Rad Protection Unit 3- patient doses

holistic patient care

• treat the patient as a whole person rather than a body part

• makes patient feel more respected comfortable and more willing to cooperate

effective communication: verbally and body language

• introduce yourself

• address the patient properly

• ease the patient’s stress and anxiety

• show understanding and dignity

• provide clear and concise intructions

• increase their cooperation

• give the patient time to ask questions

• gain their trust

  • tell them if there is discomfort or pain in volved

  • strange sensations

• be professional, be present, watch body language

• help to make the procedure successful

  • reduces repeat exposure

patient motion

• involuntary

• voluntary

involuntary motion

• caused by muscles, not controllable

  • heart

  • digestive

  • chills

  • tremors

  • spasms

  • pain

  • active withdrawal

• corrected by decreasing exposure time and increasig imaging receptor speed

voluntary motion

• controlled motion

• sometimes there can be lack of that controlled motion due to:

  • patient’s age

  • breathing patterns

  • anxiety

  • physical or mental discomfort

  • fear of exam/prognosis

  • mental instability

• corrected by gaining patient cooperation and use of proper immobilization

immobilization

• piggostat

• papoose/octostop

• sponges (radiolucent) and sandbags (radioopaque)

• mummy wrap/ bunny wrap

• tape

• velco straps

• radiolucent plexiglass

• having a non-radiology employee helping to hold

beam limiting devices

• limits the primary beam to a smaller area

• decreased exposure by reducing the amount of tissue that is exposed to radiation

• reduces scatter

types of beam limiting devices

• aperture diaphragm

• cones

• collimators

aperture diaphragm

• flat lead with shape and size cut into it that is placed below the window

  • rectangular

    • most commot

  • square

  • round

• reduces scatter

cones

• circular metal cylinders connected to the tube housing that limits the size of the beam

• can be flared or straight

• can be telescoped (10-12 inches) for smaller exposure area

  • called extensive cylinders

• have mostly been replaced by collimators

• mostly used in dental radiography but can be used for the heel, skull and spine imaging

collimators

• light-localizing variable aperture rectangular collimator

• most versatile beam restriction

  • can change size

• should not be opened larger than the size of the image receptor or body part imaging

  • post shuttering- part of ASRT Practice Standards

• can reduce exposure by 20-30%

• careful not to over collimate which causes repeat images

there are 2 sets of shutters in a collimator that are 90 degrees from one another

• near (upper)

  • located close to the window

  • reduces exposure from off focus radiation

• far (lower)

  • located closer to the light source

  • confines the beam to the area of interest

skin sparing (collimators)

• minimizes skin exposure by requiring a 15 cm distance from the skin to the collimator

• can be achieved with spacer bars mounted on the tube

positive beam limitation (PBL)

• electronic sensors in the bucky that senses the image receptor size that you are using and opens the light field to that size

  • can be slits or pegs

• reduces user errors by matching the light field to the image receptor size

• also known as automatic collimation

• regulatory guidelines require this to be within 2% accuracy

filtration

• hardens the beam by cleaning up the low energy (longer wavelength) x-rays

• reduces the skin and superficial exposure to the patient

• decreases patient’s absorbed dose because the remaining photons are higher energy (shorter wavelength)

• lower energy photons (which were removed) would be more likely to be totaly absorbed and provide no detail to the image

• total filtration built into the housing is 2.5 mm Al equivalent for units operating above 70kVp

2 types of filtration

• inherent- 0.5 mm Al equivalent

  • glass envelope, insulating oil, and glass window

• added- 2.0 mm Al equivalent

  • sheets of Al added outside the glass window above the collimator shutters

  • accessible by pervice person

  • can be changed as the tube ages

    • mobile and fluoroscopy units also require 2.5 mm Al equivalent

    • NCRP #102- list minimum required filtration for x-ray equipment

Radiation Control for Health and Safety Act of 1981 states:

• that a diagnostic x-ray beam must always have adequate filtration

  • to verify that a machine has adequate filtration, the HVL QC test (half value layer) must be measured

    • measure beam quality or effective energy of the beam

    • measured at least once a year by physicist or if the tube is replaced or repairs are made

HVL (half value layer)

• insufficient HVL test could mean improper filtration

• example

  • exposure from the tube is 350 C/kg

  • what will be the exposure for:

    • 1 HVL (50%)

      • 175 C/kg

    • 2 HVL (25%)

      • 87.5 C/kg

    • 3 HVL (12.5%)

      • 43.75 C/kg

    • 4 HVL (6.25%)

      • 21.8 C/kg

TVL (tenth value layer)

thickness that will decrease the intensity of the beam by 1/10th

shielding

• April 2019- American Association of Physicists in Medicine (AAPM)- statement that shielding of patient gonadal or fetal shielding during diagnostic imaging should be discontinured

  • CARES committee (communicating advances in radiation education for shielding)

• radiosensitive organs

  • lens of the eye

  • breasts

  • reproductive organs

• 2 types

  • gonadal

  • specific area

gonadal shielding

• should be used if the gonadal area is within 5cm of the collimation field

• could use unless covering the area of interst

• first step in gonadal protection is proper collimation

• due to the anatomical location, females recieve 3x more exposure than males

• if used, appropriate shield placement can reduce the exposure to

  • females by 50%

  • males by 90-95%

flat shields

most effective in the AP or PA recumbent positions

shadow shields

• careful to place properly or repeat image could be caused

• not suitable during fluoro

shaped shields

• contoured to enclose the male reproductive organs

• can be placed by the patient

• can not be used during PA projections

clear shields

transparent lead-plastic material

lap shields (half)

• covers only the front or back half of the patient

• attached with a velcro strap or on wheels

specific area shields

• eyes

• breast

• thyroid

• gloves

compensating filters

• used when x-raying a part that has varying thickness to reduce dose and provide a uniform density across the image

• decreases the entrance skin exposure (ESE)

• constructed of aluminum or lead-acrylic that is attached to the bottom of the collimator

types of compensating filters

• wedge filter

  • used for a foot and spines

• trough filter or bilateral wedge

  • used on chest x-rays

  • thicker on both sides and thin in the middle

• ferlic

  • hips

• boomerang

  • shoulders

kVp (kilovoltage peak)

• maximum possible energy of a photon that exits the x-ray tube, this is a unit selected on the operating console

• indirectly proportional to patient exposure

mA (milliamperage)

• measurement of x-ray tube current or the number of electrons crossing the tube from cathode, this is a unit selected on the operating console

• directly proportional to patient exposure

mAs (milliampere seconds)

• controls the amount of radiation produced by the x-ray tube

• mA x seconds= mAs

• directly proportional to patient exposure

AEC (automatic exposure control)

the cells that are selected on the operating console that will automatically select the mA according to cell selection and body part

exposure index (EI)

• the number that is found on the image after processing that measures receptor exposure

• exposure index should be in range for the equipment parameters to be a good diagnostic image

• under exposure will cause quantum noise (grainy appearance) and should be repeated

• over exposure is most cases will appear as a good image

  • in extreme cases it will cause saturation and should be repeated

use proper exposure factors

• makes an optimal image with minimal dose possible

• sufficient penetration

• higher kVp, lower mAs for body part

• when setting manual technique, measure the patient for accuracy'

• reliable technique chanrts

• AEC (automatic exposure control)

  • sets the appropriate mA for the body part being x-rayed by selecting cells

image receptor speed

• increase in image receptor speed decreased patient exposure but decreases sharpness

• digital radiography acts as a 200 or 400 speed image receptor

correct processing (image acquisition)

inadequate processing of image results in repeats

radiographic grids

• rule of thumb is to use a grid when part thickness is over 10cm at 60kVp or higher

• removes scatter photons that come from the patient before they reach the image receptor

• improves the contrast and detail of the image

• grids increase patient dose but improves the quality of the image which provides a better diagnosis

  • use the lowest grid ratio sufficient for the body part

  • higher grid ratio= higher patient dose

air gap technique

• alternative to using a grid to clean up scatter

• patient is placed 4-6 inces (10-15cm) away from the image receptor with a 10-12 feet SID

• negative side is the increase in magnification and not useful in kVp higher than 90

eliminating repeats will decrease patient exposure

• repeat image- is any image that must be done more than once due tohuman or mechanical errors

• patient recieves a “double dose”

• repeats are unacceptable if done due to carelessness or poor judgment

  • positioning

  • technique

repeat analysis

• problems with positioning

• incorrect centering

• inappropriate technical factors

• improper collimation

• foreign bodies

• processing artifacts

• patient motion

avoiding unnecessary procedure to reduce patient exposure

• chest x-ray

  • pre-admission

  • pre employment

  • routine health checkups

  • screening for TB

• lumbar x-rays

  • pre-employment

• CT whole body scans

  • check for disease

mobile radiogrpahy

• minimal source to skin distance on a mobile fluoroscopy unit is 12 inches (30cm)

• the smaller the source to skin distance the larger the entrance exposure

• only perform portable x-ray on patients that cannot be transported to the department

digital imaging and computed radiography

• just because the image can be electronically manipulated does not excuse overexposing the patient

• utilization of technique charts

• grids

fluoroscopy

largest exposure to patients in diagnostic radiology

limiting exposure in fluoroscopy

• image intesification

  • increases brightness on screen

• intermittent or pulse fluoro

• limit maginification mode

• limiting field size

• technical factors

• filtration

  • reduces skin dose

• if you must shield

  • underneath the patient if the tube is underthe table

• source to skin distance

  • NCRP states 15 inches (38cm) for fixed units and 12 inches (30cm) for mobile

limiting exposure in fluoroscopy cont.

• cumulative timing device

  • audible alarm or interrup of fluoro every 5 minutes of time

  • the technologist is responsible to record the fluoro time in the electronic medical record

• federal regulations tabletop exposure rates should not exceed 88 mGy per minute

• primary protective barrier

  • 2 mm lead equivalent for image intensifier built in the equipment

• Automatic Brightness Control/ Stabilization (ABC/ABS)

  • no matter the kVp or mA varying, the brightness of the image remains the same

  • Automatic Exposure Rate Control (AERC)

  • adjusts exposure factors automatically as the bean moves over varying thicknesses

fluoro exposure switch/ dead man switch

• foot pedal requires direct pressure to continue fluoro exposure

• so, if the user would “fall over dead” the exposure would stop

fluoroscopically guided positioning (FGP)

• using fluoroscopy to determine if you are positioned appropriately before taking an image

• ASRT stand is that this practice is unethical and should never be used

digital fluoroscopy

• beam turns off while image is scanned and then turns back on

  • pulsed

• Dose Area Product (DAP)

  • newer fluoro systems provide the sum of the air kerma (energy) over the exposed area of the patient

• Last image hold

  • when the foot comes off the pedal, it holes the last image and displays it on the screen until the foot pedal is activated again

C-arm fluoroscopy

• used in the OR, Cardiac Cath, and IR

• lengthy cases have the potential for high patient doses

• properly trained personnel to work the equipment

• 12 inch (30cm) minimal distance to the patient

  • spacers are usually placed to maintain a safe distance

• C-arm should be positioned with the image intensifier on the top

  • reduces scatter and patient dose

cinefluoroscopy

• used in cardiology and neuroradiology

• works like a movie

• reduce patient exposure

  • limit time without losing information

  • collimate

  • last frame hold

interventional radiology

• invasive sterile procedures performed by a physician under fluoro

• FDA requires documentation in the patient chart if skin does is 1-2 Gy

• federal regulations for table-top exposure rates for procedures with high level control fluoro (HLCF) exposure limits are 176 mGy per minute

  • HLCF allows for visualization of smaller and lower contrast objects

• should be performed by an educated and trained physician

  • keeps patient doses and occupational doses down

radiation patient dose measurements

• entrance skin exposure (ESE)

  • includes skin and glandular

• skin dose

  • absorbed dose to the most superficial layers

• gonadal dose

  • genetically significant dose (GSD)- assess the effects of gonadal dose

    • approximate dose in US is 0.2mSv

• bone marrow dose

  • dose to entire active bone marrow

  • also known as the mean marrow dose

pregnant patient

• asking LMP

  • RH policy should be followed

• 10-day rule

  • ICRP recommendation from 1970

• ACR’s position on pregnant patients

• elective exams should be scheduled according to the 10-day rule

• 10-25 rad rule

  • <10 ok

  • 10-25 consider options

  • >25 not good

• radiology departments are responsible to post pregnancy signs

how to reduce dose to a pregant patient

• minimize the dose

  • smallest exposure that will produce optimal images

• collimate

  • RH patient must sign a consent form if the pelvix/abdomen area

mammography

• utilizes low kVp

• limit number of projections

• adequate compression

• avoid axillary exposure unless ordered by radiologist

CT

• doses are higher than diagnostic radiology

• shielding is usually not utilized because of the nature of the exposure

• collimators are very tight in CT, exposure is caused by internal scatter

pediatric patients

• more sensitive to exposure due to rapidly dividing cells

• due to their longer life span it can increase changes of developing a radiation induced leukemia or radiogenic malignancy such as lung or thyroid

decreasing exposure to pediatric patients

• communicate at their level

• minimize repeats

• minimize number of images taken

• use collimation

• use short exposure times/ appropriate exposure factors

  • less exposure is needed to obtain optimal images

• shiel

morbid obesity

• have patient centered to table because landmarks are hard to palpate

• skeletal anatomy does not change in position and organs are not larger except:

  • thoracic cage expanded 2”

  • stomach may slightly be larger

  • colon may spread out

• increase kVp to increase penetration of the x-ray beam

• use grids to clean up scatter

• in most cases it is not appropriate to increase the image receptor size

  • smaller collimaiton decreases scatter

image gently campaigns

• CT- one size does not fit all

• digital- back to basics

• NM- go with the guidelines

• fluoro- pause and pulse

• AIR- step lightly

equipment safety

• on and off switches

• interlocks

  • detents

  • fluoro locks

• visual/audio monitors

  • control panel

  • laser light

  • tape measures

• emergency controls