Question:
A cancer patient undergoes radiotherapy. Pick the true statement regarding radiosensitivity of tissues:
A cancer patient undergoes radiotherapy. Pick the true statement regarding radiosensitivity of tissues:
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One option is a pure physics law about distance and dose; the others misstate which tissues are sensitive.
Updated On: Jun 23, 2026
- Rapidly dividing cells are resistant to radiation
- GI mucosa is one of the most radioresistant tissues in the body
- The intensity of radiation is inversely proportional to the square of the distance from the source
- Small blood vessels are least resistant to radiation
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The Correct Option is C
Solution and Explanation
Step 1: Test each statement against radiobiology.
Step 2: The inverse square law is a true physics principle: radiation intensity falls off as the inverse square of distance from the source, so \( I \propto \dfrac{1}{r^{2}} \). Doubling the distance cuts the dose to one-fourth. This is option 3 and is correct.
Why the others are false: By the law of Bergonie and Tribondeau, rapidly dividing cells are the MOST radiosensitive, not resistant, so option 1 is wrong. The GI mucosa has a high turnover and is one of the most radioSENSITIVE tissues, not radioresistant, so option 2 is wrong. Small blood vessels and mature, non-dividing tissues are relatively radioRESISTANT, so calling them least resistant in option 4 is wrong.
Ref: Radiation physics, inverse square law (J Med Phys 2012;37(2):107).
Step 2: The inverse square law is a true physics principle: radiation intensity falls off as the inverse square of distance from the source, so \( I \propto \dfrac{1}{r^{2}} \). Doubling the distance cuts the dose to one-fourth. This is option 3 and is correct.
Why the others are false: By the law of Bergonie and Tribondeau, rapidly dividing cells are the MOST radiosensitive, not resistant, so option 1 is wrong. The GI mucosa has a high turnover and is one of the most radioSENSITIVE tissues, not radioresistant, so option 2 is wrong. Small blood vessels and mature, non-dividing tissues are relatively radioRESISTANT, so calling them least resistant in option 4 is wrong.
Ref: Radiation physics, inverse square law (J Med Phys 2012;37(2):107).
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