright erythema

Michael Shortsleeve, MD & Thomas Osborne, MD

Case Report #2:

Benjamin R. Archer Louis K. Wagner Protecting patients by training physicians in fluoroscopic radiation management, Journal of Applied Clinical Medical Physics, Vol.1, No.,1, Winter, 2000.

Symptomatic Skin Reactions

•3 w s/p the procedure –Bright erythema

•5 m s/p procedure –A large ulcer the size of the collimated x-ray port

Michael Shortsleeve, MD & Thomas Osborne, MD

Case Report #2:

Benjamin R. Archer Louis K. Wagner Protecting patients by training physicians in fluoroscopic radiation management, Journal of Applied Clinical Medical Physics, Vol.1, No.,1, Winter, 2000.

Symptomatic Skin Reactions

•3 w s/p the procedure –Bright erythema

•5 m s/p procedure –A large ulcer the size of the collimated x-ray port

•8 m, s/p procedure–Debridement

Michael Shortsleeve, MD & Thomas Osborne, MD

Case Report #2:

Benjamin R. Archer Louis K. Wagner Protecting patients by training physicians in fluoroscopic radiation management, Journal of Applied Clinical Medical Physics, Vol.1, No.,1, Winter, 2000.

Symptomatic Skin Reactions

•3 w s/p the procedure –Bright erythema

•5 m s/p procedure –A large ulcer the size of the collimated x-ray port.

•8 m, s/p procedure–Debridement and a surgical flap

Michael Shortsleeve, MD & Thomas Osborne, MD

Case Report #2:

Benjamin R. Archer Louis K. Wagner Protecting patients by training physicians in fluoroscopic radiation management, Journal of Applied Clinical Medical Physics, Vol.1, No.,1, Winter, 2000.

How to decrease overall exposure

•ALARA concept–i.e. As Low As Reasonably Achievable

Michael Shortsleeve, MD & Thomas Osborne, MD

• Caution modifying equipment• Decrease fluoro time• Last image hold• Pulsed fluoro• Decrease II – patient gap• Cone down image (lead shutters)• Avoid mag views• Avoid cine run

Michael Shortsleeve, MD & Thomas Osborne, MD

Decrease patient exposure

Decrease personnel exposure

•Decrease patient exposure•Increase distance•Avoid x-ray tube side of table•Shield•Lead Aprons, gloves, glasses•Fluoro on!

Michael Shortsleeve, MD & Thomas Osborne, MD

Decrease complications

•History of prior radiation therapy

•10 day rule for women of childbearing age

Michael Shortsleeve, MD & Thomas Osborne, MD

ConclusionThe risk of adverse radiation effects originating from a medically necessary procedure is almost always offset by the benefit received by the patient

However, inadequate training can produce patient and staff doses that lead to serious consequences

ConclusionIn this talk we covered:

• 1. Background radiation to the general public• 2. X ray production and terms• 3. X ray interaction• 4. The Fluoroscopy machine

-And specific related exposure concerns • 5. Radiation Biology• 6. Tips to decrease patient and operator exposure

Michael Shortsleeve, MD & Thomas Osborne, MD

Radiation SafetyThe End

Thank You

Decrease personnel exposure

• Decrease patient exposure

• Increase distance• Avoid x-ray tube side

of table• Shield• Lead Aprons, gloves,

glasses• Fluoro on!

Michael Shortsleeve, MD & Thomas Osborne, MD

• Caution modifying equipment• Decrease fluoro time• Last image hold• Pulsed fluoro• Decrease II – patient gap• Cone down image (lead shutters)• Avoid mag views• Avoid cine run

Decrease patient exposure