Assignment 4 Flashcards
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
controlled area
What is the Maximum Permissible Dose Equivalent for a Controlled Area?
0.1 mSv/wk (5 mSv/yr)
any other area in the environment; doses suitable for the general public would apply in these areas
Noncontrolled/Uncontrolled Area
What is the Maximum Permissible Dose Equivalent for a Noncontrolled / Uncontrolled Area?
0.02 mSv/wk (1 mSv/yr)
Protection through the source housing is required against what 3 types of radiation?
- Primary
- Scattered
- Leakage
What is the definition of Primary Barrier?
a barrier sufficient to attenuate the useful beam to the required degree
What is the definition of Secondary Barrier?
the required barrier against stray radiation (leakage and scatter)
What is the definition of Workload? How is it expressed?
- 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
What is the definition of Use Factor?
fraction of the operating time during which the radiation under consideration is directed toward a particular barrier
What is the definition of Occupancy Factor?
fraction of the operating time during which the area of interest is occupied by the individual
What is the definition of Distance with regard to factors that enter into the calculation of barrier thicknesses?
distance in meters from the radiation source to the area to be protected
What is the Occupancy Factor for areas occupied full-time by an individual?
1
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?
1/40
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?
0.2% of the useful beam dose rate at the tx. Distance
The quality of leakage radiation is approximately the same as that of the ________.
primary beam.
Is leakage radiation more or less penetrating than scattered radiation?
More penetrating
Unless a maze entryway is provided, the door must provide shielding equivalent to the ______ surrounding the door.
wall
The _______ must be protected against neutrons that diffuse and reach it.
door
High energy x-ray beams over ___ MV are contaiminated with neutrons
10
What is better to reduce neutron contamination – designing a longer maze or adding more lead shielding to the door?
designing a longer maze
Should brachytherapy sources be touched with your hands? If not, what should be used instead?
No, long forceps must be used
What should be done with a leaking source?
A leaking source should be returned to an agency that is authorized for the disposal of radioactive materials.
Can ionization chambers be used to measure exposure directly?
yes
Is a Cutie Pie survey meter an ion chamber, G-M counter, or TLD?
ion chamber
Is a Geiger-Muller Detector more or less sensitive than an ion chamber?
more sensitive
Does a G-M Detector measure dose?
No
Which of the following is best for finding contamination and other low levels of radiation – ion chamber, G-M detector, or TLD?
G-M detector
Is a “Rascal” an ion chamber, G-M counter, TLD, or neutron detector?
neutron detector
How should radiation transmitted through the primary barrier be measured?
Radiation transmitted through the primary barrier should be measured with the beam at max size pointed at the barrier
How should measurements outside the secondary barrier be made?
• Measurements outside the secondary barriers should be made with a phantom in the treatment position
Why would a film monitor be used instead of a TLD or OSLD?
Film is relatively inexpensive
In a Thermoluminescent Dosimeter, what does the crystal substance typically comprised of?
typically lithium fluoride, or LiF
What does OSLD stand for?
Optically Stimulated Luminescent Dosimeters
An OSLD can be read for as long as ___ year after irradiation.
1
What acceptance test is this (below)?
*box with plus sign through it **
Light Beam with X-Ray Beam Coincidence
What is the tolerance for the light beam with x-ray beam coincidence test?
the alignment between the light beam and the x-ray beam should be within ± 2 mm or 1 % on a side
Define mechanical isocenter.
the intersection point of the collimator axis rotation and the gantry axis rotation
What may be caused by the heavy weight of the gantry frame?
the axis of the gantry rotation can miss the axis of the collimator rotation, thereby creating an uncertainty in the position of the isocenter
Define wiggler.
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
What is the tolerance for the collimator rotation mechanical isocenter check?
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.
What is the tolerance for the gantry rotation mechanical isocenter check?
The tolerance of the isocenter motion with full gantry rotation is ± 1mm.
What do the 3 star pattern tests check?
Radiation isocenter
With regard to the collimator radiation isocenter (star pattern) test, what is considered an acceptable result?
all the lines should intersect or pass within a 2-mm-diameter circle
With regard to the treatment table radiation isocenter (star pattern) test, what is considered an acceptable result?
all the lines should intersect or pass within a 2-mm-diameter circle
With regard to the gantry radiation isocenter (star pattern) test, what is considered an acceptable result?
should show the lines intersecting or passing within a 2-mm-diameter circle centered around the presumed radiation isocenter
What does the split field test detect?
- focal spot displacement,
- asymmetry of collimator jaws, and
- displacement in the collimator rotation axis or the gantry rotation axis.
What is the tolerance for calibration of leaf positions?
Deviation of more than 20% would indicate positioning problems
How can irregularly shaped fields using MLCs be tested?
Create a series of typical irregular field shapes using software, then compare that to MLC-generated fields by looking at them and radiographing them
What is the tolerance for wedge angles?
Wedge angles should be within ±2 degrees
