RADIOTHERAPHY

Question 1

KILOVOLTAGE UNITS

Answer 1

Grenz-ray Therapy
Contact Therapy
Superficial Therapy
Orthovoltage Therapy
Supervoltage Therapy
Megavoltage Therapy

Question 2

Up to about 1950, most of the external beam radiotherapy was carried out with x-rays generated at voltages up to ___

Answer 2

300 kVp.

Question 3

Subsequent development of higher-energy machines and the increasing popularity of the ___ in the 1950s and the 1960s resulted in a gradual end of the conventional kilovoltage machines.

Answer 3

cobalt-60 units

Question 4

is used to describe treatment with beams of very soft (low energy) x-rays produced at potentials below 20 kV. Because of the very low depth of penetration such radiations are no longer used in radiation therapy.

Answer 4

Grenz-ray Therapy

Question 5

The endocavitary machine operates typically at a tube current of __ mA. Applicators available with such machines can provide an SSD of __cm or less.
A filter of ___ O-mm thick aluminum is usually interposed in the beam to absorb the very soft component of the energy spectrum.
This quality of radiation is useful for tumors not deeper than __. The beam is almost completely absorbed with ___ of soft tissue.

Answer 5

2mA; 2.0cm or less SSD; 0.5-1.0mm Al; 1-2 mm; 2cm

Question 6

operates at potentials of 40 to 50kV and facilitates irradiation of accessible lesions at very short source (focal spot) to surface distances (SSD).

Answer 6

Contact Therapy

Question 7

Superficial Therapy
mA__
SSD __
Filtration __
beam quality/depth dose __

Answer 7

5 to 8 mA; between 15 and 20 cm; usually 1- to 6-mm aluminum); 5-mm depth (-90% depth dose).

Question 8

Beyond this depth (5mm), the dose drop-off is too severe to deliver adequate depth dose without considerable overdosing of the skin surface.

Answer 8

Superficial Therapy

Question 9

is used to describe treatment with x-rays produced at potentials ranging from 150 to 500 kV.

Answer 9

Orthovoltage Therapy or Deep Therapy

Question 10

Most orthovoltage equipment is operated at ___ and __.
Various filters have been designed to achieve half-value layers between ____. An orthovoltage machine
The SSD is usually set at __.
The maximum dose occurs close to the skin surface, with __%of that value occurring at a depth of about __
There are severe limitations to the use of orthovoltage beam in treating lesions deeper than__

Answer 10

200 to 300 kV; 10 to 20mA; 1- and 4-mm Cu; 50 cm; 90% 2 cm.; 2 to 3 cm.

Question 11

range of 500 to 1,000 kV has been designated as high- voltage therapy

Answer 11

supervoltage therapy

Question 12

One of these machines is the __, in which the voltage is stepped up in a very efficient manner.

Answer 12

resonant transformer

Question 13

Resonant transformer units have been used to generate x-rays from ___

Answer 13

300 to 2,000 kV.

Question 14

X-ray beams of energy 1 MV or greater can be classified as megavoltage beams.

Answer 14

MEGAVOLTAGE THERAPY

Question 15

clinical megavoltage machines are accelerators such as

Answer 15

Van de Graaff generator, linear accelerator, betatron and microtron, and teletherapy gamma ray units such as cobalt-60.

Question 15

is an electrostatic accelerator designed to accelerate charged particles. In radiotherapy, the unit accelerates electrons to produce high-energy x-rays, typically at 2 MV.

Answer 15

Van de Graaff machine

Question 15

Van de Graaff machines are capable of reaching energies up to ___, limited only by size and required high-voltage insulation. Normally the insulation is provided by a mixture of __
The generator is enclosed in a __ and is filled with the gas mixture at a pressure of about__

Answer 15

10 MV; nitrogen and CO2; steel tank 20 atm

Question 16

is a device that uses high-frequency electromagnetic waves to accelerate charged particles such as electrons to high energies through a linear tube.

Answer 16

LINEAR ACCELERATOR

Question 17

Funtions of LINAC
A power supply provides direct current (DC) power to the modulator, which includes the pulse-forming network and a switch tube known as ___

Answer 17

hydrogen thyratron.

Question 18

is a device that produces microwaves. It functions as a high- power oscillator, generating microwave pulses of several microseconds’ duration and with a repetition rate of several hundred pulses per second.
The frequency of the microwaves within each pulse is about ___

Answer 18

magnetron;3,000 MHz

Question 19

The klystron is not a generator of microwaves but rather a __. It needs to be driven by a low-power microwave oscillator.

Answer 19

microwave amplifier

Question 20

__ x-rays are produced when the electrons are incident on a target of a high-Z material such as tungsten.

Answer 20

Bremsstrahlung

Question 21

Since linear accelerators produce electrons in the megavoltage range, the x-ray intensity is peaked in the __.

Answer 21

forward direction

Question 22

To make the beam intensity uniform across the field, a __ is inserted in the beam This filter is usually made of ___ or a combination has also been used or suggested.

Answer 22

flattening filter; lead, although tungsten, uranium, steel, aluminum,

Question 23

Most of the linear accelerators currently produced are constructed so that the source of radiation canrotate ___
As the gantry rotates, the collimator axis (supposedly coincident with the central axis of the beam) moves in a __
The point of intersection of the collimator axis and the axis of rotation of the gantry is known as the __.

Answer 23

rotate about a horizontal axis; vertical plane; isocenter

Question 24

is an electron accelerator that combines the principles of both the linear accelerator and the cyclotron.

Answer 24

microtron

Question 25

operates is based on the principle that an electron in a changing magnetic field experiences acceleration in a circular orbit

Answer 25

betatron

Question 26

he microtron is an electron accelerator that combines the principles of both__

Answer 26

the linear accelerator and the cyclotron.

Question 27

In radiation therapy, these machines have been used as a source of high-energy protons for proton beam therapy. More recently, the__ have been adopted for generating neutron beams

Answer 27

cyclotrons

Question 28

__ are accelerated to high energies and then made to strike a suitable target to produce neutrons by nuclear reactions.

Answer 28

deuterons (21H+)

Question 29

Neutrons are produced by a process called __

Answer 29

stripping

Question 30

Another important use of the cyclotron in medicine is as a __ for the production of certain radionuclides.

Answer 30

particle accelerator

Question 31

MACHINES USING RADIONUCLlDES
Radionuclides such as ___ have been used as sources of gamma (y) rays for Teletheraphy.

Answer 31

radium-226, cesium-137, and cobalt-60

Question 32

__ is a method of treatment in which sealed radioactive sources are used to deliver radiation at a short distance by interstitial, intracavitary, or surface application.

Answer 32

Brachytherapy

Question 33

In the past, brachytherapy was carried out mostly with __Currently, use of artificially produced radionuclides such as ____ is rapidly increasing.

Answer 33

radium or radon sources; Cs-137, Ir-192,Au-198, I-125, Pd-103

Question 34

is the sixth member of the uranium series, which starts with Uranium238-92 and ends with stable Pb 206-82. Radium disintegrates with a half-life of about __to form radon.

Answer 34

Radium;1,600 years

Question 35

is a y ray-emitting radioisotope that is used as a radium substitute in both interstitial and intracavitary brachytherapy. it is supplied in the form of__, labeled with Cs-137, and doubly encapsulated in stainless-steel needles and tubes.

Answer 35

Cesium-137; insoluble powders or ceramic micro spheres

Question 36

__ has been used for brachytherapy but is rarely used now. The main advantages of __ is its high specific activity, which allows fabrication of small sources required for some special applicators. However, it is more expensive than Cs-137 and has a short half-life __, necessitating more frequent replacement and a complex inventory system.

Answer 36

Co-60; 5.26 years

Question 37

__ (alloy of 30% Ir and 70% Pt) sources are fabricated in the form of thin flexible wires which can be cut to desired lengths. Nylon ribbons containing iridium seeds 3 mm long and 0.5 mm in diameter, spaced with their centers 1cm apart, are also commonly used. Both the wires and the seed ribbons are quite suitable for the after loading technique

Answer 37

Iridium-192

Question 38

Au-198 has a half-life of __ and emits a __
B rays of maximum energy __ are also emitted but are absorbed by the __ wall surrounding the seed

Answer 38

2.7 days ; monoenergetic y ray of energy 0.412 MeV.; 0.96 MeV; 0.1-mm-thick platinum

Question 39

__ has gained a wide use for permanent implants in radiation therapy.
The advantages of this isotope over radon and Au-198 are its long half-life(___), which is convenient for storage, and its low photon energy, which requires less shielding.

Answer 39

Iodine-125; 59.4days

Question 40

__ seeds have recently become available for use in brachytherapy.
Their clinical applications are similar to those of l-125
Having a shorter half-life (__) than that of l-125 (59.4 days),

Answer 40

Pd-103; 17 days

Question 41

A typical teletherapy cobalt-60 source is a cylinder of diameter ranging from __ and is positioned in the cobalt unit with its circular end facing the patient.

Answer 41

1.0 to 2.0 cm

Question 42

The60CO source decays to __

Answer 42

60Ni with the emission of ß particles (Emax,=0.32 MeV) and two photons per disintegration of energies 1.17 and 1.33 MeV.

Question 43

The 60Co source, usually in the form of a ___ is contained inside a stainless-steel capsule and sealed by welding.

Answer 43

solid cylinder, discs, or pallets,