Drive Stand
Gantry
Dosimetric Calculations
Math Concepts I
Math Concepts II
100

This amplifies microwave power

What is the klystron?
100

This contains the auxiliary power distribution.

What is the modulator cabinet?

100

This calculation cannot be used in isocentric techniques, because of source to skin distance dependence.

PDD
100

Describes the change in beam intensity caused by the divergence of the beam

Inverse Square Law

100

The plan was to treat a patient at 100 cm SSD but instead you treated at 92 cm SSD. Is this an overdose or an overdose?

overdose

200

Acts like an electrical outlet in a home.

What is the waveguide?

200

Produces electrons.

What is the electron gun?

200

This calculation is used for isocenter treatments and rotational treatments

TAR (TISSUE AIR RATIO)

200

Certain treatments may require such a large treatment area that two adjacent, or abutting, treatment fields are required. What math concept is this and what formula should be used to calculate this?

GAP

200

There may be times when an extended SSD is required. This means the SSD will be greater than 100 SSD. Which formula is used for this concept?

Mayneord F Factor

300
Applifies microwaves for lower energy machines.

WHat is a Magnetron?

300

This is made of tungsten and needs to be in place so when electrons strike it, photons are produced.

What is the target?

300

This is a measurement of the patient's thickness from the point of beam entry to the point of beam exit.

SEPERATION

300

Another instance the inverse square law should be used is when trying to determine how much dose a patient received when treated at the wrong SSD. What is the equation to solve this?

treatment distance/ mistake distance x 100%

300

For ssd mu calcs what is the formula used?

dose/TMR x other factors

400

This cools components that dissipate as heat.

What is the cooling system?

400

This causes the spread of the electron beam across the field size.

What is the scattering foil?

400

This is the predominent interaction when kV imaging is used.

What is the photoelectric effect?

400

In order to determine the gantry speed, we must know how many degrees the gantry is rotating and how many MU will be delivered during a set rotation. The formula used is:

Equation:

Gantry Speed= Degrees/

MU

400
For SAD calcs what is the formula?

Dose/ TAR x other factors

500

Prevents reflected microwaves from returning into the klystron.

What is the circulator?

500

Electrons are accelerated and bunched here.

What is the accelerator guide?

500

This transmission factor depicts the amount of radiation transmitted through a physical wedge placed in the beam to shape the beam delivery. It is specific for each beam energy with which it is used.

WEDGE FACTOR

500

Thickness of an absorber required to attenuate the intensity of the beam to half its original value.

HVL

500

An object will appear larger on a radiographic image as compared to its actual size. What is this known as and give the formula?

Magnification Factor = Image size/ Object Size

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