test 1

Question 1

grenz rays
beam energy
hard/soft
uses

Answer 1

< 20 kVp
soft x-rays
no longer used–very low penetration

Question 2

contact therapy
     beam energy
     hard/soft
     uses
     SSD

Answer 2

40-50 kVp (2mA tube current)
.5mm-1.0mm Al filter to harden beam
used in tumors in 1-2mm tissue
no longer used--low penetration
very short SSDs (2cm or less)

Question 3

superficial therapy
     beam energy
     hard/soft
     uses
     SSD

Answer 3

50-150 kVp (5-8mA tube current)
varying thickness of filtration (1-6mm Al 
     harden beam)
used for tumors within 5mm depth (max
     dose is on skin surface)
SSD usually 15-20cm

Question 4

orthovoltage therapy
     beam energy
     hard/soft
     uses
     SSD

Answer 4

150-500 kVp (10-20mA tube current)
1-4mm CU--filters composed of copper, 
     tin, aluminum.
used for tumors <2cm deep (skin cancer.. 
     max dose on surface)
SSD ~ 50cm

Question 5

supervoltage therapy

beam energy

Answer 5

500kV-1MV

Question 6

megavoltage therapy
beam energy
machines used

Answer 6

> 1MV potential used to generate x-rays

vandegraaff generators, betatrons, microtrons, units Co-60 and Cs-137 teletherapy units

Question 7

VanDeGraaff generators

Answer 7

(MV therapy)
e-accelerators
2MV x-rays, 20-40 kV applied across a moving belt. e- are sprayed on the belt and carried up to spherical dome. high potential develops between the dome and the ground. the potential is applied across an x-ray tube. replaced by co-60 and linacs.

Question 8

Betatrons

Answer 8

(MV therapy)
e- are accelerated in a circular orbit in a changing magnetic field. the e- are ejected into an evacuated doughnut, and accelerated until striking an x-ray target or a scattering foil.

Question 9

Microtrons

Answer 9

(MV therapy)
e- are accelerated in a circular orbit, but constantly return to microwave cavity, which increases the e-energy whith each pass through the cavity. the e- are extracted when they reach a desired energy and sent through a beam transport system to gantry head. the microwave power is supplied by a klystron or magnetron

Question 10

radionuclide machines–Co-60 units

Answer 10

teletherapy units (tele=distant) (brachy=close)

Question 11

advantages of Co-60

Answer 11

1. high specific activity (activity/mass) – smaller source and less penumbra
2. higher radiation output/activity
3. higher average photon energy (deeper penetration into tissue)

Question 12

more advantages of Co-60

Answer 12

made in a reactor by bombarding co-59 with neutrons
comes in form of cylinder, discs, or pellets housed in stainless steel capsuls to prevent leakage of radioactive material
decays to ni-60 and emits beta particles, 0.32 MeV, which are absorbed in the housing of source.
emits 2 xrays - 1.17 MeV and 1.33 MeV. avg energy 1.25 MeV

Question 13

linear accelerators

Answer 13

accelerate e- in straight path to near the speed of light

Question 14

components of linear accelerator

Answer 14

gantry
stand
modulator cabinet
control console
treatment couch (PSA)

Question 15

gantry

Answer 15

1. accelerator structure–1m-1.5m long, e- accelerated to chosen energy. energized by microwave power from klystron or magnetron via waveguide.
2. e- gun–e- source injected into accelerator structure
3. bending magnet–steers e- emerging from accelerator structure around a 270 loop to strike a target (for xrays) or a scattering foil (for e-beams