Acr Optimizing Dose Children Ct

Front 1

ACR Quality Defined as:

Back 1

The Right Procedure done in the right way, at the right time with the correct interpretation to maximize the desired health outcomes and to satisfy the patient.

Front 2

PQI

Practice Quality Improvement

Ongoing Organization Wide Framework to Monitor all aspects of an organization's activities for the purpose of continuous improvement.

Back 2

Goals of PQI

-Improve Quality of Care for Patients

-Reduce Error

-Minimize Medical Legal Risk

-Save Money

Front 3

PQI

Practice Quality Improvement

Back 3

Important Components of PQI

-Break Down the Process Into Steps

-Understand variation that may lead to error

-Test on a small scale before implementing

-Teamwork

Front 4

Implementing PQI:

PDSA Cycle

Back 4

PDSA Improvement Method four Steps:

1. Plan a test --- start small.

2. Do the test

3. Study the Outcomes of the test

4. Act on Knowledge Gained from test

May do same test on larger scale.

Front 5

Measurement of Patient Dose?

Back 5

Patient Dose is Complex

Radiation Dose Can Only Be Estimated.

Front 6

Air Kerma

Back 6

Formerly Called "Exposure"

Air Kerma specifies the amount of radiation existing at a position in space (e.g., output of the CT Scanner)

Unit of Air Kerma is Gray (Gy) or milliGray (mGy)

Air Kerma is the Quantity Typically measured by imaging physicist.

Front 7

Absorbed Dose

Back 7

-Occurs When energy carried by an x-ray is transferred to kinetic energy of charged particles in the tissue as the x-rays pass through the tissue.-transferred energy may cause damage

--Units: Gray (Gy) or milligray (mGy)

--Absorbed dose is typically NOT directly measured. It is calculated from air kerma measurements.

Front 8

CTDI vol

Back 8

Absorbed dose given to 1 of 2 standard-sized plastic cylindrical phantoms by a CT scanner

Units: Gray (Gy) or milligray (mGy)

Imaging physicists use 1 of the 2 phantoms shown to make the measurements needed to calculate CTDI vol.

Pediatric/Head (16 cm) or body phantom (32cm)

Front 9

CTDI vol Estimate of Patient Dose?

Back 9

CTDI vol is NOT estimate of patient dose

CTDI vol is the dose to one of the CTDI phantoms. It allows comparison of the radiation output between CT scanners.

Front 10

More Dose at Center or Periphery of Phantom?

Back 10

More Dose at Periphery of Phantom

Average CTDI vol is 84

Surface dose is 2 times greater than the central dose

CTDI vol is average of central & peripheral dose.

Front 11

CTDI vol in Neonate- under or over estimate?

Back 11

CTDI vol may underestimate a neonatal dose by over 200%.

Phantoms not accurate depiction of neonate

Front 12

CTDI vol of 16 cm phantom is same as CTDI vol of 32 cm phantom-- True/False

Back 12

False! Dose Estimates May Be off by factor of 2 if you use the wrong phantom.

ex: 20 mGy estimate dose based on a 16cm phantom = a 10 mGy dose based on a 32 cm phantom.

Front 13

CTDI vol measure radiation dose to patient.

True/False

Back 13

False! CTDI vol measure the radiation dose to one of the CTDI phantoms. It is NOT an estimate of patient dose, because it does not take into account patient size, patient shape, or the varying tissue attenuating factors of the human body and, therefore, it may significantly underestimate dose.

Front 14

Dose Length Product (DLP)

Back 14

DLP = CTDI vol x scan length (cm)

Front 15

10 slices = 20 mGy CTDI vol

20 slices = 20 mGy CTDI vol

Back 15

10 slices = 200 mGy/cm DLP

20 slices = 400 mGy/cm DLP

Front 16

DLP is indicator of patient dose.

True/False

Back 16

False!

DLP, just like CTDI vol, is not indicator of patient dose.

Neither measurement accounts for changes in patient size, since both use dose delivered to 1 of 2 standard phantoms.

Front 17

With same technique (120kV, 200mA, 1 sec) Measured CTDI vol same with small phantom and large phantom?

Back 17

No!!!! Measured CTDI vol is 2.6 times larger with smaller phantom---- But the displayed CTDI vol is the the same.

Front 18

Back 18

No!!!! Measured CTDI vol is 2.6 times larger with smaller phantom---- But the displayed CTDI vol is the the same.

Front 19

Estimates of Radiation dose on CT Console.

Back 19

CTDI vol (mGy) = 31.60 (body phantom)

DLP (mGym) = 1797.20 (body phantom)

Front 20

Confusion When Talking About Radiation Output (Estimate of Radiation dose)

Radiation Output-- Not Patient Dose!

Back 20

31.6 mGy CTDI vol32 x2 = 63.2 mGy CTDI vol 16

Remember these are not patient doses.

Also depending on the size of the phantom, a conversion factor (2) may need to be used to correct from one CTDI phantom to the other.

Front 21

SSDE?

Back 21

SSDE = Size Specific Dose Estimate

Which takes into account the effect of the patient's size on their radiation dose.

SSDE is currently the best estimate of patient dose.

Front 22

Back 22

SSDE--Better estimate of patient dose

Acurrate to within 10-20%

Conversion factor is applied.

NEED 4 THINGS:

-Patient Size (lateral dimension)

-CTDI vol phantom 16 or 32 cm

-Conversion factor

-Displayed CTDI vol from clinical scan

Front 23

Largest 4 Y/O and Smallest 18 Y/O are the same size

Back 23

The Most Accurate Method to Estimate body Size is Patient Thickeness.

Avoid Using:

-Age

-Weight

Front 24

Red Line Demonstrates Lateral Width, and Dotted Line demonstrates (AP) dimension.

Back 24

Patient size can be calculated from the projection before the scan or from the axial image after the scan.

Front 25

Look Up Table TG204

Back 25

SSDE can be calculated from

- AP Dimension

-Transverse or Lateral Dimension

-AP + Lateral Dimension or

-Effective Diameter

Front 26

Back 26

One Factor That Influences Radiation Dose is Image Quality.

Image Noise is One Component of Assessing Image Quality.

Front 27

What is Image Noise?

Back 27

Image Noise Appears as the speckled Gray Background of a Uniform Phantom.

It is measured as the standard deviation of the voxel values in a homogenous (typically water) phantom.

Front 28

Higher Dose Exam

DLP 1284

Back 28

Lower Dose Exam

DLP 559

Grainer Image

But Diagnostic

Much Lower "Dose"

-Need Balance:

Best vs Acceptable (Diagnostic) Image

Front 29

Target Level for CT Radiation Dose

What is DRL?

Back 29

Diagnostic Reference Levels (DRL)-

are dose levels for typical examinations for groups of standard-sized patients or standard phantoms for different types of equipment.

Front 30

Diagnostic Reference Levels (DRLS)

If site's CT > 75% percentile compared to peers, then local action should be triggered

True/False

Back 30

DRLs -Derived from Surveys / Registries

-Tool to Compare Doses at Different Sites

-Apply to Populations of Patients, NOT Individual Exams

-Are NOT a dividing line between good and bad medicine-Are Inappropriate to use for regulatory air commercial purposes./Voluntary/Will Change

Front 31

New Upper Limit for Pass/Fail for Abdominal CT for a 5 Year Old is 20mGy using the (Pedi)16cm CTDI Phantom as a Reference

Back 31

Remember!

If you use Adult Phantom 32 cm for Pedi Abdomen then would get 10 mGy-

Instead of the 20 mGy for the Pedi Phantom 16cm.

Front 32

Registry?

Back 32

Registry is a systematic method for collection of observational data on patient health and demographics in a uniform manner to evaluate specified metrics for a population defined by a particular condition or procedure.

Front 33

ACR

Dose Index Registry DiR

Part of National Radiology DATA Registry NRDR

Back 33

CT DIR

uses CTDI vol and SSDE to collect dose data

NOT age.

SSDE more accurate estimate dose then estimates based on patient age.

Front 34

Box and Whiskers Plot

Back 34

Box and Whiskers Plot

Individual Facility's dose estimates SSDE are lower than the national medium.rP

Front 35

Practical Measures to Optimize Radiation dose for Pediatric CT

Back 35

-Consult Medical Imaging Physicist

-Adopt recommendations and protocols outlined in this module

-"Child Size" CT protocols based on patient body size

Front 36

"Universal Protocol"

Back 36

"Universal Protocol"

-allows any site with any machine to adapt their protocols and compare results to best practice as suggested by an appropriate DRL.

The Universal Protocol serve as a start to lower dose.

Front 37

Other Methods to Reduce Dose

Pediatric Patients

Back 37

-Appropriate Centering

-Optimize Projection Scans

-Limit Scan Length

-Eliminate Multiphase Scan (non-contrast, contrast, delayed CT scans)

-Organ Shielding (Gonads, thyroid, lens of eye)

-Automatic Tube Current Modulation (ATCM)

-Iterative Reconstruction

Front 38

-Appropriate Centering

Back 38

-Appropriate Centering

Entrance dose to the Skin is, in part, a function of the distance of the skin from the focal spot of the CT Scanner (Inverse-Square law), positioning the patient's body in the middle of the CT gantry reduces the radiation dose to the patient.

Front 39

Reduce Dose During Projection Views

Back 39

- Switch from AP Projection to PA Projection to reduce dose to the male gonads, breast, thyroid, lens of the eye)

-Proper High voltage and/or tube current

Front 40

Limit Scan Length

Limit Scan Length for Scout and Clinical Images

Use Appropriate FOV

Back 40

Multiphase Exams

Rarely Needed

Doubles the Dose to the Pediatric Patient

Front 41

Bismuth Shield-

Some Controversy-

Place Shield After ATCM Scout-otherwise may increase dose to patient

Back 41

Automated Tube Current Modulation

(ATCM- red line)

the scanner automatically adjusts mA according to the projection scans. Reduces Dose

Front 42

Iterative Reconstruction

--Reduces Dose Compared to Filtered Back Projection Techniques

Back 42

Post-Iterative Reconstruction

Image-

Compare to Prior

Front 43

1980 Medical Radiation was 15%

2006 Medial Radiation Increased to Almost 50% of Radiation that population receives .

Back 43

Two Types of Radiation Effects:

1. High dose>> Deterministic --Tissue Effects (acute)---Dose Dependent--threshold associated

2. Lower dose >>>>> Stochastic Effects

Potential for Cancer, Genetic Effects

No assumed Threshold

Front 44

Potential Stochastic Effects in Children

Back 44

Stochastic Effects in Children are Potential for Cancer and Genetic Effects

-Risk Depends on Dose

-There is assumed no threshold

-Children's cells are rapidly dividing, i.e. more vulnerable than adults for most cancers

-Children live longer- more time to manifest adverse effects, i.e. cancer

Front 45

Children with chromosomal deletions have increased risk of developing radiation induced cancer.

Which ones?

Back 45

-Ataxia Telangiectasia

-Fanconi anemia

-Hereditary Retinoblastoma

-Down syndrome

-Gardner syndrome

-Nijmegan breakage syndrome

-Basal Cell Nevus

-Boom, Cockayne, Usher syndromes

Front 46

Risk Cancer 4 out of 10 will get cancer without radiation from CT!

One half die from the disease

No way to tell if cancer occurred from effect of radiation.

Back 46

Background Radiation

Sun and Soil

3 mSv/year

Front 47

Abdominal CT = 20 months background radiation

Chest Xray = One day of Background Radiation

Back 47

Chest xray 0.01 mSv

Head CT 2 mSv

Chest CT 3 mSv

Abdominal 5mSv

Front 48

Practical a mGy=mSv

-A Gray is large dose for radiation therapy

--Thousand time less is a milligray - small dose for medical radiation

Back 48

Two Views

- Rising Risk

-No Risk Because Threshold, More Harm from avoiding the exam

Front 49

Medical Radiation Cause Cancer?

Back 49

We don't know.

We should act cautiously as if there may be a risk.

Front 50

Justification of Scan

Needed in Each Case

Benefit Vs Small Risk

Back 50

Clinical Question-

Will Scan Answer the Question?

If Not, then scan is not justified.