Page 1 of 173
ABR Radiation Oncology Certification
Examination Practice Questions With Verified
Answers & Rationales LATEST UPDATE THIS
YEAR
ABR Radiation Oncology Certification Examination Practice Questions
Exam Coverage Summary (Point Form)
Radiation Biology (≈25%): Cell survival models, LQ model & α/β ratios, cell cycle
radiosensitivity, DNA damage & repair, OER & hypoxia, 5 Rs of radiobiology, LET & RBE,
fractionation effects, bystander effect, apoptosis vs mitotic catastrophe, radiation sensitizers &
protectors
Radiation Physics (≈20%): Photon interactions (photoelectric, Compton, pair production), beam
quality & PDD, dosimetry & calibration, electron beam therapy, proton therapy, TG-51 & TG-43,
isodose curves, MU calculation
Clinical Oncology – Disease Sites (≈35%): Head & neck, breast, lung, prostate, gynecologic, GI,
CNS, lymphoma, sarcoma, pediatric cancers; staging (AJCC), treatment paradigms, combined
modality therapy, target volumes (GTV/CTV/PTV), OAR constraints
Treatment Planning & Delivery (≈15%): 3D-CRT, IMRT/VMAT, SBRT/SRS, brachytherapy
(LDR/HDR), IGRT, motion management, adaptive planning, proton planning
Safety, QA & Professionalism (≈5%): Machine QA, patient safety, incident learning, ethics,
informed consent, error prevention
SECTION 1: RADIATION BIOLOGY (Questions 1–70)
1. A 62-year-old patient with head and neck cancer is receiving conventionally fractionated
radiotherapy. The dominant mechanism of tumor cell death following this treatment is best
described as which of the following?
A. Immediate apoptosis triggered within hours of irradiation
,Page 2 of 173
B. Necrosis due to direct membrane damage
C. Mitotic catastrophe occurring after one or more failed divisions
D. Autophagy-mediated cell clearance
Answer: C. Mitotic catastrophe is the primary mode of radiation-induced cell death in solid
tumors, where cells with unrepaired DNA damage attempt mitosis and die from chromosomal
aberrations, typically after 1–3 divisions. Apoptosis plays a lesser role in most solid tumors
compared to hematologic malignancies.
2. A radiation biologist is studying cell survival curves for a new radiosensitizer. According to the
linear-quadratic model, the equation that best describes cell survival after a single dose of
radiation is which of the following?
A. S = e^(-αD)
B. S = e^(-αD - βD²)
C. S = αD + βD²
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D. S = e^(-βD²)
Answer: B. The LQ model equation is S = e^(-αD - βD²), where the linear (α) component
represents non-repairable lethal damage and the quadratic (β) component represents
repairable damage requiring two sublesions to interact. This model is foundational for
understanding fractionation effects.
3. A clinical trial compares hypofractionated versus conventionally fractionated prostate
radiotherapy. Which α/β ratio is most appropriate for estimating late rectal toxicity in this
comparison?
A. 10 Gy
B. 3 Gy
C. 1.5 Gy
D. 0.5 Gy
, Page 4 of 173
Answer: C. Late-responding tissues such as rectum and spinal cord have low α/β ratios
(approximately 1.5–3 Gy), making them more sensitive to changes in fraction size. This is why
hypofractionation must be carefully evaluated for late effects in prostate cancer.
4. A researcher is evaluating the radiosensitivity of different cell lines. Which phase of the cell
cycle demonstrates the greatest radiosensitivity?
A. S phase
B. G0 phase
C. G2/M phase
D. Early G1 phase
Answer: C. Cells in G2 and M phases are most radiosensitive due to condensed chromatin and
limited DNA repair capacity. S phase is most resistant because of active homologous
recombination repair. This variation underlies the redistribution (reassortment) component of
the 5 Rs.
ABR Radiation Oncology Certification
Examination Practice Questions With Verified
Answers & Rationales LATEST UPDATE THIS
YEAR
ABR Radiation Oncology Certification Examination Practice Questions
Exam Coverage Summary (Point Form)
Radiation Biology (≈25%): Cell survival models, LQ model & α/β ratios, cell cycle
radiosensitivity, DNA damage & repair, OER & hypoxia, 5 Rs of radiobiology, LET & RBE,
fractionation effects, bystander effect, apoptosis vs mitotic catastrophe, radiation sensitizers &
protectors
Radiation Physics (≈20%): Photon interactions (photoelectric, Compton, pair production), beam
quality & PDD, dosimetry & calibration, electron beam therapy, proton therapy, TG-51 & TG-43,
isodose curves, MU calculation
Clinical Oncology – Disease Sites (≈35%): Head & neck, breast, lung, prostate, gynecologic, GI,
CNS, lymphoma, sarcoma, pediatric cancers; staging (AJCC), treatment paradigms, combined
modality therapy, target volumes (GTV/CTV/PTV), OAR constraints
Treatment Planning & Delivery (≈15%): 3D-CRT, IMRT/VMAT, SBRT/SRS, brachytherapy
(LDR/HDR), IGRT, motion management, adaptive planning, proton planning
Safety, QA & Professionalism (≈5%): Machine QA, patient safety, incident learning, ethics,
informed consent, error prevention
SECTION 1: RADIATION BIOLOGY (Questions 1–70)
1. A 62-year-old patient with head and neck cancer is receiving conventionally fractionated
radiotherapy. The dominant mechanism of tumor cell death following this treatment is best
described as which of the following?
A. Immediate apoptosis triggered within hours of irradiation
,Page 2 of 173
B. Necrosis due to direct membrane damage
C. Mitotic catastrophe occurring after one or more failed divisions
D. Autophagy-mediated cell clearance
Answer: C. Mitotic catastrophe is the primary mode of radiation-induced cell death in solid
tumors, where cells with unrepaired DNA damage attempt mitosis and die from chromosomal
aberrations, typically after 1–3 divisions. Apoptosis plays a lesser role in most solid tumors
compared to hematologic malignancies.
2. A radiation biologist is studying cell survival curves for a new radiosensitizer. According to the
linear-quadratic model, the equation that best describes cell survival after a single dose of
radiation is which of the following?
A. S = e^(-αD)
B. S = e^(-αD - βD²)
C. S = αD + βD²
,Page 3 of 173
D. S = e^(-βD²)
Answer: B. The LQ model equation is S = e^(-αD - βD²), where the linear (α) component
represents non-repairable lethal damage and the quadratic (β) component represents
repairable damage requiring two sublesions to interact. This model is foundational for
understanding fractionation effects.
3. A clinical trial compares hypofractionated versus conventionally fractionated prostate
radiotherapy. Which α/β ratio is most appropriate for estimating late rectal toxicity in this
comparison?
A. 10 Gy
B. 3 Gy
C. 1.5 Gy
D. 0.5 Gy
, Page 4 of 173
Answer: C. Late-responding tissues such as rectum and spinal cord have low α/β ratios
(approximately 1.5–3 Gy), making them more sensitive to changes in fraction size. This is why
hypofractionation must be carefully evaluated for late effects in prostate cancer.
4. A researcher is evaluating the radiosensitivity of different cell lines. Which phase of the cell
cycle demonstrates the greatest radiosensitivity?
A. S phase
B. G0 phase
C. G2/M phase
D. Early G1 phase
Answer: C. Cells in G2 and M phases are most radiosensitive due to condensed chromatin and
limited DNA repair capacity. S phase is most resistant because of active homologous
recombination repair. This variation underlies the redistribution (reassortment) component of
the 5 Rs.
