Radiobiology 1 Flashcards
What does radiology stand for?
Field of clinical and basic medical sciences
What are characteristics of cancer cells?
- Large number of dividing cells
- Large, variable shaped nuclei
- Small cytoplasmic volume relative to nuclei
- Variation in cell size and shape
-Loss of normal specialised cells
Disorganised arrangement
-Poorly defined tumour boundary
What are the two types of radiation?
Direct
Indirect
What are the types of cell cycle?
G1-growth
S-DNA synthesis
G2-growth and preparation for mitosis
M-Mitosis
What cell cycles are radioresistant?
S-phase and G1(open structure)
What does plating efficiency mean?
The percentage of cells seeded that grow into colonies
What is the surviving fraction?
estimates survival are obtained for a range of doses (Doesn’t distinguish mode of death)
What does a cell survival curve?
Count of surviving of cells following irradiation at discrete intervals of dose
What are low-linear transfer?
X-rays, gamma rays
What are high LET?
Alpha, Beta particles
What are the two cell survival curves?
Linear quadratic model
Multivariate model
What are the radiation variables of the cell survival curve?
Particle size
Particle charge
Dose rate
Low or high LET
What are the tissue variables of the cell survival curve?
Mitotic Rate
Cell cycle phase
Oxygenation
What are the components of cell killing?
One proportional to dose (alpha) single radiation track
One proportional to the square of the dose (Beta) 2 track
What does the LQ model dsplay?
Cell kill both for tumour control and normal tissue complications
Whats the rule for surviving fraction?
SF=e-^(alphaD *+BD^2)
What happens at low doses?
two chromosomes breaks are the consequence of single electron (Linear)
What happens at high doses?
two chromosome breaks are a consequence of two electrons (Quadratic)
What does the alpha/ beta ratio mean?
where linear and quadratic components are equal
Theoretical measure of a tissue’s predicted response to a dose of radiation
What does a high alpha/beta ratio (10)?
- tumour response is less dependent on the radiation (most tumours)
- early responding tissue
What does a low alpha/beta ratio (3)?
Large dose of radiation is required to provide improved efficacy in terms of tumour control
-Late responding tissues
What are single and multi hits?
alpha and beta
What are more radioresistant SCC or sarcoma cells?
SCC
What does BED mean?
Means of comparing the effectiveness of different treatment regimens
What is the BED equation?
E/A=(nd) (1+d/a/b)
What are the benefits of Fractionation?
- Allows for sublethal repair of normal tissue
- increases damage due to reoxygenation and reassortment of cells into radiosensitive phase
- Excessive prolongation leads to cell proliferation
What are the 5Rs of radiobiology?
Repair of sublethal damage
- Reoxygenation of hypoxic tissue
- Redistribution or reassortment
- Repopulation or regeneration
- Radiosensitivity ( Intrinsic)
What are the three types of damage?
Lethal damage
Sublethal damage
Potentially Lethal damage
How do normal tissues repair?
repair pathways
Cell cycle arrest
In normal p53 is inactivated by mdm2
Do malignant cells repair?
No
often through mutation or inhibition of TP53 prevents repair
What are the reassortment phase?
When a small dose is delivered over a short period
cells will cycle through to more radiosenstive phases.
What is repopulation phase?
Following irradiation some cells will exhibit increased cell division (quicker in NT)
What is the reoxygenation phase?
Allow enough time to reoxygenise.
What is radiosensitivity?
Different radiosensitivity in different cells
radiosensitivity (gametes)
radioresistant( melanoma and sarcoma)
Is a high OER desirable?
Yes makes cells more sensitive to cell damage
What is OER?
Hypoxic/Aerated
What is the oxygen fixation hypothesis?
Damage produced by free radicals in DNA can be repaired but may be fixed “irreparable” if molecular oxygen is available
(Forms an organic peroxide non restorable for target material)
