22.55 Principles of Radiation Interactions
Direct comparison between protons and alpha particles of the same
LET
Background:
High LET more effective than low LETwell established in
Cell survival
Mutagenesis
Chromosome aberrations
Systematic studies of
1-3 Polar Coordinates
9.3 polar coordinates
5. The Cartesian coordinates of a point are given (a) (1,1) (b) (2 3 , 2)
(i) Find polar coordinates (r , ) of the point, where r 0 and 0 2 .
(ii) Find polar coordinates (r , ) of the point, where r 0 and 0 2 .
22.55 Principles of Radiation Interactions
In vivo dose response assays
Tumor assays
[Image removed due to copyright concerns]
1. Tumor growth measurements; tumor growth delay.
After irradiation, the tumor is measured daily to determine the mean
diameter
22.55 Principles of Radiation Interactions
Radiation Chemistry
Ionizing radiation produces abundant secondary electrons that rapidly slow down
(thermalize) to energies below 7.4 eV, the threshold to produce electronic
transitions in liquid water.
For both
Radiation Therapy
Use of radiation to kill diseased cells.
Cancer is the disease that is almost always treated when using radiation.
One person in three will develop some form of cancer in their lifetime.
One person in five will die from that cancer.
C
22.55 Principles of Radiation Interactions
Modification of Radiation Response
Biological Modification
repair of radiation damage
dose rate effects
fractionation
Repair of DNA damage
Three types of damage
Lethal damage- irrepairable, leads to cell deat
22.55 Principles of Radiation Interactions
Radiation Interactions with Matter: Energy Deposition
Biological effects are the end product of a long series of phenomena, set in
motion by the passage of radiation through the medium.
[Image removed due to copy
22.55 Principles of Radiation Interactions
Energy deposition by light charged particles
Light charged particles
electrons
positrons
All forms of ionizing radiation eventually result in a distribution of low-energy
electrons.
The interactions of light ch
22.55 Principles of Radiation Interactions
Interactions of Photons with Matter
Photons are electromagnetic radiation with zero mass, zero charge, and a
velocity that is always c, the speed of light.
Because they are electrically neutral, they do not ste
22.55 Principles of Radiation Interactions
Neutrons
Classification of neutrons by energy
Thermal:
Epithermal:
Fast:
E < 1 eV (0.025 eV)
1 eV < E < 10 keV
> 10 keV
Neutron sources
Reactors
Fusion reactions
Large accelerators
Neutron energies
neutrons in th
22.55 Principles of Radiation Interactions
Dose Calculations
Absorbed Dose from a charged particle beam
[Image removed due to copyright considerations]
A(dE / dx) x dE
=
D=
dx
Ax
D = dose rate
= fluence rate (cm-2 s-1)
= density
A = area
[Image rem
22.55 Principles of Radiation Interactions
Clustered damage in DNA: implications, simulation, and detection.
DNA damage is caused by the reactive species produced by the passage of a
charged particle.
Modeling is the only way to completely characterize
Chemical Modification of Radiation Response
Oxygen
[Image removed due to copyright considerations]
Oxygen best known and most general radiosensitizer
The slopes of survival curves for cells exposed to sparsely ionizing radiation in
hypoxia and in well oxy
22.55 Principles of Radiation Interactions
Cell, Tissue and Tumor Kinetics
Proliferation Kinetics: rate of growth of a population, change in total cell
number. Adult tissues are in homeostasis. Children (and tumors) grow.
[Image removed due to copyright c
22.55 Principles of Radiation Interactions
Cell Survival Curves
Cell death
A cell that is able to proliferate indefinitely and form a large colony from a single
cell is said to be clonogenic.
Tumor cells can be grown indefinitely in cell culture.
Normal c
22.55 Principles of Radiation Interactions
Radiological Protection
For practical purposes of assessing and regulating the hazards of ionizing radiation
to workers and the general population, weighting factors are used.
A radiation weighting factor is an e