RADIOBIOLOGY

Principles of Radiobiology based on Random nature of

radiation interactions

how radiation interacts at cellular level

factors that can alter these interactions

REMEMBER

All radiation damage occurs at cellular or subcellular level

visible effects are seen after millions of cells are impacted

Characteristics of ionizing radiation Charge Mass Energy

Vary among different types of radiation

Ionizing radiation causes injury through these concepts LET RBE OER

LET

High and low LET (chart 6-1, pg 108 Sherer)

LET IS AVERAGED DUE TO POLYENERGETIC NATURE OF IONIZING RADIATION

RBEBackground information

QF-How much biologic damage one type of radiation does vs. type of radiation

What is the QF of x-rays? What about Alpha? QF=rounded estimate of RBE

RBE (Pg. 495-Bushong)

Compares: dose of standard radiation necessary to produce a given effect

dose of test radiation necessary to produce same effect

Standard radiation is 250 KeV RBE’s of diagnostic is 1 Max. is approx. 3 As LET increases; so does RBE Alpha and Beta have high RBE

OER

The ratio of radiation damage done with oxygen vs. without oxygen

OXYGEN EFFECT

Tissue more sensitive to rad when oxygenated or in aerobic state

VS anoxic or hypoxic Oxygen produces free radicals Why would this be important in radiation

therapy?

Alpha-insensitive to oxygen (Low OER) Gamma and x-rays more sensitive

(High OER) Therefore Low LET is associated with

____OER (LOW OR HIGH)

IONIZING RADATION AND BIOLOGIC DAMAGE Direct or indirect occurs more with high LET radiation Relative Biologic Effectiveness

Direct

Can be fatal to cell high LET

A FREE RADICAL

Hydroperoxl Hydroxyl H2O2

2/3 of all biologic damage is from H2O2 which is…

hydrogen peroxide

INDIRECT

RADIOLYSIS OF WATER Breakdown of H2O produces an ion pair of HOH and e- These can attach to uncharged water

molecules (unstable)= free radical

CHROMOSOMAL EFFECT

Biologic damage occurs during breakage of chromosomal backbone or to DNA

Point mutations Frameshift mutation

RADIATION MUTATION CHARACTERISTICS Germ cells-carry on to future

generations Somatic cells-effect only occurs once undesirable probably cumulative threshold effects are not specific to radiation

TARGET THEORY

ADDRESSES LETHAL DAMAGE

THERE ARE AREAS ON THE DNA CHAIN THAT, IF DAMAGED, ARE LETHALTO THE CELL

UNDERSTANDING THE “TARGET” CELLS ARE MADE UP MOLECULES OVERABUNDANCE OF MOLECULES CRITICAL MOLECULE “WHEN RADIATION INTERACTS WITH

OR NEAR A CRITICAL MOLECULE, THIS SENSITIVE AREA IS CALLED ‘TARGET’.”

NUCLEUS VS CYTOPLASM

Principles of Radiobiology based on Random nature of

radiation interactions

how radiation interacts at cellular level

factors that can alter these interactions

NOW ON TO THE THEORIES

DNA SEQUENCE VITAL-DAMAGE TO ANY TARGET(SEQUENCE) WILL KILL THE CELL

NO SINGLE SEQUENCE IS IMPORTANT-2 TO 3 TARGETS (SEQUENCES) NEED TO BE HIT

TARGET ONLY NEEDS ONE HIT TO CAUSE FETAL DAMAGE

TARGET NEEDS TO BE HIT TWICE OR MORE TO CAUSE DAMAGE

Radiation damage

Cannot be distinguished from other sources (chemical, heat or trauma)