RADIOTHERAPHY Flashcards
(45 cards)
KILOVOLTAGE UNITS
Grenz-ray Therapy
Contact Therapy
Superficial Therapy
Orthovoltage Therapy
Supervoltage Therapy
Megavoltage Therapy
Up to about 1950, most of the external beam radiotherapy was carried out with x-rays generated at voltages up to ___
300 kVp.
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.
cobalt-60 units
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.
Grenz-ray Therapy
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.
2mA; 2.0cm or less SSD; 0.5-1.0mm Al; 1-2 mm; 2cm
operates at potentials of 40 to 50kV and facilitates irradiation of accessible lesions at very short source (focal spot) to surface distances (SSD).
Contact Therapy
Superficial Therapy
mA__
SSD __
Filtration __
beam quality/depth dose __
5 to 8 mA; between 15 and 20 cm; usually 1- to 6-mm aluminum); 5-mm depth (-90% depth dose).
Beyond this depth (5mm), the dose drop-off is too severe to deliver adequate depth dose without considerable overdosing of the skin surface.
Superficial Therapy
is used to describe treatment with x-rays produced at potentials ranging from 150 to 500 kV.
Orthovoltage Therapy or Deep Therapy
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__
200 to 300 kV; 10 to 20mA; 1- and 4-mm Cu; 50 cm; 90% 2 cm.; 2 to 3 cm.
range of 500 to 1,000 kV has been designated as high- voltage therapy
supervoltage therapy
One of these machines is the __, in which the voltage is stepped up in a very efficient manner.
resonant transformer
Resonant transformer units have been used to generate x-rays from ___
300 to 2,000 kV.
X-ray beams of energy 1 MV or greater can be classified as megavoltage beams.
MEGAVOLTAGE THERAPY
clinical megavoltage machines are accelerators such as
Van de Graaff generator, linear accelerator, betatron and microtron, and teletherapy gamma ray units such as cobalt-60.
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.
Van de Graaff machine
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__
10 MV; nitrogen and CO2; steel tank 20 atm
is a device that uses high-frequency electromagnetic waves to accelerate charged particles such as electrons to high energies through a linear tube.
LINEAR ACCELERATOR
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 ___
hydrogen thyratron.
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 ___
magnetron;3,000 MHz
The klystron is not a generator of microwaves but rather a __. It needs to be driven by a low-power microwave oscillator.
microwave amplifier
__ x-rays are produced when the electrons are incident on a target of a high-Z material such as tungsten.
Bremsstrahlung
Since linear accelerators produce electrons in the megavoltage range, the x-ray intensity is peaked in the __.
forward direction
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.
flattening filter; lead, although tungsten, uranium, steel, aluminum,
