Massachusetts Radiation Therapist Licensure
Exam Questions and Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
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1. Which of the following is the primary interaction of diagnostic x-
rays with soft tissue at energies below 100 keV?
a) Pair production
b) Photoelectric effect
c) Compton scattering
d) Coherent scattering
b) Photoelectric effect
Rationale: At lower energies, the photoelectric effect dominates
because the photon energy is close to the binding energy of inner-shell
electrons in soft tissue, leading to complete absorption of the photon.
2. The half-life of a radioactive isotope is defined as:
a) The time it takes for the isotope to decay completely
b) The time it takes for half of the radioactive nuclei to decay
, c) The time it takes for radiation intensity to double
d) The time it takes for a radioactive isotope to emit all its energy
b) The time it takes for half of the radioactive nuclei to decay
Rationale: The half-life is a statistical measure representing the time
in which 50% of a sample of radioactive nuclei undergo decay.
3. Which imaging modality uses high-frequency sound waves to
produce images?
a) MRI
b) CT
c) Ultrasound
d) PET
c) Ultrasound
Rationale: Ultrasound imaging employs high-frequency sound waves
that reflect off tissues, creating real-time images without ionizing
radiation.
4. In radiation therapy, the primary purpose of a bolus is to:
a) Increase beam energy
b) Protect underlying tissues
, c) Increase dose to superficial tissues
d) Reduce scatter radiation
c) Increase dose to superficial tissues
Rationale: A bolus is a tissue-equivalent material placed on the skin
surface to bring the dose closer to the surface, compensating for the
skin-sparing effect of high-energy photons.
5. Which of the following is considered a stochastic effect of
radiation?
a) Skin erythema
b) Cataract formation
c) Leukemia
d) Hair loss
c) Leukemia
Rationale: Stochastic effects occur by chance and have no threshold,
with severity independent of dose. Leukemia is a classic stochastic
effect of ionizing radiation.
6. The most radiosensitive phase of the cell cycle is:
a) G1 phase
, b) S phase
c) M phase
d) G0 phase
c) M phase
Rationale: Cells are most sensitive to radiation during mitosis (M
phase) because chromosomes are highly condensed and more
vulnerable to DNA damage.
7. In treatment planning, the term “isocenter” refers to:
a) The location of maximum skin dose
b) The point around which the gantry, collimator, and couch rotate
c) The geometric center of the tumor
d) The center of the radiation field at the surface
b) The point around which the gantry, collimator, and couch rotate
Rationale: The isocenter is a fixed point in space used as a reference
for precise delivery of radiation beams from multiple angles.
8. What is the purpose of multileaf collimators (MLCs) in modern
linear accelerators?
a) Increase beam energy
Exam Questions and Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
Download Pdf
1. Which of the following is the primary interaction of diagnostic x-
rays with soft tissue at energies below 100 keV?
a) Pair production
b) Photoelectric effect
c) Compton scattering
d) Coherent scattering
b) Photoelectric effect
Rationale: At lower energies, the photoelectric effect dominates
because the photon energy is close to the binding energy of inner-shell
electrons in soft tissue, leading to complete absorption of the photon.
2. The half-life of a radioactive isotope is defined as:
a) The time it takes for the isotope to decay completely
b) The time it takes for half of the radioactive nuclei to decay
, c) The time it takes for radiation intensity to double
d) The time it takes for a radioactive isotope to emit all its energy
b) The time it takes for half of the radioactive nuclei to decay
Rationale: The half-life is a statistical measure representing the time
in which 50% of a sample of radioactive nuclei undergo decay.
3. Which imaging modality uses high-frequency sound waves to
produce images?
a) MRI
b) CT
c) Ultrasound
d) PET
c) Ultrasound
Rationale: Ultrasound imaging employs high-frequency sound waves
that reflect off tissues, creating real-time images without ionizing
radiation.
4. In radiation therapy, the primary purpose of a bolus is to:
a) Increase beam energy
b) Protect underlying tissues
, c) Increase dose to superficial tissues
d) Reduce scatter radiation
c) Increase dose to superficial tissues
Rationale: A bolus is a tissue-equivalent material placed on the skin
surface to bring the dose closer to the surface, compensating for the
skin-sparing effect of high-energy photons.
5. Which of the following is considered a stochastic effect of
radiation?
a) Skin erythema
b) Cataract formation
c) Leukemia
d) Hair loss
c) Leukemia
Rationale: Stochastic effects occur by chance and have no threshold,
with severity independent of dose. Leukemia is a classic stochastic
effect of ionizing radiation.
6. The most radiosensitive phase of the cell cycle is:
a) G1 phase
, b) S phase
c) M phase
d) G0 phase
c) M phase
Rationale: Cells are most sensitive to radiation during mitosis (M
phase) because chromosomes are highly condensed and more
vulnerable to DNA damage.
7. In treatment planning, the term “isocenter” refers to:
a) The location of maximum skin dose
b) The point around which the gantry, collimator, and couch rotate
c) The geometric center of the tumor
d) The center of the radiation field at the surface
b) The point around which the gantry, collimator, and couch rotate
Rationale: The isocenter is a fixed point in space used as a reference
for precise delivery of radiation beams from multiple angles.
8. What is the purpose of multileaf collimators (MLCs) in modern
linear accelerators?
a) Increase beam energy
