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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
2
Lecture Outline
Physics is fun!Physics is easy!Physics is a push over!
3
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
4
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.”
5
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
6
WYSIWYLearn
On the machineLearn about treating patients
Why?How?
In planningLearn about planning cases
Why?How?
In simulatorLearn about simulation
Why?How?
7
Important basic concepts
You can't mess with 'The Laws'!RadioactivityQuantum PhysicsElectromagnetismAttenuationWhat physicists doWhat medical radiation physicists doSoftware/ITChemistry
8
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
9
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
10
Radioactivity
Conversion of sub-atomic particlesMatter
Protons
p+ > n + β+
p+ + β- > n
Neutronsn > p+ + β-n + β+ > p+
Anti-matter
11
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
12
Electromagnetic principles
Moving chargeElectric fieldMagnetic fieldEMR
Photon – wave or particle?Spectrum – wavelength, frequency and energyattenuation
13
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
14
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
15
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
16
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
17
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
18
Information Systems/Technology
Physicalnetworks/HDD/RAM/CPU
DataStorage [“1”]
InformationCorrelation [“1” = Erythema]
KnowledgeReport At 2Gy/day, 80% of patients have
G1 erythema by d12
19
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)
20
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
21
Keeping up with the times
“Conventional”What does this mean?What is it?“field-based”