Radiation Oncology Basics — MCQs

Radiation Oncology Basics Indian Medical PG Practice Questions and MCQs

Question 141: Stereotactic Radiosurgery is a form of –

A. Radioiodine therapy
B. Cryosurgery
C. Robotic Surgery
D. Radiotherapy (Correct Answer)

Explanation: ***Radiotherapy*** - **Stereotactic radiosurgery** is a highly precise form of **radiotherapy** that delivers a single high dose or multiple fractionated high doses of radiation to a specific target area. - It uses focused **radiation beams** to treat tumors or other lesions, often as an alternative to conventional surgery, by causing damage to the DNA of target cells. *Radioiodine therapy* - **Radioiodine therapy** primarily uses **iodine-131** to treat thyroid conditions like hyperthyroidism or thyroid cancer. - This involves the patient ingesting a radioactive isotope, unlike the external radiation beams used in radiosurgery. *Cryo Surgery* - **Cryosurgery** involves the use of **extreme cold** to destroy abnormal tissues. - It is a physical method of tissue destruction and does not involve radiation. *Robotic Surgery* - **Robotic surgery** utilizes robotic systems to assist in performing surgical procedures, enhancing precision, and control for the surgeon. - This is a mode of performing traditional surgery and does not involve radiation as its primary therapeutic agent.

Question 142: What is the radiation tolerance of the whole liver?

A. 30 Gy (Correct Answer)
B. 45 Gy
C. 15 Gy
D. 40 Gy

Explanation: ***30 Gy*** - The **whole liver** has a relatively low radiation tolerance, with a typical threshold for developing **radiation-induced liver disease (RILD)** around 30-35 Gy for conventional fractionation. - Exceeding this dose to a significant volume of the liver can lead to **hepatic dysfunction** and failure. *45 Gy* - This dose is generally too high for whole-liver irradiation and would significantly increase the risk of **severe liver toxicity** in many patients. - While small volumes might tolerate higher doses, the **mean dose to the entire organ** should remain much lower. *15 Gy* - This dose is typically considered well below the tolerance limit for the whole liver and is unlikely to cause significant complications. - It might be used for palliation or as a component of fractionated regimens with higher doses to smaller target volumes. *40 Gy* - This dose is generally considered above the safe limits for irradiating the **entire liver**, posing a substantial risk of **radiation-induced liver damage**. - While some highly conformal techniques might deliver this to very small, localized tumors, it is not the tolerance for the **whole organ**.

Question 143: In cervical cancer brachytherapy, the primary reference point for dose prescription is -

A. Point A (Correct Answer)
B. Point B
C. Side walls of pelvis
D. Point H

Explanation: ***Point A*** - **Point A** is defined as 2 cm lateral to the central canal of the uterus and 2 cm superior to the external os, representing a dose estimation to the **parametrium** and a critical reference for tumoricidal dose. - This point serves as the **primary prescription and reporting point** for brachytherapy in cervical cancer, as it is highly correlated with treatment outcomes and complications. - Established by **ICRU Report 38** as the standard reference point for dose prescription. *Point B* - **Point B** is located 5 cm from the midline (3 cm lateral to Point A) at the level of Point A, and is primarily used to estimate the dose received by the **pelvic side wall** and regional lymphatics. - It provides an indication of dose to structures further from the applicator but is **not the primary prescription point** for the target volume in brachytherapy. *Side walls of pelvis* - The dose to the **side walls of the pelvis** is relevant for assessing potential toxicity to structures like the obturator nerve and external iliac vessels, and for ensuring adequate coverage of pelvic lymph nodes. - While critical for treatment planning, the side walls themselves are not a primary dose prescription point but rather a **region of interest** for dose constraints and coverage. *Point H* - **Point H** represents the reference point for estimating the dose to the **rectum** in brachytherapy, located at the posterior vaginal wall. - While important for assessing **rectal toxicity** and as a dose-limiting structure, Point H is used for reporting organ-at-risk doses, not for primary tumor dose prescription.

Question 144: Which of the following elements is obsolete in radiotherapy:

A. Iridium 192
B. Cesium 137
C. Cobalt 60
D. Radium 226 (Correct Answer)

Explanation: ***Radium 226*** - **Radium 226** was one of the earliest radioactive sources used in brachytherapy but has largely been replaced due to its decay products producing **radon gas**, a toxic noble gas. - Its high **gamma energy** and long half-life made it difficult to shield and handle, leading to significant radiation safety concerns. *Iridium 192* - **Iridium 192** is a widely used radioisotope in **HDR (High-Dose Rate) brachytherapy** due to its relatively short half-life and suitable gamma energy for dose delivery. - It allows for flexible treatment planning and precise targeting in various cancer sites. *Cesium 137* - **Cesium 137** is commonly used in **LDR (Low-Dose Rate) brachytherapy** and some teletherapy units, offering a longer half-life than Iridium-192. - Its gamma energy is lower than that of Radium-226, making it safer to handle and shield. *Cobalt 60* - **Cobalt 60** was historically and is still used in **teletherapy units (gamma knives)** for external beam radiotherapy, especially for brain tumors. - Its high-energy gamma rays provide excellent dose penetration, though it has largely been replaced by linear accelerators in conventional external beam radiotherapy.

Question 145: True about Gamma Knife radiotherapy

A. It is used for both benign and malignant cases (Correct Answer)
B. Reduced blood loss in surgery
C. Gamma rays are emitted from uranium
D. It is a special kind of knife

Explanation: ***It is used for both benign and malignant cases*** - **Gamma Knife radiosurgery** precisely targets and treats various intracranial conditions, including both **benign tumors** (e.g., meningiomas, acoustic neuromas) and **malignant tumors** (e.g., metastatic brain lesions). - Its high precision allows for effective treatment while minimizing damage to surrounding healthy tissue. *Reduced blood loss in surgery* - While Gamma Knife is a **non-invasive procedure** that does not involve surgical incisions or general anesthesia, it is not a traditional "surgery" in the sense that involves blood loss. - The primary benefit is avoiding surgical risks, not reducing blood loss during an actual incision. *Gamma rays are emitted from uranium* - Gamma Knife technology utilizes **cobalt-60** as its radioactive source, not uranium. - Cobalt-60 emits **gamma rays** that are precisely focused to target the intended lesion. *It is a special kind of knife* - The term "knife" in Gamma Knife refers to its **precision and cutting-like accuracy** in targeting and ablating lesions, not to an actual surgical blade. - It is a form of **stereotactic radiosurgery**, delivering highly focused radiation beams.

Question 146: Stereotactic Radiotherapy is used in:

A. Inoperable Stage 1 Lung Tumor (Correct Answer)
B. Lymphangitis Carcinomatosa
C. Miliary Lung Metastasis
D. Tumor at the base of tongue with new Lymph Node enlargement

Explanation: ***Inoperable Stage 1 Lung Tumor*** - **Stereotactic Radiotherapy (SRT)** is highly effective for **inoperable Stage 1 lung tumors** because it delivers high doses of radiation with extreme precision, maximizing tumor control while sparing surrounding healthy tissue. - The **precision** of SRT makes it an excellent option for localized, small tumors that cannot be surgically removed due to patient comorbidities or tumor location. *Lymphangitis Carcinomatosa* - **Lymphangitis carcinomatosa** involves diffuse infiltration of the pulmonary lymphatic system by cancer cells and is not amenable to localized radiation techniques like SRT. - Treatment for lymphangitis carcinomatosa typically involves **systemic therapy** such as chemotherapy or targeted therapy, rather than focal radiation. *Miliary Lung Metastasis* - **Miliary lung metastases** refer to widespread, small (~2-4mm) nodules throughout both lungs, indicating advanced systemic disease. - SRT is a **localized treatment** and therefore not appropriate for diffuse, multifocal disease like miliary metastases, which requires systemic treatment. *Tumor at the base of tongue with new Lymph Node enlargement* - A tumor at the **base of the tongue with new lymph node enlargement** indicates a larger disease burden, likely requiring a combination of **surgery, conventional radiation therapy, and/or chemotherapy**. - While radiation is a component of treatment for head and neck cancers, **SRT is typically reserved for smaller, well-defined lesions**, or in specific cases as a boost or for recurrences, not usually for initial treatment of a larger primary tumor with nodal involvement.

Question 147: Gamma knife utilizes -

A. 1-131
B. P-32
C. Strontium 89
D. Cobalt-60 (Correct Answer)

Explanation: ***Cobalt-60*** - The **gamma knife** is a highly specialized radiosurgery tool that uses multiple beams of **gamma radiation** to accurately treat targets in the brain or spine. - These beams are generated from approximately 201 individual sources of **Cobalt-60**, which emit high-energy photons focused on the target area, minimizing damage to surrounding healthy tissue. *I-131* - **Iodine-131** is primarily used in the treatment of **thyroid disorders**, such as hyperthyroidism and thyroid cancer, due to its ability to concentrate in thyroid tissue. - It emits both **beta particles** and **gamma rays**, but its primary therapeutic effect comes from the beta particles, not as a source for external beam radiation in radiosurgery. *P-32* - **Phosphorus-32** is a pure beta emitter with a relatively short range, making it suitable for certain **intracavitary or interstitial applications** in oncology. - It is utilized in conditions like **polycythemia vera** or for localized treatment of certain **cancers** but not as an external radiation source for gamma knife radiosurgery. *Strontium-89* - **Strontium-89** is a pure **beta emitter** used for **palliative treatment of bone pain** caused by metastatic bone disease. - It preferentially accumulates in areas of increased bone turnover and is not used as a radiation source for brain or spinal radiosurgery devices like the gamma knife.

Question 148: 'Gamma knife' is a term used to denote which of the methods of treatment?

A. Radiotherapy (Correct Answer)
B. Chemotherapy
C. Radioisotope scan
D. Nuclear medicine

Explanation: ***Radiotherapy*** - The **gamma knife** is a highly precise form of **stereotactic radiosurgery** that delivers many small beams of gamma radiation to a target. - It is used to treat conditions like **brain tumors**, arteriovenous malformations, and trigeminal neuralgia without open surgery. *Chemotherapy* - **Chemotherapy** involves the use of drugs to destroy cancer cells, often affecting the entire body. - It does not involve focused radiation beams and is fundamentally different from a gamma knife. *Radioisotope scan* - A **radioisotope scan** (or nuclear scan) uses radioactive tracers to image the function and structure of organs. - It is a diagnostic imaging technique, not a method of treatment like the gamma knife. *Nuclear medicine* - **Nuclear medicine** is a branch of medicine dealing with the use of radioactive substances in diagnosis and treatment. - While gamma knife uses gamma radiation, the term nuclear medicine encompasses a broader range of diagnostic and therapeutic applications, and "gamma knife" specifically refers to a **radiotherapy technique**.

Question 149: Which of the following radioactive isotopes is not used for brachytherapy?

A. Iodine-125
B. Iridium-192
C. Iodine-131 (Correct Answer)
D. Cobalt-60

Explanation: ***Iodine-131*** - **Iodine-131** is primarily used for **systemic radionuclide therapy** due to its emission of **beta particles** and **gamma rays**, making it suitable for treating diffuse diseases like **thyroid cancer** and **hyperthyroidism**. - Its mechanism of action relies on systemic uptake rather than localized placement within or next to a tumor, which defines **brachytherapy**. *Iodine-125* - **Iodine-125** is a common isotope used in **low-dose-rate (LDR) brachytherapy**, particularly for **prostate cancer** and **ocular melanoma**. - It emits **low-energy gamma and X-rays**, providing highly localized radiation with a steep dose fall-off, minimizing damage to surrounding healthy tissue. *Iridium-192* - **Iridium-192** is widely used in **high-dose-rate (HDR) brachytherapy** for various cancers, including **cervical**, **prostate**, **breast**, and **skin cancers**. - It emits **gamma rays** and has a shorter half-life than Iodine-125, allowing for higher dose rates over shorter treatment durations. *Cobalt-60* - **Cobalt-60** was historically used in **brachytherapy** and **teletherapy** but has largely been replaced by newer isotopes for brachytherapy due to its high energies and larger source size. - While its use in brachytherapy has decreased, it is still employed in specific applications and **external beam radiation therapy (teletherapy)**.

Question 150: A radioisotope used in both teletherapy and brachytherapy is

A. Gold-198
B. Iodine-125
C. Cesium-137 (Correct Answer)
D. Radium-226

Explanation: ***Cesium-137*** - Cesium-137 is used in both **teletherapy (external beam radiation)** units, particularly older ones, and in **brachytherapy sources** for interstitial or intracavitary applications. - It emits **gamma rays** with an energy suitable for both types of therapy, giving it versatility. *Gold-198* - **Gold-198** is primarily used in **brachytherapy** as temporary or permanent implants, particularly for conditions like prostate cancer. - Its short half-life and primary emission of **beta particles** with accompanying gamma rays make it less suitable for external teletherapy applications. *Iodine-125* - **Iodine-125** is almost exclusively used in **low-dose-rate (LDR) brachytherapy**, commonly for prostate cancer and ocular melanomas. - It emits **low-energy gamma and X-rays**, which have a very limited range, making it unsuitable for teletherapy. *Radium-226* - **Radium-226** was historically one of the first radioisotopes used in brachytherapy but has largely been replaced due to its strong **gamma emissions** and the associated safety risks. - It was never widely adopted for teletherapy machines because its decay products include gaseous **radon**, posing significant handling and safety challenges.

Practice by Chapter

Principles of Radiation Therapy

Practice Questions

Radiation Therapy Equipment

Practice Questions

Treatment Planning Process

Practice Questions

External Beam Radiation Therapy

Practice Questions

Brachytherapy

Practice Questions

3D Conformal Radiation Therapy

Practice Questions

Intensity-Modulated Radiation Therapy

Practice Questions

Image-Guided Radiation Therapy

Practice Questions

Stereotactic Radiosurgery

Practice Questions

Total Body Irradiation

Practice Questions

Palliative Radiation Therapy

Practice Questions

Combined Modality Treatments

Practice Questions

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