Radiobiology: lethal dose: 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 · Radiobiology: lethal dose

Sample item

In an unprotected human exposed to uniform whole-body irradiation without medical treatment, the LD50/60 is approximately:

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

The answer and the reasoning

C. 4 Gy

The dose that kills half of an exposed population within 60 days, mainly from bone marrow failure, is about 3 to 5 Gy without supportive care. Medical care such as transfusion and antibiotics shifts it higher.

Option by option

  • A. 40 Gy

    Such doses cause CNS syndrome and death within days.

  • B. 0.4 Gy

    This is far too low to cause bone marrow death in half of those exposed.

  • C. 4 Gy (correct)

    Correct. About 4 Gy is the usual quoted figure.

  • D. 14 Gy

    At this dose, gastrointestinal syndrome would dominate and few would survive 60 days.

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 C, 4 Gy. The dose that kills half of an exposed population within 60 days, mainly from bone marrow failure, is about 3 to 5 Gy without supportive care.

Why is "40 Gy" not the answer?

Such doses cause CNS syndrome and death within days.

Why is "0.4 Gy" not the answer?

This is far too low to cause bone marrow death in half of those exposed.

Why is "14 Gy" not the answer?

At this dose, gastrointestinal syndrome would dominate and few would survive 60 days.

What concept does this question test?

It tests Radiobiology: lethal dose in Radiology. Medical care such as transfusion and antibiotics shifts it higher.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Radiobiology: lethal dose?

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.