Radiation Protection II Flashcards
What are protective barriers put in place for?
ensure the dose equivalent receiving by any individuals does not exceed the maximum permissible value
What is a public/uncontrolled area?
area that is not under direct supervision of a radiation protection supervisor or there is no direct exposure
What is a controlled area?
An area that is under supervision of a radiation protection supervisor or there is direct exposure
What is the limit for a public/uncontrolled area?
0.02 mSv per week or 0.02 mSv in any one hour
What is the limit of a controlled area?
0.1 mSv per week
What does limitation of a public/uncontrolled area correspond with?
Limit of a public individual of 1 mSv/yr
What does limitation of a controlled area correspond with?
The limit of a pregnant radiation worker of 0.5 mSv/month
Shielding protection is based off what 3 types of radiation?
Primary, Scatter and Leakage
What is a primary barrier?
barrier sufficient to attenuate the useful beam to the required degree
What barrier is directly radiated by the primary beam?
Primary Barrier
What is the secondary barrier?
barrier for stray radiation (leakage and scatter)
What barrier received scatter from patient, surfaces of the treatment room, and radiation through linac shielding?
Secondary Barrier
what are some factors that are considered for barrier thickness?
neglects patient attenuation, perpendicular beam assumption for effective thickness, assuming head leakage to be max allowed, occupancy factors are high, and minimum distance is set at 0.3m
What is workload?
weekly dose delivered at 1m from the source, can be found be multiply # of patients per week times the dose delivered per patient
What is a use factor?
fraction of the operating time during which radiation under consideration is directed towards a particular barrier
What is the G0 factor from khan?
31%
What is the G90 factor from khan?
21.3%
What is the G270 factor from khan?
21.3%
What is the G180 factor from khan?
26.3%
What is the occupancy factor?
fraction of the operating time during which the area of interest if occupied by an individual
What is the distance factor?
area in meters from the radiation source to the area to be protected
What is the Maximum permissible dose equivalent (p)?
Max dose per week allowed in an area outside the treatment room.
What is the maximum permissible dose for a controlled area?
0.1 mSv per week
What is the maximum permissible dose for a uncontrolled area?
0.02 mSv per week
What is the transmission factor for the primary barrier?
transmission factor for the barrier to reduce the primary dose to maximum permissible dose in the area of interest
What is the maximum permissible dose equation?
P= WUT/d^2 x Bp
d= Distance equal from the xray target to a point of 0.3m point beyond the wall P= dose per week required outside the barrier
What is the transmission factor equation?
Bp= P x d^2/ WUT
d= Distance equal from the xray target to a point of 0.3m point beyond the wall P= dose per week required outside the barrier
Equation to find the barrier thickness for the primary barrier?
n= -log10(B)
B= transmission factor
Due to what makes the thickness of the 2nd TVL greater than the first and so on?
Beam hardening?
Equation to find the thickness for primary and leakage radiation?
T=TVL1 x (n-1)TVLe
What is transmission factor for the secondary barrier for scattered radiation?
Bs= (P/(alpha) WT) x (400/F) x d^2 x dā2
What is transmission factor for the secondary barrier for leakage radiation?
BL= P x d^2 / 0.001 WT
What is to be said if the scattering angle is small?
The scattered beam has greater penetration/energy and also more of the incident beam is scattered
What is the relation of the quality of leakage radiation in comparison to primary beam?
Same quality
What is the purpose of a maze entranceway?
prevent direct incidence of radiation at door
If no maze entranceway is present, what is a requirement for a the door?
Higher shielding, equivalent to the wall surrounding the door
What is the inner maze walls task?
To be sufficiently shielded to be able to stop leakage radiation and significantly reduce intensity and energy of the scattered radiation going towards the door
If designed appropriately, what is the required shielding in the door?
6mmm of lead
What is required of maze and door shielding when utilizing 10 MV
Should provide adequate shielding against neutron contamination
With a long maze, the door receives reduced neutron fluence. True or False?
True
3 factors about mazes?
typically 8m long, reduced photon fluence at door, reduce neutron fluence at door
What type of barriers are typically sufficient in protecting against neutrons? Whats different about the door?
Concrete is typically sufficient and the door must be shielded for the neutrons that diffuse into the maze and towards door
What is used to shield against neutrons in doors, duct and has density of 1.0?
Borated Polyethylene (BPE)
What is conducted after installing a new linac?
Survey
How should shielding be evaluated?
Under the worse conditions (Open field, largest field, no attenuating structure for primary beam, large attenuating structures for scatter
How is head leakage verified?
Wrapping the linac head with film
How is room shielding verified?
Ion chambers and neutron detectors
In the case of cyberknife, what can be said about the walls?
Most are primary due to it being non-isocentric
What is the use factor for a cyberknife?
0.05 due to small beamlets used during treatment which point to different sections of the wall
