Which of the following is not used for the treatment of cancer

Options

A. `K^(40)`
B. `Co^(60)`
C. `Sr^(90)`
D. `I^(131)`

Answer

To determine which of the following isotopes is not used for the treatment of cancer, we will analyze each option provided.

1. **Potassium-40**: This isotope is naturally occurring and is not typically used in cancer treatment. It is a stable isotope and does not have therapeutic applications in oncology.

2. **Strontium-90**: This isotope is used in cancer treatment, particularly for certain types of bone cancer. It emits beta radiation, which can be effective in targeting cancerous cells.

3. **Iodine-131**: This isotope is commonly used in the treatment of thyroid cancer and hyperthyroidism. It is effective because it is selectively taken up by thyroid tissue, allowing for targeted radiation therapy.

4. **Cobalt-60**: While cobalt-60 is indeed used in radiation therapy for cancer treatment, it is primarily used as an external source of radiation rather than for direct implantation. It is widely utilized in radiotherapy for various cancers.

Based on the analysis:

- Potassium-40 is not used for cancer treatment.
- Strontium-90 and Iodine-131 are used for cancer treatment.
- Cobalt-60 is used in radiation therapy for cancer.

Thus, the correct answer to the question "Which of the following is not used for the treatment of cancer?" is **Potassium-40**.

### Summary of Steps:
1. Identify the isotopes listed in the question.
2. Analyze the use of each isotope in cancer treatment.
3. Determine which isotope is not used for cancer treatment.
4. Conclude with the correct answer.