1) The tolerance doses for the kidney and lung are highly dependent on the volume of tissue irradiated. Both of these normal tissues are very sensitive to irradiation of their entire volume. In contrast, small volumes can be irradiated to high doses without loss of function. All of the following explanations are consistent with this observation, EXCEPT, that:
A. both organs have considerable reserve capacity
B. these organs have functional subunits arranged in series
C. a functional deficit is not observed in these organs until a critical number of functional subunits are inactivated by exposure to radiation
D. above a certain threshold dose, radiation injury is usually expressed as a graded response rather than as an all or nothing response
2) The influence of field size on the severity of radiation reactions in normal tissues is a reflection of the ability of surviving clonogens to migrate from the surrounding tissue into the irradiated volume. With regard to this phenomenon, which of the following statements is FALSE?
A. Tissues comprised of structually defined functional subunits arranged in parallel are best able to take advantage of the migration of clonogens from outside the irradiation field.
B. Tissues with a high capacity for clonogen migration exhibit a decrease in tolerance dose with increasing field size above about 1 cm.
C. The kidney is an example of an organ tissue in which the FSUs are anatomically and structurally defined.
D. Examples of tissues with a high clonogen migratory capacity include intestinal epithelium, spinal cord and skin.
3) Assuming that there is no intrinsic difference in the radiosensitivities of tumor versus normal cells other than the presence of hypoxic cells in the tumor, which of the following properties of a novel drug in combination with fractionated radiotherapy would improve the therapeutic ratio?
A. stimulation of repair in hypoxic cells
B. inhibition of reoxygenation
C. radioprotection of aerobic cells
D. inhibition of repair in aerobic cells
E. stimulation of repopulation in hypoxic cells
4) A 1 cm-diameter tumor that contains 107 clonogenic cells is irradiated with daily dose fractions of 1.8 Gy. The effective dose response curve has been determined and is exponential with a D10 of 8 Gy. What total dose will correspond to the TCD90 (90% probability of tumor control), assuming no cell proliferation between dose fractions?
A. 32 Gy
B. 40 Gy
C. 48 Gy
D. 56 Gy
E. 64 Gy
5) Based on the information presented in the previous question, what would be the TCD90 if a surgical excision removed 99% of the tumor clonogens prior to radiotherapy (assume that the surgery did not otherwise affect the growth fraction of the tumor).
A. 24 Gy
B. 32 Gy
C. 40 Gy
D. 48 Gy
E. 56 Gy
6) Which of the following statements is TRUE concerning tumor control probability?
A. For a series of tumors that contain, on average, one surviving clonogen each after the completion of radiotherapy, the tumor control rate would be zero.
B. On the linear portion of a sigmoid dose response curve for tumor control, each 2% increase in tumor control corresponds to approximately one additional log of tumor cell kill.
C. The probability of curing a large group of patients with identical tumors containing the same number of clonogens is governed by Poisson statistics.
D. The time between dose fractions has little impact on tumor control probability.
E. The TCD50 will roughly double for each doubling of the diameter of a particular type of tumor.
7) For a tumor that requires 18 days to double its diameter, what is the approximate cell cycle time of its constituent cells (assume no cell loss and that all cells are actively dividing)?
A. 6 days
B. 9 days
C. 12 days
D. 15 days
E. 18 days
8) For a standard course of radiotherapy, which of the following properties of a tumor would NOT be expected to adversely affect tumor control?
A. low SF2
B. short Tpot
C. slow reoxygenation
D. large number of tumor clonogens
E. early onset of repopulation
9) Which of the following represents a possible mechanism by which a novel compound could increase tumor response to fractionated radiotherapy if applied prior to each dose fraction?
A. prevents cell cycle redistribution
B. causes G2 phase arrest
C. inhibits reoxygenation
D. radioprotects normal tissues
E. stimulates DNA repair
10) All of the following could affect the slope of a tumor control probability (TCP) curve, EXCEPT:
A. tumor size
B. tumor oxygenation
C. intrinsic tumor cell radiosensitivity
D. volume of normal tissue in the radiation field
E. histopathological tumor type and grade
11) A new agent that can alter blood flow is being assessed for its potential clinical usefulness in combination with radiation therapy. Which of the following effects on blood flow would be expected to lead to a therapeutic gain and thus lead to a potentially useful agent in the clinic?
A. increased in both tumors and normal tissues
B. increased in normal tissues but decreased in tumors
C. decreased in normal tissues and in tumors
D. not altered in normal tissue but decreased in tumors
E. increased in normal tissues and not altered in tumors
12) Normal tissue regeneration/repopulation:
A. occurs in late responding normal tissues during the course of a standard radiotherapy protocol, e.g., within about 6 weeks.
B. occurs in early responding normal tissues during the course of a standard radiotherapy protocol.
C. interferes with reoxygenation.
D. is the reason that prolonging overall treatment time spares late responding normal tissues, such as lung.
E. occurs at the same rate after irradiation in acutely responding tissues such as skin, and in late responding tissues, such as kidney.
13) Which of the following total doses, given as 1.5 Gy fractions, is approximately equivalent to a conventional schedule of 30 fractions of 2 Gy for late normal tissue reactions? Assume the α/β ratio is equal to 3 Gy.
A. 53 Gy
B. 60 Gy
C. 67 Gy
D. 75 Gy
E. 81 Gy
14) Assuming no difference in overall treatment time, which of the following statements is CORRECT concerning isoeffect curves?
A. Isoeffect curves for late-responding normal tissues are usually shallower than for early-responding tissues.
B. Tissues with a greater repair capacity have steeper isoeffect curves.
C. Increased proliferation of the critical cell population during the course of radiotherapy will decrease the slope of the isoeffect curve.
D. Tissues with steep isoeffect curves have high α/β ratios.
E. Isoeffect curves for tumor control will be steeper if significant reoxygenation occurs between dose fractions.
15) A total dose of 70 Gy delivered in 2 Gy fractions is used to treat a particular tumor. Assume that the tumor is characterized by an α/β ratio of 2 Gy and a Tpot of 30 days. For the dose-limiting normal tissue, the α/β ratio is 4 Gy. Which one of the following treatment schedules would most likely yield the highest therapeutic ratio?
A. standard fractionation
B. accelerated treatment
C. split-course treatment
D. hyperfractionation
E. hypofractionation
16) Which of the following fractionation schedules would likely produce the highest incidence of late normal tissue toxicity? (Assume α/β = 2 Gy for the critical normal tissue injury)
A. 20 Gy in 4 fractions over 1 week
B. 24 Gy in 6 fractions over 2 weeks
C. 45 Gy in 15 fractions over 3 weeks
D. 50 Gy in 25 fractions over 5 weeks
E. 60 Gy in 60 fractions over 6 weeks
17) Compared with a conventional fractionation protocol, accelerated treatment:
A. typically involves increasing the total dose
B. permits greater time for reoxygenation of hypoxic cells
C. reduces the incidence of early reactions
D. limits the amount of tumor cell repopulation taking place during the course of treatment
E. reduces the incidence of late effects
18) A standard treatment protocol for a particular type of cancer is 60 Gy delivered in once-daily 2 Gy fractions. If the fraction size is decreased to 1.3 Gy in an attempt to reduce the incidence of late effects, approximately what total dose should be delivered to maintain the same level of tumor control? (Assume an equal effect per fraction, no repopulation, and an α/β ratio for the tumor of 10 Gy.)
A. 64 Gy
B. 68 Gy
C. 72 Gy
D. 76 Gy
E. 80 Gy
19) One goal of hyperfractionation is to:
A. decrease toxicity to early-responding tissues
B. deliver the total radiation dose in a shorter overall time
C. reduce the number of fractions used
D. prevent tumor cell repopulation
E. decrease the incidence of late effects while maintaining or improving tumor control
20) Which of the following statements is TRUE concerning experimental support for the hypothesis that late-responding tissues have lower α/β ratios than early-responding tissues?
A. Neutron RBEs are greater for early effects than for late effects.
B. The use of hyperfractionation results in an increased severity of late effects if the dose is titrated to produce equal early effects.
C. Isoeffect curves are steeper for late effects than for early effects.
D. When a treatment plan is changed from many small doses to a few large fractions and the total dose is titrated to produce equal early effects, late effects tend to be less severe.
E. In clinical trials using hyperfractionation, concurrent treatment with drugs that inhibit repair of sublethal damage produce more early complications than late ones.
21) A clinician changes from the usual fractionation schedule of 1.8 Gy given once per day to an accelerated treatment using 1.6 Gy fractions delivered twice per day. In order to avoid the possibility of reduced normal tissue tolerance due to incomplete repair, what should be the minimum inter-fraction interval for the accelerated schedule?
A. 0.5-1 hour
B. 1-2 hours
C. 2-3 hours
D. 3-6 hours
E. 6-12 hours
22) A conventional treatment for a particular type of tumor is 25 fractions of 2 Gy delivered once per day. A hyperfractionated regimen is proposed that would consist of 1.2 Gy fractions delivered twice per day. What would be the approximate therapeutic gain in changing from the standard to hyperfractionated schedule if both were designed to produce the same probability of late complications? (Assume that there is no tumor cell repopulation during treatment, full repair of sublethal damage occurs, the tumor has an α/β ratio of 10 Gy and the normal tissue has an α/β ratio of 2 Gy.)
A. 0.8
B. 1.0
C. 1.2
D. 1.4
E. 1.6
23) All of the following processes could be involved in the increased efficacy of radiation dose fractionation in the clinic, EXCEPT:
A. sublethal damage repair in normal tissues between fractions.
B. reoxygenation in tumors.
C. redistribution/reassortment of cells in tumors.
D. repopulation of cells in normal tissues.
E. potentially lethal damage repair in tumors.
24) Which one of the following pairs of tumor or normal tissue with an α/β ratio is INCORRECT?
A. head and neck carcinoma – 8-10 Gy
B. early effects in the jejunum – 6-10 Gy
C. cervical carcinoma – 3 Gy
D. lung fibrosis – 3 Gy
E. myelopathy – 2-3 Gy
25) Which of the following radiobiological processes contributes to the inverse dose rate effect?
A. repair of sublethal damage
B. accumulation of cells in S phase
C. proliferation
D. repair of potentially lethal damage
E. redistribution
26) Which one of the following statements concerning brachytherapy is TRUE?
A. The linear-quadratic model predicts that high dose rate brachytherapy should produce therapeutic gain relative to low dose rate treatment for a tumor with a high α/β ratio and a dose limiting normal tissue with a low α/β ratio.
B. For breast cancer patients treated with 192Ir implants to the same total dose, the recurrence rate should decrease with increasing dose rate of the source.
C. One advantage associated with the use of 125I and 103Pd sources for permanent interstitial implants is the relatively high energy (>100 keV) of the photons emitted.
D. It would be preferable to treat a tumor characterized by a small α/β ratio with a low, as opposed to a high, dose rate implant.
E. For the same total dose, treating a patient with head and neck cancer using an 192Ir implant delivering radiation at a dose rate lower than 0.5 Gy/hour should yield better tumor control than for a patient whose implant delivered radiation at a dose rate greater than 0.5 Gy/hour.
27) Which one of the following statements concerning radiolabeled immunoglobin therapy is FALSE?
A. One disadvantage associated with the use of 90Y-labeled antibodies is that the relatively low energy (<100keV), short range β-particles, emitted limit the so-called “crossfire effect”.
B. Radiation safety is an important issue with the use of 131I-labeled compounds because this isotope emits γ-rays that may pass through the patient.
C. Antibody-labeling with 111In has proved useful for imaging.
D. The dose-limiting organ associated with the use of Baxxar/tositumomab is the bone marrow.
E. Both Zevalin and Bexxar target CD20.
