Chapter 4 Flashcards
Describe the Magnetron pulse length pulse repetition time pulse frequency Output power
The cathode is heated by an inner filament and the electrons are generated by thermionic emission. A static magnetic field is applied perpendicular to the plane of the cross section of the cavities and a pulsed DC electric field is applied between the cathode and the anode. The electrons emitted from the cathode are accelerated toward the anode by the action of the pulsed DC electric field. Under the simultaneous influence of the magnetic field, the electrons move in complex spirals toward the resonant cavities, radiating energy in the form of microwaves. The generated microwave pulses are led to the accelerator structure via the waveguide. microsecond 0.1seconds 3GHz 2-5MW
Major difference between magnetron and klystron
Klystron is an amplifier not a generator
About how deep is the 50% dose for superficial therapy (50- 150kVp) in water
~3mm
Where does photon contamination come from in e- beam therapy?
scattering foil and collimators
Why is collimation for e close to the skin
electrons scatter in air
What do monitor chambers monitor (what quantities)?
Integrated dose, dose rate, and symmetry
How are neutron beams generated
Cyclotron accelerates deuterons to tens of MeV and strike a beryllium target. (stripping)
How is <span>60</span>Co produced?
59Co is bombarded with neutrons.
How is cobalt packaged
double case of metal (welded together)
Co60 decay products and energies
Beta (max 0.32 MeV) 1.33 and 1.17 gamma Ni60
What Co60 proucts substantially contribute to dose
decay gamma rays and scattered gamma rays (scattered primary in the source itself) Beta particles and resulting scatter do not contribute due to self filtration.
Draw a Linear Accelerator

Draw the pieces of the treatment head

What Co60 proucts substantially
contribute to dose
decay gamma rays and scattered
gamma rays (scattered primary in
the source itself) Beta particles and
resulting scatter do not contribute
due to self filtration.
Define transmission penumbra
penumbra created by transmission through collimator (if collimator is not alligned with beam divergence)
Derive geometric penumbra in
terms of source-surface, source
collimator distance, depth in
phantom, and source size
P = [s(SSD+d-SDD)]
SDD
Write an equation for deutoriumtritium generator
What are the advantages
What are the disadvantages
12H+13H->n+24He+17.6MeV
Advantages: essentially
monoenergetic (14MeV)
Disadvantage: low dose rate
(15cGy/min)
Write an equation for cyclotron
generator Advantages?
Disadvantages?
1<span>2</span>H+49Be->0<span>1</span>n+510B
Advantages: forward directed,
energy 50% dueteron
Disadvantages: Spectrum of energy
requires filtration to harden beam
What energies are used for proton therapy?
150-250MeV
How are range, mass, and charge
related for charged particles?
Range is proportional to mass and
inversely proportional to charge
squared
Define specific kinetic energy
kinetic energy per nuclear mass (MeV/u)
where u is the mass number of the nucleus
the range is dependent on A/Z2, where A is the atomic number and Z is the nuclear charge. Since A/Z2 decreases as the
ions get heavier, the range of heavier ions is less than the range of lighter ions for the same MeV/u.
What is rms voltage of an ac
current
v/sqrt(2)