Practice Test Geeks(CMD) Certified Medical Dosimetrist Practice Test
← All CMD Flashcard Decks

CMD Radiation Physics & Radiobiology Flashcards

6 cards from real CMD practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 6 CMD Radiation Physics & Radiobiology flashcards as text

  1. What is the linear energy transfer (LET) of diagnostic X-rays and therapeutic photon beams classified as?

    Answer: Low LET radiation

    Photon beams (X-rays and gamma rays) are low LET radiation because they deposit energy sparsely along their track, unlike heavy charged particles.

  2. Which quantity describes the ratio of the biological effect of a given radiation compared to 250 kVp X-rays?

    Answer: Relative Biological Effectiveness (RBE)

    RBE compares the dose of reference X-rays needed to produce the same biological effect as the test radiation, and is greater than 1 for high-LET radiation.

  3. 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).

  4. What is the oxygen enhancement ratio (OER) primarily relevant to in radiation therapy?

    Answer: Hypoxic tumor cells are more radioresistant

    The OER quantifies how much more dose is required to kill hypoxic cells versus well-oxygenated cells; hypoxic cells are approximately 2.5–3× more radioresistant.

  5. Which law states that the intensity of radiation decreases inversely with the square of the distance from the source?

    Answer: Inverse square law

    The inverse square law states that radiation intensity is proportional to 1/d², where d is the distance from the point source.

  6. What is the primary purpose of bolus material in external beam radiation therapy?

    Answer: To increase surface dose and reduce skin-sparing effect

    Bolus is placed directly on the patient's skin to bring the dose maximum to the surface, eliminating the skin-sparing effect when superficial targets require full dose.