1) If a cell line exhibiting a strictly exponential radiation survival curve is exposed to a dose that produces an average of one lethal “hit” per cell, the surviving fraction after this dose would be approximately:
A. 0.01
B. 0.1
C. 0.37
D. 0.5
E. 0.9
2) The α/β ratio is equal to the:
A. surviving fraction at which the amount of cell killing caused by the induction of irreparable damage equals the amount of cell killing caused by the accumulation of sublethal damage
B. optimal fraction size to use in a fractionated regimen
C. dose below which a further decrease in fraction size will not affect the surviving fraction for a particular total dose
D. Dq
E. dose at which the αD component of cell kill is equal to the βD2 contribution to cell killing
3) A cell line characterized by a high apoptotic index after irradiation will:
A. have a relatively high α/β ratio
B. show substantial sparing with dose fractionation
C. be characterized by a large survival curve shoulder
D. have a much greater D0 than D37
E. be relatively resistant to high LET radiation
4) Cells from individuals diagnosed with which of the following diseases would be expected to display a X-ray survival curve with the largest D0?
A. Nijmegen breakage syndrome
B. LIG4 syndrome
C. ATR-Seckel syndrome
D. Xeroderma pigmentosum
E. Ataxia telangiectasia
5) Which of the following statements is CORRECT concerning cell survival curve analysis?
A. The β parameter generally increases as the radiation dose rate decreases.
B. The inverse of the Dq corresponds to the final slope of the survival curve.
C. The extrapolation number, n, of a survival curve increases with increasing LET of the radiation.
D. D0 is a measure of the incremental increase in cell survival when a given dose is fractionated.
E. If n = 1, then D37 = D0
6) When the dose rate at which cells are irradiated increases from 0.01 Gy/min to 1 Gy/min for X-rays, which of the following changes occurs in survival curve parameters?
A. n decreases
B. D10 increases
C. D0 increases
D. α/β increases
E. β increases
7) Reducing the dose rate at which a continuous γ-irradiation is delivered affects its cell killing efficacy due to several different biological processes. Which of the following pairs of dose-rate ranges and biological factors primarily responsible for the changes in cell killing efficacy for cells as the dose-rate changes over that range, is INCORRECT? (Assume that the cells are exposed to a total dose of 6 Gy)
A. 10 - 1 Gy/min : DNA repair
B. 1 - 0.1 Gy/min : cellular repair
C. 0.1 - 0.01 Gy/min : redistribution
D. 0.01 - 0.001 Gy/min : repopulation
8) The survival curve for a cell population irradiated with a form of high LET radiation is characterized by a D10 of 3 Gy. For a starting population of 108 cells, approximately how many cells will survive when a single dose of 18 Gy is given?
A. 100
B. 101
C. 102
D. 103
E. 104
9) A total dose of 12 Gy of X-rays delivered in 3 Gy fractions reduces cell survival to 10-4. Assuming that cell killing can be modeled using the equation S = e-αD, what dose would be required to reduce the surviving fraction to 10-6?
A. 9 Gy
B. 18 Gy
C. 24 Gy
D. 36 Gy
E. 72 Gy
10) In an attempt to generate a radiation survival curve for a new cell line, four Petri dishes were seeded with 102, 103, 104 and 105 cells, and X-irradiated with 0, 3, 6 and 9 Gy, respectively. At the end of a two-week incubation period, a total of 40 colonies was counted on each dish. Which one of the following statements is TRUE?
A. The D0 for this cell line is 3 Gy.
B. The survival curve for this cell line is exponential.
C. The n and Dq values for this survival curve are large.
D. The cell surviving fraction after a dose of 3 Gy is 0.04.
11) Which one of the following statements concerning the linear-quadratic model of cell killing is true?
A. High LET radiation generally produces cell survival curves characterized by low α/β ratios.
B. The survival curves for cells derived from people diagnosed with ataxia telangiectasia have unusually small α values.
C. The radioresistance of hypoxic cells results from a 3-fold increase in the β value.
D. The α/β ratio for a cell poulation can be determined without the determination of a full cell survival curve.
E. Inhibiting repair of sublethal damage would selectively increase the α parameter for the survival curve.
12) What is the approximate eD10 (effective D10) for a particular cell line if the eD0 is 4 Gy?
A. 2 Gy
B. 4 Gy
C. 6 Gy
D. 9 Gy
E. 12 Gy
13) Compared to early responding tissues, late responding tissues typically:
A. initiate compensatory proliferation during the course of radiotherapy
B. exhibit higher α/β ratios
C. have a greater neutron RBE for fractionated irradiations
D. have dose response curves that are approximately exponential
E. develop greater injury when an X-ray dose is delivered as a series of small fractions, rather than as a few, large fractions
14) Concerning RBE, OER and LET, which of the following statements is TRUE?
A. Maximum cell killing per dose delivered occurs at an LET corresponding to approximately 1000 keV/μm.
B. RBE changes the most over the LET range of 0.1 to 10 keV/μm.
C. The relationship between OER and LET is bell-shaped.
D. RBE decreases with increasing LET above about 100 keV/μm.
E. OER increases with LET.
15) High LET radiation damage, compared with low LET radiation damage:
A. is reduced in the presence of sulfhydryl compounds
B. shows more potentially lethal damage recovery
C. exhibits a greater OER
D. is less subject to split-dose recovery
E. experiences greater sparing with irradiation at a low dose rate
16) Which of the following statements concerning RBE is CORRECT? The RBE:
A. is lower for neutrons than for protons over the therapeutic energy range
B. for high LET particles is greater for hypoxic cells than for oxygenated cells of the same type
C. for carbon ions is diminished when delivered in several fractions rather than as a single dose
D. for heavy charged particles is greatest at the beginning of the particle tracks
17) Which of the following pairs of radiation type and approximate LET value is CORRECT?
A. 150 MeV protons – 0.5 keV/μm
B. 2 GeV Fe ions – 50 keV/μm
C. 60Co γ-rays – 10 keV/μm
D. 2.5 MeV α-particles – 5 keV/μm
E. 250 kV X-rays – 30 keV/μm
18) What is the approximate maximum diffusion distance of oxygen in a respiring tissue?
A. 5 nm
B. 15 μm
C. 70 μm
D. 400 μm
E. 2.6 mm
19) A dose of 10 Gy of X-rays reduces the tumor cell surviving fraction to 0.004 in an animal irradiated while breathing air, and to 0.1 in an animal irradiated under nitrogen. An estimate of the hypoxic fraction for this tumor in the air breathing mice would be:
A. 0.04
B. 0.4
C. 2.5
D. 10
E. 25
20) The Km for radiosensitization by oxygen (the oxygen concentration at which cellular radiosensitivity is halfway between the fully aerobic and fully hypoxic response) corresponds to an oxygen concentration of approximately:
A. 0.02%
B. 0.5%
C. 3%
D. 15%
E. 30%
21) The most dramatic change in radiation sensitivity occurs over which of the following ranges of oxygen tension (in units of mm Hg or Torr)?
A. 0-30
B. 30-60
C. 60-100
D. 100-250
E. 250-500
22) Which of the following statements concerning oxygen effects is TRUE?
A. OER values obtained for high energy protons used in radiotherapy are similar to those produced for X-rays.
B. During irradiation, a partial oxygen pressure of about 30% is required to produce full radiosensitization.
C. The OER is defined as the ratio of the surviving fraction of cells irradiated with a particular X-ray dose under hypoxic conditions to the surviving fraction of cells irradiated with the same dose under aerated conditions.
D. Tumors are thought to contain regions of both acute and chronic hypoxia, however only chronically hypoxic cells can reoxygenate.
E. The oxygen effect is principally a manifestation of the increased number of ionizations produced in fully aerated compared with hypoxic cells.
23) Which of the following statements is CORRECT concerning the effect of oxygen on cells irradiated with X-rays?
A. Fixation of radiation-induced free radical damage by oxygen results in decreased cell killing because oxygen stimulates DNA repair.
B. The OER decreases with increasing radiation dose.
C. Oxygen produces full radiosensitization provided it is present within 10 seconds after irradiation.
D. Cells irradiated under fully aerobic conditions are more radioresistant than cells irradiated under hypoxic conditions.
E. Oxygen acts as a radiosensitizer in plant cells.
24) For single, large radiation doses, the ratio of the OER for X-rays divided by the OER for 15 MeV neutrons is approximately:
A. 0.3
B. 1
C. 2
D. 4
E. 10
25) Which of the following statements concerning the effect of oxygen is TRUE?
A. Oxygen acts as a radiosensitizer because it inhibits DNA repair.
B. The OER and RBE both increase with increasing LET.
C. Based on pO2 microelectrode measurements, few human tumors contain regions of hypoxia.
D. At an oxygen concentration of about 3%, the radiosensitivity of cells is halfway between a fully aerobic and fully hypoxic response.
E. Exposure of cells to hypoxia may stimulate gene transcription.
