Chapter 4

Question 1

Describe the Magnetron pulse length pulse repetition time pulse frequency Output power

Answer 1

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

Question 2

Major difference between magnetron and klystron

Answer 2

Klystron is an amplifier not a generator

Question 3

About how deep is the 50% dose for superficial therapy (50- 150kVp) in water

Answer 3

~3mm

Question 4

Where does photon contamination come from in e- beam therapy?

Answer 4

scattering foil and collimators

Question 5

Why is collimation for e close to the skin

Answer 5

electrons scatter in air

Question 6

What do monitor chambers monitor (what quantities)?

Answer 6

Integrated dose, dose rate, and symmetry

Question 7

How are neutron beams generated

Answer 7

Cyclotron accelerates deuterons to tens of MeV and strike a beryllium target. (stripping)

Question 8

How is ^{<span>60</span>}Co produced?

Answer 8

⁵⁹Co is bombarded with neutrons.

Question 9

How is cobalt packaged

Answer 9

double case of metal (welded together)

Question 10

Co60 decay products and energies

Answer 10

Beta (max 0.32 MeV) 1.33 and 1.17 gamma Ni60

Question 11

What Co60 proucts substantially contribute to dose

Answer 11

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.

Question 12

Draw a Linear Accelerator

Answer 12

Question 13

Draw the pieces of the treatment head

Answer 13

Question 14

What Co60 proucts substantially
contribute to dose

Answer 14

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.

Question 15

Define transmission penumbra

Answer 15

penumbra created by transmission
 through collimator (if collimator is
 not alligned with beam divergence)

Question 16

Derive geometric penumbra in
terms of source-surface, source
collimator distance, depth in
phantom, and source size

Answer 16

P = [s(SSD+d-SDD)]

SDD

Question 17

Write an equation for deutoriumtritium generator
What are the advantages
What are the disadvantages

Answer 17

₁²H+₁³H->n+₂⁴He+17.6MeV
Advantages: essentially
monoenergetic (14MeV)
Disadvantage: low dose rate
(15cGy/min)

Question 18

Write an equation for cyclotron
generator Advantages?
Disadvantages?

Answer 18

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

Question 19

What energies are used for proton therapy?

Answer 19

150-250MeV

Question 20

How are range, mass, and charge
related for charged particles?

Answer 20

Range is proportional to mass and
inversely proportional to charge
squared

Question 21

Define specific kinetic energy

Answer 21

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.

Question 22

What is rms voltage of an ac
current

Answer 22

v/sqrt(2)