Final Exam - Treatment Delivery Equipment

Question 1

Name 4 types of Megavolt units

Answer 1

• Linear Accelerator (6,10,15,18)
• Betatron (2 MV)
• Cyclotron (2 MV)
• Cobalt-60
• Vande Graaf (2MV)

Question 2

The Grenz ray produced x-rays at which energy?

Answer 2

10-15 kVp

Question 3

Contact therapy produces x-rays at which energy?

Answer 3

40-50 kVp

Question 4

Superficial therapy produces x-rays at which energy?

Answer 4

50-150 kVp

Question 5

Orthovoltage produces x-rays at which energy?

Answer 5

150-500 kVp

Question 6

Describe the major components that are housed in the drive stand of a linear accelerator

Answer 6

KLYSTRON
source of microwave power used to accelerate electrons

CIRCULATOR
acts like valve, directs radiofrequency energy into the waveguide and prevents backflow into klystron

WAVEGUIDE
convey microwave power to the accelerator structure in the gantry

WATER COOLING SYSTEM
helps to maintain constant temperature in the functioning parts of the machine

Question 7

Describe the major components of the gantry

Answer 7

ELECTRON GUN
produces electrons and injects them into accel. structure. cathode–> tungsten

ACCELERATOR GUIDE
receives microwave power and combines with electrons to accel to speed of light

TREATMENT HEAD
collimates beam for photon therapy and also contains safety mechanisms (pertaining to dose delivery)

Question 8

Describe the components of the treatment head and their functions

Answer 8

BENDING MAGNET
-bend the electron group a total of 270 degrees and onto target or foil

X-RAY TARGET
spinning disc made of tungsten that produces the x-rays

PRIMARY COLLIMATOR
focuses the rays into a photon. still “messy” radiation

BEAM-FLATTENING FILTER
on carousel with scattering foils. shapes beam in cross sectional dimension and then spreads out the small pencil-like beam of electrons (now uniform)

ION CHAMBER
count the number of beams exiting the head. Dual ion chambers. They shut down machine when does is reached. 2nd ion chamber acts as fail safe if 1st doesn’t shut off machine.

SECONDARY COLLIMATORS
-control by using the setting knows to adjust upper and lower collimator jaws (setting field size).

ACCESSORY BLOCKS AND WEDGES
this could be MLC or Cerrobend blocking or dynamic wedges

Question 9

Which describes the order in which electron bundles and the resulting x-rays ravel through the head of the linear accelerator

Answer 9

bending magnet, target, primary collimator, flattening filter, dose chamber, MLC

Question 10

What is the half-life of cobalt-60 source?

Answer 10

5.26 years

Question 11

What is the energy of a cobalt unit?

Answer 11

1.17 and 1.33 MeV (average is 1.25)

Question 12

IGRT can be accomplished using which machines?

Answer 12

EPID
In-room CT scanner
Cone-beam CT
Ultrasound

Question 13

True or False

Scattering foil shape the x-ray beam

Answer 13

False, they refine, but don’t shape

Question 14

What makes up cerrobend?

Answer 14

Bismuth
Lead
Tin
Cadmium

Question 15

What does MLC stand for? What are they used for?

Answer 15

MLC –> multi-leaf collimator

They are used to shape the radiation field delivered to a patient. This allows us to conform and have a tighter margin around the tumor. They remain in the treatment head. Move throughout treatment if using rapid arc

Question 16

What is the goal of radiation therapy?

Answer 16

The goal of radiation therapy is to maximize the does of radiation delivered to cancerous tissue while minimizing the dose to normal surrounding tissues