Radiation Physics & Radiobiology Flashcards
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Read the first 6 Radiation Physics & Radiobiology flashcards as text
Which effect describes the increased radiosensitivity of cells in the presence of molecular oxygen?
Answer: Oxygen effect
The oxygen effect refers to the 2–3 fold increase in radiation sensitivity when cells are well-oxygenated compared to hypoxic conditions, because oxygen fixes radiation-induced free radical damage.
In conventional fractionation for radiation therapy in the US, the standard daily fraction size is:
Answer: 1.8–2.0 Gy
Conventional fractionation uses 1.8–2.0 Gy per fraction, delivered once daily, five days per week, balancing tumor control with normal tissue sparing.
Which quantity describes the rate of energy deposition by a charged particle per unit path length?
Answer: Linear Energy Transfer (LET)
LET (keV/μm) describes the energy deposited per unit length along a charged particle's track and determines the biological effectiveness of different radiation types.
The 'Four Rs of Radiobiology' include repair, reassortment, repopulation, and:
Answer: Reoxygenation
Reoxygenation is the fourth R, where hypoxic tumor cells become oxygenated between fractions as adjacent cells die, increasing overall radiosensitivity.
Which cell cycle phase is most radiosensitive?
Answer: M phase (mitosis) and G2 phase
Cells are most radiosensitive in M and late G2 phases because DNA repair mechanisms are suppressed and chromosomal aberrations are most lethal at this stage.
Tissue weighting factors (wT) in radiation protection are used to calculate:
Answer: Effective dose
Tissue weighting factors account for the relative radiosensitivity of different organs and are used with equivalent dose to calculate effective dose (measured in Sieverts).