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PARIENT DOSE MONITORING IN DIAGNOSTIC RADIOLOGY

Napapong Pongnapang, Ph.D.Department of Radiological TechnologyFaculty of Medical TechnologyMahidol UniversityBangkok, Thailand

ประชุมวิชาการสมาคมศิษยเ์ก่ารังสีเทคนิครามาธิบดี พ.ศ. 2559

ContentExposure to radiationRadiation dose and radiobiological issuesRadiation safety for patients Multi-disciplinary approach in radiation protectionPatient dose monitoring in diagnostic radiology

From the news From the news

CA state fined the hospital $25,000, additional lawsuit from familyThe child received 2.8-11 Gy radiation dose at different organs.

Exposure to Medical Radiation• Occupational Exposure

• Exposure to radiation from work related activities• Limit applied (20 mSv per year)

• Public Exposure• Exposure to radiation by members of public• Limit applied (1 mSv per year)

• Medical Exposure• Exposure to medical radiation, imaging and therapy• No limit• Justification and optimization applied

The Use of Diagnostic Radiation

UNSCEAR 2008

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Dose from Imaging and Interventional ProceduresImaging Normally low doseStochastic RiskDosimetry mainly for optimizationSometimes effective dose is used

Interventional RadiologyModerate to high doseConcern for deterministic effects to skin

Radiation health effects

DETERMINISTICsomatic

clinically attributable inthe exposed individual

CELL DEATHSTOCHASTIC

somatic & hereditaryepidemiologically attributable

in large populations

CELL TRANSFORMATIONANTENATAL

somatic and hereditaryexpressed in the fetus,

in the liveborn or descendants

BOTH

T Y P EofE F F E C T S

radiation hit cell nucleus!

No change

DNA mutation

DNA MutationCell survives but mutated

Cancer ?

Cell death

Mutation repaired

Unviable Cell

Viable Cell

Outcomes after cell exposure

DAMAGEREPAIRED

CELL DEATH(APOPTOSIS)

TRANSFORMEDCELL

DAMAGE TO DNA

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Q. What is the lowest doses of low LET radiations at which clear evidences of cancer risks are shown ?Acute exposure Adults ~ 10-50 mSv (Brenner, PNAS 2003,100:137-61)Childhood cancer risk( in utero exposure) ~ 6-10 mSv

(Doll,BJR 1997, 70: 130-9)

Protracted exposureOccupational workers ~ 50-100 mSv

(Brenner, PNAS 2003,100:137-61)

What we knowUNSCEAR (2008) - Life-time risk of dying from radiation induced cancer = 5% per sievert

ICRP recommends that the risk of fetal cancer in population receiving 1 mSv is taken to be 5 in 100,000 (0.005%)

Medical Exposure

Source: WHO

Risks from radiation A matter of risk communication

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Bonn Call for Action (2012)Action 1: Enhance the implementation of the principle of justificationAction 2: Enhance the implementation of the principle of optimization of protection and safetyAction 3: Strengthen manufacturers’ role in contributing to the overall safety regimeAction 4: Strengthen radiation protection education and training of health professionalsAction 5: Shape and promote a strategic research agenda for radiation protection in medicineAction 6: Increase availability of improved global information on medical exposures and occupationalexposures in medicineAction 7: Improve prevention of medical radiation incidents and accidentsAction 8: Strengthen radiation safety culture in health careAction 9: Foster an improved radiation benefit-risk-dialogueAction 10: Strengthen the implementation of safety requirements globally

Follow up the Bonn Call for Action• The ISRRT attending a Panel session on "International Response to Bonn Call for Action" during the 14th International

Radiation Protection Association Conference (IRPA) in Cape Town, South Africa. Members of the panelist include representatives from WHO, IAEA, IRPA, HERCA, NCRP and ISRRT. Dr Pongnapang presented the ISRRT initiatives in response to the Bonn Call for Action regarding roles of radiographers in justification and optimization of medical exposure, education of radiation protection and promotion of strategic research agenda for radiation protection in medicine. The ISRRT action plan to the Bonn Call for Action was also promoted signifying important role of radiographers and radiological technologists to continue positively to safe and effective use of radiation in medicine.

Patient dose tracking

M.Rehani and Frush D., Lancet, Vol 376, Sept, 2010

Patient dose tracking"It's only been two years since the phasedimplementation of centralised patientradiation exposure tracking in Egypt,but there's already been a significantchange, especially in referring physicians," says Dina El Husseiny of Egypt'sNational Centre for Radiation Researchand Technology."Since doctors know that they are beingaudited by the Central Directorateof Radiology, they are more carefulabout the number and type of diagnostic imaging procedures they write for patients," says El Husseiny.

IAEA Project on Justification

IAEA, Vienna, 2012 Regional Project, Asia/Pacific, Seoul, Korea , 2013

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Justification of Medical ExposureKey Points:Clinical Audit is a key toolJustification would be facilitated by ‘3A”1.Awareness2.Appropriateness3.Audit

Potential for unlimited exposureHigh Level Control (HLC)Fluoroscopic studiesAny and all digital imagingCRDRCT

Typical effective doses from IR(Stochastic-cancer risk)

Mettler et al., Effective doses in Radiology and Nuclear Medicine, Radiology 2008

Potential Effects in Skin(Deterministic Effects)

Radiographics 1999; 19: 1289-1302

Why we pay more attention intervention radiology?

Source: The US FDA

Cumulative dose of 20 Gy from one angiography and two angioplasty

If you look closely in your Department…

There were 2 cases of therapeutic cerebral angiography, where the patient entrance dose washigher than 3 Gy in the frontal view, which reached the deterministic threshold for temporary epilation.

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Typical effective doses from CT

Mettler et al., Effective doses in Radiology and Nuclear Medicine, Radiology 2008

Safety concerns in CT• The US FDA issued FDA public health notification on reducing radiation risk from CT for pediatric and small adult patients (Nov 2001)• The ACR – children have more rapidly dividing cells than adults and have longer life expectancy, the odds that children will develop cancers from x-radiation maybe significantly higher than adults• The US National Research Council’s Committee on the Biological Effects of Ionizing Radiation – children less than 10 years of age are several times more sensitive to radiation than middle aged adults• Unnecessary radiation maybe delivered when CT scanner parameters are not appropriately adjusted for patient size.

CT Optimization• Evaluate and improve clinical performance

• Advocate appropriate equipment use & compliance protocols• Provide training, e.g., “down size” protocol for children, single phase, limit to indicated areas• Implement QA program & corrective actions

• Audit and review DRLs, diagnostic data and image quality• Assess and improve scanner performance

• Performance parameters; resolution, contrast, noise• Scanner dosimetry

• Eliminate inappropriate referrals for CT

Multi-professional work

MODERN MEDICINE IS IMAGE-CENTRIC

MedicalImaging

O & G

SurgeryTrauma

Oncology

Internal MedicineKHNg

EXCELLENCE REQUIRES DEVELOPMENT AND IMPLEMENTATION OF best practice, clinical guidelines, quality assurance, standards, audit, and outcome assessment

KHNg

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MEDICAL IMAGING EQUIPMENT AND PROCEDURES MUST BE MONITORED quality control (QC),quality assessment and improvement (QAI), continuous quality improvement /total quality management (CQI/ TQM)

KHNg

A team effort in clinical setting• Radiologist – lead the effort

• Clinical information• Image quality• Protocol design

• Medical Physicist – important role• Parameters affecting IQ and dose• Patient dose monitoring and audit• Protocol management (in many places = Technologist’s role)

• Technologist – key player• Can it be done or not?• Practical concern• Patient instruction• Workflow

Multi-disciplinary effort fordose reduction

Optimization = 10-15% dose reductionJustification = 30-100% dose reduction!

Radiologists• Gate Keeper• Major role in justification• Imaging protocol design

• Low dose imaging, when possible• Keep in mind image quality vs dose – how far can you go?• Medical physicists can help

• Pediatrics protocols• Disease specific protocols

ACR appropriateness criteria ACR appropriateness criteria

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ESR- EuroSafe Medical Physicists• Patient dosimetry• Dose monitoring and audit• Protocol optimization• Image quality vs. dose

Radiological Technologists• Dose delivery• Co-operate with radiologists

and physicists in optimization process

• Clinical protocol optimization – with radiologists

• Technical protocol settings –with physicists

• Utilize information from others to optimize the technical settings

IAEA Initiatives

Patient dose in diagnostic radiology: Purposes• To evaluate stochastic risk – mSv

• To evaluate deterministic effect –mGy

• To compare/ adjust/ standardize protocols

• To optimize dose with image quality

Dose from plain film

Diagnosticprocedure

Typicaleffectivedose (mSv)

Equiv. no. ofchest x-rays

Approx. equiv.periodof natural backgroundradiation

Chest (singlePA film)

0.02 1 3 daysSkull 0.07 3.5 11 daysThoracicspine

0.7 35 4 monthsLumbarspine

1.3 65 7 months

Low dose but the lower the better for Stochastic risk

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IAEA TRS-547• Published in 2007• Serves as current international code of

practice on dosimetry in diagnostic radiology• More European protocols based

IAEA code of practice

Dosimetric quantities: Radiography• Incident air kerma Ki

• measured for phantoms• calculated for patients from measured tube output

• Entrance surface air kerma Ke• measured for patients using

TLDs• calculated for patients

• Air kerma-area product PKA• measured for patients

BUT• Patient dose measurement as described mainly aim to

evaluate or estimate dose at reference point and applied to selected standard size patient

• Now we live in Digital Radiography Era

• Number of dose parameters are readily available and even be able to be shown on DICOM header

• New approach on patient dose monitoring and auditing, digitally and electronically

UNDERSTANDING EXPOSURE INDEX

A matter of quantities

Image from Philips

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We have DAP, why not enough?• DAP does not indicate appropriateness of exposure level

in individual case• DAP cannot differentiate Under from Over –exposed

images• In Plain film, DAP will give upper limit of dose in an

average sense• Can be used for comparison purpose, DRL

What Exposure Index is good for?• Feed back fro radiographers about appropriate exposure

level in clinical routine.

• Comparison with prescribed .. Speed class.. For plian film exams

• Used as quality control tool for medical physicist as dose check or constancy check

Dosimetric system in Interventional Radiology• ICRU – there is a need of harmonization of quantities and

terminology for dosimetry in diagnostic and interventional radiology

• IAEA TRS-457 provides standard on diagnostic dosimetry

Reasons to measure dose• To assess/quantify the risk of radiation damage to both

healthy and unhealthy tissues• To establish a “calibration” mechanism for the assessment

and comparison of outcomes/performance for particular applications

QUANTITIES FORPATIENT DOSIMETRY

From: Avoidance of radiation injuries from interventional procedures. ICRP.

IAEA Code of Practice• Dosimetry in fluoroscopy

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Dosimetry in fluoroscopy• Quality assurance

• Acceptance and constancy test• air kerma rate for different acquisition modalities

• Patient dosimetry• Comparison with reference levels

• Air kerma area product• Dose analogues: fluoroscopy time and no. of acquired images

• Organ dose evaluation

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• 4 geometries• Under couch• Over couch• C-arm• C-arm-lat

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Example of under couch measuremetn set-up63 Measuring entrance

dose, scatter dose and image quality

Scatter dose detector (lens of the interventionalist position)Test object to measure image quality, at the isocenterFlat ionization chamber to measure patient entrance dose

Measurements on patients• In examinations using fluoroscopy, irradiation geometry and time vary individually from patient to patient. • Effects on patient exposures of these variations are captured by the air kerma–area product (PKA), • KAP is easily measured using a flat transmission ionization chamber (KAPmeter) mounted on the collimator housing. • The KAP meter does not disturb the examination and gives real time information. • In the Code of Practice, measurement of the air kerma–area product (PKA) is recommended for monitoring patient exposures in examinations involving fluoroscopy

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KAP meters• KAP meter with flat trasparent ionisation chamber

In some systems: • KAP is calculated from kV, filtration, mAs, diaphragms positions

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KAP meter calibration• The KAP meters should be calibrated for each stand where they are used.• Calibrations both in situ and at a standard laboratory are possible.• Modern radiology departments usually possess a number of machines with KAPs. It is not realistic to calibrate each instrument at the SSDL and for built-in KAP meters this is not even possible. • The calibration coefficient provided by the manufacturer should be checked before the instrument is used.

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Patient Dosimetry in CT• Assessment of risk• Dose evaluation• Dose audit• Compare doses from different protocols

CT Dosimetry Methods• TLD Measurement

• Computer Based Simulation Method

• Dose Measurement using Ionization Chamber

TLD Measurement• is the direct method by using an anthropo-morphic physical phantom• doses are measured in the location of organs or

tissues of interest by using TLDs

• effective dose can then be calculated

Dose Measurement using Ionization Chamber

• based on the FDA definition of CTDI

• normally used for QA measurement

• does not provide a direct assessment of the risk to the patient

Computer Based Simulation Method• Dose estimates are based on

MC calculations for anthropomorphic mathematical phantoms or using data previously collected from the survey

• The phantoms were based on the original MIRD phantom with specification of all organs andwere modified as Adamand Eva including sex-specific characteristics Adam Eva

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TLD Measurement Method Definitions of Quantities For Assessing Dose In CT• Computed Tomography Dose Index (CTDI)• Weighted CTDI (CTDIW)• Volume CTDI (CTDIVOL)• Dose-Length Product (DLP) • Limits to CTDI Methods• Effective Dose (E)

Computed Tomography Dose Index• Applies to single axial scan only• Measured on axis of scanner using pencil ionisation chamber

• Calculated as integral of air kerma along chamber divided by nominal slice thickness

• Several different versions!!

Weighted CTDI (CTDIW)• Average CTDI across field of view• Useful indicator of scanner radiation output for a specific kVp and mAs

• CTDI two higher at the surface than at the center of FOV

• TRS 457 = Cw

32 3

1,100,100 edgecenterw CTDICTDICTDI

Volume CTDI (CTDIVOL)• Absorbed radiation dose over the x ,y and z-direction within scan volume for standardized phantom, TRS = Cvol• Dose to standardized phantom for a specific scan protocol• Take gap or overlaps between the x-ray beam from consecutive rotations of the x-ray source

I = the table increment per axial scan (mm)ICTDITNCTDI wvol

Limitation of CTDIVOL• Does not represent the average dose for objects of different

- size- shape- attenuation

• Does not indicate the total energy deposited into the scan volume because it is independent of the length of the scan

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Dose-Length Product (DLP) Overall energy delivered by a given scan protocol, the absorbed dose integrated along the scan length, TRS = P KL,CT Air Kerma Length Product

)( )()( cmlengthscanmGyCTDIcmmGyDLP vol

Effective Dose (E)Biological effects from radiation depend on

• Radiation dose• Biological sensitivity

• Compare biological effects between diagnostic exam of different types

• Communication with patient regarding the potential harm

Estimation of dose to patients undergoing CT exams - Direct measurement of organ dose in phantom- Calculation by Monte Carlo method

E (mSv) = k x DLPk = conversion factorerror 10-15%

Effective Dose (E) Effective Dose Conversion

Monitoring the dose• Regulatory requirements• Accreditation requirements • Liability and Public Relations • Research • Quality Assurance • Awareness & Patient Safety • Individual Patient cumulative dose record

Patient dose metrics• • Dose

• – Organ Dose (Gy) /Equivalent Dose (Sv) • – Effective Dose (Sv)

• • Dose Surrogates • – Cumulative Exposure Time (min) • – Entrance Air Kerma (Gy) • – Dose Area Product (Gy- cm2) • – Cumulative Dose (Gy) • – Peak Skin Dose (Gy) • – CTDI (Gy) • – Dose Length Product (Gy-cm)• – Size Specific Dose Estimate (Gy)

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Individual Patient Dose Measurement • • Measurement of Patient Dose –Difficult

– Dosimeters – Computational Predictions

• Dose Surrogates – Easier to obtain – Easier measurement – Difficult interpretation for radiation detriment – Not uniformly defined or applied

• Depend on biological endpoint

Dedicated dose tracking software• Integrate dose metrics from imaging systems or PACS• typical formats: DICOM RDSR preferred • Integrate with PACS, RIS, EMR • Analysis capabilities • Selection of Reference Doses • Automated notification

Examples of Dedicated Dose Tracking Systems • DoseMonitor (PACS Health)

• DoseTrack (Sectra)

• DoseWatch (GE)

• RADAR360 (MedPhys360)

• Radimetrics/eXposure(Bayer)

Example – Radimetrics

In Summary• Diagnostic dose ranges between 0.2-20 mSv• High dose procedures include interventional radiology and CT• Dose optimization is needed to reduce stochastic risks of radiation• Dose from investigations that reach deterministic threshold must be monitored• Quality of care in radiology needs team works• Justification and Optimization are the “MUST” for diagnostic radiology – this needs multi-disciplinary collaborative work