Tx machine and monitoring devices

Main parts that make up the linac(7)

-drive stand

-gantry

-treatment couch

-console

-electronic cabinet

-modulator

Drive stand contains (4)

-klystron

-waveguide

-circulator

-cooling system

Water cooling system

Prevents the LINAC from overheating (located in drive stand)

3 parts of the linac that can move around isocenter

-gantry

-collimator

-couch

A linac starts with a power supply, which provides ____ to the modulator

direct current (DC)

What kind of current does the linac have

Direct

The modulator powers the

Microwave source (magnetron or klystron) AND electron gun

Sources of microwaves in the linac come from

Klystron or magnetron

Microwaves are injected into the ________ to

Waveguide to accelerate electrons

Klystron:

Amplifies microwaves

Which provides higher power? Magnetron/klystron

Klystron

Klystron used in linacs above ___MV

12

Klystron requires a ___ ___

Low power microwave oscillator

Magnetron generates

Microwaves

Circulator is used to

Stop microwaves from being reflected and reentering the klystron

Circulator is located between the

klystron and waveguide

Electron gun

Generates electrons and sends them into the accelerator (wave guide)

Electron gun is made of

Tungsten

Electrons start at ______ keV but then accelerate when they interact with _________

50 keV ; microwaves

Accelerator structure

Tube where electrons flow to the gantry under a vacuum

Accelerator structure is a ____ tube with _____ discs and diaphragms inside with vary in aperture's and spacing between each disc

Copper;copper

Uses microwaves from the klystron to accelerate the electrons to the target

Accelerator structure

Accelerator structure aka

Wave guide

What part of linac uses sulfur hexaflouride to prevent arching in the wave guide

Accelerator strucutre

What prevents arching in wave guide

Sulfur hexafluride

Accelerator is positioned _____ in higher energy machines and _____ in lower energy machines

Horizontally;vertically

Magnet system is

Used to bend electrons 90 -270 degrees to aim them TOWARD the target

____ degree magnet system creates a more confined beam than the ______ degree magnet system

270 and 90

Treatment head

where the beam shape is formed and the beam output is monitored

in photon therapy, the components used in the treatment head are (in order):

x-ray target,

primary collimator,

beam-flattening filter,

ion chambers,

secondary collimators,

slots for wedges,

blocks,

compensators.

Flattening filters are made of

Lead

Tungsten

Uranium

Steel

Aluminum

Ion chambers

small chambers located in the path of the radiation beam and check the beam dose rate/output and symmetry

most ion chambers are __________ and will not be affected by temperature or pressure

Sealed

In electron therapy the components used in the treatment head are similar but ____ are used instead of the target and flattening filter

Scattering foils

Scattering foils spread out the ________ _______ ________ beam to a larger area suitable for treatments

3mm pencil electron beam

CT sim consists of (4)

-ct scanner

-flat couch top

-virtual sim workstation

-laser marking system

The CT scanner obtains volumetric images of the patient, which are used for

treatment planning

The ct scanner obtains ________ images of the patient

Volumetric

Rad therapy ct sim has a larger bore than conventional (______ to ______ cm)

70-85

LARGER CT BORES ALLOW FOR A LARGER

SFOV

An ionization chamber is a

Gas filled chamber that has two electrodes with an applied voltage and a meter that measures the electrical signal

Ionization chamber: when the gas is irradiated,_____ _____ are produced and create an electrical current that flowers to the electrodes

Ion pair

Ionization chamber; Larger chambers have more ______ and are more _______

Gas; sensitive

Ionization chamber; Exposure is_____ proportional to the current

Directly

Most common way to measure linac output

Ion chambers

Ion chamber read out is measured in

MR/hr

Ion chamber is accurate within +- _____ %

2

Correction factors for ion chamber for calibration

Temperature pressure volume

Ion chamber examples

Pocket dosimeters and cutie pies

Farmer chamber is a type of ______

Thimble chamber

A cutie pie is a

Portable ion chamber

Geiger-Muller counter (Geiger counter)

an instrument that measures the rate of radioactive decay based on the ions and electrons produced as a radioactive particle passes through a gas-filled chamber

Is a GM counter a dose measuring device

NO

GM counter can detect radiation _______ mR/hr

100

Is a GM more sensitive than an ion chamber

Yes

TLD/ OSL are Solid-state detectors and _____ devices

Personnel monitoring

TLD when _______ this dosimeter ______ in proportion to the amount of rad that was absorbed

Heated; lights up

Has a Crystal material embedded in the dosi and when irritated electrons are released from their valence bonds and remain trapped within a gap

TLD

TLDs chemical

Lithium flouride (atomic # similar to human tissue)

TLD accuracy %

5%

TLDs are commonly used for patient dosi ______ measurements and are used to measure______ dose

Invivo ;entrance/skin dose

What kind of dosi is a ring form made of

TLD

OSL crystals release electrons when they are excited by _______ instead of heat

Light

Can determine deep eye and shallow dose

OSL

Made of aluminum oxide

OSL

Most common detector used to measure occupational personnel exposure today

OSL

Diodes are

A small solid state detector that are very sensitive to radiation

Can give a real time reading

Diode

Equipment of choice for patient dosimetry bc it can measure the beam delivered for treatment

Diode

Used to check daily QA for linac output

Diode

T/f Diodes are used to callibrate the beam

False

Neutron detectors are filled with a gas called

Boron trifluoride

Slip ring ct

ability of electricity going through ring with no wires; spiral acquisition of data. x ray tube and detector rotate around patient in continuous motion as fast as rotations per second through the use of slip ring

Ct generator range

120-140 kV

Ct Xray tube focal spot size

0.5-1.0 mm

Collimation in CT sim will help adjust

Scatter and slice thickness

Detectors in ct are ______ ______ and are also called

Solid state ; scintillation

Newer CT machines have _____-______ parallel rows

4-64

Pitch that will give patients a higher dose

0.5-1

Pitch that will give patients a lower dose

2;1 (interpolation )

Number of HU represented in an image

Window width

Selects which HU will be displayed on an image

Window level

External laser system CT distance from internal lasers

500 mm(50 cm) from internal laser MOVEABLE

Aquisition interpretation and storage of digital images

Pacs

Creates standards for transferring images and radiologic information

DICOM