Assignment 4

Question 1

a limited-access area in which the occupational exposure of personnel to radiation-producing equipment or radioactive materials is supervised by an individual in charge of radiation protection

Answer 1

controlled area

Question 2

What is the Maximum Permissible Dose Equivalent for a Controlled Area?

Answer 2

0.1 mSv/wk (5 mSv/yr)

Question 3

any other area in the environment; doses suitable for the general public would apply in these areas

Answer 3

Noncontrolled/Uncontrolled Area

Question 4

What is the Maximum Permissible Dose Equivalent for a Noncontrolled / Uncontrolled Area?

Answer 4

0.02 mSv/wk (1 mSv/yr)

Question 5

Protection through the source housing is required against what 3 types of radiation?

Answer 5

• Primary
• Scattered
• Leakage

Question 6

What is the definition of Primary Barrier?

Answer 6

a barrier sufficient to attenuate the useful beam to the required degree

Question 7

What is the definition of Secondary Barrier?

Answer 7

the required barrier against stray radiation (leakage and scatter)

Question 8

What is the definition of Workload? How is it expressed?

Answer 8

• for megavoltage machines, W is usually stated in terms of weekly dose delivered at 1 m from the source. This can be estimated by multiplying the number of patients treated per week with the dose delivered per patient at 1m
• W is expressed in dose / wk. at 1m

Question 9

What is the definition of Use Factor?

Answer 9

fraction of the operating time during which the radiation under consideration is directed toward a particular barrier

Question 10

What is the definition of Occupancy Factor?

Answer 10

fraction of the operating time during which the area of interest is occupied by the individual

Question 11

What is the definition of Distance with regard to factors that enter into the calculation of barrier thicknesses?

Answer 11

distance in meters from the radiation source to the area to be protected

Question 12

What is the Occupancy Factor for areas occupied full-time by an individual?

Answer 12

1

Question 13

What is the Occupancy Factor for outdoor areas with only transient pedestrian or vehicular traffic, unattended parking lots, unattended vehicular drop-off areas, stairways, and unattended elevators?

Answer 13

1/40

Question 14

On a therapeutic source assembly over 500 kVp, what is the maximum absorbed dose rate due to leakage radiation (excluding neutrons) at any point outside the maximum field size, but within a circular plane of 2m radius that is perpendicular to and centered on the CAX at the normal treatment distance?

Answer 14

0.2% of the useful beam dose rate at the tx. Distance

Question 15

The quality of leakage radiation is approximately the same as that of the ________.

Answer 15

primary beam.

Question 16

Is leakage radiation more or less penetrating than scattered radiation?

Answer 16

More penetrating

Question 17

Unless a maze entryway is provided, the door must provide shielding equivalent to the ______ surrounding the door.

Answer 17

wall

Question 18

The _______ must be protected against neutrons that diffuse and reach it.

Answer 18

door

Question 19

High energy x-ray beams over ___ MV are contaiminated with neutrons

Answer 19

10

Question 20

What is better to reduce neutron contamination – designing a longer maze or adding more lead shielding to the door?

Answer 20

designing a longer maze

Question 21

Should brachytherapy sources be touched with your hands? If not, what should be used instead?

Answer 21

No, long forceps must be used

Question 22

What should be done with a leaking source?

Answer 22

A leaking source should be returned to an agency that is authorized for the disposal of radioactive materials.

Question 23

Can ionization chambers be used to measure exposure directly?

Answer 23

yes

Question 24

Is a Cutie Pie survey meter an ion chamber, G-M counter, or TLD?

Answer 24

ion chamber

Question 25

Is a Geiger-Muller Detector more or less sensitive than an ion chamber?

Answer 25

more sensitive

Question 26

Does a G-M Detector measure dose?

Answer 26

No

Question 27

Which of the following is best for finding contamination and other low levels of radiation – ion chamber, G-M detector, or TLD?

Answer 27

G-M detector

Question 28

Is a “Rascal” an ion chamber, G-M counter, TLD, or neutron detector?

Answer 28

neutron detector

Question 29

How should radiation transmitted through the primary barrier be measured?

Answer 29

Radiation transmitted through the primary barrier should be measured with the beam at max size pointed at the barrier

Question 30

How should measurements outside the secondary barrier be made?

Answer 30

• Measurements outside the secondary barriers should be made with a phantom in the treatment position

Question 31

Why would a film monitor be used instead of a TLD or OSLD?

Answer 31

Film is relatively inexpensive

Question 32

In a Thermoluminescent Dosimeter, what does the crystal substance typically comprised of?

Answer 32

typically lithium fluoride, or LiF

Question 33

What does OSLD stand for?

Answer 33

Optically Stimulated Luminescent Dosimeters

Question 34

An OSLD can be read for as long as ___ year after irradiation.

Answer 34

1

Question 35

What acceptance test is this (below)? | *box with plus sign through it **

Answer 35

Light Beam with X-Ray Beam Coincidence

Question 36

What is the tolerance for the light beam with x-ray beam coincidence test?

Answer 36

the alignment between the light beam and the x-ray beam should be within ± 2 mm or 1 % on a side

Question 37

Define mechanical isocenter.

Answer 37

the intersection point of the collimator axis rotation and the gantry axis rotation

Question 38

What may be caused by the heavy weight of the gantry frame?

Answer 38

the axis of the gantry rotation can miss the axis of the collimator rotation, thereby creating an uncertainty in the position of the isocenter

Question 39

Define wiggler.

Answer 39

an adjustable pointer device with a sharp point that may be attached to the distance-measuring rod that is attached to the accessory mount for the purpose of performing a mechanical isocenter check

Question 40

What is the tolerance for the collimator rotation mechanical isocenter check?

Answer 40

For an acceptable alignment, the isocenter should stay within a 2-mm-diameter circle when the collimator is rotated through its full range of rotation.

Question 41

What is the tolerance for the gantry rotation mechanical isocenter check?

Answer 41

The tolerance of the isocenter motion with full gantry rotation is ± 1mm.

Question 42

What do the 3 star pattern tests check?

Answer 42

Radiation isocenter

Question 43

With regard to the collimator radiation isocenter (star pattern) test, what is considered an acceptable result?

Answer 43

all the lines should intersect or pass within a 2-mm-diameter circle

Question 44

With regard to the treatment table radiation isocenter (star pattern) test, what is considered an acceptable result?

Answer 44

all the lines should intersect or pass within a 2-mm-diameter circle

Question 45

With regard to the gantry radiation isocenter (star pattern) test, what is considered an acceptable result?

Answer 45

should show the lines intersecting or passing within a 2-mm-diameter circle centered around the presumed radiation isocenter

Question 46

What does the split field test detect?

Answer 46

* focal spot displacement, * asymmetry of collimator jaws, and * displacement in the collimator rotation axis or the gantry rotation axis.

Question 47

What is the tolerance for calibration of leaf positions?

Answer 47

Deviation of more than 20% would indicate positioning problems

Question 48

How can irregularly shaped fields using MLCs be tested?

Answer 48

Create a series of typical irregular field shapes using software, then compare that to MLC-generated fields by looking at them and radiographing them

Question 49

What is the tolerance for wedge angles?

Answer 49

Wedge angles should be within ±2 degrees