, Radiobiology for the Radiologist, 8th Edition
Hall & Giaccia | Wolters Kluwer
Complete 840-Question Test Bank (30 Questions per
Chapter)
PART 1: FOR STUDENTS OF RADIOLOGY, NUCLEAR MEDICINE, AND RADIATION ONCOLOGY
Chapter 1: Physics and Chemistry of Radiation Absorption
(Questions: 1-30)
Question 1
What is the primary mechanism by which X-rays and gamma rays deposit energy in biological
tissues?
A. Direct excitation of atomic electrons
B. Photoelectric effect and Compton scattering
C. Nuclear fission reactions
D. Bremsstrahlung radiation only
Correct Answer: B
,Rationale: X-rays and gamma rays are indirectly ionizing radiation. They deposit energy
primarily through the photoelectric effect (dominant at lower energies, <100 keV)
and Compton scattering (dominant at higher energies, 100 keV to 10 MeV). These interactions
produce high-energy electrons (secondary electrons) that subsequently cause ionization and
excitation of atoms and molecules in the tissue. Direct excitation (A) is minimal. Nuclear fission
(C) is not relevant at diagnostic or therapeutic energies. Bremsstrahlung (D) is a process of X-ray
production, not energy deposition.
Question 2
Which of the following best describes the direct action of radiation on biological molecules?
A. Ionization of water molecules that then damage DNA
B. Direct ionization of the DNA molecule itself
C. Activation of cellular repair enzymes
D. Production of reactive oxygen species from oxygen
Correct Answer: B
Rationale: Direct action occurs when radiation directly ionizes a critical target molecule (such as
DNA) within the cell. This is a significant mechanism for high-LET radiation like neutrons or
alpha particles, where the probability of directly hitting DNA is high. For low-LET radiation (X-
rays, gamma rays), indirect action (A, D) through water radiolysis dominates. Activation of
repair enzymes (C) is a cellular response, not a primary energy deposition mechanism.
Question 3
What is the role of the photoelectric effect in diagnostic radiology?
A. It is the primary interaction responsible for image contrast
B. It is the primary interaction responsible for dose to the patient
C. It increases with increasing photon energy
D. Both A and B
, Correct Answer: D
Rationale: The photoelectric effect is dominant in diagnostic X-ray energies (<100 keV). Its
probability is proportional to the cube of the atomic number (Z³) , which is why it produces
excellent image contrast between bone (high Z) and soft tissue (low Z). It also contributes
significantly to patient dose because the entire photon energy is absorbed locally. Its
probability decreases sharply with increasing photon energy (C is false).
Question 4
At which photon energy range does Compton scattering dominate in soft tissue?
A. <10 keV
B. 10-50 keV
C. 100 keV to 10 MeV
D. >10 MeV
Correct Answer: C
Rationale: Compton scattering is the dominant interaction for photons in the 100 keV to 10
MeV range. This is the range used in many radiation therapy treatments and nuclear medicine
imaging. In this process, a photon interacts with a loosely bound outer electron, transferring
part of its energy and scattering in a different direction. The scattered photon can then undergo
further interactions, contributing to scatter and dose to tissues outside the primary beam.
Question 5
What is the average energy required to create one ion pair in air?
A. 10 eV
B. 34 eV
C. 100 eV
D. 1,000 eV
Hall & Giaccia | Wolters Kluwer
Complete 840-Question Test Bank (30 Questions per
Chapter)
PART 1: FOR STUDENTS OF RADIOLOGY, NUCLEAR MEDICINE, AND RADIATION ONCOLOGY
Chapter 1: Physics and Chemistry of Radiation Absorption
(Questions: 1-30)
Question 1
What is the primary mechanism by which X-rays and gamma rays deposit energy in biological
tissues?
A. Direct excitation of atomic electrons
B. Photoelectric effect and Compton scattering
C. Nuclear fission reactions
D. Bremsstrahlung radiation only
Correct Answer: B
,Rationale: X-rays and gamma rays are indirectly ionizing radiation. They deposit energy
primarily through the photoelectric effect (dominant at lower energies, <100 keV)
and Compton scattering (dominant at higher energies, 100 keV to 10 MeV). These interactions
produce high-energy electrons (secondary electrons) that subsequently cause ionization and
excitation of atoms and molecules in the tissue. Direct excitation (A) is minimal. Nuclear fission
(C) is not relevant at diagnostic or therapeutic energies. Bremsstrahlung (D) is a process of X-ray
production, not energy deposition.
Question 2
Which of the following best describes the direct action of radiation on biological molecules?
A. Ionization of water molecules that then damage DNA
B. Direct ionization of the DNA molecule itself
C. Activation of cellular repair enzymes
D. Production of reactive oxygen species from oxygen
Correct Answer: B
Rationale: Direct action occurs when radiation directly ionizes a critical target molecule (such as
DNA) within the cell. This is a significant mechanism for high-LET radiation like neutrons or
alpha particles, where the probability of directly hitting DNA is high. For low-LET radiation (X-
rays, gamma rays), indirect action (A, D) through water radiolysis dominates. Activation of
repair enzymes (C) is a cellular response, not a primary energy deposition mechanism.
Question 3
What is the role of the photoelectric effect in diagnostic radiology?
A. It is the primary interaction responsible for image contrast
B. It is the primary interaction responsible for dose to the patient
C. It increases with increasing photon energy
D. Both A and B
, Correct Answer: D
Rationale: The photoelectric effect is dominant in diagnostic X-ray energies (<100 keV). Its
probability is proportional to the cube of the atomic number (Z³) , which is why it produces
excellent image contrast between bone (high Z) and soft tissue (low Z). It also contributes
significantly to patient dose because the entire photon energy is absorbed locally. Its
probability decreases sharply with increasing photon energy (C is false).
Question 4
At which photon energy range does Compton scattering dominate in soft tissue?
A. <10 keV
B. 10-50 keV
C. 100 keV to 10 MeV
D. >10 MeV
Correct Answer: C
Rationale: Compton scattering is the dominant interaction for photons in the 100 keV to 10
MeV range. This is the range used in many radiation therapy treatments and nuclear medicine
imaging. In this process, a photon interacts with a loosely bound outer electron, transferring
part of its energy and scattering in a different direction. The scattered photon can then undergo
further interactions, contributing to scatter and dose to tissues outside the primary beam.
Question 5
What is the average energy required to create one ion pair in air?
A. 10 eV
B. 34 eV
C. 100 eV
D. 1,000 eV
