Radiobiology Flashcards
(27 cards)
What are the two main categories of Radiation ?
Non-Ionising & Ionising
What are the two major categories of Ionising Radiation?
Directly Ionising Radiation - (charged particles) electrons, protons, alpha particles, heavy ions.
Indirectly Ionising Radiation - (neutral particles) photons (x-rays, gamma rays), neutrons
What is this the definition of:
defining the quality of an ionizing radiation beam.
Linear Energy Transfer (LET)
In Radiation Damage what is Direct Action?
Interaction of radiation with atoms within the cell’s Nucleus, Damaging the DNA, α particles, protons electrons, β-, β+
What is the most common form of radiation damage, what does it affect and cause?
Indirect Radiation
Affects the cytosol (intracellular fluid)
Ionisation of the H2O causes free radicals which in turn can damage the target.
What are the 3 phases of Time Scale of Radiation Biology?
1.Physical Phase - Interactions between charged particles and atoms of the tissue
2.Chemical Phase - Period in which these damaged atoms react with other cellular components in chemicals reaction - to form free radicals (free radical reactions complete within 1ms of radiation exposure)
3.Biological Phase - All subsequent processes - Enzymatic reactions that act on chemical damage, Some damage can be repaired, and some cannot. It is these that lead to Cell Death - or lack of proliferation (growth/increase in numbers), Cells take time to die – sometimes need a number of divisions. This damage manifests during weeks/months after exposure.
What is the Law of Bergoine and Tribondeau defining?
The dose needed to destroy cell function.
What dosage is needed to destroy differentiated cells?
~100 Gy
What dosage is needed to destroy Proliferating cells?
< 2 Gy
What are the 5 steps in the cell cycle?
G1 (Gap 1) - Cells increase in size
S (synthesis) - DNA replication occurs during this phase
G2 (Gap 2) - the cell will continue to grow & replication is checked before mitosis (cell division)
M (Mitosis) - the orderly division into two daughter cells.A checkpoint in the middle (Metaphase Checkpoint ) ensures that the cell is ready to complete cell division.
G0 (Gap 0) - A resting phase where the cell has left the cycle and has stopped dividing, some (highly differentiated) cells like neurons spend a long time in this phase
What are the 3 categories of Sensitivity?
Stem - divide to maintain one’s own and other’s population e.g. basal cells in epidermis of skin, bone marrow cells.
Transit - in between a stem cell to an end cell destination. May or may not divide
Static - loses cells throughout life, highly differentiated (specialised) little mitotic activity e.g. nervous tissue and muscle - least sensitive
What are radioresistant areas?
Bone, Liver, Kidney, Cartilage, Muscle, Nervous Tissue
What are radiosensitive areas?
Germinal cells, Lymphoid tissues, basal cells, Mucosa, Hematopoietic tissues, Epithelium of the GI tract
What enhances the effectiveness of radiotherapy?
Chemotherapy, Radioprotectors, Hyperbaric Oxygen, Hyperthermia, Use of different radiations
What are the 5/6 Rs of Radiobiology?
Repair, Radiosensitivity, Repopulation, Redistribution, Reoxygenation, Reactivation of the anti-tumour immune response
Repair - Repair of sub-lethal damage to DNA 20 mins to 1.5 hours after irradiation, degree of repair varies in different tissue, Slowly proliferating cells can repair better than tumour cells (and other highly proliferating cells) as long as there is a sufficient gap between fractions, Oxygen affects repair.
Radiosensitivity - The inherent sensitivity of cells and tissues to radiation.
Repopulation - During a multi-fraction treatment, cells in both the tumour and the normal tissue proliferate. (divide & multiply), Dead cells are replaced by Repopulation from resting stages of the cell cycle (G0), This process can be fast for highly proliferating cells-Tumour cells (differs with histology) e.g. skin and mucosa, As in repair, acutely responding (normal) tissues can repopulate better than tumour cells, Late responding tissues have little/no re-population during treatment e.g. neurons
Redistribution - he movement of cells through the cell cycle, which can affect their sensitivity to radiation, cells are selectively killed in the most sensitive phases of the cell cycle (M & G2), Cells surviving irradiation are those which were in relatively resistant phases. (S & G0), Cycle duration depends in tissues, tumours, cell heterogeneity within tumour stroma, cell maturity. This movement or Redistribution of surviving cells within the cycle, results in self-sensitization as it creates movement to sensitive phases in between each fraction of dose-tumour control, However this only affects cells that divide frequently during the 4 to 8 week course of curative radiotherapy, Acute responding tissues - active & proliferating, Late responding tissues - slow/inert more time in G0 = resistance (also later emergence of damage)
Reoxygenation - The improvement in oxygenation of tumour tissue, which can increase the effectiveness of radiation. More free radicals produced if more oxygen present. so = more indirect action = more strand breaks so each exposure is more Effective, Oxygen ‘fixes’ or ‘sets’ the DNA breaks caused (by binding to the ends of the break)-so no repair is possible = more lethal damage, Hypoxic cells are about 2.5 to 3.0 times more resistant to X-irradiation than euoxic (well oxygenated) cells, These chronically hypoxic cells might limit radio curability of the tumor.
Reactivation of the anti-tumour immune response: The activation of the immune system by radiation therapy, leading to a potential systemic anti-tumour effect.
Why do hypoxic cells arise in tumours?
imbalances between the rate of production of new cells and the vascularization of the tumor,
What is the latent period in redistribution?
irradiated cells show a lot of inflammatory activity long after treatment during this latency period.
suggesting that on a cellular level radiation damage is ongoing
Cascades of cytokines = prompt collagen genes to turn on = emergence of
clinical late effect
What are serial organs?
If small volume is irradiated beyond the TD it can lead to whole organ failure
What are parallel organs?
The magnitude of the effect depends upon the volume & dose
What is vascular sequelae?
Organ damage. Some types of vasculitis can damage major organs. Blood clots and aneurysms.
How are early reactions defined?
Observed within 1st 90 days & repaired due to rapid proliferation of stem cells
How are late reactions defined?
Any symptoms first diagnosed at a later time & damage may improve but never completely repair
Skin reaction early vs late effects?
Early - Erythema 2nd-3rd week, Dry Desquamation 30Gy, Moist Desquamation 40Gy, Ulceration
Late - Telangiectasia (widened blood vessels on skin) & Fibrosis (repair response of fibrous connective tissue)
Lung reaction early vs late effects?
Early - mild dyspnoea, non-productive cough, chest discomfort, and low-grade fever to respiratory insufficiency.
Late - chronic lung fibrosis, a progressive disease that occurs months to years after treatment, disease tends to stabilize approximately 2 years post-treatment, but lung volumes may continue to retract until ∼5 years post-exposure.
