ARRT - American Registry of Radiologic Technologists Radiation Physics and Radiobiology Questions and Answers — Questions and Answers
Question 1: According to the Law of Bergonie and Tribondeau, which of the following cells would be MOST radiosensitive?
- Nerve cells
- Muscle cells
- Lymphocytes (Correct answer)
- Chondrocytes
Correct answer: Lymphocytes
The Law of Bergonie and Tribondeau states that radiosensitivity is highest in cells that have a high mitotic rate, are undifferentiated (unspecialized), and have a long dividing future. [17, 20] Lymphocytes are highly mitotic and undifferentiated, making them one of the most radiosensitive cell types in the body. [21] Nerve and muscle cells are highly specialized and do not divide, making them radioresistant. [13] Chondrocytes (cartilage cells) are also specialized and have a low mitotic rate.
Question 2: A radiation effect that has a threshold dose below which it does not occur, and whose severity increases as the dose increases, is known as what type of effect?
- Stochastic
- Deterministic (Non-stochastic) (Correct answer)
- Genetic
- Latent
Correct answer: Deterministic (Non-stochastic)
Deterministic effects, also known as non-stochastic or tissue reactions, are characterized by a threshold dose. The severity of the effect, such as skin erythema or cataracts, increases with the dose received above this threshold. [8, 25] In contrast, stochastic effects (like cancer) have no threshold and their probability of occurrence increases with dose, not severity. [3, 19]
Question 3: Which of the following is a key characteristic of the photoelectric effect in diagnostic imaging?
- It is the primary interaction at very high kVp settings.
- It involves an interaction with an outer-shell electron.
- It results in total absorption of the incident x-ray photon. (Correct answer)
- It is the main contributor to scatter radiation reaching the image receptor.
Correct answer: It results in total absorption of the incident x-ray photon.
The photoelectric effect occurs when an incident x-ray photon interacts with an inner-shell electron and is completely absorbed. [16, 33] This interaction is a primary contributor to patient dose and subject contrast in the image because it removes the photon from the beam. It is most dominant at lower kVp settings and in materials with high atomic numbers (like bone and contrast media). [29, 31] Compton scattering is the main source of scatter.
Question 4: The presence of oxygen in tissue during irradiation increases the biological damage caused by low-LET radiation. This phenomenon is known as the:
- Relative Biologic Effectiveness (RBE)
- Linear Energy Transfer (LET) effect
- Law of Bergonie and Tribondeau
- Oxygen Enhancement Effect (Correct answer)
Correct answer: Oxygen Enhancement Effect
The Oxygen Enhancement Effect describes how the presence of molecular oxygen makes tissue more sensitive to radiation. [2, 4] Oxygen reacts with radiation-induced free radicals to 'fix' the damage, making it permanent and harder for cells to repair. [6] The Oxygen Enhancement Ratio (OER) is the ratio of dose required under hypoxic conditions versus aerated conditions to produce the same biological effect. [9] This effect is most pronounced for low-LET radiations like x-rays.
Question 5: Which of the following describes the relationship between Linear Energy Transfer (LET) and Relative Biologic Effectiveness (RBE)?
- As LET decreases, RBE always increases.
- LET and RBE are completely independent of each other.
- As LET increases, RBE increases to a maximum point and then decreases. (Correct answer)
- As LET increases, RBE always decreases.
Correct answer: As LET increases, RBE increases to a maximum point and then decreases.
Relative Biologic Effectiveness (RBE) is a measure of the capacity of a specific type of radiation to cause biological damage, compared to a reference radiation (usually 250 kVp x-rays). [5, 10] As Linear Energy Transfer (LET) increases, the concentration of ionizations increases, leading to more effective cell killing and thus a higher RBE. However, this relationship holds only up to a point (around 100 keV/µm). Beyond this, the energy deposition becomes excessive (the 'overkill' effect), and the RBE begins to decrease because the extra energy is wasted on cells that have already been inactivated. [14]
Question 6: A technologist is exposed to a small dose of radiation during a fluoroscopic procedure. Years later, a radiation-induced cancer develops. This type of late effect is classified as a:
- Deterministic effect
- Acute effect
- Stochastic effect (Correct answer)
- Somatic threshold effect
Correct answer: Stochastic effect
Cancer induction from radiation is a classic example of a stochastic effect. Stochastic effects are probabilistic, meaning the likelihood of the effect occurring increases with dose, but the severity is independent of the dose. [22] There is no known dose threshold for stochastic effects. [3, 25] Deterministic effects have a threshold and their severity is dose-dependent.
ARRT - American Registry of Radiologic Technologists Radiation Physics and Radiobiology Questions and Answers
According to the Law of Bergonie and Tribondeau, which of the following cells would be MOST radiosensitive?