Radiation Flashcards
Cells in this phase(s) are most resistant to radiation
Late S-phase
Cells in this phase(s) are most sensitive to radiation
Late G2 and M phases
Which are more sensitive to radiation, normoxic or hypoxic cells?
Normoxic cells are up to 3x more sensitive to XRT than hypoxic
What does 1 Gy equal?
1 Gy = one joule absorbed per kilogram tissue
Photons interact w tissue primarily by which effect?
The Compton effect
The Compton effect produces high energy electrons which have 2 effects
- cause ionization events either to critical molecules (direct effect) or
- from water molecules located w/in nanometers of critical molecules (indirect effect)
Hyperfractionated radiation is what?
Hyperfractionated radiation: dose per fraction is reduced and total dose is increased
Accelerated fraction radiation is what?
Accelerated fraction radiation: overall time of treatment is reduced but dose per fraction and total dose are unchanged
Hypofractionated radiation is what?
Hypofractionated radiation: administration of high doses per fraction given in a small # of fractions to a lower dose
Name the 4 R’s of radiation therapy
o Repair of DNA damage
o Redistribution of cells in the cell cycle
o Reoxygenation of tumor cells
o Repopulation of tumor and normal tissues
Describe accelerated repopulation.
Accelerated Repopulation:
When radiation treatment lasts longer than 4 weeks, tumors may repopulate faster than otherwise.
What are the 4 criteria for radiation-induced neoplasia?
4 Criteria for Radiation-Induced Neoplasia:
- Malignancy must arise in radiation field
- Sufficient latency must have elapsed bt tx & tumor (usu > 1y)
- Original and new tumors must be different
- Tissue in which new tumor forms must have been normal tissue before RT exposure
The sensitivity of a tumor/tissue to radiation is shown as a graph of what?
The sensitivity of a tumor/tissue to radiation is shown as a graph of the radiation dose (D) vs the surviving fraction (S)
- S (D) = e-(aD+BD2)
- S = surviving fraction at dose D
- Alpha (a) and beta (B) are constants that vary according to the tissue with
- “a” corresponding to the cell death that increases linearly with dose and
- “B” corresponding to cell death that increases in proportion to the square of the dose (aka the quadratic component)
What is the alpha beta ratio?
The a/B ratio is a useful # that is the dose in Gy when cell kill from the linear and quadratic components of the cell survival curve is equal
• Cells w a higher a/B ratio have a more linear appearance on a log scale
• Cells w a lower a/B ratio have a parabolic shape
Do most early-responding tissues have a HIGH or a LOW a/B ratio?
Most EARLY responding tissues/tumors have a HIGH a/B ratio (more linear curve)
