Radiation Oncology Basics — MCQs

Radiation Oncology Basics Indian Medical PG Practice Questions and MCQs

Question 171: Which one of the following radioisotopes is not used as a permanent implant?

A. Iodine-125
B. Palladium-103
C. Gold-198
D. Caesium-137 (Correct Answer)

Explanation: ***Caesium-137*** - **Caesium-137** is primarily used in **high-dose-rate (HDR) brachytherapy** or teletherapy, where the source is temporarily placed to deliver a high dose over a short period. - Its **long half-life** (30.17 years) and high energy gamma emissions make it unsuitable for permanent implants, as it would expose patients to radiation for an extended and unsafe duration. *Iodine-125* - **Iodine-125** is a commonly used radioisotope for **permanent prostate brachytherapy implants** due to its relatively low energy and long half-life (59.4 days). - Its **low photon energy** allows for precise dose delivery within the target tissue with minimal dose to surrounding healthy tissues. *Palladium-103* - **Palladium-103** is another radioisotope frequently used in **permanent prostate brachytherapy implants**, similar to Iodine-125. - It has a shorter half-life (17 days) and lower energy compared to Iodine-125, making it suitable for treating **faster-growing tumors** that require a quicker dose delivery. *Gold-198* - **Gold-198** is a historical radioisotope used for **permanent interstitial implants**, particularly for head and neck cancers or sometimes prostate. - It has a relatively short half-life (2.7 days) and emits both beta particles and gamma rays, which can be useful for localized treatment but less commonly used now compared to Iodine-125 or Palladium-103.

Question 172: The element used for intracavitary brachytherapy in carcinoma of the cervix is:

A. Radio iodine
B. Cobalt-60
C. Caesium-137 (Correct Answer)
D. Strontium

Explanation: ***Caesium-137*** - **Caesium-137** is the most commonly used radioisotope for **intracavitary brachytherapy** in cervical carcinoma due to its suitable half-life and gamma-ray energy. - It allows for effective localized radiation delivery to the tumor while minimizing exposure to surrounding healthy tissues. *Cobalt-60* - While **Cobalt-60** is a radioisotope used in radiation therapy, its higher energy and longer half-life make it more suitable for **external beam radiotherapy** rather than intracavitary brachytherapy. - Its use in brachytherapy is less common compared to Caesium-137 for cervical cancer. *Radio iodine* - **Radio iodine (Iodine-131)** is primarily used for the treatment of **thyroid cancers** and hyperthyroidism, as the thyroid gland selectively absorbs iodine. - It is not indicated for the treatment of **cervical carcinoma**. *Strontium* - **Strontium-90** is a beta-emitting radioisotope primarily used in **superficial brachytherapy** for conditions like pterygium, not deep-seated tumors like cervical cancer. - Its beta radiation has limited penetration depth, making it unsuitable for intracavitary treatment of the cervix.

Question 173: Which radioisotope is commonly used in teletherapy?

A. Ra-226
B. Cs-137
C. Co-60 (Correct Answer)
D. Ir-192

Explanation: ***Co-60*** - **Cobalt-60** is a widely used radioisotope in teletherapy (external beam radiotherapy) due to its high-energy gamma emissions (1.17 and 1.33 MeV). - Its relatively long half-life of **5.27 years** makes it practical for sustained clinical use in **teletherapy units**. *Ra-226* - **Radium-226** was historically used in brachytherapy but has largely been replaced due to its alpha emissions, which are difficult to shield, and its long-lived radioactive decay products. - Its use for teletherapy is **not common** because of these safety concerns and the availability of more suitable isotopes. *Cs-137* - **Cesium-137** is primarily used in **brachytherapy** and some low-dose rate teletherapy machines for specific applications, but not as commonly as Co-60 for general teletherapy. - Its lower gamma energy (0.662 MeV) and shorter half-life than Co-60 (30.17 years) make it less ideal for the widespread **deep penetration** required in many teletherapy treatments. *Ir-192* - **Iridium-192** is predominantly used in **high-dose-rate (HDR) brachytherapy** for temporary implants, delivering radiation over short periods. - Its relatively short half-life of **73.8 days** and lower average gamma energy make it unsuitable for typical long-term teletherapy external beam applications.

Practice by Chapter

Principles of Radiation Therapy

Practice Questions

Radiation Therapy Equipment

Practice Questions

Treatment Planning Process

Practice Questions

External Beam Radiation Therapy

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Brachytherapy

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3D Conformal Radiation Therapy

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Intensity-Modulated Radiation Therapy

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Image-Guided Radiation Therapy

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Stereotactic Radiosurgery

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Total Body Irradiation

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Palliative Radiation Therapy

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Combined Modality Treatments

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