CMD Radiation Physics & Radiobiology Flashcards

In the linear-quadratic (LQ) model, which term accounts for 'single-hit' cell killing?

Answer: The αD term

The αD term represents irreparable single-event (single-hit) lethal damage, while βD² represents repairable two-event damage.

What is the concept of 'isoeffective dose' used for in radiation therapy planning?

Answer: Comparing biological effects of different fractionation schedules

Isoeffective dose allows dosimetrists to compare different fractionation regimens by expressing them in terms of an equivalent biological effect, often using EQD2.

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 'therapeutic ratio' (therapeutic window) in radiation oncology?

Answer: The difference between tumor control probability and normal tissue complication probability

The therapeutic ratio describes the differential between the probability of controlling the tumor (TCP) and the probability of causing unacceptable normal tissue complications (NTCP).

What does 'megavoltage' refer to in the context of linear accelerator therapy beams?

Answer: Photon beam energies in the range of 1–25 million electron volts

Megavoltage (MV) beams from linear accelerators have photon energies of 1–25 MeV, providing skin-sparing, forward-peaked dose distributions suitable for deep tumors.

Which radiobiological concept describes tumor cell proliferation that occurs between radiation fractions, potentially reducing treatment efficacy?

Answer: Repopulation

Repopulation is the accelerated proliferation of surviving tumor clonogens during a protracted course of radiotherapy, which can reduce the probability of tumor control.