Types of radiation
* radiation oncology-be defined as therapeutic manipulation of radiation delivered to a target for cure or for palliation.
*electromagnetic radiation is energy that is transmitted at the speed of light through oscillating electric and magnetic fields.
*particulate radiation uses subatomic particles, instead of photons, to deliver the dose of radiation.
Dosage theory
Normal tissue as well as malignant cells are susceptible to toxicity induced by radiation therapy, the extent of which depends on total dose, fractionization, and tumor volume.
A. Repair of sublethal injury
When a specified radiation dose is divided into two doses given at separate times, the number of cells surviving is higher than that seen when the same total dose is given at one time.
B. Repopulation
The reactivation of stem cells that occurs when radiation is stopped is necessary for further tissue growth
C. Reoxygenation: hypoxic cells are known to be relatively resistant to radiation. Cells located farther than 100mm from capillary flow are at risk for hypoxia and may not be killed by radiation therapy.
D. Radiation-induced synchrony
Malignant cells are most sensitive to radiation while in the mitotic phase of the cell cycle.
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