Treatment Planning & Dosimetry Flashcards
7 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 7 Treatment Planning & Dosimetry flashcards as text
The tissue-maximum ratio (TMR) is preferred over the tissue-air ratio (TAR) for high-energy photon beams because:
Answer: TAR requires impractically large phantom measurements at high energies
At high photon energies, measuring TAR requires enormous phantoms to achieve electronic equilibrium at depth, making TMR with scatter factors more practical.
Which contouring structure type is used in treatment planning to expand a target volume to account for subclinical disease extension?
Answer: Clinical Target Volume (CTV)
The CTV expands the GTV to include areas of suspected microscopic disease extension, representing the true anatomical extent of disease requiring treatment.
In 4D CT-based treatment planning for lung cancer, the Internal Target Volume (ITV) is derived by:
Answer: Taking the union of GTVs contoured across all respiratory phases
The ITV is the union of all phase-specific GTVs across the breathing cycle, encompassing the full range of tumor motion.
A symmetric 4-field box technique for prostate treatment typically uses which beam arrangement?
Answer: AP, PA, right lateral, left lateral
The classic 4-field box for prostate uses anterior-posterior, posterior-anterior, and bilateral lateral beams to distribute dose and spare anterior normal tissue.
Which effect describes the increase in relative biological effectiveness (RBE) of radiation as linear energy transfer (LET) increases?
Answer: High-LET radiation reduces the oxygen enhancement ratio and increases RBE simultaneously
High-LET radiation both increases RBE (more lethal per unit dose) and reduces the oxygen enhancement ratio (less dependent on oxygen for cell kill).
For a wedged pair technique, the hinge angle between two beams is related to the wedge angle by which formula?
Answer: Wedge angle = 90° - (hinge angle / 2)
For a wedged pair, the optimal wedge angle equals 90° minus half the hinge angle between the two beams to produce a uniform dose distribution.
In brachytherapy, the term 'dose rate constant' (Λ) for a source is defined as the dose rate at:
Answer: 1 cm in water per unit air kerma strength at 1 cm in air
The dose rate constant Λ is the dose rate to water at 1 cm from the source per unit air kerma strength (1 U = 1 cGy·cm²/h), linking source strength to dose rate.