Low and high energy treatment modalities

1895

discovery of xray

1898

discovery of radium

1920

fractionated RT

1930

orthovoltage RT

1950

megavoltage RT, Co-60, linac

1960

radiosurgery, gamma knife

1970

CT scan, proton therapy

1980

MRI, LINAC-based radiosurgery

1990

3D conformal RT FSRT, 3D RTP CT-sim

2000

IMRT, PET, IGRT, cyberknife, tomotherapy

beam quality aka

energy of the beam

each energy has a specified

Dmax

superficial, orthovoltage D-max (cm)

0

cesium-137 dmax (cm)

.1

cobalt-60 dmax (cm)

.5

4MV dmax (cm)

1

6M dmax (cm)

1.5

10 MV dmax (cm)

2.5

15 MV dmax (cm)

3

18 MV dmax (cm)

3.5

25 MV dmax (cm)

4-5

isodose chart is a composite of the actual %

depth dose as it enters the phantom

teletherapy EBRT (3)

long distance, external source radiation, low or high energy

filtration expressed in

HVL

HVl absorbs

damaging low energy xrays that scatter

HVL material used

various depending on energy produced

Grenz-Ray Therapy

treatment with beams of very soft or low energy xrays

Grenz-Ray therapy produced at potentials below

20 kV

contact therapy operates at

40-50 kV, tube current of 2mA

contact therapy SSD

very short

contact therapy uses ___ to apply beam

applicators

contact therapy filter

.5-1mm aluminum

superficial energy

50-150 kV

superficial dose to

skin with rapid fall off

superficial filter

1-6mm aluminum

superficial collimator

cones attached to machine

superficial SSD

15-20cm

orthovoltage therapy energy

200-500 kV

orthovoltage usually operates at energy of

200-300 with 10-20 mA

orthovoltage therapy dmax on skin with 90% at about

2cm

orthovoltage therapy filter

1-4mm copper

ACT (aluminum tin copper) up orthovoltage order

patient to source

orthovoltage therapy SSD with cones or moveable diaphragm

50-70

supervoltage therapy designated as a higher voltage machine with energy of

500-1000 kV

supervoltage therapy difficulty with insulating

high-voltage transformer, turned to resonant transformer

resonant transformer voltage is

stepped up

low energy machines disadvantages

low penetration, high skin dose, low output, large penumbra

low energy machines are difficult to aim beams accurately for

bilateral or orthog beams

van de graaff generator

electrostatic generator applies charge of 20-40kV on moving belt

van de graaff generator electrons are sprayed onto

belt and transferred to dome to create high negative potential

van de graaff generator high negative potential is applied across

xray tube

when electrons strike target van de graaff generator it produces

xrays

energy of van de graaff generator is determined by

voltage on the dome (1-7 mV, possibly 10)

van de graaff generator is a

non isocentric unit

betatron works on

electromagnetic induction

betatron has a magnetic field that

accelerates electrons through a donut

betatron tube is placed between poles of

alternating current, increasing e- acceleration

length of time electrons accelerates helps determine

energy

when electrons reach desired energy, they are deflected

out of orbit to strike target

betatron energy range from

5-45 MeV, commonly 20-25 MV

betatrons can produce

photons and electrons beams