Radiobiology Flashcards

Relative biological effectiveness (RBE) is defined as:

Answer: The ratio of a reference radiation dose to the test radiation dose required to produce the same biological effect

RBE is the ratio of the reference radiation dose (typically 250 kV X-rays or Co-60) to the test radiation dose needed to produce the same biological effect.

Which type of radiation has the highest linear energy transfer (LET)?

Answer: Alpha particles

Alpha particles have the highest LET (~80–100 keV/μm), depositing energy densely over a very short distance, resulting in high RBE and significant biological damage.

Reoxygenation in tumors during fractionated radiotherapy refers to:

Answer: Movement of previously hypoxic tumor cells into better-oxygenated positions after irradiation kills oxic cells

Reoxygenation occurs when previously hypoxic tumor cells receive improved oxygen supply after radiation kills surrounding oxygenated cells, increasing the radiosensitivity of remaining tumor cells.

Which of the following is NOT one of the classic '5 Rs' of radiobiology?

Answer: Regeneration

The 5 Rs of radiobiology are Repair, Redistribution, Repopulation, Reoxygenation, and Radiosensitivity; 'Regeneration' is not part of this framework.

The abscopal effect in radiotherapy refers to:

Answer: Tumor regression at sites distant from the irradiated field

The abscopal effect describes regression of tumors at sites outside the irradiated field, thought to be mediated by systemic immune activation triggered by local radiation.

Which of the following is a clinically established radiosensitizer used concurrently with radiotherapy?

Answer: Cisplatin

Cisplatin is a well-established radiosensitizer used concurrently with radiotherapy in cervical, head and neck, and lung cancers, primarily by inhibiting DNA repair.

Radiation-induced secondary malignancies arise primarily through which mechanism?

Answer: Induction of mutations in oncogenes or tumor suppressor genes in normal cells

Radiation induces mutations in oncogenes or inactivates tumor suppressor genes in normal cells, which can lead to secondary malignancies after a latency period.