Radiation safety and radiobiology: oxygen enhancement ratio: 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: oxygen enhancement ratio

Sample item

A radiation oncologist chooses a carbon ion beam for a hypoxic radioresistant tumour. Which property explains the advantage over photons?

ACarbon ions act only through indirect damage by free radicalsBHypoxic cells are more sensitive to densely ionising radiation than aerobic cellsCCarbon ions have a lower LET than photonsDHigh LET radiation has an oxygen enhancement ratio close to 1

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

The answer and the reasoning

D. High LET radiation has an oxygen enhancement ratio close to 1

With low-LET photons, oxygen increases cell kill about three times (OER about 3). With high-LET radiation, most damage is direct and does not rely on oxygen, so the OER approaches 1 and hypoxic cells are killed nearly as well.

Option by option

A. Carbon ions act only through indirect damage by free radicals
High LET radiation causes mainly direct DNA damage and indirect damage is less important.
B. Hypoxic cells are more sensitive to densely ionising radiation than aerobic cells
Hypoxic cells are not more sensitive, but their relative resistance is lost.
C. Carbon ions have a lower LET than photons
Carbon ions are high LET, not low LET.
D. High LET radiation has an oxygen enhancement ratio close to 1 (correct)
Correct. Direct damage by densely ionising radiation is not oxygen dependent.

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, High LET radiation has an oxygen enhancement ratio close to 1. With low-LET photons, oxygen increases cell kill about three times (OER about 3).

Why is "Carbon ions act only through indirect damage by free radicals" not the answer?

High LET radiation causes mainly direct DNA damage and indirect damage is less important.

Why is "Hypoxic cells are more sensitive to densely ionising radiation than a…" not the answer?

Hypoxic cells are not more sensitive, but their relative resistance is lost.

Why is "Carbon ions have a lower LET than photons" not the answer?

Carbon ions are high LET, not low LET.

What concept does this question test?

It tests Radiation safety and radiobiology: oxygen enhancement ratio in Radiology. With high-LET radiation, most damage is direct and does not rely on oxygen, so the OER approaches 1 and hypoxic cells are killed nearly as well.

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: oxygen enhancement ratio?

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.