Page 1 of 134
ABR Radiation Oncology Certification Exam
ACTUAL QUESTIONS AND ANSWERS LATEST
UPDATE THIS YEAR
ABR Radiation Oncology Certification Exam coverage,
SUMMARIZED EXAM COVERAGE (High-Yield Topics)
Based on ABR exam blueprints, ASTRO study guides, and RABEX/RAPHEX topic weighting :
Radiobiology (≈35-40% of exam)
• DNA damage/repair mechanisms (DSB, SSB, BER, NHEJ, HR)
• Cell survival curves (LQ model: α/β, SF2, D0, Dq)
• The 5 Rs of radiobiology: Repair, Repopulation, Redistribution, Reoxygenation, Radiosensitivity
• LET and RBE relationships (OER for low-LET: 2.5-3.0)
• Cell cycle radiosensitivity (G2/M most sensitive, late S most resistant)
• Tumor microenvironment: hypoxia, angiogenesis, pH
• Bystander effect, abscopal effect, adaptive response
• Normal tissue complications (TD5/5, TD50/5, serial vs. parallel organ architecture)
• Fractionation effects (early vs. late responding tissues, α/β values)
Radiation Physics (≈25-30%)
• Photon interactions: photoelectric, Compton, pair production (dominance by energy)
• Electron beam characteristics (dmax, Rp, R90, R50)
• Dose measurement: TPR, PDD, OAR, Sc,p, tissue-maximum ratio (TMR)
• Linac components: waveguide, bending magnet, flattening filter, MLC, EPID
• Small field dosimetry (diode > microchamber > TLD)
• TG-51, TG-142 QA requirements (daily output constancy)
• Brachytherapy: HDR (>12 Gy/h), LDR, PDR; air kerma strength (U), reference air kerma rate
Clinical Oncology (≈30-35%)
• Site-specific natural history, staging (AJCC 8th/9th), treatment paradigms
o CNS: glioblastoma (Stupp protocol), medulloblastoma (CSI), meningioma
o H&N: HPV+ vs. HPV- oropharynx, larynx preservation (RTOG 91-11)
o Thorax: NSCLC (stage III: PACIFIC, CROSS), SCLC (TRT + PCI)
o Breast: DCIS, whole breast vs. APBI, postmastectomy RT, regional nodal irradiation
(MA.20)
o GI: esophageal (CROSS), rectal (TME + SCRT/LCRT), anal (Nigro protocol)
o GU: prostate (RTOG 0126, CHHiP, HYPRO), bladder, kidney
o Gynecologic: cervix (Pembroke/EMBRACE), endometrial (PORTEC), vulvar
o Lymphoma: Hodgkin (ISRT, Stanford V, BEACOPP), NHL
o Sarcoma, pediatric tumors, skin, palliative RT (8/1, 20/5, 30/10)
Emerging / Updated Topics (per ABR April 2025 Focus on RO)
• Unsealed sources, radiopharmaceuticals, theranostics (Lu-177 PSMA, I-131, Ra-223, Sm-153)
• Proton therapy (SOBP, distal edge, range uncertainty)
• SBRT/SABR (RTOG 0236, 0618, Nordic/HyTEC normal tissue constraints)
• Immunotherapy + RT (iRT, abscopal effect)
PRACTICE QUESTIONS (300 Random, Scenario-Based)
, Page 2 of 134
Q1. A 14-year-old male presents with a posterior fossa medulloblastoma. After maximal safe resection,
the next appropriate radiation therapy approach is:
A. Focal boost to the tumor bed only
B. Craniospinal irradiation (CSI) with posterior fossa boost
C. Whole brain radiotherapy without spinal coverage
D. Observation alone with chemotherapy
Answer: B
*Rationale: Medulloblastoma has a high propensity for CSF seeding, requiring CSI (36 Gy) followed by
tumor bed/posterior fossa boost (54-55.8 Gy).*
Q2. Which of the following cell survival curve parameters is most directly associated with intrinsic
radiosensitivity of a tumor cell line?
A. α (alpha) from the LQ model
B. β (beta) from the LQ model
C. D (mean lethal dose)
D. Oxygen enhancement ratio
Answer: A
, Page 3 of 134
Rationale: The α coefficient represents the linear (non-repairable) component of cell kill. Higher α
correlates with greater radiosensitivity.
Q3. A 65-year-old male with T2N0M0 squamous cell carcinoma of the glottis is treated with definitive
radiotherapy. Standard fractionation for this presentation is:
A. 2.0 Gy × 35 fractions (70 Gy)
B. 2.25 Gy × 28 fractions (63 Gy)
C. 1.8 Gy × 28 fractions (50.4 Gy)
D. 3.0 Gy × 10 fractions (30 Gy)
Answer: B
*Rationale: Early glottic cancer is often treated with hypofractionation (2.25 Gy/fx to 63 Gy) with high
local control and acceptable toxicity.*
Q4. The oxygen enhancement ratio (OER) for 6 MV photons is approximately:
A. 1.0
B. 1.5-2.0
C. 2.5-3.0
D. 5.0-6.0
, Page 4 of 134
Answer: C
*Rationale: For low-LET radiation (photons, electrons), OER ranges from 2.5-3.0, meaning hypoxic cells
require 2.5-3× the dose for equivalent cell kill.*
Q5. Which of the following late-responding normal tissues has the lowest α/β ratio?
A. Skin (late effects)
B. Spinal cord
C. Lung (fibrosis)
D. Bladder
Answer: B
*Rationale: Spinal cord α/β ≈ 2 Gy (very low). Late-responding tissues typically have α/β 2-5 Gy.*
Q6. According to the linear-quadratic model, the equation for cell survival is:
A. S = e^(αD + βD²)
B. S = e^(-αD - βD²)
C. S = e^(-αD/β - D²)
D. S = 1 - e^(-αD - βD²)
Answer: B
ABR Radiation Oncology Certification Exam
ACTUAL QUESTIONS AND ANSWERS LATEST
UPDATE THIS YEAR
ABR Radiation Oncology Certification Exam coverage,
SUMMARIZED EXAM COVERAGE (High-Yield Topics)
Based on ABR exam blueprints, ASTRO study guides, and RABEX/RAPHEX topic weighting :
Radiobiology (≈35-40% of exam)
• DNA damage/repair mechanisms (DSB, SSB, BER, NHEJ, HR)
• Cell survival curves (LQ model: α/β, SF2, D0, Dq)
• The 5 Rs of radiobiology: Repair, Repopulation, Redistribution, Reoxygenation, Radiosensitivity
• LET and RBE relationships (OER for low-LET: 2.5-3.0)
• Cell cycle radiosensitivity (G2/M most sensitive, late S most resistant)
• Tumor microenvironment: hypoxia, angiogenesis, pH
• Bystander effect, abscopal effect, adaptive response
• Normal tissue complications (TD5/5, TD50/5, serial vs. parallel organ architecture)
• Fractionation effects (early vs. late responding tissues, α/β values)
Radiation Physics (≈25-30%)
• Photon interactions: photoelectric, Compton, pair production (dominance by energy)
• Electron beam characteristics (dmax, Rp, R90, R50)
• Dose measurement: TPR, PDD, OAR, Sc,p, tissue-maximum ratio (TMR)
• Linac components: waveguide, bending magnet, flattening filter, MLC, EPID
• Small field dosimetry (diode > microchamber > TLD)
• TG-51, TG-142 QA requirements (daily output constancy)
• Brachytherapy: HDR (>12 Gy/h), LDR, PDR; air kerma strength (U), reference air kerma rate
Clinical Oncology (≈30-35%)
• Site-specific natural history, staging (AJCC 8th/9th), treatment paradigms
o CNS: glioblastoma (Stupp protocol), medulloblastoma (CSI), meningioma
o H&N: HPV+ vs. HPV- oropharynx, larynx preservation (RTOG 91-11)
o Thorax: NSCLC (stage III: PACIFIC, CROSS), SCLC (TRT + PCI)
o Breast: DCIS, whole breast vs. APBI, postmastectomy RT, regional nodal irradiation
(MA.20)
o GI: esophageal (CROSS), rectal (TME + SCRT/LCRT), anal (Nigro protocol)
o GU: prostate (RTOG 0126, CHHiP, HYPRO), bladder, kidney
o Gynecologic: cervix (Pembroke/EMBRACE), endometrial (PORTEC), vulvar
o Lymphoma: Hodgkin (ISRT, Stanford V, BEACOPP), NHL
o Sarcoma, pediatric tumors, skin, palliative RT (8/1, 20/5, 30/10)
Emerging / Updated Topics (per ABR April 2025 Focus on RO)
• Unsealed sources, radiopharmaceuticals, theranostics (Lu-177 PSMA, I-131, Ra-223, Sm-153)
• Proton therapy (SOBP, distal edge, range uncertainty)
• SBRT/SABR (RTOG 0236, 0618, Nordic/HyTEC normal tissue constraints)
• Immunotherapy + RT (iRT, abscopal effect)
PRACTICE QUESTIONS (300 Random, Scenario-Based)
, Page 2 of 134
Q1. A 14-year-old male presents with a posterior fossa medulloblastoma. After maximal safe resection,
the next appropriate radiation therapy approach is:
A. Focal boost to the tumor bed only
B. Craniospinal irradiation (CSI) with posterior fossa boost
C. Whole brain radiotherapy without spinal coverage
D. Observation alone with chemotherapy
Answer: B
*Rationale: Medulloblastoma has a high propensity for CSF seeding, requiring CSI (36 Gy) followed by
tumor bed/posterior fossa boost (54-55.8 Gy).*
Q2. Which of the following cell survival curve parameters is most directly associated with intrinsic
radiosensitivity of a tumor cell line?
A. α (alpha) from the LQ model
B. β (beta) from the LQ model
C. D (mean lethal dose)
D. Oxygen enhancement ratio
Answer: A
, Page 3 of 134
Rationale: The α coefficient represents the linear (non-repairable) component of cell kill. Higher α
correlates with greater radiosensitivity.
Q3. A 65-year-old male with T2N0M0 squamous cell carcinoma of the glottis is treated with definitive
radiotherapy. Standard fractionation for this presentation is:
A. 2.0 Gy × 35 fractions (70 Gy)
B. 2.25 Gy × 28 fractions (63 Gy)
C. 1.8 Gy × 28 fractions (50.4 Gy)
D. 3.0 Gy × 10 fractions (30 Gy)
Answer: B
*Rationale: Early glottic cancer is often treated with hypofractionation (2.25 Gy/fx to 63 Gy) with high
local control and acceptable toxicity.*
Q4. The oxygen enhancement ratio (OER) for 6 MV photons is approximately:
A. 1.0
B. 1.5-2.0
C. 2.5-3.0
D. 5.0-6.0
, Page 4 of 134
Answer: C
*Rationale: For low-LET radiation (photons, electrons), OER ranges from 2.5-3.0, meaning hypoxic cells
require 2.5-3× the dose for equivalent cell kill.*
Q5. Which of the following late-responding normal tissues has the lowest α/β ratio?
A. Skin (late effects)
B. Spinal cord
C. Lung (fibrosis)
D. Bladder
Answer: B
*Rationale: Spinal cord α/β ≈ 2 Gy (very low). Late-responding tissues typically have α/β 2-5 Gy.*
Q6. According to the linear-quadratic model, the equation for cell survival is:
A. S = e^(αD + βD²)
B. S = e^(-αD - βD²)
C. S = e^(-αD/β - D²)
D. S = 1 - e^(-αD - βD²)
Answer: B
