Page 1 of 139
ABR Medical Physics Maintenance of Certification (MOC) /
Continuing Certification Exam ACTUAL EXAM COMPLETE
QUESTIONS AND CORRECT ANSWERS LATEST UPDATE THIS
YEAR
ABR Medical Physics Maintenance of Certification (MOC) / Continuing Certification Exam
SUMMARIZED EXAM TOPICS (Point Form – Accurate for ABR MOC Coverage Areas)
• External Beam Radiation Therapy (Conformal, IMRT, VMAT, stereotactic procedures –
SRS/SBRT, electron therapy, total body irradiation TBI, total skin electron therapy TSET)
• Brachytherapy (HDR, LDR, permanent seed implants, applicators, source calibration, treatment
planning, dose calculation formalisms)
• Particle Therapy (Proton therapy, range, modulation, spread-out Bragg peak SOBP, beam
delivery systems, relative biological effectiveness RBE)
• Machine QA, Commissioning, and Calibration (TG-51, TG-142, TG-198, annual/monthly/daily
QA, output constancy, mechanical and imaging isocenter alignment, Winston-Lutz test)
• Radiation Protection and Shielding (Tenth-value layer TVL, barrier design, neutron shielding,
NCRP reports, ALARA, area monitoring, personnel dosimetry)
• Treatment Planning Systems (Dose calculation algorithms (collapsed cone, Monte Carlo, AAA),
heterogeneity corrections, contouring, dose-volume histograms DVH, optimization, uncertainty
management)
• Imaging in Radiotherapy (CBCT, MV/kV image guidance, IGRT, fusion, registration, synthetic CT,
adaptive radiotherapy)
• Radiobiology (Linear-quadratic model, α/β ratios, fractionation, 5 R’s of radiobiology, normal
tissue tolerance, tumor control probability TCP, normal tissue complication probability NTCP)
• Incidents and Reporting (Root cause analysis, near-miss reporting, FMEA, fault tree analysis,
safety checklists, FDA/IAEA/NRC reporting requirements)
• Professionalism and Ethics (Informed consent, patient confidentiality, conflict of interest, scope
of practice, medical ethics principles, ABR Code of Ethics)
• Non-clinical Skills (NCS) (Biostatistics, clinical informatics, quality assurance methodologies,
patient safety science, bioethics, practice quality improvement PQI)
• Clinical Physics Practice (TG-100 risk assessment, peer review, incident learning systems,
physician-physicist communication, equipment acquisition and acceptance testing)
, Page 2 of 139
1. During IMRT planning for a head and neck case, the optimizer fails to meet the parotid constraint
despite multiple attempts. What is the most appropriate physics intervention to improve plan quality
while preserving target coverage?
A) Decrease the number of beam angles
B) Increase the maximum parotid dose constraint priority weight
C) Reduce the PTV minimum dose constraint
D) Switch from step-and-shoot to VMAT delivery
Answer: B
Rationale: Increasing constraint priority weight forces optimizer to better spare parotids; changing
delivery technique or reducing target coverage is not appropriate first-line action.
2. A linear accelerator’s electron beam output deviates by 3.5% from baseline at reference depth.
According to TG-51, what is the required action?
A) No action needed, within 3% tolerance
B) Correct output immediately and investigate cause
C) Adjust only the electron cone factor
D) Continue use but document for monthly review
, Page 3 of 139
Answer: B
*Rationale: TG-51 requires output constancy within ±2% for electrons; 3.5% exceeds tolerance and
requires immediate correction and investigation.*
3. During a prostate HDR brachytherapy procedure, the afterloader reports a “source dwell position
deviation” error. What is the FIRST safety action the physicist should take?
A) Increase the source strength in the treatment plan
B) Manually retract the source using emergency procedures
C) Reboot the afterloader and continue treatment
D) Ask the physician to complete the case with interstitial needles only
Answer: B
Rationale: Source position error is a serious safety event; manual retraction per emergency procedure is
required before any troubleshooting to prevent unintended high dose.
4. A proton therapy patient is treated with passive scattering. The range shifter thickness is changed
from 5 cm to 7 cm water equivalent. What happens to the beam range in tissue?
A) Range decreases by approximately 2 cm
B) Range increases by 2 cm
, Page 4 of 139
C) Range unchanged, only modulation affected
D) Range increases by 5 cm
Answer: A
Rationale: Range shifter adds material upstream, reducing residual proton range in patient; increased
thickness reduces range proportionally.
5. During Winston-Lutz testing for SRS, the imaging isocenter is found 1.2 mm from the mechanical
isocenter. This measurement violates which TG-142 action threshold?
A) Monthly tolerance of 1.0 mm
B) Annual tolerance of 1.5 mm
C) Daily tolerance of 0.5 mm
D) Weekly tolerance of 0.75 mm
Answer: A
*Rationale: TG-142 monthly tolerance for imaging isocenter coincidence with mechanical isocenter is
1.0 mm; 1.2 mm exceeds this limit.*
6. A physicist performing a root cause analysis after a near-miss event identifies inadequate training as a
contributing factor. What is the most effective corrective action to prevent recurrence?
ABR Medical Physics Maintenance of Certification (MOC) /
Continuing Certification Exam ACTUAL EXAM COMPLETE
QUESTIONS AND CORRECT ANSWERS LATEST UPDATE THIS
YEAR
ABR Medical Physics Maintenance of Certification (MOC) / Continuing Certification Exam
SUMMARIZED EXAM TOPICS (Point Form – Accurate for ABR MOC Coverage Areas)
• External Beam Radiation Therapy (Conformal, IMRT, VMAT, stereotactic procedures –
SRS/SBRT, electron therapy, total body irradiation TBI, total skin electron therapy TSET)
• Brachytherapy (HDR, LDR, permanent seed implants, applicators, source calibration, treatment
planning, dose calculation formalisms)
• Particle Therapy (Proton therapy, range, modulation, spread-out Bragg peak SOBP, beam
delivery systems, relative biological effectiveness RBE)
• Machine QA, Commissioning, and Calibration (TG-51, TG-142, TG-198, annual/monthly/daily
QA, output constancy, mechanical and imaging isocenter alignment, Winston-Lutz test)
• Radiation Protection and Shielding (Tenth-value layer TVL, barrier design, neutron shielding,
NCRP reports, ALARA, area monitoring, personnel dosimetry)
• Treatment Planning Systems (Dose calculation algorithms (collapsed cone, Monte Carlo, AAA),
heterogeneity corrections, contouring, dose-volume histograms DVH, optimization, uncertainty
management)
• Imaging in Radiotherapy (CBCT, MV/kV image guidance, IGRT, fusion, registration, synthetic CT,
adaptive radiotherapy)
• Radiobiology (Linear-quadratic model, α/β ratios, fractionation, 5 R’s of radiobiology, normal
tissue tolerance, tumor control probability TCP, normal tissue complication probability NTCP)
• Incidents and Reporting (Root cause analysis, near-miss reporting, FMEA, fault tree analysis,
safety checklists, FDA/IAEA/NRC reporting requirements)
• Professionalism and Ethics (Informed consent, patient confidentiality, conflict of interest, scope
of practice, medical ethics principles, ABR Code of Ethics)
• Non-clinical Skills (NCS) (Biostatistics, clinical informatics, quality assurance methodologies,
patient safety science, bioethics, practice quality improvement PQI)
• Clinical Physics Practice (TG-100 risk assessment, peer review, incident learning systems,
physician-physicist communication, equipment acquisition and acceptance testing)
, Page 2 of 139
1. During IMRT planning for a head and neck case, the optimizer fails to meet the parotid constraint
despite multiple attempts. What is the most appropriate physics intervention to improve plan quality
while preserving target coverage?
A) Decrease the number of beam angles
B) Increase the maximum parotid dose constraint priority weight
C) Reduce the PTV minimum dose constraint
D) Switch from step-and-shoot to VMAT delivery
Answer: B
Rationale: Increasing constraint priority weight forces optimizer to better spare parotids; changing
delivery technique or reducing target coverage is not appropriate first-line action.
2. A linear accelerator’s electron beam output deviates by 3.5% from baseline at reference depth.
According to TG-51, what is the required action?
A) No action needed, within 3% tolerance
B) Correct output immediately and investigate cause
C) Adjust only the electron cone factor
D) Continue use but document for monthly review
, Page 3 of 139
Answer: B
*Rationale: TG-51 requires output constancy within ±2% for electrons; 3.5% exceeds tolerance and
requires immediate correction and investigation.*
3. During a prostate HDR brachytherapy procedure, the afterloader reports a “source dwell position
deviation” error. What is the FIRST safety action the physicist should take?
A) Increase the source strength in the treatment plan
B) Manually retract the source using emergency procedures
C) Reboot the afterloader and continue treatment
D) Ask the physician to complete the case with interstitial needles only
Answer: B
Rationale: Source position error is a serious safety event; manual retraction per emergency procedure is
required before any troubleshooting to prevent unintended high dose.
4. A proton therapy patient is treated with passive scattering. The range shifter thickness is changed
from 5 cm to 7 cm water equivalent. What happens to the beam range in tissue?
A) Range decreases by approximately 2 cm
B) Range increases by 2 cm
, Page 4 of 139
C) Range unchanged, only modulation affected
D) Range increases by 5 cm
Answer: A
Rationale: Range shifter adds material upstream, reducing residual proton range in patient; increased
thickness reduces range proportionally.
5. During Winston-Lutz testing for SRS, the imaging isocenter is found 1.2 mm from the mechanical
isocenter. This measurement violates which TG-142 action threshold?
A) Monthly tolerance of 1.0 mm
B) Annual tolerance of 1.5 mm
C) Daily tolerance of 0.5 mm
D) Weekly tolerance of 0.75 mm
Answer: A
*Rationale: TG-142 monthly tolerance for imaging isocenter coincidence with mechanical isocenter is
1.0 mm; 1.2 mm exceeds this limit.*
6. A physicist performing a root cause analysis after a near-miss event identifies inadequate training as a
contributing factor. What is the most effective corrective action to prevent recurrence?
