Radiotherapy Flashcards
What is the difference between ionising and non ionising radiation?
The size of the individual energy packets, not the total energy.
How important are indirect effects of ionising radiation?
Account for ~2/3 biological action of X-rays.
Propagates effect as OH can travel further within tissues.
Less important with High-LET radiation (most bio effect due to direct actions here!).
Why is oxygen beneficial in radiotherapy?
Prolongs the lifespan of radiation-induced FRs, increasing the INDIRECT effect.
Trials being conducted to increase O2 delivery as tumours contain hypoxic areas making them more resistant to RT.
These areas may change day to day due to variation in dilatation and contriction.
Why have O2 sensitization methods not been shown to be effective?
(hyperbaric O2 or hypoxic cell sensitizers)
Sensitization of normal tissues OR
sensitizer []s needed are toxic.
What is the basis for the molecular and cellular effects of IR?
Molecular - DNA is target and critical lesion is unrepaired or misrepaired DSBs.
Cellular; inhibit biochemical processes, chromosomal abnormalities, mitotic delay, cell killing.
What mechanisms of cell death can be seen?
Interphase death - non dividing cells & >20y needed.
Mitotic death - death on attempting mitosis (low doses needed).
What are the new technologies?
VMAT - lots of directions so can shape dose around tumour & minimise dose.
IGRT Elekta Synergy - CT scans during treatment.
Cyberknife - 360 - not just one plan.
Gamma Knife - for for brain.
