Questions for RHP 483/583 Final
Joe Fisher
Winter 2008
Fisher, J
11
48
85
122
160
11. Why is the biological effect from high-LET radiations essentially non-impacted by dose rate?
ANS: Because the cell repair process is not significant at higher LET. Thus, the dose rate doesn't
matter. In low-LET radiations, we have a cell repair process so dose rate including fractionating
matters.
Source: Slides -- Linear Energy Transfer (LET), Relative Biological Effectiveness (RBE) and Radio
sensitivity through the Mitotic Cycle (Chapters 4 & 7), slide number 19.
48. Why is it recommended that persons exposed to high doses (>5 Gy) be sterilized and be put in a
sterile room with sterile food?
ANS: To reduce the risk of infection."In some countries, isolation and barrier nursing -- that is,
isolation from others so that they do not come in contact with possible infections while their blood
count is low -- is recommended".
Source: Slides -- Acute Effects of Total-Body Irradiation and Cataracts and Radiation Exposure
(Chapters 8 & 13), slide number 24. Textbook -- Radiobiology for the Radiologist, 6th edition, Hall and
Giaccia, page 124.
85 (17). Measurement of which one of the following chromosomal aberrations in peripheral blood
lymphocytes many years following a putative whole body radiation exposure would provide the best
estimate as to the dose received?
A. reciprocal translocations
B. rings
C. dicentrics
D. chromosome breaks
E. chromatid breaks
ANS: A -- reciprocal translocations, but note referred in Hall as "Symmetric Translocations".
Source: Slides -- Basic Cell Structure, Cycle and Division - and - DNA, Strand Breaks and
Chromosomal Aberrations (Chapter 2), slide numbers 72. Textbook -- Radiobiology for the
Radiologist, 6th edition, Hall and Giaccia, page 26.
122 (54). Which of the following statements concerning tumor cell cycle kinetic parameters is true?
A. Values for TS and MI are required in order to calculate Tpot.
B. Tpot can be estimated from a single tumor biopsy taken approximately 48
hours after the administration of either bromo- or iododeoxyuridine.
C. TS can be estimated from the time required for the earliest S phase cells in a
population at the time of labeling to progress into G2.
D. Randomized, prospective clinical trials have confirmed that tumors with short
Tpot values are the best candidates for accelerated fractionation.
E. Tumors with long Tpot’s are most likely to benefit from hyperfractionation.
ANS: C -- TS can be estimated from the time required for the earliest S phase cells in a population at the
time of labeling to progress into G2. (Source: Hall page 370 "... midway between the characteristic of
G1 and that of G2, Ts would be simply 12 hours". )
Source: A: Tpot = λ * Ts / LI (page 370 Hall), B: An estimate of Tpot can be made by flow cytometry
from a single biopsy specimen taken 4 to 8 hours after the injection of a tracer amount of a thymidine
analogue (bromodeoxyuridine or iododeoxyurine). (page 370 Hall) C: The S period (Ts) is given
approximately by the width of the first peak, from the 50% level on the ascending portion of the wave
to the corresponding point on the descending curve. (page 367 Hall). D: Fast (Tpot < 4 days), For fast
growing tumors, accelerated treatment results in substantially better local control. (Slides -- Tumor
Growth Kinetics and Time, Dose and Fractionation in Radiotherapy (Chapters 21 & 22) slide number
29). E: For slow growing tumors, no apparent difference between results of conventional and
accelerated treatments. (Slides -- Tumor Growth Kinetics and Time, Dose and Fractionation in
Radiotherapy (Chapters 21 & 22) slide number 29).
160 (92). Radiation-induced deterministic effects:
A. are rarely produced by doses in the range used in radiotherapy
B. generally have long latent periods that are independent of dose
C. may be produced at any dose, however small
D. vary in severity in a dose-dependent manner
E. include genetic effects
ANS: D -- vary in severity in a dose-dependent manner.
Source: Textbook -- Radiobiology for the Radiologist, 6th edition, Hall and Giaccia, page 135.