18 Questions
What is the approximate Oxygen Enhancement Ratio (OER) for neutrons?
1.6
What is the primary factor that determines the extent of radiation-induced DNA damage?
Presence or absence of oxygen
What is the minimum time required for oxygen to be present after irradiation to produce the oxygen effect?
5 milliseconds
What is the primary mechanism by which oxygen acts to produce the oxygen effect?
Acting at the level of free radicals
What is the characteristic of chronic hypoxia in tumors?
Results from the limited diffusion distance of oxygen through tissue
What is the reason for the smaller OER at low doses compared to high doses in rapidly growing cells?
G1 cells are more radiosensitive than G2 cells and dominate the low-dose region
What is the primary mechanism by which oxygen enhances the effect of radiation?
By 'fixing' the radiation-induced DNA damage
What is the effect of hypoxia on chemoresistance?
It decreases the sensitivity of cells to chemotherapy
What is the Oxygen Enhancement Ratio (OER) equal to?
The ratio of hypoxic to aerobic doses required to achieve the same biological effect
Which of the following types of radiation has an OER of unity?
Alpha particle
What is the effect of linear energy transfer on OER?
It has no effect on the OER
Which of the following cells have a higher OER?
Radiation-resistant cells
What is the primary reason for the development of acute hypoxia in tumors?
Malformed vasculature of the tumor
What is the phenomenon by which hypoxic cells become oxygenated after a dose of radiation?
Reoxygenation
What is the primary mechanism by which hypoxia cell sensitizers increase radiosensitivity of hypoxic cells?
Free-radical formation that mimics oxygen fixation of damage
What is the primary benefit of fractionation in reducing hypoxia in tumors?
Limiting damage to normal tissue
What is the approximate proportion of hypoxic cells in an untreated tumor, as observed by Van Putten and Kallman in mouse sarcoma?
14%
What is the primary advantage of using hypoxia cell sensitizers over increasing oxygen delivery to tumor cells?
Sensitizers are more metabolically stable than O2
Test your understanding of the oxygen effect, reoxygenation, and its role in radiation biology. Covers the mechanism of oxygen effect, oxygen enhancement ratio, and factors affecting OER, as well as hypoxia and its relation to chemoresistance and tumor progression.
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