L20 - Introduction to radiotherapy Flashcards
What is radiotherapy?
The priciple of using ionising radiation or neutral particle beams to treat tumours.
What is radiobiology?
The study of the action of radiation on living things (how radiation gets integrated in the cell population.
What are the 4 R2 of radiobiology? (the factors that influence the response of tumours and tissue to radiotherapy)
Repair - occurs within a few hours
Redistribution - occurs in a few hours, damaged DNA from radiotherapy spreads to other cells.
Reoxygenation - tumours are less sensitive to radiotherapy when they are deprived of oxygen
Repopulation - occurs in 5-7 weeks, process of one area being affected by raiotherapy and repopulated by tumour cells from other parts of body.
When are cells most sensitive to radiotherapy?
When they are in mitosis, cells in G0 are not sensitive to radiotherapy so it is given in many rounds to kill as many cells in mitosis as possible.
What can cause accelerated repopulation?
Giving radiotherapy for greater than 4 weeks causes increased repopulation.
How does radiotherapy lead to aeration of more cells and more killing?
The first round of killing kills the oxygenated surface cells which leads to oxygenation of lower down cells which kills them also.
What is the difference between direct and indirect ionisation?
Direct action involves photon depositing energy into tissue that directly damages the DNA.
Indirect action involves the electrons interacting with water molecules that lead to production of hydroxyl radicals that damage the DNA.
Aiming to achieve double strand breaks as these are harder to repair and more likely to cause apoptosis.
What factors affect tumour growth?
Rate of mitogenic binding
Proportion of cells dividing
Cell loss rate
What is the norton simon hypothesis?
As tumours grow their growth rate decreases
As tumours shrink their growth rate increases.
What is the skipper cell kill hypothesis?
Survival is inversely related to tumour burden
A single cell can multiply to kill the host
There is a dose response relationship for drugs
What are the acute and long term effects of radiotherapy?
Acute
Affects rapidly turning over membranes e.g. mucous membranes and hair follicles
Long term
Affects slow dividing cells such as glial tissues, vascular endothelium and the kidneys.
What are the typical schedulaes of radiotherapy that are used?
Radical - head and neck tumours
Palliative - for pain control etc.
Adjuvant - in addition to main therapy
What is brachytherapy?
Where the source of radiation is placed inside the body next to the tumour.
