NEET-PG 2023 — Radiology

Question 1: A woman with endometrial carcinoma is undergoing radiotherapy. Which of the following statements about radiation therapy is true?

• A. Small intestinal mucosa is radioresistant.
• B. Rapidly proliferating cells are radioresistant.
• C. Intensity is inversely proportional to the square of the distance from the source. (Correct Answer)
• D. Small blood vessels are radioresistant.

Explanation: ***Intensity is inversely proportional to the square of the distance from the source.*** - This statement accurately describes the **inverse square law**, a fundamental principle in radiation physics, meaning radiation intensity decreases rapidly as the distance from the source increases. - This principle is crucial in **radiotherapy planning** to ensure precise dose delivery to the tumor while minimizing exposure to surrounding healthy tissues. *Small blood vessels are radioresistant.* - **Small blood vessels** (capillaries and arterioles) are actually **radiosensitive** and are often damaged by radiation, leading to late effects such as fibrosis and atrophy. - Damage to the vascular endothelium can cause **vascular insufficiency**, contributing to long-term tissue damage in irradiated areas. *Rapidly proliferating cells are radioresistant.* - Cells that are **rapidly proliferating** (have a high mitotic rate) are generally **radiosensitive**, making them more susceptible to radiation-induced damage. - This is the basis for using radiation therapy to target fast-growing cancers, as the radiation effectively destroys cells during their division phase. *Small intestinal mucosa is radioresistant.* - The **small intestinal mucosa** is composed of rapidly dividing cells and is therefore among the **most radiosensitive tissues** in the body. - This radiosensitivity often leads to common side effects of abdominal and pelvic radiotherapy, such as **nausea, vomiting, and diarrhea**.