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Radiation Therapy II Chapter 9 Exam Questions and Answers $12.49
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Radiation Therapy II Chapter 9 Exam Questions and Answers
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  • Course
  • Radiation therapy
  • Institution
  • Radiation Therapy

Grenz - Answer--10-15 kVp -used for benign skin conditions contact - Answer--applicators in direct contact with treatment area -used for rectal (RT 50-kVp) and skin cancers superficial - Answer-- 50-150 kVp - SSD was typically 15-20 cm source to skin distance with cone in contact with lea...

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  • October 7, 2024
  • 6
  • 2024/2025
  • Exam (elaborations)
  • Questions & answers

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  • radiation therapy ii chapter 9 exam questions and
  • grenz answer 10 15 kvp used for benign skin co

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  • Radiation therapy

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Radiation Therapy II Chapter 9 Exam
Questions and Answers
Grenz - Answer--10-15 kVp
-used for benign skin conditions

contact - Answer--applicators in direct contact with treatment area
-used for rectal (RT 50-kVp) and skin cancers

superficial - Answer-- 50-150 kVp
- SSD was typically 15-20 cm source to skin distance with cone in contact with lead cut-
out or skin

orthovoltage - Answer-- 200-300 kVp
-most common SSD was 50 cm
-cones used to collimate beam

dmax - Answer--the depth of dmax is directly related to the energy of the beam
-for energies in the KV range, dmax occurs at the surface of the skin

What could cause the dose to increase below the surface? - Answer-secondary
ionization events caused by electrons that are set in motion

When did cobalt 60 first start being used? - Answer-1950s

cobalt 60 - Answer-- teletherapy unit no longer used in USA
-gamma ray source (radioactive) with average energy 1.25 MV
-capable of isocentric treatment

What offered skin sparing for the first time? - Answer-cobalt 60

Linear accelerators - Answer--came into widespread use in USA in 1970s
-dual photon energies ranging from 4-20 MV
-multiple electron energies ranging from 4 MeV to 22 MeV

What does cobalt 60 decay through? - Answer--beta decay to Nickel
- It decays continuously and has a half life of 5.25 years
-because of continuous decay the amount of time to deliver a specified dose increases
over time

What is the average energy of cobalt 60? - Answer-1.25 MV

What was the SAD of a teletherapy cobalt 60 unit? - Answer-80 cm

, Source to skin distance (SSD) - Answer-distance from the source (target) of the
machine to the surface of the patient

source to axis distance (SAD) - Answer-distance from the source (target) of the
machine to the isocenter

isocenter - Answer--the intersection of the gantry, collimator and couch rotations of axis
-a point in free space that is independent of patient position

what is the distance from the source to the isocenter? (SAD) - Answer--100 cm for a
linear accelerator
-80 cm for cobalt 60 units

Where are the collimator and gantry axis of rotation in reference to each other? -
Answer--perpendicular to each other
-if their axes do not intersect then parallel opposed beams will not be truly opposed

Major components of linear accelerator treatment unit - Answer--modulator cabinet
-drive stand
-gantry
-patient support assembly
-control console

Major components of a modulator cabinet - Answer--fan control
-primary power distribution
-auxiliary power distribution

Fan control - Answer-allows for cooling of power distribution systems

primary power distribution - Answer-major power route for accelerator

auxiliary power distribution - Answer--emergency off buttons
-timers to record use of klystron, gun filament for purposes of preventative maintenance
and warranty

Major components of the drive stand - Answer--klystron or magnetron (one or the other)
-waveguide
-circulator
-water cooling system

Magnetron - Answer-a direct source of microwaves; used for low energy photon beams
<6MV

Klystron - Answer-is an amplifier of microwaves; used for 10 MV and above

Microwaves in linacs - Answer--needed in order to accelerate the electrons

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