The Nature of Physicsradonc.wdfiles.com/local--files/part-1-2009course/... · 2012-09-17 ·...

21-03-2009

RANZCR Part 1 CourseSt Vincent's Hospital,

Paddington NSW

A/Prof Natalka SuchowerskaA/Prof Andrew MillerRANZCR

Part 1 Physics Examination Panel

The Nature of Physics

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Lecture Outline

Physics is fun!Physics is easy!Physics is a push over!

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Now the Proper Lecture Outline!

IntroductionSpecialty

Is Physics necessary?Force feeding

Who sits the exams alone?Responsibility

YoursDeep learning?

OursKnowledge, understanding sufficient for the job

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Importance of Physics

“The medical oncologist needs to know nothing about pharmacology.”“The surgical oncologist needs to know nothing about tensile strength.”

“Just get past your physics examinations and then get on with the real stuff.”“The most important thing is to be clinically very good so that you treat only the right patients.”

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Introduction

Physics is thinkingInch wide, mile deep

The hard part of Physics is UNDERSTANDINGThat's why we keep asking to see your understanding

Expressed in your explanationsThat's why you need to teach a friend your physics

A special branch of PhysicsYou are studying Radiotherapeutic Physics

This is an applied subjectUse your eyes to see it“Why do we do this?”Basis of new curriculum

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WYSIWYLearn

On the machineLearn about treating patients

Why?How?

In planningLearn about planning cases

Why?How?

In simulatorLearn about simulation

Why?How?

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Important basic concepts

You can't mess with 'The Laws'!RadioactivityQuantum PhysicsElectromagnetismAttenuationWhat physicists doWhat medical radiation physicists doSoftware/ITChemistry

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The Laws

Conservation of Energy/MassEquivalence (a la Einstein)

Conservation of ChargeConservation of Momentum

AN EXAMPLE Pre PostEnergy >1.022 MeV KE (>1.022MeV)Mass 0 2 x me

Charge none +1, -1Momentum 0o +θo, -θo (α KE)

me = rest mass of an electronE = mec

2 = 0.511 MeV

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The Laws

… and the reversal

Pre Post

Energy KE 2 x 0.511 MeVMass 2 x me 0

Charge +1, -1 noneMomentum 0o +90o, -90o

me = rest mass of an electronE = mec

2 = 0.511 MeV

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Radioactivity

Conversion of sub-atomic particlesMatter

Protons

p+ > n + β+

p+ + β- > n

Neutronsn > p+ + β-n + β+ > p+

Anti-matter

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Quantum Physics

Occurrence of physical phenomena in “quanta”Photoelectric effect (electron emission by radiation)

Nobel Prize 1921Light quanta

Characteristic SpectrumSpecific light frequencies only

Matter/Antimatter annihilationLinear accelerator operation

Use of EMR (microwave) to accelerate a moving charged particle (e-)

Bohr, Einstein, Schrödinger, Heisenberg, etc

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Electromagnetic principles

Moving chargeElectric fieldMagnetic fieldEMR

Photon – wave or particle?Spectrum – wavelength, frequency and energyattenuation

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Attenuation

Issue of Constant proportionalityConstant decrease by “x” every “y”

Radioactive decay

Light absorption (Beer-Lambert Law)

Constant increase by “a” every “b”Malthusian growth

N t =N 0e−λt

N(t) = N0 e- .tλ

x(t) = x0 ek.t

I = I0 e- .xα

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What physicists do

They describe and speak to each otherThey speak very, very precisely

Definitions are importantWhat is their language?

Mathematics & logicThey are pedantic

Subdivide and define phenomenon and give it mathematics

They measureUnitsDefinitionsObjectivity

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What radiotherapeutic physicists do

They defineCommission Hardware

Linear accelerator operationsCar testing by dealer (“Acceptance Testing”, it works!)Car testing by you (close enough?)Car testing by F1 (absolute responsibility)

They describeCommission Software

Planning systemYour electronic banking by you (absolutely accurate)Your electronic banking by me (close enough?)

They objectifyQuality assure the hardware (WYPIWYT)

cf field-based & 3DCRT V IMRT

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Physics Concepts

Most examination answers require concepts explained

Thermionic emissionBremsstrahlungCharacteristic radiationPhotoelectric Effectf FactorHalf-lifeAttenuationKERMAParis SystemZ, A, amuBinding Energy

Atomic Model (Thomson, Rutherford, Chadwick, Bohr)Coulomb interactionsMetastabilityRadioactivityTransient/Secular EquilibriumAuger/Electron CaptureStopping Power/LETIonizationAngular distributionCompton, PEE, PPHVL

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Software

Computers run the departmentAppointments/Resources/Billing

At the patient's sideDiagnosis/Staging/Intent/Modality Prognostic/Eligibility/Exclusion factorsSide effects/Disease status

At simulation/planningPrescriptionDICOM-RT file

CT scan/Prescription/Beam parameters/Dose profile

At treatment machineR&V software

Purpose/Components/Use/Safety

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Information Systems/Technology

Physicalnetworks/HDD/RAM/CPU

DataStorage [“1”]

InformationCorrelation [“1” = Erythema]

KnowledgeReport At 2Gy/day, 80% of patients have

G1 erythema by d12

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Important basic chemistry concepts

States of MatterSolid

Metal/Liquid/Gas - malleabilityPowder - soluble/insolubleceramic/crystal

Biological solubilityBiological substitution

Ca2+ (alkaline earth metal)Na+/K+ (alkali metal)Isotopes of biological elements (32P)

ReactivityNoble gases (Rn)/Inert metals (Au, Pt)

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What is the perfect isotope?

Example of an answerLong half-life

for infrequent transportation (reduced risk of exposure)Solid

for easy containment (reduced spills)Unreactive element

for clinical use (body fluid contamination irrelevant)Non-absorbed parent or daughter

for improved protection (nothing left behind)Easily moulded

for multipurpose use

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Keeping up with the times

“Conventional”What does this mean?What is it?“field-based”