Introduction – The Nature of
Electromagnetic Radiation
George
George Starkschall,
Starkschall, Ph.D.
Ph.D.
Department
Department of
of Radiation
Radiation Physics
Physics
U.T.
U.T. M.D.
M.D. Anderson
Anderson Cancer
Cancer Center
Center
Purpose
•• To
To identify
identify and
and describe
describe some
some of
of the
the basic
basic
properties
properties common
common to
to all
all forms
forms of
of
electromagnetic
electromagnetic radiation
radiation
•• To
-rays and
xx-rays
To recognize
recognize xand gamma
gamma rays
rays as
as aa form
form
of
of electromagnetic
electromagnetic radiation
radiation
•• To
To differentiate
differentiate between
between waves
waves and
and particles
particles
•• To
To identify
identify analogous
analogous properties
properties among
among waves
waves
and
and particles
particles
Introduction – Patient Case
• 62 yr old woman with Stage IIIB (T1N3M0)
NSCLC rt lower lobe
• Dose prescription
–– 66 MV
-rays
xx-rays
MV x–– 1.8
1.8 Gy/fraction
Gy/fraction xx 35
35 fractions
fractions
–– IMRT
IMRT
1
Introduction – Patient Case
Introduction – Patient Case
•• 100%
100% of
of the
the CTV
CTV gets
gets 63
63
Gy
Gy
•• 93%
93% of
of the
the PTV
PTV gets
gets 63
63
Gy
Gy
•• V20
V20 for
for total
total lung
lung is
is 37%
37%
•• Max
Max cord
cord dose
dose is
is 44.9
44.9 Gy
Gy
Help! – I’m lost
••
••
••
••
••
••
••
••
Why
-rays?
xx-rays?
Why are
are we
we treating
treating the
the patient
patient with
with xWhat
6 MV”
”?
MV
What do
do we
we mean
mean by
by ““6
MV”?
What
Gy”
Gy”?
What is
is aa ““Gy”?
What
What is
is IMRT?
IMRT?
What
What is
is aa dose
dose distribution
distribution and
and what
what do
do the
the
lines
lines mean?
mean?
What
What is
is aa DVH?
DVH?
What
What is
is aa CTV?
CTV? PTV?
PTV?
What
What do
do we
we mean
mean by
by V20?
V20?
2
Basic premise
•• We
We transfer
transfer energy
energy
–– Power
Power mains
mains to
to electrons
electrons
–– Electrons
-rays
xx-rays
Electrons to
to x–– X
-rays to
X-rays
to atoms
atoms in
in patient
patient
•• Energy
Energy causes
causes things
things to
to happen
happen
–– Electrons
Electrons removed
removed from
from atoms
atoms
–– Chemical
Chemical reaction
reaction
–– Cellular
Cellular changes
changes
–– Clinical
Clinical changes
changes
Basic premise
•• Follow
Follow the
the energy!
energy!
•• Transfer
Transfer energy
energy through
through space
space by
by means
means of
of
waves
waves –– radiation
radiation
•• Transfer
Transfer energy
energy through
through space
space by
by means
means of
of
electric
electric and
and magnetic
magnetic waves
waves –– electromagnetic
electromagnetic
radiation
radiation
•• If
If the
the energy
energy of
of the
the electromagnetic
electromagnetic radiation
radiation is
is
sufficient
sufficient to
to remove
remove electrons
electrons from
from atoms
atoms ––
ionizing
ionizing radiation
radiation
Waves and particles
• Electromagnetic radiation can be looked
on either as waves or as particles.
• To understand the properties of
electromagnetic radiation and how
electromagnetic radiation can be used to
transfer energy, we must understand
properties of both waves and particles.
3
Properties of waves
• Definition
Definition –– aa periodic
periodic disturbance
disturbance that
can be propagated
Two types of waves
• Compare direction of disturbance with
direction of propagation
• Longitudinal
Longitudinal –– disturbance
disturbance moves
moves
along direction of propagation
• Transverse – disturbance moves
perpendicular to direction of
propagation
Example of transverse waves
4
How waves are characterized
• Amplitude – magnitude of
of disturbance
• Frequency
–
number
of
peaks
per unit
Frequency – number
time
–– Frequency
Frequency denoted
denoted by
by νν
–– Units
Units are
are 11 Hertz
Hertz (Hz)
(Hz) == 11 cycle/sec
cycle/sec
How waves are characterized
• Wavelength – distance between successive
peaks
–– Wavelength
Wavelength denoted
denoted by
by λλ
–– Units
Units are
are units
units of
of length
length
Relation between wavelength
and frequency
λν = c
c is speed of propagation of wave
5
Nature of electromagnetic
waves
• Periodic fluctuations in electric and
magnetic fields
• Caused by interactions of charges
• Electromagnetic waves are transverse
waves
Speed of propagation
• All electromagnetic waves travel at same
propagation speed c = 3.00 × 1088 m/sec in
vacuum
Problem
• KUHF radio broadcasts at a frequency of
88.7 MHz. What is its wavelength?
λ =
c
ν
3.00 × 1088 m/sec
=
88.7 × 1066 sec --11
=
3.38 m
6
Spectrum of electromagnetic
radiation
Wave
Wave
Category
Category
Specific
Specific
Kind
Kind
Typical
Typical
Wavelength
Wavelength
Radio
Radio
Broadcast
30,000
Broadcast
30,000 cm
cm
(1000
(1000 kHz)
kHz)
TV
300
TV
300 cm
cm
(10
(10 MHz)
MHz)
Radar
10
Radar
10 cm
cm
(3,000
(3,000 MHz)
MHz)
Approximate
Approximate
Corresponding
Corresponding
Photon
Photon Energy
Energy
0.000
0.000 000
000 004
004 eV
eV
0.000
0.000 000
000 44 eV
eV
0.000
0.000 012
012 eV
eV
Spectrum of electromagnetic
radiation
Wave
Wave
Category
Category
Specific
Specific
Kind
Kind
Light
Light
Infrared
Infrared
Visible
Visible
Ultraviolet
Ultraviolet
Typical
Typical
Wavelength
Wavelength
12,000
12,000 Å
Å
6,000
6,000 Å
Å
3,000
3,000 Å
Å
Approximate
Approximate
Corresponding
Corresponding
Photon
Photon Energy
Energy
11 eV
eV
22 eV
eV
44 eV
eV
Spectrum of electromagnetic
radiation
Wave
Wave
Category
Category
Specific
Specific
Kind
Kind
Typical
Typical
Wavelength
Wavelength
X
-rays and
X-rays
and Diagnostic
Diagnostic
γγ rays
Orthovoltage
rays
Orthovoltage
60
60Co
Co
Linear
Linear Accel
Accel
High-energy
High
High-energy
Linac
Linac
0.4
0.4 Å
Å
0.1
0.1 Å
Å
0.01
0.01 Å
Å
0.06
0.06 Å
Å
0.0015
0.0015 Å
Å
Approximate
Approximate
Corresponding
Corresponding
Photon
Photon Energy
Energy
30
30 keV
keV
120
120 keV
keV
1200
1200 keV
keV
2000
2000 keV
keV
8000
8000 keV
keV
7
Spectrum of electromagnetic
radiation
Wave
Wave
Category
Category
Specific
Specific
Kind
Kind
Cosmic
Ray
Cosmic RayRay-- Photons
Photons
Produced
produced
Produced
produced
Waves
by
Waves
by cosmic
cosmic
particles
particles
Typical
Typical
Wavelength
Wavelength
Approximate
Approximate
Corresponding
Corresponding
Photon
Photon Energy
Energy
>> 1,000,000
1,000,000 keV
keV
0.000012
0.000012 Å
Å
Wave properties
• Electromagnetic waves can exhibit both wave
properties and particle properties:
–– Wave
Wave properties
properties
•• Diffraction
Diffraction –– bending
bending of
of waves
waves around
around corners
corners
•• Interference
Interference –– constructive
constructive or
or destructive
destructive adding
adding of
of
wave
wave amplitudes
amplitudes
Interference
constructive
destructive
8
Particle properties
•• Electromagnetic
Electromagnetic waves
waves can
can exhibit
exhibit both
both wave
wave
properties
properties and
and particle
particle properties:
properties:
•• Particle
Particle properties
properties
–– View
View electromagnetic
electromagnetic waves
waves as
as discrete
discrete clumps
clumps of
of
energy
energy
–– Massless
Massless particles
particles called
called photons
photons –– quantum
quantum theory
theory
–– Energy
Energy of
of photon
photon given
given by
by
E(keV)=12.4/λ
λ(Å)
E(keV)=12.4/
E(keV)=12.4/λ(Å)
Waves vs particles
• Photons travel only at 3.00 × 1088 m/sec
• Photons have no mass
• Electromagnetic waves exhibit either
wave properties or particle properties, but
never both simultaneously
Waves vs particles
Waves
Particles
Amplitude
Intensity
Frequency
Energy
9