100+ Free ABR Radiation Oncology Practice Questions

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Question 1

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A 6 MV photon beam interacts in soft tissue at therapeutic energies. Which interaction dominates at these megavoltage energies?

Pair production

Photoelectric effect

Compton scattering

Coherent (Rayleigh) scattering

to track

2026 Statistics

Key Facts: ABR Radiation Oncology Exam

~300

Total MCQ Items

ABR Radiation Oncology Qualifying (CBE)

~8 hr

Total Exam Time

1-day computer-based test including breaks

~10-12%

Physics + Biology Weight

Largest combined domain on 2026 ABR content outline

$1,950

2026 Initial Cert Fee

ABR Radiation Oncology

5 yr

Required Training

1 clinical + 4 RadOnc residency (ACGME)

Pearson VUE

Test Delivery

Computer-based testing at authorized centers

The ABR Radiation Oncology Qualifying (CBE) exam is a 1-day Pearson VUE CBT with ~300 single-best-answer MCQs over ~8 hours. The 2026 content outline emphasizes radiation physics (~10-12%), radiation biology (~10-12%), palliative/brachytherapy/skin/QA (~8-10%), treatment planning/simulation (~8-10%), breast (~7-9%), prostate/lung/HNSCC/CNS/GI (~6-8% each), lymphoma/pediatric/sarcoma (~5-7%), and gynecologic oncology (~4-6%). Initial Certification fee is ~$1,950; prerequisite is ACGME-accredited Radiation Oncology residency.

Sample ABR Radiation Oncology Practice Questions

Try these sample questions to test your ABR Radiation Oncology exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1A 6 MV photon beam interacts in soft tissue at therapeutic energies. Which interaction dominates at these megavoltage energies?

A.Pair production

B.Photoelectric effect

C.Compton scattering

D.Coherent (Rayleigh) scattering

Explanation: Compton scattering dominates in the therapeutic megavoltage range (~0.1-10 MeV) and depends on electron density (nearly equal for soft tissue, fat, and bone), which is why MV imaging shows poor bone-soft-tissue contrast. Photoelectric dominates <50 keV (Z^3 dependence — bone visible on kV imaging). Pair production requires >1.02 MeV threshold and becomes dominant above ~10 MeV.

2What is the threshold photon energy for pair production?

A.0.511 MeV

B.1.02 MeV

C.0.1 MeV

D.10 MeV

Explanation: Pair production has a threshold of 1.02 MeV, equal to the combined rest-mass energy of an electron-positron pair (2 × 0.511 MeV). Below this threshold the interaction cannot occur. Pair production becomes dominant at very high energies (>10 MeV) and in high-Z materials, with cross-section increasing with Z^2.

3Which particle has an approximate RBE of 1.1 relative to photons for most clinical endpoints?

A.Neutrons

B.Photons

C.Carbon ions

D.Protons

Explanation: Clinical proton therapy uses a generic RBE of 1.1 (some evidence of higher RBE near distal Bragg peak). Photons have RBE 1.0 by definition. Carbon ions have RBE 2-3 depending on tissue and fractionation. Fast neutrons have RBE 3-10 — high LET, more complex DNA damage, reduced oxygen dependence.

4What is the oxygen enhancement ratio (OER) for X-rays at therapeutic doses?

A.~1.0

B.~2.5-3

C.~5-6

D.~10

Explanation: The OER for low-LET radiation (X-rays, gamma rays) is approximately 2.5-3 at therapeutic doses — meaning ~2.5-3 times more dose is required under hypoxic conditions to achieve the same biological effect as under well-oxygenated conditions. OER decreases as LET increases (neutrons OER ~1.6; alpha particles ~1.0). Oxygen enhancement explains the importance of reoxygenation in fractionated RT.

5In which phase of the cell cycle are cells MOST radiosensitive?

A.G0

B.Late S

C.G1

D.Mitosis (M)

Explanation: Radiosensitivity by cell cycle phase: M > G2 > G1 > S (late S most resistant). During mitosis, chromatin is condensed and DNA repair capacity is low. Late S is most radioresistant due to homologous recombination repair availability. Reassortment (one of the 4 R's) refers to redistribution of cells through sensitive phases between fractions, enhancing tumor kill with fractionated RT.

6Which of the following is NOT one of the 4 R's of fractionated radiobiology?

A.Reassortment

B.Repair

C.Radiosensitization

D.Repopulation

Explanation: The 4 R's of radiobiology are: REPAIR (sublethal damage between fractions, spares late-responding normal tissue), REASSORTMENT (redistribution through cell cycle, sensitizes tumor), REPOPULATION (proliferation during treatment — harmful for tumor, beneficial for early-responding normal tissue), and REOXYGENATION (hypoxic cells reoxygenate between fractions, sensitizing them). A 5th R — intrinsic Radiosensitivity — was later added, but Radiosensitization is not one of the classical R's.

7Which α/β ratio is most consistent with a late-responding normal tissue?

A.0.1 Gy

B.8-12 Gy

C.20 Gy

D.2-3 Gy

Explanation: Late-responding normal tissues (spinal cord, kidney, lung late fibrosis) have LOW α/β ratios ~2-3 Gy — highly sensitive to fraction size. Early-responding tissues and most tumors have HIGH α/β ~8-12 Gy — less sensitive to fraction size, dose determines effect. Prostate cancer has an unusually LOW α/β ~1.5 Gy, which biologically favors hypofractionation (CHHiP, SBRT).

8Using the linear-quadratic model, what is the BED of 60 Gy in 30 fractions of 2 Gy for a tumor with α/β = 10 Gy?

A.72 Gy

B.60 Gy

C.84 Gy

D.48 Gy

Explanation: BED = nd × (1 + d/(α/β)) = 60 × (1 + 2/10) = 60 × 1.2 = 72 Gy. BED (biologically effective dose) allows comparison across fractionation schemes. EQD2 = BED / (1 + 2/(α/β)) converts BED to equivalent 2-Gy-fraction dose. For late-responding tissues (α/β = 3), the same 60 Gy in 30 fx has BED = 60 × (1 + 2/3) = 100 Gy_3.

9According to QUANTEC, what is the approximate full-cord dose producing ~0.2% risk of myelopathy with conventional fractionation?

A.70 Gy

B.30 Gy

C.50 Gy

D.80 Gy

Explanation: QUANTEC spinal cord tolerance: Dmax 50 Gy ≈ 0.2% myelopathy risk; Dmax 60 Gy ≈ 6%; Dmax 69 Gy ≈ 50%. Clinical practice typically limits Dmax to 45-50 Gy conventional. SBRT cord Dmax <14 Gy in single fraction (<10 Gy if re-irradiation). Cord has a low α/β ~2 Gy making it exquisitely sensitive to fraction size.

10What QUANTEC lung V20 threshold is associated with increased risk of symptomatic radiation pneumonitis?

A.V5 >5%

B.V20 >10%

C.V20 >50%

D.V20 >30-35%

Explanation: QUANTEC: total lung V20 >30-35% increases risk of symptomatic radiation pneumonitis (~20% risk at V20 35%). Mean lung dose (MLD) also correlates — MLD <20 Gy preferred, <13-15 Gy ideal. V5 matters for large irradiated volumes. Post-pneumonectomy tolerance is much lower. Patients receiving immunotherapy (e.g., durvalumab in PACIFIC) have higher pneumonitis risk.

About the ABR Radiation Oncology Exam

The ABR Radiation Oncology Initial Certification (Qualifying / Computer-Based) Examination is the written certifying exam for US radiation oncology residents. The 1-day Pearson VUE CBT contains approximately 300 single-best-answer MCQs spanning radiation physics (photon interactions, LET/RBE/OER, IMRT/VMAT/proton dosimetry, linac QA), radiation biology (4 R's, α/β ratios, LQ model, BED/EQD2, fractionation), treatment planning and simulation, and site-specific management across breast, prostate, lung, head and neck, CNS, GI, GYN, lymphoma, pediatric, skin, and palliative radiation therapy. Brachytherapy (LDR/HDR isotopes, cervical tandem-and-ovoid/ring, prostate seeds), SBRT/SRS, and RO-ILS/peer-review quality assurance are also assessed. Requires completion of an ACGME-accredited Radiation Oncology residency (1 clinical year + 4 RadOnc years).

Questions

300 scored questions

Time Limit

1-day CBT at Pearson VUE (~8 hours including breaks)

Passing Score

Criterion-referenced scaled score set by ABR (modified Angoff)

Exam Fee

~$1,950 ABR Radiation Oncology Initial Certification fee (2026) (American Board of Radiology (ABR) / Pearson VUE)

ABR Radiation Oncology Exam Content Outline

~10-12%

Radiation Physics

Photon-matter interactions — photoelectric dominant at low energies (<50 keV, Z^3 dependence), Compton dominant 0.1-10 MeV (electron density dependent), pair production threshold 1.02 MeV (dominant at high energies). LET and RBE (photons 1.0, protons 1.1, carbon ions 2-3, neutrons 3-10). Percent depth dose, D-max, build-up, output factors. IMRT, VMAT, 3D-CRT, TomoTherapy, protons (Bragg peak, SOBP). Linac QA (TG-142). Small-field dosimetry. Imaging (CBCT, MRI-linac Unity/MRIdian).

~10-12%

Radiation Biology

4 R's of radiobiology (repair, reassortment, repopulation, reoxygenation). Cell cycle radiosensitivity M > G2 > G1 > S. OER ~2.5-3 for X-rays (reduced for high LET). Linear-quadratic model α/β ratios — early-responding tumors 8-12 Gy, late-responding tissues 2-3 Gy, prostate ~1.5 Gy (favors hypofractionation). BED = nd(1 + d/(α/β)); EQD2. Hyperfractionation (HNSCC RTOG 9003), accelerated fractionation, SBRT ablative biology. DNA damage repair (HR, NHEJ). QUANTEC tolerance doses.

~8-10%

Treatment Planning & Simulation

CT simulation, immobilization (thermoplastic head/neck mask, Vac-Lok, breast board), 4D-CT for respiratory motion, MRI fusion (CNS, pelvis, soft tissue), PET-CT (HNSCC, lung, lymphoma, cervix). ICRU target volumes — GTV (visible), CTV (microscopic), PTV (setup + motion margin), ITV (motion envelope), OAR, PRV. IGRT — kV/MV CBCT, orthogonal kV, MRI-linac. DIBH for left breast. SGRT surface-guided. Adaptive planning. Plan evaluation (DVH, conformity index, heterogeneity index).

~8-10%

Palliative, Skin, Brachytherapy & QA

Bone mets RTOG 97-14 showed 8 Gy × 1 equivalent to 30 Gy/10 fx for pain relief — single fraction preferred for uncomplicated mets; SBRT spine mets 24 Gy/2 fx. Spinal cord compression — Patchell 2005 favored surgery + RT over RT alone in select. Brain mets — SRS preferred for 1-4 lesions (Patchell, EORTC 22952), WBRT + hippocampal avoidance + memantine (NRG CC001). Skin BCC/SCC superficial orthovoltage/electrons. Brachytherapy isotopes (Ir-192 HDR, I-125 T½ 60 d, Pd-103 17 d, Cs-131, Ra-223 alpha for prostate bone mets). RO-ILS safety, peer review, plan check.

~7-9%

Breast Cancer

Z11 supported SLNB+ with cT1-2 cN0 BCT avoiding ALND. Adjuvant whole-breast RT after lumpectomy — hypofractionated 40-42.5 Gy/15-16 fx (START-B) preferred; ultra-hypofractionated 26 Gy/5 fx (FAST-Forward). Tumor-bed boost for ≤50 yo or high grade (EORTC boost). Partial-breast irradiation (NSABP-B39, RAPID, Florence). Post-mastectomy RT for pN2+, pN1 with features, T3+, close/positive margins (EBCTCG meta). Regional nodal irradiation — MA.20, EORTC 22922. DCIS — NSABP-B17 (RT reduces LR). Inflammatory breast. DIBH for cardiac sparing.

~6-8%

Prostate Cancer

NCCN risk stratification (very low/low/favorable intermediate/unfavorable intermediate/high/very high/regional). Active surveillance for low and very low risk. Dose-escalated EBRT 78-80 Gy (PROG 95-09, MRC RT01). Moderate hypofractionation 60 Gy/20 fx (CHHiP, PROFIT). SBRT 36.25-40 Gy/5 fx (HYPO-RT-PC, PACE-B). ADT duration — short 4-6 mo intermediate (RTOG 9408), long 18-36 mo high/very high (STAMPEDE, LATITUDE). Brachytherapy (LDR I-125/Pd-103 monotherapy, HDR boost). Post-op — RADICALS, RAVES, GETUG-17 favor early salvage over adjuvant. Radium-223 for symptomatic bone mets.

~6-8%

Lung Cancer

NSCLC stage I SABR/SBRT peripheral 54 Gy/3 fx or 50 Gy/5 fx (RTOG 0236, 0915); central 50 Gy/5 fx (RTOG 0813); ultracentral caution (HILUS). Stage III concurrent chemoRT 60-66 Gy + weekly carbo/paclitaxel or cis/etoposide + durvalumab consolidation (PACIFIC). SCLC limited-stage 45 Gy BID (CONVERT) or 60-66 Gy daily + concurrent platinum/etoposide + PCI if CR (Auperin meta). Extensive SCLC — chemo + atezo/durva + consolidation thoracic RT selected (CREST). Oligomets — SABR (SABR-COMET, MD Anderson). Immunotherapy + RT abscopal.

~6-8%

Head and Neck Cancer

NPC — concurrent cisplatin + RT 70 Gy IMRT, induction chemo for high-risk (Intergroup 0099). HPV+ oropharynx favorable prognosis — RTOG 1016 showed cetuximab inferior to cisplatin. Larynx organ preservation (RTOG 91-11) — concurrent chemoRT vs total laryngectomy. Oral cavity — surgery primary with post-op chemoRT if close margin/ECE/pN2+ (EORTC 22931, RTOG 9501). Thyroid RAI I-131. Re-irradiation SBRT selected. Acute toxicity — mucositis, xerostomia, dysphagia, dermatitis. Late — xerostomia, ORN, hypothyroidism, carotid stenosis.

~6-8%

CNS Tumors

Glioblastoma — surgery + 60 Gy/30 fx concurrent TMZ + adjuvant TMZ (Stupp). MGMT methylation predicts TMZ benefit. TTFields adjuvant (EF-14). Elderly — hypofractionated 40 Gy/15 fx (Perry). Anaplastic oligodendroglioma IDHmut 1p/19q co-del — RT + PCV (RTOG 9402). Low-grade glioma high-risk — RT + PCV (RTOG 9802). CNS lymphoma — HD-MTX-based; reduced-dose WBRT after CR. Brain mets single-lesion SRS 15-24 Gy (Patchell, EORTC 22952). Hippocampal-avoidance WBRT + memantine (NRG CC001). Vestibular schwannoma, AVM, trigeminal neuralgia SRS.

~6-8%

GI Malignancies

Esophageal — CROSS neoadjuvant chemoRT 41.4 Gy + carbo/paclitaxel + surgery. Rectal — neoadjuvant LCRT 50.4 Gy + capecitabine + TME + adjuvant chemo, or total neoadjuvant (RAPIDO, PRODIGE-23); short-course 25 Gy/5 fx (Polish, Stockholm III, RAPIDO). PROSPECT — selective RT omission for clinical stage II/III. Anal — Nigro 5-FU/MMC + RT 54-59.4 Gy (RTOG 9811, 0529 IMRT). Pancreatic — borderline resectable neoadjuvant chemoRT (PREOPANC); LAP-07 chemoRT equivocal. HCC — SBRT unresectable non-transplant. Cholangiocarcinoma. Liver mets SBRT.

~4-6%

Gynecologic, Lymphoma, Pediatric

Cervical IB3-IVA — concurrent cisplatin + EBRT 45 Gy + intracavitary brachytherapy (tandem-and-ovoid/ring HDR); image-guided adaptive EMBRACE — HR-CTV D90 ≥85 Gy EQD2. Endometrial — vaginal cuff brachytherapy 21 Gy/3 fx HDR (PORTEC-2). Hodgkin — ABVD × 2-4 + ISRT 20-30 Gy (RAPID, HD10). DLBCL — R-CHOP × 6 ± consolidation RT 30-40 Gy for bulky. Rhabdomyosarcoma — VAC + RT risk-adapted. Ewing — VDC/IE + local control. Medulloblastoma — CSI (proton preferred for kids). Wilms — flank RT stage-based.

How to Pass the ABR Radiation Oncology Exam

What You Need to Know

Passing score: Criterion-referenced scaled score set by ABR (modified Angoff)
Exam length: 300 questions
Time limit: 1-day CBT at Pearson VUE (~8 hours including breaks)
Exam fee: ~$1,950 ABR Radiation Oncology Initial Certification fee (2026)

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

ABR Radiation Oncology Study Tips from Top Performers

1Photon interactions by energy: Photoelectric effect DOMINATES below ~50 keV (Z^3 dependence — why bone shows on kV imaging). Compton scattering DOMINATES at megavoltage therapeutic energies (0.1-10 MeV, depends on electron density — why megavoltage does not show bone like kV). Pair production has a THRESHOLD at 1.02 MeV (2 × 0.511 MeV rest mass of e-/e+) and becomes dominant above ~10 MeV. Memorize the dominant interaction at each energy range — high-yield physics question.

2α/β ratios and fractionation strategy: Early-responding tissues/tumors have HIGH α/β (8-12 Gy) — relatively spared by smaller fractions. Late-responding tissues have LOW α/β (2-3 Gy) — more sensitive to fraction size, spared by standard 1.8-2 Gy/fx. Prostate has an UNUSUALLY LOW α/β (~1.5 Gy) — behaves like a late-responding tissue, which is WHY hypofractionation (CHHiP 60 Gy/20 fx, SBRT 36.25 Gy/5 fx) is biologically favorable for prostate. BED = nd(1 + d/(α/β)); EQD2 converts to equivalent 2-Gy-per-fraction dose.

3QUANTEC dose constraints to memorize cold: Spinal cord TD5/5 ~50 Gy conventional fractionation; lung V20 <30% (pneumonitis risk); mean liver dose <30 Gy (<28 Gy for primary HCC); kidney mean <18 Gy; heart V25 <10% (breast cardiac risk); optic chiasm TD5/5 ~55 Gy; brainstem TD5/5 ~54 Gy; parotid mean <26 Gy to preserve salivary function; rectum V70 <20%; bladder V65 <50%. These constraints appear repeatedly in plan evaluation and toxicity questions.

4Landmark trials by disease site (key takeaways): Z11 (BCT + SLNB+ can skip ALND); START-B (40 Gy/15 fx equals 50 Gy/25 fx for breast); FAST-Forward (26 Gy/5 fx non-inferior); CHHiP (60 Gy/20 fx prostate hypofrac); STAMPEDE (ADT + RT in high-risk prostate); RTOG 0236 (54 Gy/3 fx SBRT stage I NSCLC); PACIFIC (durvalumab after chemoRT stage III NSCLC); Stupp (RT + TMZ for GBM); CROSS (41.4 Gy + carbo/taxol neoadjuvant esophageal); Nigro (5-FU/MMC + RT anal); Patchell (SRS > WBRT for 1-4 brain mets; surgery + RT > RT for MSCC); RTOG 97-14 (8 Gy × 1 = 30 Gy/10 bone mets); RTOG 1016 (cetuximab inferior to cisplatin HPV+ oropharynx).

5Brachytherapy isotopes by half-life and use: Cs-137 (30 yr — LDR historical); Ir-192 (74 days — HDR workhorse); I-125 (60 days — prostate seeds, low-energy ~28 keV); Pd-103 (17 days — prostate seeds, faster delivery for higher-grade); Cs-131 (9.7 days); Ra-223 (11.4 days — alpha emitter, prostate symptomatic bone mets, short range spares marrow). Ir-192 is the HDR source used in tandem-and-ovoid/ring for cervical cancer. Prostate LDR monotherapy targets peripheral zone (145 Gy I-125 or 125 Gy Pd-103).

Frequently Asked Questions

What is the ABR Radiation Oncology Initial Certification exam?

The ABR Radiation Oncology Initial Certification Qualifying (Computer-Based) Examination is the written certifying exam administered by the American Board of Radiology for US radiation oncology residents. It is a 1-day computer-based test at Pearson VUE assessing knowledge across radiation physics, radiation biology, treatment planning/simulation, and site-specific management (breast, prostate, lung, HNSCC, CNS, GI, GYN, lymphoma, pediatric, skin, palliative). The Qualifying exam is followed by a separate Certifying exam; both must be passed for initial ABR certification in Radiation Oncology.

Who is eligible to take the ABR Radiation Oncology Qualifying exam?

Candidates must have completed an ACGME-accredited Radiation Oncology residency program, which is a 5-year postgraduate training: 1 clinical/preliminary year plus 4 years of dedicated Radiation Oncology residency. Candidates must hold a valid unrestricted medical license and have program director attestation of satisfactory completion. Application is submitted through the ABR website within the designated eligibility window.

What is the format of the ABR Radiation Oncology Qualifying exam?

The Qualifying (Computer-Based) Exam is a 1-day computer-based examination administered at Pearson VUE test centers, consisting of approximately 300 single-best-answer multiple-choice questions delivered over roughly 8 hours including breaks. Questions include clinical vignettes, DVH plots, treatment plans (IMRT/VMAT/proton), imaging (CT simulation, MRI, PET-CT), and dose-volume constraints. Content is distributed across the 2026 ABR Radiation Oncology content outline.

How much does the 2026 ABR Radiation Oncology exam cost?

The 2026 ABR Radiation Oncology Initial Certification fee is approximately $1,950, covering the Qualifying and Certifying exam cycle. Cancellation and refund policies follow the ABR schedule with decreasing refunds as the exam date approaches. ABR Continuing Certification uses Online Longitudinal Assessment (OLA) — weekly questions replacing the 10-year MOC cycle — with annual fees. Retakes within the eligibility window require full re-registration and fee payment.

When is the 2026 exam administered?

The ABR Radiation Oncology Qualifying (CBE) exam is typically offered once per year (historically early summer after PGY-5 completion). Applications open in the preceding year with submission deadline prior to the testing window. Candidates schedule specific Pearson VUE appointments after ABR approval. Exact 2026 dates should be confirmed on the ABR website.

How is the exam scored?

ABR uses a criterion-referenced scaled scoring system with a passing standard set by subject-matter experts using the modified Angoff method. A candidate's pass/fail result depends on performance relative to the fixed cut-score rather than on other test-takers. Score reports include subdomain performance to guide future study. Results are typically released several weeks after the testing window closes.

What are the highest-yield topics?

Highest-yield topics include: photon interactions and dominance ranges (photoelectric low energy; Compton 0.1-10 MeV; pair production >1.02 MeV); LET and RBE values (protons 1.1); 4 R's of radiobiology and α/β ratios (early 8-12, late 2-3, prostate 1.5); BED/EQD2 calculations; QUANTEC tolerance doses (cord 45-50 Gy, lung V20 <30%, mean liver <30 Gy); breast hypofractionation (FAST-Forward 26 Gy/5); prostate SBRT and ADT duration; lung SABR for stage I NSCLC; PACIFIC for stage III; Stupp regimen for GBS; CROSS for esophageal; anal Nigro; cervical brachytherapy with EMBRACE D90 ≥85 Gy; bone mets 8 Gy × 1 (RTOG 97-14); brain mets SRS (Patchell); and HPV+ oropharynx RTOG 1016 showing cet inferior to cis.

How should I study for ABR Radiation Oncology?

Use a structured 18-24 month plan across PGY-4 and PGY-5. Map to the ABR Qualifying content outline: lead with radiation physics and biology (foundational), then site-specific disease management by volume (breast, prostate, lung, HNSCC, CNS, GI, GYN, lymphoma, pediatric, palliative, brachytherapy, QA). Core resources include Perez and Brady's Principles and Practice of Radiation Oncology, Khan's Physics of Radiation Therapy, Hall and Giaccia's Radiobiology for the Radiologist, Gunderson and Tepper's Clinical Radiation Oncology, ASTRO self-assessment questions, and RAPHEX physics questions. Review QUANTEC paper, NCCN guidelines for each site, and landmark trials. Drill high-volume MCQs with timed sets and complete 2-3 full-length timed mock exams before test day.