Radiation Oncology Basics — MCQs

Q: Which type of lung tumor is most responsive to radiotherapy?

Small cell lung cancer (SCLC). ***Small cell lung cancer (SCLC)*** - SCLC is **highly sensitive to chemotherapy and radiation therapy** [2] due to its rapid growth rate and proliferative nature. - While frequently presenting with metastatic disease, local control with **radiotherapy** combined with chemotherapy is crucial, especially in limited-stage disease, and leads to significant tumor shrinkage. *Squamous cell CA* - Squamous cell carcinoma (SCC) is generally **less sensitive** to radiation therapy compared to SCLC, though it is often included in treatment plans for local control. - It tends to grow slower than SCLC and is primarily associated with a **smoking history**. *Adeno CA* - Adenocarcinoma (Adeno CA) is the **most common type of non-small cell lung cancer (NSCLC)**, and its response to radiotherapy varies. - While radiation is used, particularly for **local control or palliation** [1], it is not as uniquely responsive as SCLC, and targeted therapies are often preferred for systemic treatment. *All types respond differently to treatment.* - While it is true that all tumors respond differently based on their histology and individual patient factors, this option does not identify the **most responsive type** as requested by the question. - This statement is a general truth but **lacks the specificity** needed to answer which specific type is most responsive to radiotherapy.

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.

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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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