Radiation safety and radiobiology: G2-M arrest as radiosensitiser: practice question

A Radiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Radiology · Radiation safety and radiobiology: G2-M arrest as radiosensitiser

Sample item

A radiation oncologist adds paclitaxel to radiotherapy. Which cell-cycle effect explains its radiosensitising action?

AIt arrests cells in late S phase, which is the most radiosensitiveBIt drives cells into G0 where repair is maximalCIt removes cells from the cycle by blocking G1 entryDIt arrests cells in the G2-M phase, which is the most radiosensitive part of the cycle

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. It arrests cells in the G2-M phase, which is the most radiosensitive part of the cycle

Taxanes stabilise microtubules and hold cells in G2-M, where radiation damage is least repairable. Cells in late S phase are the most resistant. Synchronising tumour cells into G2-M raises the kill from a given dose.

Option by option

A. It arrests cells in late S phase, which is the most radiosensitive
Late S phase is the most resistant phase, not the most sensitive.
B. It drives cells into G0 where repair is maximal
G0 cells are generally resistant and are not the target of this drug.
C. It removes cells from the cycle by blocking G1 entry
Taxanes act at mitosis, not by blocking entry from G1.
D. It arrests cells in the G2-M phase, which is the most radiosensitive part of the cycle (correct)
Correct. G2-M accumulation increases radiosensitivity.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Radiology question

What is the answer to this Radiology question?

The best answer is D, It arrests cells in the G2-M phase, which is the most radiosensitive part of the cycle. Taxanes stabilise microtubules and hold cells in G2-M, where radiation damage is least repairable.

Why is "It arrests cells in late S phase, which is the most radiosensitive" not the answer?

Late S phase is the most resistant phase, not the most sensitive.

Why is "It drives cells into G0 where repair is maximal" not the answer?

G0 cells are generally resistant and are not the target of this drug.

Why is "It removes cells from the cycle by blocking G1 entry" not the answer?

Taxanes act at mitosis, not by blocking entry from G1.

What concept does this question test?

It tests Radiation safety and radiobiology: G2-M arrest as radiosensitiser in Radiology. Cells in late S phase are the most resistant. Synchronising tumour cells into G2-M raises the kill from a given dose.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Radiation safety and radiobiology: G2-M arrest as radiosensitiser?

Learn signs with the image, and the disease they point to. Then use the flashcards and the other Radiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.