Khan Outline Chapter 4: Clinical Radiation Generators

Front 1

List the capable energies, filtration, tx capabilities, and any other pertinent information for: "Grenz-ray"

Back 1

Energy: 20 kV
Filtration: N/A
TX capabilities: No longer used in radiation therapy

Front 2

List the capable energies, filtration, tx capabilities, and any other pertinent information for: "Contact Therapy"

Back 2

Energy: 40 to 50 kV
Filtration: 0.5-1.0 thick aluminum
TX capabilities: Is useful for tumors not deeper than 1 to 2 mm
SSD: 2.0 cm or less

Front 3

List the capable energies, filtration, tx capabilities, and any other pertinent information for: "Superficial Therapy"

Back 3

Energy: 50 to 150 kV
Filtration: 1 to 6 mm aluminum
TX capabilities: Useful for irradiating tumors confined to about 5 mm depth (90% depth dose).
SSD: 15 to 20 cm

Front 4

List the capable energies, filtration, tx capabilities, and any other pertinent information for: "Orthovoltage Therapy"

Back 4

Energy: 150 to 500 kV
Filtration: 1 to 4 mm Cu
TX capabilities:
SSD: 50 cm

Front 5

List the capable energies, filtration, tx capabilities, and any other pertinent information for: "Supervoltage Therapy"

Back 5

Energy: 500 to 1,000 kV
Filtration:
TX capabilities:
SSD:

Front 6

List the capable energies, filtration, tx capabilities, and any other pertinent information for: "Megavoltage Therapy"

Back 6

Energy: 1 MV or greater
Examples of clinical Megavoltage machines are accelerators such as Van de Graaff generator, linear accelerator, betatron and microtron, and teletherapy y ray units such as cobalt-60.

Front 7

List the capable energies, filtration, tx capabilities, and any other pertinent information for: "Van De Graff generator"

Back 7

Energy: 2 to 10 MV
TX capabilities: No longer used.

Front 8

List the capable energies, filtration, tx capabilities, and any other pertinent information for: "Linear Accelerator"

Back 8

Energy: 4MV to 20MV
Filtration: Flattening Filter made of lead, tungsten, uranium, steel, aluminum, or combination.
TX capabilities:
SSD: 100 cm

Front 9

List the steps that occur for treating a patient with a linear accelerator in high energy photon mode. Make sure to state what each part along the beam path does. Start with incoming power.

Back 9

-Modulator is a section of electronics where direct current (DC) voltage is converted into high-voltage flat-topped DC pulses of a few microseconds in duration. It contains the pulse-forming network and a high-voltage switch tube known as hydrogen thyratron.
-High-voltage pulses from the modulator are delivered to the magnetron or klystron and simultaneously to the electron gun.
-Microwave pulses from the magnetron or klystron are injected into the accelerator structurethrough a waveguide system. At the proper instant, electrons from an electron gun are also in-jected into the accelerator structure.
-In the higher-energy linacs, the accelerator structure is too long and, therefore, placed horizon-tally or at an upward angle with respect to the horizontal. The electrons are then bent througha suitable angle (usually about 90º–270º).
-Transmission type tungsten target intercepts the electron beam to generate x-ray beam(bremsstrahlung).
-Since the kinetic energy of electrons striking the target is in the megavoltage range, the x-raybeam intensity is peaked in the forward direction. To make the intensity uniform in cross sec-tion, a flattening filter is inserted in the beam.

Front 10

List the steps that occur for treating a patient with a linear accelerator in electron mode. Make sure to state what each part along the beam path does. Start with incoming power.

Back 10

--Modulator is a section of electronics where direct current (DC) voltage is converted into high-voltage flat-topped DC pulses of a few microseconds in duration. It contains the pulse-forming network and a high-voltage switch tube known as hydrogen thyratron.
-High-voltage pulses from the modulator are delivered to the magnetron or klystron and simultaneously to the electron gun.
-Microwave pulses from the magnetron or klystron are injected into the accelerator structurethrough a waveguide system. At the proper instant, electrons from an electron gun are also in-jected into the accelerator structure.
-In the higher-energy linacs, the accelerator structure is too long and, therefore, placed horizon-tally or at an upward angle with respect to the horizontal. The electrons are then bent througha suitable angle (usually about 90º–270º).
-In the electron mode of accelerator operation, both the target and the flattening filter moveout of the way and a scattering foil is inserted to intercept the electron beam.

Front 11

List the characteristics of a cobalt treatment device.

Back 11

-A typical cobalt teletherapy source consists of 60 Co disks encapsulated in a steel cylinder of diameter ranging from 1 to 2 cm. It is housed in a well-shielded shell, called the sourcehead.
-A typical cobalt teletherapy source consists of 60 Co disks encapsulated in a steel cylinder of diameter ranging from 1 to 2 cm. It is housed in a well-shielded shell, called the sourcehead.
-Because of the relatively large source size (1–2 cm diameter), a 60 Co beam is associated with amuch larger geometric penumbra than a linac x-ray beam that has a focal spot size of approxi-mately 2 to 3 mm.

Front 12

List the formula for geometric pneumbra.

Back 12

Pd= s(SSD + d - SDD) / SDD
s=source diameter, SDD=source to diaphragm distance, d=depth

Front 13

Calc the geometric penumbra for a 1.5 cm source, 100 cm SSD, depth 4 cm and 38 cm SDD

Back 13

2.60 cm

Front 14

State how the factors of the geometric penumbra affect the penumbra size if you increase one and the others remain constant. i.e. if source size and all other factors fixed.

Back 14

Penumbra width increases with increase in source diameter, SSD, and depth
Penumbra decreases with an increase in SDD

Front 15

List the characteristics of a betatron.

Back 15

Based on the principle that an electron in a changing magnetic field experiences acceleration in a circular orbit.
Energy ranges from 6 to more than 40 MeV
Low dose rate and small field size

Front 16

List the characteristics of a microtron.

Back 16

A magnetic field forces the electrons to move in a circular orbit and return to the cavity.

Front 17

Define what Bragg Peak is and describe it. What does it occur for?

Back 17

The dose deposited is approximately constant with depth until near the end of the range where the dose peaks
out to a high value followed by a rapid falloff to zero. The region of high dose at the end of the particle range is called the Bragg peak.
Protons and Heavy Ions

Front 18

What are the characteristic of protons and what are they used for?

Back 18

Proton beams for therapeutic application range in energy from 150 to 250 MeV.
Produced by a cyclotron or a linear accelerator.
Used for brain, head and neck, prostate.

Front 19

What are the characteristics of heavy ions and what are they used for?

Back 19

Exhibit a sharp drop-off in dose (Bragg Peak)

Front 20

What are the characteristics of a negative pion?

Back 20

Pions of energy close to 100 MeV are of interest in radiation therapy, providing a range in water of about 24 cm.
The Bragg peak exhibited by pions is more pronounced than other heavy particles because of the additional effect of nuclear disintegration by π- capture.
Low dose rates, beam contamination, and high cost.