Unit 4Protection of the Patient and Technologist During Diagnostic Radiography

Radiation Protection RAD 101

Objectives• Explain the need for effective communication between the radiographer and the

patient.

• Explain the significance of adequate immobilization of the patient during a radiographic exposure.

• Describe the various beam-limiting devices and identify the device which best confines the radiographic beam.

• Explain the function of x-ray beam filtration in diagnostic radiology.

• State the reason for using gonadal shielding during radiologic examinations and identify the types of shields used.

• Discuss the need for using appropriate exposure factors for all radiologic procedures.

• Explain how the use of IR combinations reduces radiographic exposure for the patient.

• Discuss the value of good radiographic processing techniques in reducing radiographic exposure for the patient.

• State the reason for reducing the number of repeat radiographs.

• Explain how patient exposure can be reduced during fluoroscopic procedures

Chapter 11

Equipment Design for Radiation Protection

Equipment Design• Control Panel

– Must be behind protective barrier w/ window

– Must indicate condition of exposure and have light or audible x-ray indicator

• Tube housing – Must be lead lined metal (protective tube housing)

• Protects from off-focus or leakage radiation • Leakage can not exceed 100mR/hr at a distance of 1 meter when operating at

the highest voltage

• Table– Uniform thickness

– Radiolucent- absorbs only minimal amount of radiation- commonly carbon fiber

• SID – Must have a means of measurement from anode focal spot to IR

– Distance must be accurate to 2% of SID

– Centering must be accurate to 1% of SID

Beam Limiting Devices• Devices that limit the x-ray beam before it enters the patient

• Benefits– Amount of tissue irradiated is less

– Dose received is less

– Amount of scatter radiation produced in the body is less

– Image quality is improved

• Types– Aperture diaphragm – fixed and variable

– Cone/cylinders

– Collimator

Aperture Diaphragm

• Lead square with a fixed circular opening-fixed

• Placed below ( under) the tube

• Restricts the beam dimensions to a given size

Pg 236

Cones/Cylinders• Fixed aperture device consisting of an extended metal structure

– Cone – flared metal tube

– Cylinder- straight tube , more restricting- • Longer cylinders are more restricting

• Slide into attachment under tube housing

• Uses: – Dental, detail , sinuses, spot L-spine

Collimators• “Variable aperture or variable rectangular”

• Most versatile

• More control over beam limitation

• 2 sets of shutters

• 1st set reduces off focus radiation from the primary beam- located below tube window– Off focus- radiation in tube that results from electrons hitting areas other that the focal spot)

• 2nd Set- 2 pairs; each pair can be independently adjusted- located below the light source and mirror

• Most machines have PBL- positive beam limitations – but can be reduce further

• NCRP requires light field to be accurate to no more than 2% of the SID – 40” x2%= .8 “ of light showing around cassette

Filtration

• The process of eliminating undesirable low-energy x-ray photons by the insertion of absorbing materials into the primary beam

• Effects of filtration– Increase quality of the beam because boo penetrating x-rays are left- Beam

gets “hardened”- removes low energy

– Decreased quantity of x-rays- by absorbing some low energy beams- fewer overall beams are left

– Reduces patient dose- especially to skin and superficial tissue

• 2 types– Inherent

– Added

Inherent filtration

• Result of tube and housing composition

• Glass envelope surrounding tube

• Oil that surrounds tube ( oil helps in heat dissipation)

• Glass window- most of inherent comes from here

• Typical x-ray tube may have total inherent filtration of .5-1.0 mm Al equivalent

Added Filtration• Any filtration occurring outside the tube and housing and before the IR

• The collimators themselves are considered added filtration – avg 1.0mmAl eq.

• Sheets of Al also added after tube window

• Al is considered standard filtering material – All filtration is expressed in Al equivalences

• Inherent + Added = total filtration

• Operating levels require certain amts of filtration per NCRP #102

• When filtration is increased, technical factors must be increased to maintain same density on film

• Although exposure needs to be increased to pt, there is still a greater decrease in overall exposure to pt with filtration

Require Filtration NCRP #102 Box 11-2

OPERATING kVp Total filtration Required (HVL)

Below 50kVp .5 mm Al

50-70 kVp 1.5 mm Al

Above 70 kVp 2.5 mm Al

Mobile & fluoro units 2.5 mm Al

Half Value Layer - HVL• The amount ( thickness) of an absorber ( Al) required to decrease the

intensity of the primary beam by ½ (50%) of its original value

• Expressed in terms of Al equivalent

• Physicist measures beam quality

• Shielding devices use HVL

• TVL- amount of shielding required to reduce the radiation intensity to one-tenth its original value

Compensating Filters• Placed outside under collimators

• Designed to solve a problem of unequal subject densities

• Adds an absorber to compensate for unequal absorption with the subject

• Result – overall absorption of primary beam will be more equal and even densites on radiograph ( one end won’t be black and other underexposed)

• Made of aluminum, leaded plastic or plastic ( acrylic)

• Types– Wedge – bone and joint – T-spine, feet

– Trough ( bilateral wedge) CXR-PA

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Reproducibility/ Linearity• Reproducibility

– Consistent output in radiation intensity for identical generator setting from one exposure to the next

– Any combo of kVp,mA and time

– Variance of 5% or less

• Linearity– Consistent output of radiation intensity at any selected kVp setting when

generator setting are changed from mA/time combo to another

– Cannot exceed 10%

Image Receptors• Film Screen –

– intensifying screens – convert x-ray energy to visible light- screens have phosphors ( crystals) that luminesce(give off visible light) when struck by x-rays

– Screen-Speed- how fast a screen is capable of converting x-rays to light

– Slow screens need more radiation to produce same density- higher pt dose but better detail

• CR- computed radiography – Photostimulable phosphor plate- aprox equal to 200 speed screen film

– Dose creep- results from practice of overexposing patients to create good images and avoid repeat images

• DR- digital radiography– Latent image is formed by x-ray photons on a radiation detector- electronic latent image

– Matrix size and pixel size determine image detail

– Reduction in repeats reduce overall patient dose

Grids• Devices that remove scattered x-ray photons that emerge from the

patient before the scatter reaches the film

• Improves contrast and visibility of detail- image quality

• Placed between the patient and IR

• Pt dose will increase because bore technique is necessary

• Used when thickness of part is >10cm

• Made of alternating strips of lead and aluminum or plastic

• Come in varying grid ratios- the higher the grid ratio the more grid lines-better absorption of scatter- higher patient dose

Dose Reduction for Mobile X-Ray ( portable)• Mobile radiography requires SSD of at least 30 cm (12 inches)

• Recheck your positioning

• Check previous radiographs for exposure factors, SID and body habitus – useful for CXR

• Use high kVp technique ( gives a wider margin for exposure error and reduces dose)

• Shield pt

• Collimate

• Warn personnel and family to reduce their dose- have family leave room

Dose Reduction during Fluoro

X-ray exam is performed and demonstrates dynamic, or active, motion of selected anatomy- real time (Regular x-ray is considered static images )

• Use intermittent rather than continuous beam on

• Dead-man switch for foot pedal must be equipped- fluoro only when switch is depressed

• Collimate

• Filtration of 2.5 mmAL required

• Exposure rate cannot exceed 10R/min

• 5 minute reset timer- audible

Dose Reduction during Fluoro

• Bucky slot shielding device of at least .25mmPb is required

• Protective curtain min .25 mm lead

• Stationary Fixed Fluoro SSD no less that 38 cm ( 15 inches)

• Mobile fluoro (c-arm) requires SSD of at least 30 cm (12 inches)

• Cannot operate in parked position

• Primary protective barrier must be 2mmPb equivalent

• Lower exposure factors for peds

• Fluoroscopically Guided Positioning (FGP)– Practice of using fluoro to determine exact location of the central ray before

taking a radiographic exposure– ASRT says “ unethical practice that increases patient dose”

Chapter 12

Management of Patient Dose

Effective Communication

• “ The holistic approach” the use of verbal messages and body language to communicate with your patient

• Advantages: – Reduces patient anxiety

– Creates better tech/patient relationship- trust and caring

– Increases chance of completing exams and reduce repeats

• Consists of : – Clear concise instructions

– Give patient time to ask questions and answer truthfully

– Listen and offer empathy

– Respond according to ethical guidelines

– Don’t overemphasize pain ( may cause more anziety)

Immobilization

• Sometimes needed based on patient and exam being performed

• Reduces motion

• 2 types of motion– Voluntary- patient controlled

• Age• Breathing• Fear

– Involuntary- body systems • Muscle spasms• Chills • Tremors

• Shortened exposure time while maintaining mAs ( high mA , low seconds)

• Good instructions

Protective Shielding

• Devices made of lead or lead impregnated materials that will adequately attenuate ionizing radiation

• Should reduce or eliminate radiation doses that can cause biological damage

• Areas that should be shielded– Eyes

– Breasts

– Reproductive organs

• Types of shields– Gonadal

• Flat, shadow, shaped, clear

– Specific area shielding• Breast, thyroid

Gonadal Shielding

• Used to protect reproductive organs when organs are within 5cm of the beam

• Used unless it will compromise the exam (pelvic, abdominal )

• Females receive 3 x the exposure to reproductive organs than males during exams of the pelvic region

• Female dose- can be reduced by up to 50% with contact shield – placed 2.5cm medial to ASIS

• Male dose- can be reduced by up to 90-95% with contact shield- placed below symphysis pubis

Types of Gonadal Shielding

• Flat contact shields– Lead strips

– Placed directly over patient’s reproductive organs

– Best when used in AP or PA recumbent position

– Under the patient during fluoro

• Shadow shields– Made of radiopaque material

– Suspend from above the tube collimator box

– Hang over patient and shadow area to be shielded- gonad and breast

– Can’t use during fluoro

– Can use during sterile procedures

– Reduce patient embarrassment

Types of Gonadal Shielding Cont’d

• Shaped Contact shields – 1 mm of lead and are contoured to enclose male

reproductive organs

– Can be used with disposable or washable briefs

– Can be used for recumbent or nonrecumbent positions- AP, oblique, and lateral – not for use with PA projections- only covers anterior and lateral

– Can be used for fluoro exams

– Have patient place when changing for exam

• Clear Lead Shields– Transparent lead acrylic impregnated with approx. 30% lead by weight

– Can be gonad and breast shielding for scoliosis exams

Specific Area Shielding• Used for radiosensitive organs and tissues

– Thyroid

– Breast ( or PA positioning can reduce dose)

– Eyes

• Can be contact, shadow or clear plastic

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Technical Exposure Factors • Essential to ensure a diagnostic image with minimal patient dose

• Images must have:– Sufficient density (brightness) to display structures

– Good contrast to differentiate structures

– Maximum special resolution( detail) and minimal distortion

– Low quantum noise or mottle – results from insufficient technique

Technique Charts• Used when AEC ( automatic exposure control) is not used

• Standardized set of techniques based on equipment and patient size

• Departments establish own protocols

• Ensures consistency

• Minimizes errors if used correctly

SAMPLE TECHNIQUE CHART

Chest 20 - 25 PA 117 72 YES 4 8 1637 - 32 Lat 117 72 YES 8 16 4020 - 25 Port Grid 100 YES20 - 25 Port Non <85 NO

Thorax 20 - 25 Sternum RAO 80 40 YES 20 30 4027 - 32 Sternum Lat 85 40 YES 30 40 50

Ribs 20 - 25 AP Upper 70 40 YES 15 25 4020 - 25 AP Lower 80 40 YES 20 36 50

Shoulder 12 - 16 AP 80 40 YES 6 12 154 - 6 Axillary Non 70 40 NO 3 5 8

Scapula 12 - 16 AP 80 40 YES 10 20 3613 - 17 Lat 80 40 YES 12 24 40

Abdomen 18 - 22 KUB 80 40 YES 24 40 6418 - 22 UP/Decub 85 40 YES 28 48 64

ANATOMY MEASURE EXAM KVP SID GRID SM MAS MD MAS LG MAS

Exposure Factor

• Typically high kVp and low mAs will reduce dose

• Increasing kVp by 15% and reducing mAs ( ½) will reduce radiation exposure

• Select the highest practical kVp within optimal range for the position and part along with sufficient mAs that will produce and optimal radiograph

Radiographic Processing

• Of main concern with film-screen imaging

• Correct processing promotes archival quality

• Inadequate processing will produce poor films leading to repeats and extra exposures

• Digital Imaging- also concern on post-processing– Artifacts

– Software problems

Quality Control Program/ Repeat Analysis Program

• Ensures standardization in processing in film and digital

• Regular monitoring and maintenance of processor and image display

• Types of QC– Acceptance testing

– Calibration

– PM schedule

• Repeat analysis program– Repeats and reasons for repeats are evaluated

– Increases awareness about quality of images

– In-service if consistent problems arise

The Pregnant Patient

• Screen all women of child bearing age – Some hospitals have specific ages outlined

• Ask LMP – NCRP- Elective exams should be completed in the first few days after the onset of

menses to minimize possible radiation of an embryo.

- “Ten day rule” ICRP for woman of reproductive age. States that "whenever possible, one should confine the radiological examination of the lower abdomen and pelvis to the 10-day interval following the onset of menstruation.”

- Consideration for replacing with 28 day rule. Pt is considered not pregnant until a menstrual period is skipped then they are until proven otherwise.

• Shield is recommended if the ovaries and uterus are less than 5 cm from edge

• Some facilities will require HCG

Figuring Fetal Dose

• List in as much detail about the x-ray exam– Projections

– Number of views

– Film size

– Technique

– SID

– Shielding used?

– Patient thickness

– Fluoro time

– Number Spot films taken

• Report information to RSO or Medical Physicist- they will determine EqD

Chapter 13

Management of Tech Dose

The Patient as a Beam Emitter• During the exam- the patient becomes a source of radiation for the

tech- scattered radiation because of Compton interaction

• Greatest occupational hazard

• Lowest scatter area is at 900 to the patient

• Ways of reducing – Beam limiting devices –PBL

– Filtration- (primarily benefits pt)

– Protective apparel

– Technical factors

– Cardinal principles

– Structure of dept

Protective Apparel• Lead aprons, gloves and shielded barriers

• Protect from secondary ( scatter and leakage)

• Standard apron thickness .5 mm lead equivalent at 100kVp reduces by 75%

• .25 mm is minimum (mammo) 1 mm is maximum ( rare because of weight)

• Lead should be hung on racks or draped over a bar- never folded or crunched

• Must be inspected yearly for integrity ( use high kVp to reduce dose)

• Thyroid shields- .5 mm lead

• Glasses .35 mm lead

• Gloves .25 mm lead

Cardinal Principles (Time, Distance, Shielding )

• Distance– The most effective means of protection from ionizing radiation

• Inverse Square Law– Expresses the relationship between distance and intensity ( quantity) of radiation

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

– Decrease in radiation intensity physically occurs because of the area-

– Expressed as an equation:

I 1 = (d2)2

I2 (d1)2

Where : I 1 = original intensity & I2 = new intensity

(d2)2 = new distance & (d1)2 = original distance

Practice Problem• If a radiographer stands 3 m from an x-ray tube and is subjected to an

exposure of 9mR/h, what will the exposure be if the same radiographer moves to a position 6 m from the x-ray tube?

I 1 = (d2)2 9 = (6)2

I2 (d1)2 I2 (3) 2 cross multiply

36I2 = 81 divide

I2 = 2.25 mR/h

Protective Structural Shielding• Primary Protective Barrier-

– prevents DIRECT or unscattered, radiation from reaching personnel or public

– perpendicular to line of travel of primary beam

– 1/16 inch lead

– Extends 7 feet

• Secondary Protective Barrier-– protects against leakage and scatter-

– Any wall or barrier that is never struck by primary beam

– Located parallel to the direction of the beam

– 1/32 inch lead

– Extends to ceiling and should overlap primary by 1/2”

– Includes ceiling and control booth

– Doors are considered secondary 1/32 inch lead – must remain closed during exposure

Protective Structural Shielding• Control Booth Barrier- considered secondary barrier

– Permanent or nonportable equipment require permanent control booth

– Should be positioned where x-rays scatter a min of 2 x before reaching behind barrier

– Contains window for personnel 1.5 mm lead equivalent ( can be .3-2 mm)

– Max allowance of 1 mSv (100mrem) per week

– Exposure cord must be short enough that the tech cannot operate outside booth

– Tube should never be pointed at control booth

• Ceiling mount - Overhead lead acrylic– Used during special procedures

– Typically .5 mm

Workload• Used to determine barrier shield requirements

• Since x-ray units do not have constant on-time a formula is used to determine approx. amount of radiation “output-weighted time”

• Expressed in mAs per week or mA-min per week

• Workload (W)= mA x time x days per week x #pts x #img per pt

Use Factor & Occupancy FactorIf no one will ever be present beyond an existing wall- no additional shielding is needed ( courtyard)

• Use Factor- the factor that represent the portion of beam-on time that the x-ray beam is directed at a primary barrier during the week ( table 13-2 pg 328)

• Occupancy Factor- use to modify shielding based on the fraction of the work week during which the space beyond the barrier is occupied (table 13-3 p 329)

• Controlled area- used only by x-ray personnel – 1mSv (100mrem)

• Uncontrolled area- general public – hallway, stairwell – Weekly max dose 20microsieverts ( 2mrem)

Caution SignsPosted signs warning for radiation

“Catution” and radiation symbol : Must be magenta, purple or black on a yellow background

Must read:

“Radiation Area”

“High Radiation Area”

“Very High Radiation Area”

Departments usually have “If you think you are pregnant please tell the technologist”

Where to stand during exams• Fluoro

– Stand as far away from the patient as practical or behind radiologist

– Book recommends control booth….. Usually not practical

• Portable– Cord must be 6 foot

– 90 degrees to beam

• C-arm– As far as achievable – use of foot pedal for exposure helps

– Position image intensifier as close to patient as possible ( decreases scatter)

– If possible place tube under table and image intensifier over table

Holding Patients• DO NOT stand in primary beam to restrain patient

• Use mechanical holding devices first : tape, Pigg-O-Stat

• Use nonoccupational persons second– family / parent / ancillary staff/ nursing

• Order– Male relative

– Female relative

– Nonradiology personnel

– Radiology personnel

• Always provide lead

• Pregnant women are never to hold patients

• Rotate human holder

Resources:  Radiation Protection in Medical Radiography by Mary Alice Statkeiwicz Sherrer, Paula Visconti, E. Russell Ritenour and Kelli Welch Haynes. 6th and 7th Edition. Elsevier online.  Essentials of Radiographic Physics and Imaging. James N. Johnston and Terri L Fauber. 1st Edition. Elsevier Online.

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