Radiation safety and radiobiology: redistribution in fractionation: 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: redistribution in fractionation

Sample item

Between daily radiotherapy fractions, surviving tumour cells that were in the resistant late S phase move into the more sensitive G2/M phase. Which of the four Rs of radiobiology is this?

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

The answer and the reasoning

A. Redistribution (reassortment)

The four Rs are repair, reassortment (redistribution), repopulation and reoxygenation. Cells that survive a fraction because they were in a resistant phase progress through the cycle, and some of them reach sensitive phases by the next dose.

Option by option

  • A. Redistribution (reassortment) (correct)

    Correct. Movement into sensitive phases of the cell cycle is redistribution.

  • B. Repopulation

    Repopulation is regrowth of surviving clonogenic cells during the course of treatment.

  • C. Repair of sublethal damage

    Repair is restoration of sublethal DNA damage between fractions and spares normal tissue.

  • D. Reoxygenation

    Reoxygenation is the improvement of oxygen supply to hypoxic tumour regions between fractions.

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.

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Questions about this Radiology question

What is the answer to this Radiology question?

The best answer is A, Redistribution (reassortment). The four Rs are repair, reassortment (redistribution), repopulation and reoxygenation.

Why is "Repopulation" not the answer?

Repopulation is regrowth of surviving clonogenic cells during the course of treatment.

Why is "Repair of sublethal damage" not the answer?

Repair is restoration of sublethal DNA damage between fractions and spares normal tissue.

Why is "Reoxygenation" not the answer?

Reoxygenation is the improvement of oxygen supply to hypoxic tumour regions between fractions.

What concept does this question test?

It tests Radiation safety and radiobiology: redistribution in fractionation in Radiology. Cells that survive a fraction because they were in a resistant phase progress through the cycle, and some of them reach sensitive phases by the next 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: redistribution in fractionation?

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.