Radiation Oncology Basics — MCQs

Q: Which is used in both teletherapy and brachytherapy?

Cobalt 60. ***Cobalt 60*** - **Cobalt-60** is the correct answer as it is used in both **teletherapy and brachytherapy**. - **Teletherapy**: Cobalt-60 teletherapy machines (cobalt units) have been widely used for external beam radiation therapy and remain in use globally. - **Brachytherapy**: Cobalt-60 is used in both low-dose rate (LDR) and high-dose rate (HDR) brachytherapy applications, with Co-60 seeds and sources for various tumor sites. - Its high energy (1.17 and 1.33 MeV gamma rays) and suitable half-life (5.27 years) make it versatile for both modalities. *Iridium 192* - **Iridium-192** is predominantly used in **HDR brachytherapy** as a temporary implant source. - It is the most common radioisotope for modern HDR brachytherapy systems. - While it emits gamma radiation, it is **not routinely used for teletherapy** in clinical practice due to its lower energy and shorter half-life (74 days). *Palladium* - **Palladium-103** is used exclusively in **low-dose rate (LDR) brachytherapy**, particularly for permanent seed implants in prostate cancer. - Its lower energy photons and short half-life (17 days) make it unsuitable for teletherapy. *Iodine 131* - **Iodine-131** is primarily used in **nuclear medicine** for thyroid cancer treatment and hyperthyroidism (targeted radionuclide therapy). - It is not used for conventional external beam teletherapy or brachytherapy implants.

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

Caesium-137. ***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.

Q: Which radioisotope is commonly used in teletherapy?

Co-60. ***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

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Radiation Therapy Equipment

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Treatment Planning Process

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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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