8 Principles of Radiation Oncology

Hak Choy and Aaron Laine

QUESTIONS

Each of the numbered items below is followed by lettered answers. Select the ONE lettered answer that is BEST in each case unless instructed otherwise.

Question 8.1 Which of the following describes the specific pathways for the repair of double-stranded DNA breaks?

A. The repair may be by homologous recombination (HR) or nonhomologous end-joining (NHEJ) pathway.

B. The HR repair pathway functions by degrading the single strand at each side of the break and then annealing the two ends.

C. The NHEJ pathway functions by replicating the missing genetic information from the homologous DNA template.

D. NHEJ is a minor component of mechanism for repair of double-stranded DNA breaks in mammalian cells.

Question 8.2 Which of the following is TRUE about ionizing events in tissues caused by x-rays?

A. Radiation dose describes the quantity of energy deposited.

B. The direct effect of radiation is primarily due to injury to cellular membranes.

C. The relative biological effectiveness (RBE) describes the ratio of doses required to give the same amount of killing under normoxic and hypoxic conditions.

D. Indirect action of ionizing radiation where hydroxyl radicals damage target tissues is commonly seen.

Question 8.3 Which of the following statements describes the DNA damage/repair process associated with ionizing radiation?

A. Single-stranded breaks of the DNA are thought to represent the lethal event.

B. All of the radiation-induced, double-stranded breaks are rejoined in cells within 2 hours.

C. In mammalian cells, choice of repair can be biased by phase of the cell cycle and by abundance of repetitive DNA.

D. Nonhomologous end-joining (NHEJ) is effective in rejoining DNA double-strand break because it is an error free process.

Question 8.4 Which of the following statements describes the dose-related cellular response to radiation?

A. In mammalian cells, there is generally a linear and quadratic relationship between the cell killing and the dose given.

B. The term “D₀” describes the quasi-threshold dose, defining the width of the shoulder

C. Densely ionizing radiation leads to an extended shoulder on the survival curve.

D. In general, postirradiation conditions that accelerate the cell division are the ones most favorable to repair of potentially lethal damage.

Question 8.5 Which of the following statements is TRUE regarding independent events (4 R’s) that occur during fractionated radiotherapy?

A. Repopulation refers to spontaneous repopulation and induced cell proliferation or recruitment of cells after irradiation.

B. Repair explains the linear portion of the radiation survival curve showing that cells can repair some of the radiation damage.

C. Redistribution explains migration of cells away from an irradiation source.

D. Reoxygenation describes the decrease of tumor oxygen levels during fractionated radiation.

Question 8.6 Which of the following acute effects are related to radiation-induced cell death?

A. Cystitis

B. Esophagitis

C. Dermatitis

D. Proctitis

E. All of the above

Question 8.7 The abscopal effect of radiation is

A. Attributed to the activation of antigen and cytokine release.

B. Commonly seen because immune system evasion by cancer cells is rarely present.

C. Seen more frequently with lower doses and greater fractions.

D. Activation of the humoral immune response.

E. Double-stranded breaks in DNA in nonirradiated cells

Question 8.8 Which of the following best describes the modern linear accelerator?

A. A modern linear accelerator (LINAC) can deliver energies up to 1 MeV.

B. Generate Bremsstrahlung x-rays by bombarding a target with high-energy electrons

C. Primarily uses ⁶⁰Cobalt which is always “on” and must be kept in a shielded position until the beam is needed for treatment.

D. The focal point of the gantry’s rotation is called the field edge.

Question 8.9 Which of the following statements describes the role of oxygen in radiation effects?

A. A greater dose of radiation is required for cell killing in an oxic condition compared with a hypoxic condition.

B. A randomized trial showed that epoetin b improved survival in patients with head and neck cancer.

C. Oxygen need not be present at the time of irradiation for oxygen enhancement of radiotherapy to occur.

D. Hyperbaric oxygen often shows a dramatic increase in curability with standard fractionated radiotherapy.

E. The oxygen enhancement ratio (OER) has more relevance on the exponential portion of the cell survival curve.

Question 8.10 Which of the following best describes the concept of altered fractionation?

A. Accelerated fractionation does not reduce the overall treatment time.

B. Hyperfractionation refers to a radiotherapy schedule that uses multiple daily treatments more than 6 hours apart with reduced fraction size and increased number of fractions.

C. Standard fractionation is commonly defined as 3 to 5 Gy/day

D. The goal of accelerated fractionation is to complete radiation before accelerated reoxygenation occurs

Question 8.11 Which of the following statements regarding interaction of chemotherapy and radiation therapy is TRUE?

A. Rationale for combining radiation therapy with radiosensitizing chemotherapy is primarily to confer an additive effect.

B. Gemcitabine is a potent radiosensitizer and special consideration is not required when administered with radiation for treatment of lung and head and neck cancers.

C. Paclitaxel radiosensitizing effect to due to G1 cell-cycle arrest

D. Mechanism of radiosensitization by cisplatin may be due to its ability to inhibit DNA repair of radiation induced DNA double-strand breaks.

Question 8.12 Which of the following statements is TRUE regarding intensity-modulated radiation therapy (IMRT)?

A. It is an uncomplicated method to deliver radiation in a nonconformal manner.

B. Is delivered only using a limited number of beam orientations.

C. Optimization of each individual beamlet can create sharp dose gradients.

D. Does not take into account organs at risk (OARs) when developing the treatment plan.

Question 8.13 Which of the following statements best describes the tissue effects from radiation?

A. Early or acute effects typically occur within months after irradiation.

B. Large α/β> ratio has a small “shoulder” in the low-dose portion.

C. The frequencies of late effects depend strongly on radiation fraction size.

D. Typical human tumors and early-responding normal tissues have a small α/β ratio.

Question 8.14 Which of the following statements describes of the interaction of x-rays with biologic material?

A. In modern treatment with greater than 4 MeV photons, photoelectric effect dominates the interaction.

B. In Compton scattering, an incoming x-ray transfers all its energy to an inner orbit electron, which is ejected from the atom. A photon is produced as an outer shell electron fills the vacant hole.

C. In photoelectric effect, energy from the x-ray is both absorbed and scattered. The photon emerges with reduced energy and a change in direction.

D. In pair production, an electron and a positron are produced.

Question 8.15 Which of the following statements describes the depth dose characteristics of radiation?

A. Higher-energy photons deposit more dose to the skin surface.

B. For a given energy, electrons generally penetrate deeper in tissue compared with photons.

C. Electron beams deposit less dose to the skin surface as the incident electron energy increases.

D. Depth of maximum dose increases as the energy of the incident beam increases.

Question 8.16 Which of the following statements is TRUE regarding brachytherapy?

A. Isotopes with properties of long half-lives and high energy are typically used for permanent implants.

B. Brachytherapy refers to placement of radioactive sources next to or inside the tumor, or within body or surgical cavities.

C. The fluence drops in intensity as 1 over the distance from the source.

D. A potential advantage of brachytherapy is its ability to produce conformal treatments with high normal tissue dose.

Question 8.17 Which of the following can be a subacute toxicity from radiation therapy?

A. Pneumonitis

B. Myelitis.

C. Brain necrosis.

D. B and C.

Question 8.18 Which of the following best describes the treatment planning process?

A. At the time of image acquisition for planning, tumor motion caused by respiration must be determined.

B. Immobilization is not important because it does not add to accuracy.

C. Three-dimensional dose distribution in each patient is easily measured.

D. Intensity-modulated radiation therapy (IMRT) cannot control the shaping of the dose distribution.

Question 8.19 Which of the following is TRUE regarding charged particle beams?

A. Charged particle beam therapy includes photon-based therapy.

B. Protons have shown to confer a definite clinical benefit over photon-based therapies for most clinical cancer applications.

C. Ability of charged particles to stop at a given depth gives it a potential advantage for treatment of tumors in close proximity to critical structures.

D. Charged particle therapy is relatively inexpensive in terms of the cost involved with production and operation of such facility.

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