Mixed Deck — All CMD Topics Flashcards

Which quantity describes the rate of energy deposition by a charged particle per unit path length?

Answer: Linear Energy Transfer (LET)

LET (keV/μm) describes the energy deposited per unit length along a charged particle's track and determines the biological effectiveness of different radiation types.

The percentage depth dose (PDD) for a photon beam increases with:

Answer: Increasing beam energy and field size

PDD increases with higher beam energy (deeper penetration) and larger field size (more scatter contribution), both of which increase dose at depth relative to dmax.

Which image-guided radiation therapy (IGRT) technique uses implanted fiducial markers to verify prostate position before each treatment?

Answer: Kilovoltage (kV) orthogonal imaging with fiducials

Implanted gold fiducial markers imaged with kV orthogonal or CBCT systems allow daily prostate localization and couch corrections to account for inter-fraction organ motion.

In brachytherapy, which quantity describes the strength of a radioactive source?

Answer: Air Kerma Strength (AKS)

Air Kerma Strength (U = μGy·m²/h) is the standard quantity for specifying brachytherapy source strength, replacing older activity-based specifications.

What ethical consideration is most relevant to communication & interprofessional collaboration in CMD practice?

Answer: Maintaining confidentiality and acting in the best interest of stakeholders

Maintaining confidentiality and acting in the best interest of stakeholders is the cornerstone ethical consideration for communication & interprofessional collaboration in professional practice.

Which radiation monitoring device provides the most accurate measurement of cumulative whole-body dose for regulatory compliance purposes?

Answer: Optically stimulated luminescence (OSL) dosimeter

OSL dosimeters (and TLDs) are the standard personnel dosimeters for regulatory compliance because they provide accurate cumulative dose records that can be analyzed by a NVLAP-accredited laboratory.

What is the primary goal of treatment planning in radiation therapy?

Answer: Optimize tumor dose and minimize healthy tissue exposure

The primary goal of treatment planning in radiation therapy is to create a plan that delivers a high, curative dose of radiation to the tumor while simultaneously minimizing the dose to surrounding healthy tissues and critical organs. This delicate balance, known as the therapeutic ratio, aims to maximize tumor control probability and minimize treatment-related side effects. Achieving this requires precise targeting and dose calculation.

Which type of radiation interaction dominates in bone at diagnostic X-ray energies (<100 keV)?

Answer: Photoelectric effect

The photoelectric effect is strongly dependent on atomic number (Z³) and dominates in high-Z materials like bone at diagnostic energies, explaining the high contrast of bone on X-ray images.

What is the role of the medical physicist in quality assurance for radiation therapy?

Answer: Ensuring that equipment is properly calibrated and functioning

The medical physicist plays a crucial role in quality assurance by overseeing the technical aspects of radiation therapy. Their responsibilities include the commissioning of new equipment, developing and implementing QA programs, and regularly testing and calibrating all radiation delivery and dosimetry equipment. They ensure that the machines are operating safely and accurately, providing the foundation for precise treatment delivery.

What is the design goal (P) for uncontrolled areas used in NCRP 151 shielding calculations?

Answer: 1 mSv/week

NCRP 151 uses a design goal of 1 mSv/week for uncontrolled areas, which corresponds to the 1 mSv/year public dose limit divided by a 50-week occupancy assumption.

For breast cancer radiation therapy, the tangential field technique is designed primarily to:

Answer: Treat the breast/chest wall while minimizing lung and heart dose

Tangential fields are angled to treat the breast/chest wall volume while minimizing the dose to underlying lung and, for left-sided cancers, the heart.

A patient has a Pd-103 prostate seed implant. When should radiation precautions for family members typically be lifted based on residual activity?

Answer: After the activity decays to < 1.11 MBq (30 μCi) per the NRC release criteria

NRC regulations allow patient release when the total effective dose equivalent to any individual is unlikely to exceed 5 mSv, typically when residual activity falls below release thresholds.

In photon beam dosimetry, what does the term 'dmax' refer to?

Answer: The depth of maximum dose deposition

Dmax is the depth at which the maximum dose occurs in a water phantom; it increases with beam energy (e.g., ~1.5 cm for 6 MV, ~3.5 cm for 18 MV).

In ICRU Report 62, which volume encompasses the Clinical Target Volume (CTV) plus a margin for setup uncertainty and organ motion?

Answer: Planning Target Volume (PTV)

The PTV adds a geometric margin around the CTV to account for setup uncertainties and internal organ motion, ensuring the CTV receives the prescribed dose.

For HDR brachytherapy cervical cancer treatment using a ring-and-tandem applicator, Point A is defined as:

Answer: 2 cm lateral and 2 cm superior to the cervical os along the tandem

Point A is defined as 2 cm superior to the mucous membrane of the lateral vaginal fornix and 2 cm lateral to the tandem, representing the paracervical triangle dose point.

A 4D-CT scan is acquired for a lung SBRT patient. Which QA procedure should be performed on the 4D-CT system to ensure accurate motion characterization?

Answer: Validation of phase binning accuracy using a motion phantom

A motion phantom with known, reproducible motion patterns verifies that the 4D-CT system correctly bins projection data into respiratory phases for accurate motion characterization.

Which dosimetric parameter is most critical to monitor when treating head and neck cancers with IMRT to prevent xerostomia?

Answer: Mean parotid gland dose

Mean parotid gland dose should ideally be kept below 26 Gy to at least one parotid to preserve salivary function and prevent permanent xerostomia.

Which of the following best describes a key competency required for professional ethics & legal compliance in CMD certification?

Answer: Critical thinking and evidence-based decision making

Critical thinking and evidence-based decision making is essential for professional ethics & legal compliance, as professionals must analyze situations and apply knowledge appropriately.

Which documentation practice is most important for communication & interprofessional collaboration in the CMD field?

Answer: Maintaining complete, accurate, and timely records

Maintaining complete, accurate, and timely records is crucial for accountability, quality assurance, and legal compliance in communication & interprofessional collaboration.

A dosimetrist observes that a patient's performance status has visibly declined since the last simulation visit. The appropriate action is to:

Answer: Alert the radiation oncologist and document the observation in the patient's record

Observable clinical changes must be reported to the physician; plan modifications require medical authorization.