MEDICAL DOSIMETRY ALL EXAMS SCRIPT TIPS
ACTUAL QUESTIONS AND ANSWERS SURE A+
✔✔any error in the reproducible positioning of the flattening filter will affect what three
things? - ✔✔-beam flatness
- beam symmetry
- beam output
✔✔in one month, the output of a 60 Co machine would reduce by about_____ - ✔✔1%
✔✔The diameter of a typical teletherapy source is about_____ - ✔✔2 cm
✔✔The geometric penumbra of a 60 Co unit depends on_____ - ✔✔- source diameter
- diaphragm to patient distance
- source to diaphragm distance
(does not depend on source length)
✔✔an added filter used with a teletherapy kV unit_____ - ✔✔achieves desired filtration
for therapeutic purposes
✔✔The effective energy of an x-ray beam is the energy of that monoenergenic beam
that would_____ - ✔✔give the same HVL as the X-ray beam in question
,✔✔The target of a therapy x-ray tube must have_____ - ✔✔High Z. and high melting
point
✔✔The efficiency of x-ray production in the KV X-ray therapy tubes is about_____ -
✔✔1%
✔✔the focal spot of a KV X-ray therapy tube is about_____ - ✔✔3 mm
✔✔The focal spot of a clinical linac is about_____ - ✔✔3 mm
✔✔name three advantages of a 60 Co unit in radiation therapy are - ✔✔1. High gamma
energy
2. high specific activity
3. reasonably long half-life
(con: expensive)
✔✔for a therapy x-ray unit operating at 150 kVp, the maximum energy in keV of the
photon produced in the target is_____ - ✔✔150
✔✔shutter timer ever arises due to what? - ✔✔The finite travel time of the source to
reach the treatment position
✔✔shutter timer error of a 60 CO unit can be_____ - ✔✔positive or negative
✔✔how long is the approximate shutter timer error length for a 60 Co unit? - ✔✔0.1
minute to 0.2 minute
✔✔what can be used to determine a shutter timer error? - ✔✔in ionization chamber
✔✔if the shutter timer error is positive, to set the treatment time on the unit - ✔✔it must
be added to the computed beam on time
✔✔if the shutter timer error is negative, to set the treatment time on the unit - ✔✔it must
be subtracted from the computed beam on time
✔✔The shutter timer error of a 60 Co unit was determined to be + 2 seconds. if the
treatment time was computed to be 58 seconds, what time must be set on the machine?
- ✔✔60 seconds
✔✔what is the source of electrons in an electron accelerator? - ✔✔electron gun
✔✔what shaped fields can the collimators of conventional teletherapy units produce? -
✔✔square fields or rectangle fields
,✔✔what are two important features of a Linac compared to a 60 Co unit? - ✔✔the linac
has a higher beam output and a sharper beam
✔✔in addition to square and rectangle, what shaped fields can modern accelerators
produce? - ✔✔asymmetric fields (and irregular fields if the accelerator has MLC's)
✔✔Telecobalt machines can provide field sizes (at SAD) in the range of about_____ -
✔✔5 cm x 5 cm to 40 cm x 40 cm
✔✔how can you reduce the geometric penumbra of a 60 Co unit? - ✔✔use a source of
smaller diameter or use a penumbra trimmer
✔✔what type of target is used in high-energy linear accelerator? - ✔✔transmission type
✔✔out of diagnostic x-ray, ortho-voltage x-ray, electron, or megavoltage which will have
the highest skin sparing effect? - ✔✔megavoltage X-ray beam
✔✔which power source is used to generate electromagnetic waves for the accelerator
guide in a linear accelerator? - ✔✔magnetron
✔✔what is the clinically acceptable limit or tolerance of flatness over the central 80% of
the x-ray beam used in radiotherapy? - ✔✔2%
✔✔out of 60Co, deep therapy x-rays, 10 MV x-rays, 10 MV electron which will have the
highest beam penetration? - ✔✔10 MV X-rays
✔✔why is a trimmer bar attached to the collimator? - ✔✔to reduce the effect of
penumbra
✔✔which is the best absorbing material for neutrons? - ✔✔polyethylene
✔✔which detector is used in accelerators as a monitor chamber? - ✔✔ionization
chamber
✔✔what system do computers work on? - ✔✔binary system
✔✔what numbers does a binary system involve? - ✔✔0 and 1
✔✔what is the value of a binary number 1001 in decimal system? - ✔✔9
✔✔in a computer the data 0 or 1 is called_____ - ✔✔a bit
, ✔✔what is a group of eight bits called? - ✔✔a byte
✔✔computer memory is organized in terms of_____ - ✔✔bytes
✔✔a group of 64 bits corresponds to_____ - ✔✔8 bytes
✔✔a two-bit binary number can give _____ - ✔✔4 bits of information
✔✔in decimals, a 3-bit binary number can represent_____ - ✔✔8 numbers
✔✔a byte can represent_____ - ✔✔256 bits of information
✔✔determine the different configurations of 2 bits - ✔✔00, 01, 10, 11
✔✔determine the different possible configurations of a group of 3 bits - ✔✔000, 001,
010, 011, 100, 110, 101, 111
✔✔a kilobyte actually corresponds to how many bytes? - ✔✔2^10 bytes or 1024 bytes
✔✔a megabyte corresponds to_____ - ✔✔2^20 bytes
✔✔alpha numeric characters can be_____ - ✔✔letters, numbers, and special symbols
✔✔what information can one byte of information content represent? - ✔✔digits 0 to 9
and all the special characters and symbols one usually encounters
✔✔Data are stored in manipulated in a computer_____ - ✔✔digital form only
✔✔Data are transmitted or received by a computer in____ - ✔✔digital form only
✔✔detectors used in CT generate_____ - ✔✔analog data
✔✔CT scanners convert analog data to digital data using______ - ✔✔analog to digital
converters
✔✔is there a loss of information when in an analog to digital conversion? - ✔✔yes
✔✔a video monitor handle signals in what form? - ✔✔analog form
✔✔in ASCII code each character's represented in_____ - ✔✔one byte
✔✔a computer stores an image as_____ - ✔✔a group of image elements or pixels into
which the image is divided
ACTUAL QUESTIONS AND ANSWERS SURE A+
✔✔any error in the reproducible positioning of the flattening filter will affect what three
things? - ✔✔-beam flatness
- beam symmetry
- beam output
✔✔in one month, the output of a 60 Co machine would reduce by about_____ - ✔✔1%
✔✔The diameter of a typical teletherapy source is about_____ - ✔✔2 cm
✔✔The geometric penumbra of a 60 Co unit depends on_____ - ✔✔- source diameter
- diaphragm to patient distance
- source to diaphragm distance
(does not depend on source length)
✔✔an added filter used with a teletherapy kV unit_____ - ✔✔achieves desired filtration
for therapeutic purposes
✔✔The effective energy of an x-ray beam is the energy of that monoenergenic beam
that would_____ - ✔✔give the same HVL as the X-ray beam in question
,✔✔The target of a therapy x-ray tube must have_____ - ✔✔High Z. and high melting
point
✔✔The efficiency of x-ray production in the KV X-ray therapy tubes is about_____ -
✔✔1%
✔✔the focal spot of a KV X-ray therapy tube is about_____ - ✔✔3 mm
✔✔The focal spot of a clinical linac is about_____ - ✔✔3 mm
✔✔name three advantages of a 60 Co unit in radiation therapy are - ✔✔1. High gamma
energy
2. high specific activity
3. reasonably long half-life
(con: expensive)
✔✔for a therapy x-ray unit operating at 150 kVp, the maximum energy in keV of the
photon produced in the target is_____ - ✔✔150
✔✔shutter timer ever arises due to what? - ✔✔The finite travel time of the source to
reach the treatment position
✔✔shutter timer error of a 60 CO unit can be_____ - ✔✔positive or negative
✔✔how long is the approximate shutter timer error length for a 60 Co unit? - ✔✔0.1
minute to 0.2 minute
✔✔what can be used to determine a shutter timer error? - ✔✔in ionization chamber
✔✔if the shutter timer error is positive, to set the treatment time on the unit - ✔✔it must
be added to the computed beam on time
✔✔if the shutter timer error is negative, to set the treatment time on the unit - ✔✔it must
be subtracted from the computed beam on time
✔✔The shutter timer error of a 60 Co unit was determined to be + 2 seconds. if the
treatment time was computed to be 58 seconds, what time must be set on the machine?
- ✔✔60 seconds
✔✔what is the source of electrons in an electron accelerator? - ✔✔electron gun
✔✔what shaped fields can the collimators of conventional teletherapy units produce? -
✔✔square fields or rectangle fields
,✔✔what are two important features of a Linac compared to a 60 Co unit? - ✔✔the linac
has a higher beam output and a sharper beam
✔✔in addition to square and rectangle, what shaped fields can modern accelerators
produce? - ✔✔asymmetric fields (and irregular fields if the accelerator has MLC's)
✔✔Telecobalt machines can provide field sizes (at SAD) in the range of about_____ -
✔✔5 cm x 5 cm to 40 cm x 40 cm
✔✔how can you reduce the geometric penumbra of a 60 Co unit? - ✔✔use a source of
smaller diameter or use a penumbra trimmer
✔✔what type of target is used in high-energy linear accelerator? - ✔✔transmission type
✔✔out of diagnostic x-ray, ortho-voltage x-ray, electron, or megavoltage which will have
the highest skin sparing effect? - ✔✔megavoltage X-ray beam
✔✔which power source is used to generate electromagnetic waves for the accelerator
guide in a linear accelerator? - ✔✔magnetron
✔✔what is the clinically acceptable limit or tolerance of flatness over the central 80% of
the x-ray beam used in radiotherapy? - ✔✔2%
✔✔out of 60Co, deep therapy x-rays, 10 MV x-rays, 10 MV electron which will have the
highest beam penetration? - ✔✔10 MV X-rays
✔✔why is a trimmer bar attached to the collimator? - ✔✔to reduce the effect of
penumbra
✔✔which is the best absorbing material for neutrons? - ✔✔polyethylene
✔✔which detector is used in accelerators as a monitor chamber? - ✔✔ionization
chamber
✔✔what system do computers work on? - ✔✔binary system
✔✔what numbers does a binary system involve? - ✔✔0 and 1
✔✔what is the value of a binary number 1001 in decimal system? - ✔✔9
✔✔in a computer the data 0 or 1 is called_____ - ✔✔a bit
, ✔✔what is a group of eight bits called? - ✔✔a byte
✔✔computer memory is organized in terms of_____ - ✔✔bytes
✔✔a group of 64 bits corresponds to_____ - ✔✔8 bytes
✔✔a two-bit binary number can give _____ - ✔✔4 bits of information
✔✔in decimals, a 3-bit binary number can represent_____ - ✔✔8 numbers
✔✔a byte can represent_____ - ✔✔256 bits of information
✔✔determine the different configurations of 2 bits - ✔✔00, 01, 10, 11
✔✔determine the different possible configurations of a group of 3 bits - ✔✔000, 001,
010, 011, 100, 110, 101, 111
✔✔a kilobyte actually corresponds to how many bytes? - ✔✔2^10 bytes or 1024 bytes
✔✔a megabyte corresponds to_____ - ✔✔2^20 bytes
✔✔alpha numeric characters can be_____ - ✔✔letters, numbers, and special symbols
✔✔what information can one byte of information content represent? - ✔✔digits 0 to 9
and all the special characters and symbols one usually encounters
✔✔Data are stored in manipulated in a computer_____ - ✔✔digital form only
✔✔Data are transmitted or received by a computer in____ - ✔✔digital form only
✔✔detectors used in CT generate_____ - ✔✔analog data
✔✔CT scanners convert analog data to digital data using______ - ✔✔analog to digital
converters
✔✔is there a loss of information when in an analog to digital conversion? - ✔✔yes
✔✔a video monitor handle signals in what form? - ✔✔analog form
✔✔in ASCII code each character's represented in_____ - ✔✔one byte
✔✔a computer stores an image as_____ - ✔✔a group of image elements or pixels into
which the image is divided
