Radiosensitivity of tumour depends on:
**Core Concept**
Radiosensitivity refers to the susceptibility of a tumor to damage caused by ionizing radiation. It is a critical factor in radiation therapy, as it determines the effectiveness of treatment and the potential for side effects. The radiosensitivity of a tumor depends on various cellular and molecular characteristics.
**Why the Correct Answer is Right**
The correct answer is related to the presence of hypoxic cells within the tumor. Hypoxic cells are more resistant to radiation damage due to the lack of oxygen, which is necessary for the formation of free radicals that cause DNA damage. Tumors with a high proportion of hypoxic cells are more resistant to radiation therapy and may require higher doses or more frequent treatments. The presence of hypoxic cells is often associated with a poorer prognosis and a lower response to radiation therapy.
**Why Each Wrong Option is Incorrect**
**Option A:** DNA repair mechanisms are indeed important in determining the sensitivity of cells to radiation, but they are not the primary factor in radiosensitivity.
**Option B:** Tumor vascularity is an important factor in determining the effectiveness of radiation therapy, but it is not directly related to radiosensitivity.
**Option C:** Tumor size is not a direct factor in radiosensitivity, although larger tumors may require higher doses of radiation.
**Clinical Pearl / High-Yield Fact**
When considering radiation therapy, it is essential to assess the tumor's radiosensitivity by evaluating factors such as tumor hypoxia, DNA repair mechanisms, and vascularization. This information can help guide treatment decisions and optimize patient outcomes.
**Correct Answer:** C. Tumor hypoxia.