ABR Radiation Oncology Certification
Examination Practice Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
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1. The most common mechanism of cell death following conventional
fractionated radiation therapy is:
A. Mitotic catastrophe
B. Apoptosis
C. Senescence
D. Necrosis
A. Mitotic catastrophe
Mitotic catastrophe is the dominant mode of radiation-induced cell
death, particularly in rapidly dividing tumor cells, resulting from
lethal chromosomal damage.
2. The oxygen enhancement ratio (OER) primarily reflects which
biological effect?
, A. Increased DNA repair in hypoxic cells
B. Increased radiosensitivity in oxygenated cells
C. Cell cycle redistribution
D. Increased apoptosis in normoxic tissue
B. Increased radiosensitivity in oxygenated cells
Oxygen stabilizes radiation-induced DNA damage, making cells more
radiosensitive compared with hypoxic cells.
3. Which phase of the cell cycle is most radiosensitive?
A. G1
B. S
C. G2/M
D. G0
C. G2/M
Cells in the G2 and M phases have the least capacity for DNA repair
and are therefore most radiosensitive.
4. The linear-quadratic model best describes which clinical concept?
A. Tumor hypoxia
B. Fractionation effects
C. Dose-rate dependence
D. Repopulation
B. Fractionation effects
The linear-quadratic model explains cell kill as a function of dose per
fraction and is central to understanding fractionation.
,5. A tissue with a low alpha/beta ratio is most sensitive to:
A. Total dose
B. Dose per fraction
C. Overall treatment time
D. Dose rate
B. Dose per fraction
Late-responding tissues have low alpha/beta ratios and are
particularly sensitive to changes in fraction size.
6. Which radionuclide is commonly used in permanent prostate
brachytherapy?
A. Iridium-192
B. Cesium-137
C. Iodine-125
D. Cobalt-60
C. Iodine-125
Iodine-125 is widely used in permanent low-dose-rate prostate
brachytherapy due to its favorable half-life and photon energy.
7. The primary advantage of intensity-modulated radiation therapy
(IMRT) is:
A. Reduced treatment time
B. Improved dose conformity
C. Elimination of setup error
D. Increased skin dose
, B. Improved dose conformity
IMRT allows highly conformal dose distributions that better spare
surrounding normal tissues.
8. Which imaging modality is most useful for target delineation in
glioblastoma?
A. CT without contrast
B. MRI with contrast
C. PET with FDG
D. Ultrasound
B. MRI with contrast
Contrast-enhanced MRI provides superior soft-tissue definition and is
standard for brain tumor target delineation.
9. The most common site of distant metastasis in prostate cancer is:
A. Lung
B. Liver
C. Bone
D. Brain
C. Bone
Prostate cancer most frequently metastasizes to bone, often
producing osteoblastic lesions.
10. Androgen deprivation therapy enhances radiation response
primarily by:
A. Increasing tumor hypoxia
Examination Practice Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. The most common mechanism of cell death following conventional
fractionated radiation therapy is:
A. Mitotic catastrophe
B. Apoptosis
C. Senescence
D. Necrosis
A. Mitotic catastrophe
Mitotic catastrophe is the dominant mode of radiation-induced cell
death, particularly in rapidly dividing tumor cells, resulting from
lethal chromosomal damage.
2. The oxygen enhancement ratio (OER) primarily reflects which
biological effect?
, A. Increased DNA repair in hypoxic cells
B. Increased radiosensitivity in oxygenated cells
C. Cell cycle redistribution
D. Increased apoptosis in normoxic tissue
B. Increased radiosensitivity in oxygenated cells
Oxygen stabilizes radiation-induced DNA damage, making cells more
radiosensitive compared with hypoxic cells.
3. Which phase of the cell cycle is most radiosensitive?
A. G1
B. S
C. G2/M
D. G0
C. G2/M
Cells in the G2 and M phases have the least capacity for DNA repair
and are therefore most radiosensitive.
4. The linear-quadratic model best describes which clinical concept?
A. Tumor hypoxia
B. Fractionation effects
C. Dose-rate dependence
D. Repopulation
B. Fractionation effects
The linear-quadratic model explains cell kill as a function of dose per
fraction and is central to understanding fractionation.
,5. A tissue with a low alpha/beta ratio is most sensitive to:
A. Total dose
B. Dose per fraction
C. Overall treatment time
D. Dose rate
B. Dose per fraction
Late-responding tissues have low alpha/beta ratios and are
particularly sensitive to changes in fraction size.
6. Which radionuclide is commonly used in permanent prostate
brachytherapy?
A. Iridium-192
B. Cesium-137
C. Iodine-125
D. Cobalt-60
C. Iodine-125
Iodine-125 is widely used in permanent low-dose-rate prostate
brachytherapy due to its favorable half-life and photon energy.
7. The primary advantage of intensity-modulated radiation therapy
(IMRT) is:
A. Reduced treatment time
B. Improved dose conformity
C. Elimination of setup error
D. Increased skin dose
, B. Improved dose conformity
IMRT allows highly conformal dose distributions that better spare
surrounding normal tissues.
8. Which imaging modality is most useful for target delineation in
glioblastoma?
A. CT without contrast
B. MRI with contrast
C. PET with FDG
D. Ultrasound
B. MRI with contrast
Contrast-enhanced MRI provides superior soft-tissue definition and is
standard for brain tumor target delineation.
9. The most common site of distant metastasis in prostate cancer is:
A. Lung
B. Liver
C. Bone
D. Brain
C. Bone
Prostate cancer most frequently metastasizes to bone, often
producing osteoblastic lesions.
10. Androgen deprivation therapy enhances radiation response
primarily by:
A. Increasing tumor hypoxia
