Radiation Doses and Safety Considerations Medical College of Georgia G. David, M.S., DABR Associate Professor of Radiology

Radiation Safety Whom are we protecting? Patient Physicians & Staff General Public *

Patient Dose Factors / Considerations Fluoroscopic exposure time or # of radiographic exposures Beam parameters Intensity Penetration Distance from x-ray tube Beam size Sensitivity of exposed organs damage threshold

It is possible to inflict damage during radiology procedures! Courtesy FDA Web Site: weeks post fluoroscopic procedure months post procedure Close-up *

Joint Commission Sentinel Event Policy Prolonged fluoroscopy with cumulative dose >1500 rads to a single field Each accredited health care organization is encouraged, but not required, to report to The Joint Commission any sentinel event meeting these criteria.

Patient Dose Depends Upon patient thickness body part in beam Operator-controlled factors Technique settings magnification mode operational mode normal / high dose Collimation (beam size) *****

Patient Dose - Exposure Time / # exposures Fluoroscopy patient exposure proportional to beam-on time Radiography # studies ordered # of films / study Cine / angio Long fluoro times Many images recorded *

Beam Size (Collimation) Reduces volume of tissue irradiated II Tube X-Ray Tube II Tube X-Ray Tube

Minimizing Patient Exposure Consistent with clinical goals minimize fluoroscopic beam-on time # of exposures cine / angio fluoro times & images Beam size (as small as clinically feasible)

Operator Protection Considerations Time Distance Shielding Collimation

Operator Protection - Time Minimize “beam-on” time Your exposure is directly proportional to beam time

Operator Protection – Distance (“Inverse Square Law”) Exposure rate falls off quickly with distance If distance doubles, exposure rate drops by 4

Radiation Protection of Operator - Shielding Sources of radiation for operator Primary Scatter Leakage

Primary X-Ray Beam Beam coming from x-ray tube Operator should avoid primary beam keep hands, etc. out of primary beam area Source of most patient exposure II Tube X-Ray Tube X Primary Beam (High Intensity)

Scatter (Indirect) Radiation Arises mostly from patient Emitted in all directions intensity varies Much lower intensity than primary Source of virtually all operator exposure II Tube Table Patient X-Ray Tube TV Camera

Leakage Radiation Some radiation leaks through x-ray tube housing Intensity much lower than scatter Negligible contribution II Tube Table Patient X-Ray Tube TV Camera

Operator Protection - Shielding Shield between patient & operator significantly reduces exposure to operator

Operator Protection - Shielding Apron Gloves Lead Drapes Face Shield Thyroid Shield Ceiling-mounted shield

Collimation Reducing field size significantly reduces scatter radiation Smaller scattering volume More shielding from patient Image Receptor X-Ray Tube Image Receptor X-Ray Tube

Minimizing Operator Exposure Consistent with clinical goals minimize time fluoroscopic exposure times cine run lengths & frame rates Use available lead protective apparel whenever possible. Collimate as tightly as feasible Education

Protecting the General Public: Lead Shielding for x-ray Rooms Physicist calculates shielding for each wall or barrier Shielding requirement depends on Workload Distances Exam Types Use of adjacent space

Radiation Risk Categories Deterministic (non-stochastic) Stochastic

Deterministic (non-stochastic) Radiation Risks Effect has known threshold radiation dose Examples Erythema Cataract formation Clearly addressed by regulations

Stochastic Radiation Risks Radiation affects probability of condition which also occurs naturally Cause of condition cannot be determined Severity of condition independent of dose Examples Genetic effects Fetal abnormalities Cancer

Stochastic Effects Published data based primarily on high doses Regulations based on a linear model 1/10,000 of the dose produces 1/10,000 the frequency of the effect Linear model is controversial!!!

Background Radiation Earth Air Cosmic People

Threshold for Skin Effects from Radiation 300 rad temporary epilation 600 rad main erythema rad moist desquamation dermal necrosis secondary ulceration Reference: Triumf Safety Group

Threshold for Other Biological Effects from Radiation Cataract induction 200 rads Acute radiation syndrome rads whole body irradiation Permanent Sterility rads to gonads females rads to gonads males Reference: Huda

Threshold for Other Biological Effects from Radiation Fetal doses below 1 rad result in negligible congenital abnormalities Risk from acute doses below 10 rads considered “small” Abortion not commonly considered Reference: Huda

Diagnostic Radiology Exposures Generally very low compared to previous values Greatest concerns Fetal doses Angiography / cardiac cath / interventional studies CT

Exposure Measurement Protocols Standardized methodology for determining how much radiation patient receives Different protocol for each modality Usually provided for “average” or “typical” patient

Exposure Measurement Protocols Radiograpy Entrance Skin Exposure (ESE) Mammography Mean glandular dose CT CT dose index (CTDI) Dose length product (DLP)

Radiography / Fluoroscopy Entrance Skin Exposure Ionization measured where radiation enters patient Does not address internal doses which depend upon Beam penetrability Absorber Tabletop “Patient” R

Entrance Skin Exposures u PA Chest mR u Abdomen: ~300 mR

Entrance Skin Exposures u Elbow: ~20 mR u Hand ~ 20 mR u Femur ~ 200 mR u AP Skull ~ 150 mR

Entrance skin exposures. Internal doses will be substantially less.

Typical Fluoroscopy Exposure Tabletop “Cruise control” varies exposure rate automatically Varies greatly with Patient Imaged anatomy Typical Skin Exposure for “Average” patients R / minute Beam on time Legal maximum table top exposure: 10 R/min (20 R/min in high dose mode)

Angiography / Interventional / Cardiology Long fluoroscopic beam times Multiple imaging exposures Cine (cardiology) Subtraction images (Angiography) Caution

Mammography Mean Glandular Dose (MGD) Calculated from entrance skin exposure “Typical” breast assumptions 4.2 cm thick (accreditation phantom) Breast firmly compressed Breast composed of 50% adipose / 50% glandular tissue average breast closer to 70% adipose / 30% glandular tissue

Measuring Mean Glandular Dose (MGD) Measure ESE with chamber Compression paddle & accreditation phantom in place MGD calculated from ESE Mammo Tube Compression Device Breast Support Image Receptor Grid Phantom R

Mammography Mean Glandular Dose Limits ACR 100 mrad w/o grid 300 mrad w/ grid MQSA 300 mrad CC View FDA approved phantom Typical ~100 mrad (digital)

CT Patient Dose Because tube rotates around patient, dose distribution different from radiography Skull dose distribution Fairly uniform Body dose distribution Dose to center of body ~ half of skin dose

CT Dose Phantom Lucite 5 holes One center Four in periphery Comes in two flavors “Head” “Body”

CT Dose Measurement Chamber placed in one hole Lucite plugs placed in remaining 4 holes Slice centered on phantom Standardize technique kVp mAs scan time pitch beam thickness Chamber Plugs

Measuring CT Dose “Pencil” ion chamber used Pencil pointed in “Z” direction Dose Phantom Chamber Z Beam

Typical CT Doses 4 rads head 2 rads body Surface doses for body scans may be 2X the dose at center

CT Usage Annual growth U.S. Population: <1% CT Procedures: >10% ~ 67,000,000 procedures in 2006 about 10% pediatric CT Computed Tomography — An Increasing Source of Radiation Exposure David J. Brenner, Ph.D., D.Sc., and Eric J. Hall, D.Phil., D.Sc. New England Journal of Medicine, 2007

500% medical exposure increase in 24 years

CT Usage 16% of imaging procedures 23% of total per capita exposure 49% of medical exposure

CT Causes Cancer? “On the basis of …data on CT use from 1991 through 1996, it has been estimated that about 0.4% of all cancers in the United States may be attributable to the radiation from CT studies…By adjusting this estimate for current CT use this estimate might now be in the range of 1.5 to 2.0%.” Computed Tomography — An Increasing Source of Radiation Exposure David J. Brenner, Ph.D., D.Sc., and Eric J. Hall, D.Phil., D.Sc. New England Journal of Medicine, 2007

CT Causes Cancer? In the United States, of approximately 600,000 abdominal and head CT examinations annually performed in children under the age of 15 years, a rough estimate is that 500 of these individuals might ultimately die from cancer attributable to the CT radiation. Estimated Risks of Radiation-Induced Fatal Cancer from Pediatric CT; Brenner, Elliston, Hall, & Berdon; AJR-176 Feb. 2001

Other Modalities Ultrasound No known biological effects as used clinically Greatest concerns Fetus Temperature elevation MRI No known biological effects as used clinically