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100+ Free CMD Practice Questions

Pass your Certified Medical Dosimetrist (CMD) exam on the first try — instant access, no signup required.

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70-75% Pass Rate
100+ Questions
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Question 1
Score: 0/0

Which quality assurance procedure is specifically designed to verify that the MLC leaf positions match the planned positions before IMRT delivery?

A
B
C
D
to track
2026 Statistics

Key Facts: CMD Exam

175

Exam Questions (150 scored)

MDCB content specifications

3h 30m

Exam Time

MDCB exam information

$450

Exam Fee

MDCB exam information

5 years

Certification Cycle

MDCB certification maintenance

70-75%

First-Time Pass Rate

MDCB published data

MDCB administers the CMD certification exam with 175 multiple-choice questions (150 scored, 25 pilot) in 3 hours 30 minutes. The exam fee is $450. MDCB uses criterion-referenced scoring. CMD certification is valid for 5 years with continuing education requirements. BLS reports strong demand for radiation therapy professionals.

Sample CMD Practice Questions

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

1In a standard four-field box technique for pelvic treatment, what is the primary advantage of using lateral fields in addition to AP/PA fields?
A.Better coverage of the anterior–posterior dimension of the target
B.Improved dose homogeneity and reduced dose to anterior/posterior normal structures
C.Elimination of the need for bolus material
D.Reduced overall treatment time due to fewer monitor units
Explanation: Adding lateral fields to AP/PA fields creates a box technique that improves dose homogeneity across the target volume. The lateral fields help spare anterior structures like the bladder and posterior structures like the rectum by redistributing the dose contribution, rather than relying solely on AP/PA beams that deliver high entrance/exit doses to those tissues.
2What is the tissue–phantom ratio (TPR) used to determine in treatment planning?
A.The percentage of dose absorbed by lead shielding
B.The ratio of dose at a given depth in tissue to dose at the same point in free space
C.The ratio of dose at a given depth to dose at a reference depth for the same source-to-point distance
D.The total monitor units required to deliver a prescribed dose
Explanation: Tissue–phantom ratio (TPR) is defined as the ratio of the dose at a given depth in a phantom to the dose at a reference depth, measured at the same source-to-point distance. TPR is independent of source-to-surface distance, making it particularly useful for isocentric treatment planning calculations.
3Which imaging modality is considered the gold standard for electron density information used in dose calculation algorithms?
A.MRI
B.PET/CT
C.CT simulation
D.Ultrasound
Explanation: CT simulation provides Hounsfield unit (HU) data that is directly converted to electron density values through a calibration curve. This electron density information is essential for heterogeneity-corrected dose calculations. While MRI offers superior soft-tissue contrast, it does not provide electron density data natively.
4In brachytherapy, what does the term 'dwell time' refer to?
A.The time between fractions of external beam treatment
B.The duration a radioactive source remains at a specific position within an applicator
C.The half-life of the radioactive isotope used
D.The time required to insert the applicator into the patient
Explanation: In high-dose-rate (HDR) brachytherapy, dwell time refers to the length of time the radioactive source remains at each programmed position (dwell position) within the applicator or catheter. By varying dwell times at different positions, the dosimetrist can optimize the dose distribution to conform to the target while sparing organs at risk.
5What is the purpose of the inverse square law in radiation therapy dose calculations?
A.To determine the energy spectrum of a photon beam
B.To calculate how radiation dose changes with distance from a point source
C.To measure the attenuation coefficient of tissue
D.To calculate the half-value layer of shielding material
Explanation: The inverse square law states that radiation intensity is inversely proportional to the square of the distance from a point source. In treatment planning, this principle is used to account for changes in dose rate when the source-to-surface distance or source-to-axis distance varies, directly affecting monitor unit calculations.
6What is the standard tolerance for daily output constancy checks on a linear accelerator?
A.Within ±1% of baseline
B.Within ±3% of baseline
C.Within ±5% of baseline
D.Within ±10% of baseline
Explanation: According to TG-142 guidelines from the AAPM, daily photon and electron output constancy checks should be within ±3% of the baseline value. If readings fall outside this tolerance, the machine should be taken out of clinical service until the issue is investigated and resolved.
7Which structure is most commonly identified as an organ at risk (OAR) when planning a brain treatment?
A.Liver
B.Optic chiasm
C.Bladder
D.Esophagus
Explanation: The optic chiasm is a critical organ at risk in brain radiation therapy planning. It has a relatively low tolerance dose (typically 50–54 Gy in conventional fractionation), and exceeding this tolerance can result in vision loss. Other brain OARs include the brainstem, cochlea, and lenses.
8What unit is used to express absorbed dose in radiation therapy?
A.Roentgen (R)
B.Curie (Ci)
C.Gray (Gy)
D.Sievert (Sv)
Explanation: The Gray (Gy) is the SI unit of absorbed dose, defined as 1 joule of energy deposited per kilogram of matter. In radiation therapy, treatment doses are prescribed in Gray or centigray (cGy), where 1 Gy = 100 cGy. The Sievert is used for equivalent dose, and the Curie measures radioactivity.
9In a tandem and ovoid intracavitary brachytherapy application for cervical cancer, what is Point A historically defined as?
A.2 cm lateral and 2 cm superior to the external cervical os along the uterine axis
B.The center of the obturator nodes
C.5 cm lateral to the midline at the level of the pubic symphysis
D.The geometric center of the pelvic inlet
Explanation: Point A is a historically defined reference point in cervical brachytherapy, located 2 cm lateral to the uterine canal and 2 cm superior to the external cervical os (or the flange of the tandem). It approximates the crossing point of the uterine artery and ureter and has been used for dose specification, though modern practice increasingly uses volumetric 3D-based planning.
10What is the primary function of a multileaf collimator (MLC) in radiation therapy?
A.To filter out low-energy photons from the beam
B.To shape the radiation field to conform to the target volume
C.To monitor the beam output in real time
D.To flatten the photon beam profile
Explanation: A multileaf collimator (MLC) consists of numerous individual tungsten leaves that can be independently positioned to shape the radiation field, conforming it to the projected shape of the target volume. MLCs are essential for conformal therapy, IMRT, and VMAT, replacing or supplementing traditional cerrobend blocks.

About the CMD Exam

The CMD exam certifies medical dosimetrists in radiation treatment planning, dose calculations, brachytherapy, IMRT/VMAT, radiation physics, quality assurance, and image-guided radiation therapy. The MDCB exam is administered at Pearson VUE test centers nationwide.

Questions

100 scored questions

Time Limit

3 hours 30 minutes

Passing Score

Scaled score (criterion-referenced)

Exam Fee

$450 (Medical Dosimetrist Certification Board (MDCB) / Pearson VUE)

CMD Exam Content Outline

30-35%

Treatment Planning

External beam planning, IMRT/VMAT optimization, field design, dose constraints, and plan evaluation

15-20%

Dose Calculations

Monitor unit calculations, dosimetric quantities, heterogeneity corrections, and BED/EQD2 concepts

10-15%

Brachytherapy

HDR/LDR planning, TG-43 formalism, source selection, and intracavitary/interstitial techniques

15-20%

Radiation Physics

Photon/electron interactions, beam characteristics, radiobiology, and beam generation

15-20%

Quality Assurance

TG-51/TG-142, IMRT QA, IGRT, safety systems, and calibration procedures

How to Pass the CMD Exam

What You Need to Know

  • Passing score: Scaled score (criterion-referenced)
  • Exam length: 100 questions
  • Time limit: 3 hours 30 minutes
  • Exam fee: $450

Keys to Passing

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

CMD Study Tips from Top Performers

1Prioritize treatment planning — it carries the highest exam weight and integrates all other topic areas
2Master monitor unit calculations for isocentric and SSD setups, including wedge, tray, and output factors
3Study TG reports systematically: TG-43 for brachytherapy, TG-51 for calibration, TG-142 for linac QA
4Build dose constraint reference charts for common treatment sites (lung, H&N, prostate, brain, breast)
5Practice IMRT/VMAT optimization concepts including objective weighting and plan evaluation metrics
6Review radiobiology concepts (LQ model, BED, alpha/beta ratio) and apply them to fractionation problems

Frequently Asked Questions

How many questions are on the CMD exam?

The MDCB CMD exam consists of 175 multiple-choice questions (150 scored and 25 unscored pilot questions) with a time limit of 3 hours and 30 minutes.

What score do I need to pass the CMD exam?

The CMD exam uses criterion-referenced scoring. MDCB determines the passing standard through a psychometric process rather than a fixed percentage or raw score.

What topics are tested on the CMD exam?

The CMD exam covers treatment planning (30-35%), radiation physics, dose calculations, brachytherapy, quality assurance, and professional responsibilities as outlined in the MDCB content specifications.

How much does the CMD exam cost?

The MDCB CMD examination fee is $450. This fee is payable upon application and covers one exam attempt.

How should I study for the CMD exam?

Focus on treatment planning and dose calculations first (highest weight), then brachytherapy and physics. Use TG reports (TG-43, TG-51, TG-142) as key references. Practice monitor unit calculations and plan evaluation under timed conditions.

What are the eligibility requirements for the CMD exam?

Candidates typically need a bachelor's degree plus completion of an accredited medical dosimetry program or equivalent clinical experience. Check the MDCB website for current eligibility routes and documentation requirements.