radiobiology IV

Question 1

what is ionizing radiation?

Answer 1

type of radiation that can detach electrons from, or ionize, other atoms as they pass through matter
-electromagnetic radiation: high energy ultraviolet radiation, x-rays, gamma rays
-particles radiation: alpha particle, beta particles, neutrons

Question 2

what is the linear-quadratic model (L-Q)?

Answer 2

-grey=quadratic
-dashed= linear
-there is a point when D=alpha/beta
-quadratic is double hit and linear is single hit
-beta is the curved line in the first graph and has more cell killing

Question 3

what are the graphs of aberrations vs cell death dose dependence?

Answer 3

P53=major regulator of cell apoptosis
-wildtype show slightly more killing per aberration

Question 4

when is the linear-quadratic model used?

Answer 4

-exchange type chromosome aberrations as a result of 2 breaks (ex: lethal dicentric, acentric rings, anaphase bridges). Continuously bending curve that does not straighten
-the components of a cell killing that are proportional to dose and to the square of the dose are equal if dose is D=alpha/beta

Question 5

what damage can occur?

Answer 5

-lethal=majority is killed
-sub-lethal= fast growers can recover and slow growers need days
-potentially lethal= we all deal with on a daily basis

Question 6

what is the effective dose-survival curve for multi-fraction regimen?

Answer 6

-several fractions (shoulders) spaced enough to repair sub-lethal damage; thus preventing the quadratic killing or bent curve and restricting the linear (ex: exponential curve)
-D10: dose required to kill 1 decade or 90% of the cell population (or 10% surviving fraction)
-Do: dose required to kill 63% of the cell population (or 37% surviving fraction)

-1 fraction=single exposure
-multiple fractions, spaced equally, doses at different time
-dose increases as we go down Do’s, green line shifts to the right

Question 7

what is the effect of dose fractionation?

Answer 7

-shoulder determines the repair part element of the cell

Question 8

what are the ionizing potentials of radiation?

Answer 8

-densely ionizing radiation (high LET ex, linear transfer energy) (ex:alpha particles, low energy neutrons)
-sparsely ionizing radiation (low LET) (ex; x-rays)

Question 9

what is the cell kill potential of each radiation?

Answer 9

sparsely
-low doses of x-rays produce a comparatively low (shallow slope of the initial part of the cell survival curve), linear killing potential or a decreased in cell survival
-a few higher grays of x-ray dose causes a bend and at much higher doses there is re-established of the exponential killing potential

densely
-alpha particles, low energy neutrons show an exponential killing potential or loss of cell survival

Question 10

what is the multi-target model?

Answer 10

Question 11

what is the summary of how multi-target and L-Q models are similar?

Answer 11

Question 12

what is the refresh of the L-Q and multi-target model?

Answer 12

Question 13

what is heterogeneity in dose response?

Answer 13

-not all cell lines or tumor are identical (proliferating vs non-proliferating tissues)
-even if they are, they are usually of different size
-and if they are, not all tumor are equally clonogenic

Question 14

how can different types of cell response to radiation?

Answer 14

-survival curves for asynchronous cultures of several lines of human and rodent origin
-note the wide range of radiosensitivity (size of shoulder) between EMT6 cells, the most resistant and two human neuroblastoma cell lines
-the cell survival curve for mitotic cells is very steep, and there is little difference in radiosensitivity for cell lines