Chapter 3

1. Define Output.

Output is Dose Rate

2. State three condition that the design distance of a machine must fulfill
   1. dose rate must be high enough to yield treatment times of reasonable length
   2. operating characteristics of the beam (such as penumbra) must be acceptable at this distance
   3. distance must provide enough room for machine rotation

3. Define Initial Conditions.

Initial Conditions are:

• field size 10x10
• "in air" or at depth
• at a fixed distance (80cm Co60 / 100cm LINAC)

4. State the three types of initial conditions.

Three types of Initial Conditions are :

1. SAD setup using TAR
   • FS = 10x10
   • Ionization chamber at 80 or 100cm with buildup cap
   • dose rate measured "in air"
2. SAD setup using TMR
   • FS = 10x10
   • Ionization chamber at 80 or 100cm with phantom at Dmax
   • dose rate measured at Dmax
3. SSD setup using PDD
   • FS = 10x10
   • phantom placed at 80 or 100cm
   • Ionization chamber at Dmax
   • dose rate measured at Dmax

 

5. State why Cobalt 60 "TIME ON's" are in real time.

They are in real time because Co60  decays slowly over time (has a half life of 5.26 years)

6. State the general equation for "Beam On Time".

   

7. State the restriction on that equation.

Both the dose and dose rate must be at the same depth

8. Calculate a simple Cobalt 60 "Time On" problem.

9. State why real time, as in a Cobalt 60 unit, is NOT used in Linacs.

Because LINAC's are highly sensitive pieces of electronic equipment  and the dose rate will vary

10. Define a monitor unit.

Monitor Unit - a number chosen by physics used to represent a certain amount of ionizations

11. Calculate a simple Linac "Time On" problem.

Chapter 4

1. Define dose to a point in an ideal setup.

Dose to a point for an ideal setup is made up of the primary radiation plus the scatter radiation

2. Define primary beam.

Primary beam - photons that originate from the source and deposit their energy at points along the beam

3. Define primary beam attenuated.

Primary beam attenuated - originate from the source and travel straight out / if it is attenuated

4. Define scatter radiation.

Scatter radiation - radiation that comes from other parts of the irradiated phantom and deposit its energy at that point and also every other point in the phantom

5. State the distribution of scatter radiation in a phantom and its dependency on energy.

The distribution of scatter radiation is dependent primarily on the energy of the beam.  Thus the lower the energy the greater the amount of backscatter because the photons will be larger thus creating more reactions in the phantom.

6. State the Half-Value Layer for maximum backscatter.

HVL = .6 - .8 mm of copper HVL

7. State the effect of field size on dose to point.

The larger the field the larger the dose to the point

The smaller the field size the lower the dose to that point

(changing the field size will  cause the primary radiation to stay the same and increasing the field size will increase the scatter and decreasing field size will decrease scatter)

8. State the effect of field size on PDD, TAR and TMR.

Increasing field size will increase PDD, TMR and TAR

Decreasing field size will decrease PDD, TMR and TAR

9. Calculate Backscatter Factor (BSF) from the equation.

Chapter 5

1. State five names that are used to define the highest dose on the central axis.

Highest dose on the central axis = Dmax

• dose @ dmax
• dose @ electronic equilibrium
• Applied Dose
• Given Dose
• Entrance Dose

2. State the dependency of the depth of the Dose at Dmax to field size and distance.

The Dose at Dmax is not dependent of field size and distance.  It occurs at the same depth regardless of field size and distance.

3. State the equation for Percentage Depth Dose.

4. State the depth of Dmax for a4MV LINAC.

1cm

5. Define Output

Output = dose rate

6. State the value of  PDD for Depth Dmax.

PDD @ Dmax = 100% or 1.00

7. Calculate the FDD for different depths,

8. Calculate simple Beam On Time problems.

9. Define Output Factors.

10. Calculate the Dose to a second point in an SSD setup

Chapter 6

1. Define equivalent square.

Equivalent squares are numbers that correspond to square field sizes for non-square field sizes.  They are put into table form which is made up of different rectangular field sizes and their equivalent square field sizes.

Equation:

2. Calculate "time on" problems using equivalent square tables

3. Calculate equivalent squares using the equation and not the table

4. Define A/P

A/P = area / perimeter

5. State the relationships between equivalent square and A/P

The relationship between ES and A/P is  that the equivalent square(ES) is 4 times the A/P.  They are just different ways of  doing the same thing. Some sites us ES tables others use A/P tables.

6. Calculate "time on" problems where the depths are not whole numbers

7. Calculate "time on" problems where the field sizes are not on the tables