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lecture 8 meyer

2 general uses of radiation in ca tx as (neo)adjunct to surg; can be also used with definitive intent i.e. as the primary radical therapy for a certain type of tumor
types of radiation used for tx ionizing radiation breaks down into electromagnetic (XR and gamma rays) and particulate (electrons, protons, neutrons, heavily charged ions) types
unit of measurement for radiation exposure two are important: rad is 100 ergs/g absorbed dose of radiation // gray (Gy) is 1 joule/kg energy absorbed
mechanism of radiation effects on tissue indirect: dominant for sparsely ionizing like XRs and gamma rays - free radical generation that leads to apoptosis or classical necrosis // direct: densely ionizing radiation like neutrons and charged particles, results in direct damage to DNA/proteins
4 modifiers of radiation exposure cell cycle, type of radiation, fractionation and oxygenation
how being mindful of cell cycle during radiation exposure can enhance the effect of radiation the clinician will try to catch cells when they are in M or G2 phase b/c they're most sensitive to radiation; least sensitive in S phase
early and late side effects of radiation tx
cells are much more sensitive to radiation damage when they are in oxygen-rich environment less sensitive in a hypoxic state
how being mindful of the type of radiation during exposure can enhance its effect for densely ionizing radiation, survival is an exponential function of dose (the higher the dose, the greater log kill); for sparsely ionizing radiation there is an initial linear slope followed by a shoulder then curve becomes straight at higher doses
how being mindful of oxygenation during radiation exposure can enhance its effects radiation response can be enhanced by drugs that increase the oxygen content in the hypoxic area of the tumor
how being mindful of fractionation during radiation exposure can enhance its effect providing radiation in a single dose or fraction gives a greater cell kill than giving the same dose of radiation in multiple, smaller doses due to the repair of sublethal damage btwn fractions
2 methods of delivering radiation therapy teletherapy and brachytherapy
teletherapy or external beam radiation most freq used method: photons or electrons directed at the tumor from outside the body; may be from radioactive source (e.g. cobalt-60) or generated from electron acceleration (linear accelerator) and directed at several angles to pinpoint tumor
brachytherapy intracavity or interstitial radioactive source & emits radiation to surrounding tissues; dropoff of radiation - inverse square effect
3 types of information a radiation oncologist needs to make a confident clinical tx decision histopathology (rapidly dividing undifferentiated cells are most radiosensitive), stage, goal of tx (palliative vs cure)
acute effects of radiation tx within days-weeks in tissues with rapid turnover, result from death of large #s of cells, can be reversible if rapidly repaired by proliferation of stem cells
chronic effects of radiation tx occurs after months-yrs primarly from slowly growing tissues, combo of vascular change and loss of parenchymal cells. may never be completely repaired, permanent late effects in normal tissues
Created by: sirprakes