optimization of protection in

Optimization of Protection in Digital radiography - CT

aspects

وبینار حفاظت در برابر اشعه ویژه مراکز پزشکی دانشگاه علوم پزشکی و خدمات بهداشتی درمانی بیرجند

دانشکده پیراپزشکی و بهداشت فردوس

1399/09/18

Mohammad Reza Deevband, Ph.D.

Medical engineering and medical physics section

Shahid Beheshti Medical Science University

• Regulatory aspects of occupational protection

• Basic methods for radiation protection

• Factors affecting patient and staff dose in CR & DR

• Factors affecting patient in CT

• Practical rules

• Protection devices

• Individual dose monitoring

• Health surveillance

Key topics

Regulatory basis of radiation protection

Recommendations of the

International Commission of Radiological Protection (ICRP)

General – in 1990 and last in 2007

BSS= “International Basic Safety Standards for

Protection against Ionizing Radiation and for the Safety

of Radiation Sources, ” IAEA, Vienna 2011 (interim edition)

National regulations

BSS - Responsibilities of employers

“Registrants, licensees and employers of workers

are responsible for ensuring that exposures are

limited that protection and safety is optimized, and

that appropriate radiological protection programmes

are set up and implemented”

BSS - Dose limits

For effective dose:

For equivalent dose:

*BSS interim edition

“The occupational exposure of any worker shall be so controlled that the following limits be not exceeded:

20 mSv per year averaged over five consecutive years and 50 mSv

in any single year;

to the lens of the eye of 20 mSv* in a year; averaged over 5 years;

not exceeding 50 mSv in any single year.

Dose limit for the extremities (hands and feet) or the skin

of 500 mSv in a year.

Workers shall:

• follow any applicable rules and procedures for protection and safety specified by the employer;

• use properly the monitoring devices and the protective equipment and clothing;

• co-operate with the employer with respect to the operation of radiological health surveillance and dose assessment programmes;

• abstain from any wilful action that could put themselves or others in situations that contravene the requirements of the Standards;

• accept such information, instruction and training concerning protection and safety

BSS - Responsibility of workers

• Factors affecting staff doses in fluoroscopy

• Practical rules

Key topics

Basic Radiation Protection

“Golden rules” :

• Time – minimize exposure time

• Distance – increasing distance

• Shielding –Lead or non-lead equivalent apron is MUST inside

the room with X ray machine

• fixed, portable and pull- down shields as appropriate;

• Personal protective devices

• Technique factors e.g. collimation, pulse fluoroscopy,

magnification, filters, grids etc.

Minimize Exposure Time

• Everything you do to minimize

exposure time reduces radiation dose!!

Minimize fluoro and cine times

Whenever possible, step out of room

Use pulsed fluoroscopy– minimizes time x-ray tube is

producing x rays

Maximize Distance – Inverse Square Law

Helps Protect You

“Inverse Square Law” - radiation dose varies inversely with the square of the distance

• The patient is the main source of scattered radiation!!

0.5 m 1 m 1.5 m

dose rate 100 units

25 units

11 units

distance

• Move from 0.5 m to 1 m (doubling the distance) dose

rate decreases 4 times or to 25%!!

patient

Inverse Square Law Helps Protect You

Stay as far away as possible when radiation

is ON, use extension tubing, remote injector,

longer instruments, etc.

Practical rule

• Factors affecting patient and staff dose in CR &

• Practical rules

• Health surveillance and records

Key topics

Optimisation includes …

• All activities that ensure consistent, maximum

performance from physician and imaging facility1

• “A distinct series of technical procedures which

ensure the production of a satisfactory product”

• Four steps …

• Acceptance Testing (AT)

• Establishment of baseline performance

• Diagnosis of changes in performance

• Verification of correction of deterioration

1National Council on Radiation Protection and Measurements. (1988) Quality Assurance for Diagnostic Imaging, NCRP Report No. 99, Bethesda, MD;

Optimisation includes both personnel

and equipment

• Identifying aspects of facility operation that require

decisions or actions

• Establishing policies with respect to these

• Encouraging compliance through education and

recognition

• Analyzing records at regular intervals

• Dose optimisation

• Image quality optimisation

“What’s my motivation?”

• Regulatory Compliance • International BSS

• National Regulations

• Standards of Care • Standards established by professional

societies

• Providing the highest quality medical care

• MANAGING RADIATION DOSE!!!

Factors that affect image quality and patient

dose Factor Contrast Resolution Noise Patient Dose

Focal spot size X

Off-focus

radiation

x (x) x

Beam filtration x X

Voltage

waveform

(x) x x

kVp X (x) X

mA (x)

mAs (x) X X

SID X X

Field size X X

Scatter rejection X X

Wolbarst (1993) Table 19-1

X: very important

connection

x: sometimes

significant

(x): sometimes

noticeable

Quantifiable Consequences of Degraded

Performance

• Loss of Contrast Sensitivity

• Loss of Sharpness/Spatial Resolution

• Loss of Dynamic Range

• Increase in Noise

• Decrease in System Speed

• Geometric Distortion

• artefacts

• Decrease in diagnostic accuracy

• Increase in observer time/fatigue

• Delay of diagnosis

• Increase in patient radiation dose

• Decrease in efficiency of imaging operation

Reasons for differences between CR

and DR optimisation • CR cassette-based vs. integrated

receptor DR

• Cleaning

• Physical defects

• Erasure

• Mis-identified patient, view, orientation

• Need adequate knowledge of radiographic technique

• Separation between image acquisition and development

• Time

• Geographic (PACS)

• Distinctions are blurring

• Poorly integrated DR

• Integrated CR

3. Verify

exam with

physician

5."Arrive"

patient in RIS

6. Escort patient

to exam room

7. Explain exam

to patient

8. Select and ID

cassettes

9. Position patient,

cassette, x-ray tube

10. Perform exam

11. Scan cassette

14. Review

images at QC

15. Repeat

necessary?

17. Complete exam

in RIS

4. Schedule exam in

12. Preview images

13. Repeat

necessary?

18. Release patient

1. Patient arrives in

imaging department

2. Is exam

scheduled?

16. Release images

to PACS

Process map

• Flowchart of steps

• Identify potential QC control points • actions to be taken

• Identify “work-arounds” • Example: What if RIS is

out-of-service? • How to continue

operations?

• Don’t forget actions on restoration of service

Step 1. Patient reports for an examination.

• The technologist verifies: • the patient is the person identified in the exam request • the anatomy to be examined matches the exam request • other information about the patient, such as

• Pregnancy

• Restricted motion

• Allergies

• Appliances

• QC accomplished by training or checklist

Step 2. Technologist identifies the patient

and exam to the imaging system

• Usually occurs before, but sometimes after the exam is performed

• Misidentification has consequences • incorrect information can cause image

unavailability • incorrect exam info can affect image

development • mis-association complicates error

detection • proliferation of digital images

complicates correction

• Automation of association = imperfect QC! • New classes of errors

The best image, improperly identified, is

useless. • Consequences of

misidentification:

• Broken studies

• Orphans

• Exceptions

• Penalty Box

• Automation of association: • RIS interfaces

• Bar code scanner augmentation

• DICOM Modality Worklist Management (MWL)

• unscheduled exams

• resource re-allocation

Step 3. Technologist positions the patient in the

radiation field and performs the examination

• Potential errors • mispositioning • patient motion • incorrect radiographic technique selection • poor inspiration • improper collimation • incorrect alignment of x-ray beam and grid • wrong exam performed • double exposure

• QC accomplished at acquisition station? • Image processing inadequate to correct • Correction requires repeated exam (s)

Results:

Rejects during one month

Re a so n Numb e r %

mispositioned 240 53.3%

artifacts 40 8.9%

test images 22 4.9%

nondiagnostic 20 4.4%

patient motion 14 3.1%

misplaced marker 10 2.2%

no marker 6 1.3%

under-exposed 5 1.1%

inadequate contrast 4 0.9%

over-exposed 2 0.4%

wrong exam 2 0.4%

wrong patient 2 0.4%

T o ta l 450 100.0%

Step 4. Image receptor captures the

radiographic projection

• Potential errors • Inadequate erasure, lag, ghosting • Improper compensation for non-uniform gain • Incorrect gain adjustment • Incorrect exposure factor selection • artefacts

• Interference with the projected beam

• Receptor defects

• Interference with converting the captured projection into a digital image

• Detection possible at acquisition station? • Correction may require repeated exam • Can be averted by active QC

Active QC countermeasures:

emphasize avoiding vs. correcting errors

• Prophylactic erasure at start of shift

• Periodic checks of non-uniformity corrections

• Periodic gain re-calibration

• Technique guide

• Periodic checks of Automatic Exposure Control (AEC) calibration

• Periodic cleaning of equipment and environment

• Thorough Acceptance Testing of new receptors • Also incidental to service events and software upgrades

Step 5. Image receptor renders the

captured projection for viewing

• Potential errors • Incorrect Exposure Field recognition; incorrect

determination of values of interest (VOI)

• Incorrect histogram re-scaling

• Incorrect gray-scale rendition

• Incorrect edge restoration

• Inappropriate noise reduction

• Incorrect reorientation

• QC possible at acquisition station? • Correction usually possible without repeated exam

Functions of the QC workstation:

sometimes integrated into acquisition station • Modify image processing

• Imprint demographic overlays

• Add annotations

• Apply borders or shadow masks

• Flip and rotate

• Increase magnification

• Conjoin images • Scoliosis

• Full leg

• Modify sequence of views

• Verify exposure indicator

• Select images for archive

• Delete images

Step 6. Acquisition station transfers the

image to the archive

• Potential errors

• Transmission failure

• Image deletion from local cache

• Information omitted from transmitted image

• Exposure indicator

• Processing parameters

• Shutters

• Annotations

Step 7. Digital image is displayed for

viewing by a physician

• Potential errors (hard or soft copy) • Incorrect GSDF calibration • Inadequate matrix

• Moire’ (interference) patterns

• Inadequate spatial resolution

• Incorrect or missing demographics or annotations • Inadequate viewing conditions • Errors not filtered by previous QC

• QC => Radiologist “Film” critique

Task Allocation Matrix

Task Responsibility Frequency

Verify Patient ID and exam info Radiographer Each exam

Verify Patient Positioning Radiographer Each view

Verify Image Quality – release or repeat Lead Radiographer Each image

Verify exam in PACS Lead Radiographer Each exam

Reconcile patient data/image counts in PACS Medical Informatics Incidental

Report substandard images Radiologist Incidental

Erase cassette-based image receptors Radiographer Start-of-shift

Test image receptor uniformity Radiographer Weekly

Clean cassette-based image receptors Radiographer Monthly

Compile and review reject analysis data Lead Radiographer Monthly

Verify display calibrations Clinical Engineer Quarterly

Review QC indicators QA Committee Quarterly

Verify receptor calibrations Medical Physicist Semi-Annual

Verify x-ray generator functions Medical Physicist Annual

Commitment to optimisation

• The optimisation effort is integral to how you organize and perform the work.

• The cost of optimisation is trivial compared to the cost of inefficiency: consider one bad patient outcome.

• Training for optimisation is professional development for hospital staff.

• Leverage local resources for optimisation expertise. • Biomedical engineering

• Medical informatics / Information services

• Medical Physicists

• Hospital QA personnel

Who is responsible for optimisation?

(“It takes a village …” )

• Physician responsible for clinical service is

ultimately responsible

• Medical Physicist oversees the program

• Radiographer makes day-to-day measurements,

verifies post-repair integrity

• Service engineer carries out repairs, PM,

calibrations

Answer True or False

• Random error is a source of inherent

limitation of human operators

• It is the responsibility of the physician to

ensure appropriate delivery of all images to

• High doses can go undetected with the use of

DR or CR systems

Answer True or False

• True. Every process that depends on a human

operator is a source of random errors and every

process that automation performs independently is

source of systematic errors.

• False. The technologist/supervisor is responsible

for appropriate delivery of all images to the PACS

• True. DR and CR have wide latitude and high

doses can go undetected. Optimised exposure

parameters should be used in digital systems.

• Factors affecting patient and staff dose in CR &

• Practical rules

Key topics

Radiation protection of patients in CT

1. Perform scan only if it is indicated!

• It is estimated that a significant number of imaging

examinations are unnecessary

• Consultation between the referring physician and the

radiologist is recommended

2. Encourage use of alternative non-ionizing imaging (MRI,US)

when appropriate especially in younger patients

3. Always check if patient may be pregnant

• Use special signs and informative material notifying patients that they

MUST disclose any possibility of pregnancy

4. High quality /Crisp images may look nice but they impart

higher radiation dose to patients

• Start using images with some noise without loss of diagnostic

information

5. Use indication-specific CT protocols for each body region, e.g.

for lung nodule follow up or kidney stones, diagnostic images

can be obtained at 50-75% lower radiation dose compared to

routine or general use protocols

6. Multiple pass or phase CT should NOT be performed

routinely

• Multiphase CT can increase the dose by as much as 2-3 folds over

single phase CT

7. Adjust exposure parameters according to patient

and body part

8. Know your equipment: Learn how to adjust the

parameters of the automatic exposure control (AEC)

system to fine tune radiation dose for different clinical

indications and body regions • Most body CT examinations should be performed with use of AEC

9. Good technique: Lower kVp, mAs,

Higher pitch

Restrict scan length to what is necessary

Always center the area of interest in isocenter of CT gantry

All CT protocols should state the start and end location for different clinical indications

Thin slices only when necessary

10. Pay attention to radiation dose values and compare

with diagnostic reference levels (DRLs)

• Be aware of CT dose metrics and recommended dose levels

for different body regions

• Practical rules

Key topics

Whenever possible collimate the X-ray beam to

the area of interest

Practical rules

Collimation

•reduces staff dose

•reduces patient dose

•improves image quality

Staff and patient dose are partially linked

They are function of: available X-ray system

real conditions of the system

how the system is used

RP tools available and applicable

number and type of the procedures

staff skills

used operational protocols

Factors affecting staff doses

IF PATIENT SIZE

INCREASES

PATIENT SKIN DOSE

AND THE LEVEL OF

SCATTERED

RADIATION INCREASE

SUBSTANTIALLY

Factors affecting patient

and staff doses

Influence of patient thickness

Increase from 16 to 24 cm,

Scatter dose rate could increase by a

factor of 5 (10 mSv/hr x 5=50 mSv/hr)

and staff doses

CHANGING

FROM NORMAL

FLUOROSCOPY

MODE TO THE

HIGH DOSE

RATE MODE

INCREASES

DOSE RATE BY A

FACTOR OF

2 OR MORE

and staff doses

Practical advice

for staff protection

• Increase distance from the patient.

• Minimize the use of fluoroscopy and use low

dose rate fluoroscopy modes.

• Acquire only the necessary number of images per

series and limit the number of series.

• Collimate the X-ray beam to the area of interest.

• Use under couch tube systems

• Consider the size of the patient and the position of

the X-ray tube (C-arm angulation).

• Stand on image intensifier side as far from patient

as possible

• Use suspended screen and other personal shielding

tools if available.

Practical advice

for staff protection

Optimization of

Radiation Protection

• Ensure adequate image quality by optimization of

dose rate

• Must optimize dose to patient and minimize dose to

• Minimization of dose to patient and staff should not

be the goal.

If image quality is inadequate,

any radiation dose results in

needless radiation dose!

• Practical rules

Key topics

Personal protective equipment

• Employer shall ensure that workers are provided with

suitable and adequate personal protective equipment

which meets any relevant regulations or standards (BSS).

But it is the responsibility of

workers to use this devices!

However, protective clothing must not be used as a

substitute for proper protective measures.

Protective clothing:

• Protective equipment includes lead aprons,

thyroid protectors, protective

eye-wear and gloves.

• Aprons should be equivalent to :

at least 0.25 mm Pb if the X-ray equipment

operates up to 100 kV and

0.35 mm Pb if it operates above 100 kV

• Aprons may be of the style which is open, or

contains less lead, at the back, due to the

extra weight of lead required - this assumes,

however, that the wearer is always facing

the radiation source

0.25 mm lead

60 kV; 100% 2 - 3 %

100 kV; 100% 8 - 15 %

Attenuation of lead

Courtesy of Prof. E. Vano

Higher kV, lower protection

0.50 mm lead

60 kV; 100% < 1 %

100 kV; 100% 3 - 7 %

Attenuation of lead

Courtesy of Prof. E. Vano Higher kV, lower protection

• Leaded shielding may reduce doses to 5% or

less(1-15%)

• Shielding must be between the patient and

the person to be protected.

If back is facing patient (radiation scatter

source), protection on back is essential

• Everyone in the procedure room

must wear a protective apron

Vest-Skirt Combination distributing 70% of the total weight onto the

hips leaving only 30% of the total weight on the shoulders.

Option with light material reducing the weight by over 23% while still

providing 0.5 mm Pb protection at 120 kVp

Hang aprons! Do not fold them!

Expensive light protective apron sent to Laundry without

the appropriate instructions

Expensive protective apron sent to Laundry

Before After cleaning

…$1000 loss!

IAEA Training Course on Radiation Protection for Doctors (non-radiologists, non-cardiologists) using Fluoroscopy

L05. How do I reduce my radiation risk?

Thyroid protectors

Protective goggles

Lead Equiv: 0.75mm front and

side shields leaded glass;

Weight: 80 grams

DETERMINISTIC

LENS THRESHOLD

AS QUOTED BY

OPACITIES

THRESHOLD

>0.1 Sv/year

CONTINUOUS

ANNUAL RATE

>0.15 Sv/year

CONTINUOUS

ANNUAL RATE

CATARACT

Gauntlets are heavy gloves. They

have limited value because they are

difficult to use and should therefore

only be used where appropriate

Protective Surgical Gloves

• Minimal effectiveness

• Transmission on the order of 40% to 50%, or more

• Costly ($40 US), not reusable

• Reduces tactile sensitivity

• Dose limit for extremities is 500 mSv

• Hands on side of patient opposite of x-ray tube so dose

rate is already low compared to entrance side

• Lead containing disposable products are environmental

pollutants

Radiation Protection of Hands

Best way to minimize dose to fingers and hand:

Keep your fingers out of the beam!!!

Dose rate outside of the beam and on side of patient opposite x-ray tube: Very low compared to in the beam!

Protective devices

• Additional protective devices should be available

in fluoroscopy and interventional rooms as

appropriate:

• Ceiling suspended protective screens.

• Protective lead curtains mounted on the patient table.

• Protective lead curtains for the operator if the

X-ray tube is placed in an over couch geometry and if

the radiologist must stand near the patient

Ceiling suspended screen

Typically equivalent to 0.5 - 1mm

Very effective if well positioned.

Not available in all the rooms.

Not used by all the

interventionalists.

Not always used in the correct

position.

Not always used during the whole

procedure.

Protective lead curtains and ceiling

suspended screens

Under-couch tube

Head level

Without

protection

protection Pb

Head level

Height from the floor

Protective lead curtains

Height from the floor

Over-couch tube

(GOOD Practice) (BAD Practice)

Image Intensifier close to

patient, X ray tube far from

patient

Image intensifier far from

patient, X ray tube close to

patient From: J American College of Cardiology 2004; 44(11): 2259-82

Entrance Dose to Patient vs. Imaging

Geometry

• Practical rules

Key topics

Individual dose monitoring

• Individual external doses should be determined by

using individual dosimeter

• Worn at breast level, between the shoulders and

the waist

Types of Personal Radiation Monitors

1. Film badges

Courtesy of J. Jankowsky

Metal filters

Open window

2. Thermoluminescent dosimeters (TLDs)

3. Optically stimulated luminescence (OSL)

dosimeters

Courtesy of M. Goodsitt

Personal dosimetry

ICRP report 85 (2001) states ...

In interventional procedures:

• In addition, it is possible to combine the two

dosimeter readings to provide an improved

estimate of effective dose (NCRP-122; 1995).

Additional:

outside and above the

apron at the neck

•Better estimation of effective

•gives also an estimation of

thyroid and eye lens doses

with two dosimeters

The main:

under the lead apron

at the breast level

For accurate dose estimation

The use of electronic

dosimeters to measure

occupational dose per

procedure helps in the

optimization

• The monitoring period shall not exceed three months,

preferably one month.

• The exchange of dosimeters and report receipt should not

exceed three months

• It is important that workers return dosimeters on time for

processing

• Delays in the evaluation of a dosimeter can result in the

loss of the stored information

• Employer should make every effort to recover any

missing dosimeters

Special aspects of

individual monitoring

• In case of loss of a dosimeter, the dose estimation may

be carried out from:

• recent dose history,

• co-workers dose

• or, workplace dosimetry

• Individual monitoring devices should be calibrated

• Laboratory performing personnel dosimetry should be

approved by the regulatory authority

• Monthly individual effective dose or equivalent

dose higher than those specified by national

regulations should be evaluated as a part of the

regulatory compliance.

Special aspects of

individual monitoring

Individual monitoring

when a lead apron is used

• The dosimeter should be worn under the apron for estimating the effective dose

• The other body areas not protected by the apron will receive higher dose

• One dosimeter worn under the apron will yield a reasonable estimate of effective dose for most instances

• In case of high workload (interventional radiology) an additional dosimeter outside the apron should be considered by the Radiation Protection Officer

• Extra dosimeters (when available):

• At neck or eye level for estimation of eye lens dose

• Finger ring dosimeter for estimation of finger dose

Individual monitoring

when a lead apron is used

• When expected doses are high, two dosimeters are required:

• 1 under the apron at waist level

• 1 over the apron at collar level

• The effective dose E is given by:

E = 0.5 Hw + 0.025 Hn

where:

• Hw : dose at waist level under the apron

• Hn : dose recorded by a dosimeter worn at neck level over the apron

• Note: The thyroid shielding allows additional 50% reduction of the E

• The dosimeter worn over the apron at collar level gives also an estimation of thyroid and eye lens doses

• Practical rules

Key topics

Health surveillance

• Primary purpose is to assess the initial and

continuing fitness of employees for their intended

• Medical surveillance (medical examinations) to

workers as specified by the Regulatory Authority.

• Counselling should be provided for women who are

or may be pregnant

This is especially relevant

in interventional radiology.

Protection of the

embryo or foetus

• The female worker should, on becoming aware that she is

pregnant, notify the employer in order that her working

conditions may be modified if necessary.

• The pregnancy shall not be considered as a reason to

exclude a female worker from work,

• But it is the responsibility of the employer to adapt the

working conditions in respect of occupational exposure so

as to ensure that the embryo or foetus is afforded the same

broad level of protection as required for members of the

public (< 1 mSv equivalent dose to the foetus to the end of

the pregnancy period”

X-RAY TUBE POSITION

RELATIVE POSITION WITH

RESPECT TO THE PATIENT

IRRADIATED PATIENT VOLUME (FIELD SIZE)

kV, mA and time (NUMBER AND

CHARACTERISTICS OF PULSES)

EFFECTIVE USE OF ARTICULATED

SHIELDING AND/OR PROTECTION

GOGGLES

Factors affecting staff doses

A final general recommendation

Be aware of the radiological protection of your

patient and you will also be improving your

own occupational protection

Where to Get More Information

• ICRP publication 103. http://www.icrp.org/

• Radiological Protection for Medical Exposure to

Ionizing Radiation. http://www-

pub.iaea.org/MTCD/publications/PDF/Pub1117_scr.pdf

• International Basic Safety Standards for Protection

Against Ionizing Radiation and for the Safety of

Radiation Sources. 115, Safety Standards. IAEA, 2011

(Interim Edition).

• International Atomic Energy Agency. Occupational

Radiation Protection. Safety Guide RS-G-1.1

Where to Get More Information

• ICRP Report 85 (2001): Avoidance of Radiation Injuries from Interventional Procedures

• Education and Training in Radiological Protection for Diagnostic and Interventional Procedures

• ICRP Publication 113

• Ann. ICRP 39 (5), 2009 E. Vaño, M. Rosenstein, J. Liniecki, M. Rehani, C.J. Martin, R.J. Vetter

•http://rpop.iaea.org

Thank you

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