Exposures Exam II

Ways to Reduce Patient Exposure

• proper body or part immobilization

• motion reduction techniques

• collimation (appropriate beam limitation devices)

• adequate filtration of the x-ray beam

• gonadal or other specific area shielding

• suitable technical exposure factors in with computer-generated digital images

• appropriate digital image processing

• eliminate repeats

Effective Communication

when verbal and nonverbal messages are understood as intended

Immobilization: Consequences, Minimization, Types + Examples

Consequences: repeated & additional exposure

Minimized by: proper body or part immobilization & use of motion reduction techniques

Types of motion: voluntary & involuntary

• children, conditions, dementia

Protective Shielding (Parts & Steps)

Parts to Shield: eye lens, breasts, gonads & thyroid

Steps: collimate THEN shield

JRCERT on Protective Shielding

do not use shielding for abdominopelvic radiography exams when it could interfere with diagnostic value and may lead to repeats

Gonadal Shielding + Types

Female gonads receive ~3x more exposure during exams than males

Types

• flat contact - like a blanket

• shadow - piece of metal placed right below tube

• shaped contact - cup-like shape (may be held in place by suitable carrier)

• clear lead

What kind of shielding is this?

Flat contact shield

What kind of shielding is this?

Shadow shield

What kind of shielding is this?

Clear lead shield (shadow shield)

What kind of shielding is this?

Shaped contact shield

What kind of shielding is this?

Clear lead shield

Specific Area Shielding

Shielding used for radiosensitive organs and tissues other than reproductive organs

• use clear lead shadow shield for breasts & gonads

• used in conjunction with PA than AP

• minimizes the number of potentially deleterious x-ray induced mutations expressed in future generations

Repeat Images

“double dose” to skin & possibly gonads

Repeat Analysis Program + Reasons

By determining # & reasons of repeats, existing problems & conditions in an imaging department will be identified

Reasons

• mispositioning

• incorrect centering of CR

• motion during exposure

• incorrect collimation

• presence of external foreign bodies

• postprocessing artifacts

Unnecessary Radiologic Procedures

• benefit vs. risk lays on the referring physician’s responsibility to order it

• exams performed in the absence of definite medical indications (no benefit for the patient in terms of useful information gained)

Unnecessary Radiologic Procedures

1. chest X-ray upon automatic hospital admission

2. chest X-ray for preemployment physical

3. lumbar spine exam for preemployment physical

4. chest X-ray for routine health checkup

5. chest X-ray for TB screening

6. whole-body CT

Specifying Radiation Amount Received from Diagnostic Imaging Procedures

1. entrance skin exposure (ESE)

   1. includes skin & glandular

   2. most frequently used because the simplest to determine

   3. use of TLDs to measure skin directly

2. bone marrow dose (estimated)

3. gonadal dose

GSD

• Genetically Significant Dose

• used to assess impact of gonadal dose

• equivalent to EqD to gonads that, if received by every human, would expect to bring identical gross genetic injury to total population

• GSD for U.S. population: 0.20 mSv

FGP

• Fluoroscopically Guided Positioning

• ASRT DOES NOT CONDONE

• causes excessive unneccessary exposure

Protecting Potentially Pregnant Patients

1. ask patient the date of last mentrual period (LMP)

   1. fine if within 10 days

2. ordering physician may order pregnancy test (if receiving substantial pelvic iradiation) & obtain results BEFORE pelvis is irradiated

3. ordering physician (or patient) determines to do or not to do X-ray examination

ACR’s Position on Abdominal Radiologic Exams on Female Patients

Abdominal exams requested after full consideration of patient’s clinical status including pregnancy cannot be postponed or be scheduled

Protecting KNOWN Pregnant Patients

1. if physician feels it’s best to undergo radiologic examination, perform without delay

2. take special effort to minimize dose of radiation in lower abdomen & pelvic region

   1. restrictively select minimal exposure factors for useful image

   2. precisely collimate

3. if patient’s lower abdomen & pelvic region don’t need to be included, SHIELD

   1. also shield ovaries & uterus less than 5 cm from any edge of field

Position of NCRP Concerning Risk & Fetal Exposure with Regard to Pregnancy Termination

• negligible risk if 5 or less cGy to the fetus BUT chance of malformations is significantly increased if more than 15 cGy

• diagnostic imaging should NOT be blamed for a therapeutic abortion

Irradiating an UNKNOWN Pregnant Patient

• usually done in emergency scans!

• first, list the particulars of the X-ray exam in as much detail as possible

  • X-ray unit(s) used

  • projections taken

  • # of images associated with each exam

  • each projection’s technical factors (kVp, mAs & IR size)

  • SID for each projection

  • patient’s AP or lateral dimensions at site of each projection

  • if fluoroscopic, the ~ kVp, mA & especially duration

  • if spot films, the # taken, the kVp, mA & ~ exposure time

Absorbed EqD Determination to Embryo & Fetus Procedure & Responsibilities

1. collect necessary details on summary form & relate to RSO/medical physicist

2. determine embryo-fetus absorbed EqD

   1. calculations include measurements of radiation output on X-ray unit(s)

   2. dose estimate of ~EqD from exam is supplied to physician

   3. refer to sample cases used to estimate ~EqD to the embryo-fetus

Pediatric Considerations During Radiographic Imaging

• children are much more vulnerable to late somatic effects AND genetic effects than adults

• require smaller radiation doses than adults

• motion reduction methods

  • very short exposure times & select high mAs

  • effective immobilization

• gaining cooperation during procedure

  • use specially designed rooms for pediatric exams with entertainment & distraction devices

  • communication is important!!

• gonadal shielding & gonadal dose

• collimation

Image Gently Campaign

• initiative of the Alliance for Radiation Safety in Pediatric Imaging

• goal: raise awareness about methods for lowering radiation dose during pediatric medical imaging examinations

Image Wisely Campaign

objective: lowering the amount of radiation used in medically necessary procedures (all ages)

Procedures That Increase Radiographer’s Exposure Risk from Scatter Radiation

• general fluoroscopy

• interventional procedures that emply high-level control (HLCF)

• mobile exams

• C-arm fluoroscopy

Why should no radiographer approach an EfD of 50 mSv?

By keeping with ALARA & diligent supervision of personnel cumulative radiation exposure records

EfD Review! (excludes…, Occupational CumEfD & annual limits)

Excludes

• personal medical exposure

• natural background exposure

Occupational CumEfD: should not exceed their age x 10 mSv

Frequent general population individuals: 1 mSv annually

Infrequent general population individuals: 5 mSv

Allowance for Larger EqD for Radiation Workers

• radiation-related workforce is small compared to whole population

• amount of radiation received by this workforce can be larger than the public without alteration in the genetically significant dose (GSD)

• EqD still minimized to reduce potential for somatic damage & genetic damage

Dose-Reduction Methods & Techniques (7)

Patient is source of scattered radiation (greatest occupational hazard; Compton interactions)

• @ 90° angle to primary X-ray beam at 1 m, scattered intensity is ~ 1/1000

1. filtration benefits patient & reduces scatter

   1. removes non-useful low-energy photons that interact with patient’s body → increases scatter → increase radiographer EqD

2. protective apparel (from secondary/scatter & leakage)

   1. minimum of 0.25mm, standard of 0.5mm (fluoro) & 1mm

   2. wraparound is best!

3. technical exposure factors

4. eliminate repeats

   1. digital image contrast & brightness can be manipulated AFTER capture

5. patient restraint (immobilization)

   1. use mechanical restraining devices if necessary & possible

   2. try to ask non-occupationally exposed persons (not pregnant women)

6. radiographers should never stand in primary/useful beam during exposure

   1. when holding patient

7. use film holder for IR (never hold!)

Dose Reduction Technical Exposure Factors

• use higher kVp - increases mean photon ENERGY of photons in beam

  • as average energy increases, % of forward-scatter increases AND side-scatter decreases

• use lower mAs - decreases photon beam INTENSITY/# of photons

  • fewer photons to produce Compton scatter

Imaging Department Protocol for Pregnant Personnel (+ duties & EqD limit) (7)

Should be able to continue duties without interruption & follows policies to protect themselves from radiation

EqD limit designed to significantly restrict total lifetime risk of leukemia and other malignancies in person exposed in utero

1. voluntary “declaration” of the pregnancy

2. facility officially recognizes pregnancy

3. RSO provides counseling & furnishes waist monitor (under any aprons)

4. pregnant technologist must read & sign form acknowledging that she has received counseling & understands safety practices

5. dosimeter companies provide a separate monthly report that trackers worker & embro-fetus exposure

6. maternity protective aprons

   1. 0.5 mm Pb/eq over entire length & width

   2. 1 mm Pb/eq

   3. 0.5 mm Pb/eq wraparound

7. work schedule alteration

   1. work schedules designed to distribute risk evenly to all employees

   2. no reassign needed because of increased risk of others

   3. not to exceed 0.5 mSv monthly & 5.0 mSv for entire gestation

Time Principle of Radiation Protection for Personnel

Time: decreasing length of time spent in room where X-radiation is being produced

• directly proportional

• most fluoroscopy equipment have 5-min timers

Distance: standing @ greatest possible distance from energized X-ray beam

• most effective means of protection

• inverse square law

Shielding: interposing radiation-absorbent shielding material between worker & source

• used when not possible to use time and/or distance principles

• lead & concrete art the most common structural protective barrier materials

• protective shielding of appropriate thickness

• accessory devices: aprons, gloves, eyeglasses & thyroid are made of lead-impregnated vinyl

Distance Principle of Radiation Protection for Personnel

Distance: standing @ greatest possible distance from energized X-ray beam

• most effective means of protection

• inverse square law

Shielding Principle of Radiation Protection for Personnel

Shielding: interposing radiation-absorbent shielding material between worker & source

• used when not possible to use time and/or distance principles

• lead & concrete are the most common structural protective barrier materials

• protective shielding of appropriate thickness

• accessory devices: aprons, gloves, eyeglasses & thyroid are made of lead-impregnated vinyl

• effectiveness depends on: atomic number, density & thickness

• qualified medical physicist determines exact protection requirements of protective structural shielding

Inverse Square Law

• expresses relationship between distance & intensity (quantity) of radiation

• “The intensity of radiation is inversely proportional to the square of the distance from the source”

• I₁/I₂ = (D₂)²/(D₁)²

What does attenuate mean?

Stops X-rays

Primary Protective Barrier

Purpose: to prevent direct, or unscattered, radiation from reaching personnel or general public on other side of barrier

Location: perpendicular to the undeflected line of travel of the X-ray primary beam

Specifications for 120 kVp beam…

• 1.6 mm (1/16 in.) Pb

• extends 2.1 m (7 ft) upward from floor if tube is 1.5-2.1 m (5-7 ft) from wall in question

Secondary Protective Barrier

Purpose: protects against secondary radiation (leakage & scatter)

Location: any wall or barrier that is never struck by primary beam (primary can be hit too)

Specifications

• consist of 0.8 mm (1/32 in.) Pb

• should overlap primary protective barrier by ~1.27 cm (1/2 in.)

Other Information

• personnel must remain completely behind barrier

• observation window w/ lead in barrier typically consists of 1.5 mm Pb/eq (~30%)

• exposure of radiographer will not exceed 1 mSv/week or 0.02 mSv/week in well-designed facility

• exposure cord should be short enough to only be operated when radiographer is completely behind the control-booth barrier

Control-Booth Barrier

Purpose: to protect radiographe from secondary radiation (leakage & scatter)

Location: in X-ray rooms housing permanent/nonportable radiographic equipment

Specifications

• must extend 2.1 m (7 ft) upward from floor (permanently secured)

Other Information

• should scatter 2+ times before reaching any area behind this barrier

Clear Lead-Acrylic Secondary Protective Barrier

Purpose: permits panoramic view to observe patient more completely

Location: mobile

Specifications

• impregnated with ~30% Pb by weight

• can extend 2.1 m (7 ft) upward from floor

• available in Pb/eq from 0.3-2 mm

Other Information

• shatter resistant

Clear Lead-Acrylic Overhead Protective Barrier

Purpose: can be used as overhead X-ray barrier to provide open view during special procedures & cardiac catheterization

Specifications

• typically offers 0.5 mm Pb/eq

Accessory Protective Devices

Aprons

• physical weight concerns

• can be impregnated with tin

• for 100 kVp, must be 0.25 mm Pb/eq

• 0.5 mm Pb/eq is most widely recommended

Gloves

• 0.25 mm Pb/eq

Thyroid

• guards during general fluoroscopy & X-ray special procedures

• minimum of 0.5 mm Pd/eq

Eyeglasses

• reduce scatter radiation to eye lens

• minimal 0.35 mm Pb/eq

X-Ray Tube Housing Cables

Radiographers should avoid handling or severely bending the high-tension cables connected to the (+) & (-) terminals of the tube, ESPECIALLY during any procedure

Fluoroscopy: Personnel Protection

• stand as practically far away from patient and ONLY move closer when assistance is required

• apron: no less than 0.5 mm Pb/eq (wraparound is best!)

• gloves: no less than 0.25 mm Pb/eq

• thyroid: no less than 0.5 mm Pb/eq

• protective curtain: no less than 0.25 mm Pb/eq

• bucky slot: no less than 0.25 mm Pb/eq

• stand behind physician or behind booth unless assistance needed

Fluoroscopy: Dose-Reduction Techniques

• adequate beam collimation

• adequate filtration

• control of technical exposure factors

• appropriate source-to-skin distance (SSD)

• use of cumulative timing device

• diagnostic-type protective X-ray tube housing

Fluoroscopy: Remote Control Systems

• provides personnel best radiation protection opportunity

• permits personnel to remain outside of fluoroscopic room at console behind barrier

• added ISL protection

Fluoroscopy: Bucky Slot Shielding Device

• must automatically cover Bucky slot opening in table side during standard fluoroscopic exam when tray is positioned at the foot of table

• protects personnel at gonadal level

Mobile Exams: Protection

• use mobile X-ray unit remote control if available!

• for non-remote-controlled, cord must be at least 2 m (~6 ft) from patient, tube & useful beam

• should stand 90° to beam-scattering object (patient) when distance & shielding have been accounted for

C-Arm Fluoroscopy: Protection

• patterns of exposure direction are less predictable

• physicians who operate equipment may have less training & experience of an experienced technologist

• exposure from scatter radiation (probably because it’s from the side of patient)

• exposure rate near entrance surface (X-ray tube side) of patient EXCEEDS exposure rate caused by scatter near exit surface (image intensifier side)

C-Arm Fluoroscopy: Need for Protective Apparel for All Personnel & Monitoring

• procedures needing C-arm to be energized for long periods of time increase radiation exposure

• personnel that routinely operate C-arm must wear Pb apron & neck/thyroid 0.5 Pb/eq

• appropriate monitoring of imaging personnel is MANDATORY

C-Arm Fluoroscopy: Positioning

best to place tube under table & image intensifier over table for increased radiation safety

• helps contain scatter radiation on floor

C-Arm Fluoroscopy: Exposure Reduction for Personnel

• minimize beam-on time

• be aware of cumulative timer

• use image storage device (e.g. last image hold)

• position image intensifier end close to the patient

• collimate

• use distance whenever possible

• use magnification feature sparingly (should be used ONLY on performing physician request)

HLCF: Importance of Safety

• extended length of these procedures

• large number of digital images that are taken

• frequent use of high-level-control (boost) mode of operation

  • can range up to 20-40 cGy/min

• exposure rate may significantly exceed rate used in routine fluoroscopy

HLCF: Radiographer Should Verify Dose-Reducing Features Are Available & In Good Working Order

• high-quality low-dose fluoroscopy mode

• pulsed beam operation

• collimation

• filtration

• removable grids

• “roadmapping”

• time-interval differences

• last-image-hold mode

HLCF: How the Interventional Physician Can Reduce Radiation Exposure

• decreasing procedure duration (& beam-on time)

• taking fewer digital images

• reducing continuous fluoroscopic mode compared to pulsed mode

• keeping protective curtain on image intensifier or scatter shield during procedure

• regularly using last-image-hold feature

HLCF: Extremity Monitoring

• performing physician hands & forearms must be monitored

  • subject to large radiation exposure if protocol not followed

• physicians need to be aware of NCRP dose limits for extremities

  • annual EqD limit: 500 mSv for skin

  • wear gloves!!

Diagnostic X-Ray Suite Protection Design

every room in X-ray department must be equipped with radiation-absorbed barriers to reduce EqD to radiographers, other personnel & the public to levels safe by federal & international bodies

Reasons for Over-Shielding

1. to meet necessary radiation protection standards by taking all factors into account (designer)

2. designer plans conservatively to satisfy potentially more strict rules + ALARA = over-shielding

3. more expensive to add more shielding after suite done than during its initial construction

Radiation Source Categories in an X-Ray Room

1. primary radiation

2. scatter radiation (secondary)

3. leakage radiation (secondary)

Diagnostic X-Ray Suite Protection Design Calculation Considerations

• Workload (W) - radiation output-weighted time that the unit is actually delivering (weekly) (e.g. min/week)

• Inverse Square Law - intensity of the beam is lessened as the distance from its source increases

• Use Factor (U)/beam direction factor - quantity introduced to select fractional contact time that most structures in a diagnostic X-ray suite are struck by radiation to some degree

• Occupancy Factor (T) - modify shielding requirement from fraction of work week with the space beyond the barrier is occupied

• leakage radiation penetrates through X-ray tube walls or through collimator sides when beam is on

• maximum permissible leakage exposure rate at 1 m from the target of a diagnostic X-ray tube in all directions cannot exceed 100 mR/hour when tube is being operated continuously at its maximal permitted kVp and mA combination

Use Factors Recommended by the ICRP

• U=1 (full use) - in routine X-ray room

• U=1/4 (partial use) - nonroutine doors & walls

• U=1/16 (nonroutine ceilings)

Suggested Occupancy Factors

• T=1 - fully occupied

• T=1/2 - exam & treatment rooms

• T=1/5 - hallways, patient rooms & staff rest rooms

• T=1/8 - hallway doors

• T=1/20 - public toilets, unattended rooms, storage, seating outdoors, patient holding areas, etc.

• T=1/40 - outdoors, stairways, attics, unattended elevators, janitor closets, etc.

Controlled & Uncontrolled Areas

Weekly maximum permitted equivalent dose (MPED)

• controlled: 1000 μSv or 1 mSv

• uncontrolled: 20 μSv or 0.02 mSv

Radiation Warning Signage

• must be posted in any room or area where radioactive materials or sources are used or stored

• beam-on indicator sign

  • should be self-illuminating whenever X-ray equipment is energized

Characteristics

• lightweight

• durable

• detects even small exposures consistently

• outside influences shouldn’t affect performance

• should be reasonably inexpensive to purchase & maintain

• permit facilities to use large numbers of monitors in a cost-effective manner

Requirement for Personnel Monitoring

• personnel dosimetry - monitoring of eqD to occupational person (regularly exposed)

• ensure occupational exposure levels are kept well below annual EfD limits

• create awareness of various radiation exposure monitoring devices & their functions

• required when radiation workers are likely to risk receiving 10% or more of annual occupational EfD limit (50 mSv/5rem) monthly

  • with ALARA, most facilities issue dosimetry devices for anyone who could receive 1% of annual occupation EfD (~0.05 mSv/50 mrem) in any month

Purpose of Personnel Dosimeter

• provides indication of working habits & conditions of diagnostic imaging personnel

• determines occupational exposure by detecting & measuring exposure over time

• does NOT protect wearer from exposure

Placement of Personnel Dosimeters

• wear on collar level anteriorly

• with apron, wear outside of apron at collar level, anteriorly

• if pregnant, put secondary monitor under Pb apron at abdominal level

What is Monitored by the Radiation Safety Program?

• Deep Dose Equivalent (DDE) mrem

  • exernal whole-body exposure at 1+ cm tissue depth

  • dose to internal organs

• Shallow Dose Equivalent (SDE) mrem

  • external exposure of skin at or below 0.007 cm tissue depth

• Eye (lens) Dose Equivalent (LDE) mrem

  • dose to eye lens at 0.3 cm tissue depth

Radiation Safety Program Monitoring Periods

• monthly

• quarterly

• year to date

• lifetime

OSL

Optically Stimulated Luminescence

• uses Al₂O₃ detector

• detector lumeneces when struck by a laser (proportional to amount of radiation exposure)

• sensitivity range 5 Kev-40 Mev

Pros

• accuracy down to 1 mrem or 10 μSv

• ideal for diagnostic imaging personnel (especially for the pregnant)

• can be worn up to a 1 year

• temperature and heat resistance

• provides permanent record

• allows for reanalysis

Cons

• exposure cannot be immediately determined (1 month)

• only records in body area where it’s worn

• not effective if not worn

TLD

Thermoluinescent Dosimeter

• uses LiF crystals as sensing material

• LiF attracts & stores e^- when exposed

• emits light when heated (light intensity proportional to radiation exposure)

Extremity Dosimeter

• TLD ring badge worn as second monitor when hands required near primary beam

• laser-etched cover contains ID

• reusable TLD element of the dosimeter

Pros

• not affected by heat or humidity

• worn up to 3 months

• TLD crystals can be reused

• crystals interact with radiation just like tissue - makes doses more accurate

Cons

• no permanent legal record

• high initial cost

• not effective if not worn

PIC

Pocket Ionization Chamber (dosimeter)

• pen-sized ionization chamber attached to small capacitator

• charge created when chamber exposed, charge is read by external device or on PIC itself

Pros

• small

• immediate readout

Cons

• no permanent legal record

• expensive

• lost readings

• fragile-damage can lead to false high readings

• not effective if not worn

Digital Ionization Dosimeter

• small device that provides immediate measurement & long term tracking

• plug into computer & use dosimetry software

Pros

• light weight

• instant access to reports

• no wait time for mailing dosimeters

• can be dropped/scratched without harm

Cons

• not effective if not worn

Radiation Report

• monthly report of deep, shallow & eye dose for each badge

• report follows the imaging professional throughout their career

Annual Dose Limits for Radiation Workers Review

Whole Body Dose: 50 mSv/year

• Cumulative: 10 mSv x age in years

Equivalent Limits

• Eye Lens: 150 mSv

• Localized Area of Skin, Hands & Feet: 500 mSv

Embryo & Fetus Exposures

• Monthly: 0.5 mSv

• Entire Gestation: 5.0 mSv

Radiation Survey Instruments for Area Monitoring (+ Categories)

• most common have Geiger-Müller tube as detector

• simlest form indicates presence of radiation about background level

• do not provide a cumulative exposure reading

Categories

1. without readout scale

2. with readout scale

3. ionization-chamber based

Types of Area Monitoring Instruments

• instruments repond to charged particles produced by radiation (radiographic & fluroscopic) interacting with and ionizing the gas in the detector

• measure either quantity of electrical charge resulting from the gas ionization rate at which electrical charge is produced

Gas-Filled Detectors Include…

1. ionization chamber-type survey meter (cutie pie)

   1. also used for radiation protection surveys

   2. medical physicists connect to electrometers to perform standard measurements required by state, federal, and health accredited organizations

2. proportional counter

3. Geigger-Müller (GM) Survey meter

Requirements for Area Monitoring Instruments

1. portable

2. durable

3. reliable

4. interacts with radiation just like tissue (for more accuracy)

5. detects all common types of ionizing radiation

6. radiation energy shouldn’t affect detector response

7. cost effective

8. calibrated annually to ensure accurate operation (periodically to meet state & federal requirements)

Ionization Chamber-Type Survey Monitor

Cutie Pie

• measures both exposure rate and cumulative exposure

• measures X-radiation, gamma radiation & beta radiation

• very good at measuring fluoroscopic applications as well as radioactive isotope

Geiger-Müller (GM) Detector

• used primarily in nuclear medicine facilities

• sensitivity allows for detection of individual particles

• good for detecting areas of contamination