semis radbio 2

Radiosensitivity

it is the relative susceptibility of cells or tissue respond, tissues, organs or organisms to the harmful effect of ionizing radiation.

Law of Bergonie and Tribondeau (1906)

A law which states that the radiosensitivity of living tissues varies with maturation and metabolism.

Linear Energy Transfer (LET)

• it is a measure of the rate at which energy is transferred from ionizing radiation to soft tissue.

• it is another way of determining the value of the radiation weighting factor (WR)

kiloelectron volt (keV/um)

LET is expressed in what units?

Relative Biologic Effectiveness (RBE)

it is a measure of the biological effectiveness of different types of ionizing radiation relative to a standard reference, typically X-rays or gamma rays.

orthovoltage in a range of 200 to 250 kVp

it is the standard radiation of RBE, by convention?

1 or 3.0 keV

what is the standard range of RBE in diagnostic x-ray?

Protraction

A dose delivered continuously over a specific period of time.

Fractionation

• A dose delivered in smaller equal doses.

• this Dose causes less effect due to intracellular repair & recovery between doses.

• Routinely used in oncology.

1. Oxygen Effect

2. Age

3. Recovery

4. Chemical Agents

5. Hormesis

what are the Biological Factors That Affect Radiosensitivity?

anoxic

conditions to produce a given effect

aerobic

conditions to produce the same effect

OER

it is the ratio of the radiation dose necessary to produce a given effect under anoxic tissue conditions to that required to produce the same effect under aerobic conditions.

Chemical Agents

Radiosensitivity of cells, tissues, and organs can be modified by what?

interphase death

it occurs when the cell dies before replicating.

atrophy

it is the process by which a tissue or organ shrinks or wastes away due to the reduction in cell size or number. This can occur as a result of cell death, but also from other processes like decreased cell activity or reduced blood supply.

Point Mutation

• results in the change or loss of a base, which creates an abnormal gene. 

• This is therefore a genetic mutation that is passed to one of the daughter cells.

age

• Age of biological structure affects radiosensitivity.

• Humans are most sensitive at birth.

• Sensitivity decreases until maturity.

• In old age radiosensitivity, increases

Recovery

• cells are capable of recovering from radiation damage

• At whole body level, recovery is assisted via repopulation by surviving cells

• Recovery = Repair + Repopulation

Chemical Agents

• Radiosensitivity of cells, tissues, and organs can be modified by?.

• Must be present during irradiation

Hormesis

• Evidence that a small dose of radiation produces helpful effect.

• Prevailing Explanation: Stimulation of hormonal and immune responses to other toxic environmental agents.

Main-chain scission

This type of radiation effect to DNA is only one side rail cut.

Rung breakage

This type of radiation effect to DNA is causing the bases to separate.

Chromatid deletion

The breakage of a chromatid is called what??

dicentrics or Ring chromosomes

In multiple hit chromosome aberration, it is produced when the two hits occur on the same chromosome.

Dicentrics

Are produced when adjacent chromosomes each sustain one hit and recombine

Cell-cycle time

When human cells replicate by mitosis, the average time from one mitosis to anoyher is called what?

visible chromosome aberrations may be detected

If radiation damage to the DNA is severe enough what will gonna happened?

Cell cycle effects

it refers to the impact of ionizing radiation on the various phases of the cell cycle. 

cell cycle

• is a series of events that a cell goes through as it grows and divides.

• It consists of distinct phases, including:

  G1 (gap 1), S (synthesis), G2 (gap 2), and M (mitosis).

mitosis phase

It is the most sensitive in radiation in terms of phases in cell cycle time.

G1–S transition

It is the 2nd most sensitive in radiation in terms of phases in cell cycle time.

s phase

It is the most resilient in radiation in terms of phases in cell cycle time.

Cellular Radiation Effects

• this radiation effects refer to the impact of ionizing radiation on living cells.

• such as Ionizing radiation, which includes X-rays, gamma rays,

Interphase death

• this type of cellular cell death that occurs during the interphase stage of the cell cycle.

• can occur before the cell progresses to mitosis.

• it can result from severe DNA damage caused by ionizing radiation.

mitotic death

• this type of cellular cell death is also known as genetic death, occurs during or because of mitosis, the phase of the cell cycle where cells divide to produce two daughter cells.

• it may be result from induced by ionizing radiation if the damage to the DNA is not detected and repaired during the interphase.

mitotic delay

• this cellular affects of radiation refers to a temporary arrest or prolongation of the cell cycle, particularly at the G2 checkpoint.

• particularly DNA damage, activates cell cycle checkpoints.

Reproductive Failure

• this cellular effect of radiation occurs when a cell exposed to ionizing radiation undergoes cell death, preventing it from producing viable daughter cells.

Interference

this type of cellular radiation effect refers to the disruption of normal cellular functions or processes due to radiation-induced damage, particularly in the form of altered gene.

Deterministic Effects

• effects are also known as non-stochastic or tissue reactions.

• They exhibit a threshold dose below which these effects do not occur, and their severity increases with higher radiation doses.

Stochastic Effects

• also known as probabilistic effects, have no threshold dose.

• The likelihood of occurrence of these effects increases with higher radiation doses, but the severity of the effect is not dose-dependent.

Short-term Effects (Acute):

also known as acute effects, manifest relatively soon after radiation exposure, typically within a short period following the exposure.

Long-term Effects

also termed chronic effects, manifest over an extended period following radiation exposure, often months, years, or even decades after the initial exposure.

Genetically Significant Dose (GSD):

• it is a measure used to estimate the potential genetic impact of radiation exposure on future generations.

• It quantifies the radiation dose received by the reproductive organs (gonads) and its potential impact on genetic material.

Teratogenic Effects

High doses of radiation during early pregnancy can result in congenital malformations or abnormalities in the developing fetus, known as teratogenic effects.

Developmental Effects

Radiation exposure at later stages of pregnancy may impact fetal growth, organ development, and can increase the risk of childhood cancers later in life.

dose rate

The rate at which radiation is delivered to the body.