Radiation Oncology Basics — MCQs

Radiation Oncology Basics Indian Medical PG Practice Questions and MCQs

Question 151: Mantle irradiation is used in:

A. Hodgkin's disease (Correct Answer)
B. Neuroblastoma
C. Chest secondaries from some cancers
D. Leukaemia

Explanation: **Hodgkin's disease** - **Mantle irradiation** is a historical radiation therapy technique specifically designed for **Hodgkin's lymphoma**, targeting lymph node regions above the diaphragm (cervical, supraclavicular, axillary, and mediastinal). - This method was used to irradiate contiguous lymph node chains, which is characteristic of Hodgkin's lymphoma spread. *Neuroblastoma* - **Neuroblastoma** is a solid tumor of childhood originating from neural crest cells, typically treated with surgery, chemotherapy, and sometimes local radiation to the primary tumor site, not mantle fields. - It does not primarily involve the cervical, supraclavicular, axillary, and mediastinal lymph nodes in a pattern suitable for mantle irradiation. *Chest secondaries from some cancers* - **Chest secondaries**, or metastases, from other cancers would require radiation fields tailored to the specific metastatic sites, which vary greatly depending on the primary cancer and spread pattern. - Mantle fields are too broad and specific to lymph node regions to be appropriate for varied metastatic disease. *Leukemia* - **Leukemia** is a cancer of the blood and bone marrow, typically treated with systemic chemotherapy and sometimes total body irradiation (TBI) if bone marrow transplantation is planned. - It does not involve localized lymph node chains in a way that would be effectively treated with mantle irradiation.

Question 152: Most radiosensitive tumor among the following is

A. Dysgerminoma (Correct Answer)
B. Osteogenic sarcoma
C. Parotid carcinoma
D. Bronchogenic carcinoma

Explanation: ***Dysgerminoma*** - **Dysgerminomas** are highly **radiosensitive** tumors, meaning they respond very well to radiation therapy. - This characteristic is often exploited in their treatment, especially for widespread disease or as adjuvant therapy. *Osteogenic sarcoma* - **Osteogenic sarcomas** (osteosarcomas) are generally **radioresistant**, requiring high doses of radiation for local control, often with limited success. - Treatment primarily relies on **surgery** and **chemotherapy**. *Parotid carcinoma* - **Parotid carcinomas** exhibit variable radiosensitivity depending on their histology, but generally are not considered among the most radiosensitive tumors. - Postoperative **radiotherapy** is often used for high-risk features rather than as primary monotherapy. *Bronchogenic carcinoma* - **Bronchogenic carcinomas** (lung cancers) show variable radiosensitivity. **Small cell lung carcinoma** is more radiosensitive than **non-small cell lung carcinoma**, but neither is considered as radiosensitive as dysgerminoma. - Treatment often involves **multimodality therapy** including chemotherapy, surgery, and radiation, with radiation efficacy depending on tumor type and stage.

Question 153: The technique employed in radiotherapy to counteract the effect of tumour motion due to breathing is known as –

A. Tracking
B. Gating (Correct Answer)
C. Modulation
D. Arc technique

Explanation: ***Gating*** - **Respiratory gating** involves delivering radiation only during specific phases of the patient's breathing cycle when the tumor is within a defined target window. - This technique helps to **minimize the irradiated volume** of healthy tissue by avoiding treatment when the tumor moves out of the planned treatment field. *Tracking* - **Respiratory tracking** involves actively adjusting the radiation beam in real-time to follow the motion of the tumor during breathing. - While it aims to compensate for motion, it is a different mechanism from gating, which involves turning the beam on and off. *Modulation* - **Intensity-modulated radiation therapy (IMRT)** and similar techniques focus on varying the intensity of the radiation beam across the treatment field to conform the dose to the tumor shape. - Modulation addresses dose distribution within a target, rather than directly managing tumor motion due to respiration. *Arc technique* - **Arc therapy** (e.g., VMAT) involves continuous delivery of radiation as the treatment machine rotates around the patient. - This technique optimizes dose delivery angles and conformity but does not inherently counteract tumor motion, although it can be combined with motion management.

Question 154: Which radiotherapy technique involves the use of remote afterloading to deliver radiation directly to the tumor?

A. Brachytherapy (Correct Answer)
B. External Beam Radiotherapy
C. Stereotactic Radiotherapy
D. Proton Beam Radiotherapy

Explanation: ***Correct: Brachytherapy*** - **Remote afterloading** is a hallmark of modern brachytherapy, where radioactive sources are automatically advanced into catheters placed within or near the tumor. - This technique allows for the delivery of a **high dose of radiation directly to the tumor** while sparing surrounding healthy tissues. - Examples include **intracavitary** (cervical cancer), **interstitial** (prostate cancer), and **intraluminal** (esophageal cancer) brachytherapy. *Incorrect: External Beam Radiotherapy* - This technique involves delivering radiation from a machine **outside the body** to target a tumor. - It does not involve the direct placement of radioactive sources within the patient or the use of **remote afterloading**. *Incorrect: Stereotactic Radiotherapy* - While a precise form of external beam radiotherapy using focused beams, it still involves an **external source** of radiation. - It does not utilize internal radioactive sources or **afterloading techniques**. *Incorrect: Proton Beam Radiotherapy* - This is an advanced form of external beam radiotherapy that uses **protons instead of photons** to deliver radiation with high precision. - It does not involve the placement of radioactive sources within the patient or the use of **remote afterloading**.

Question 155: What is the next imaging study recommended for evaluating a patient with suspected radiation-induced lung injury?

A. Standard chest radiograph
B. Magnetic resonance imaging
C. Thoracic ultrasound
D. High-resolution computed tomography (Correct Answer)

Explanation: ***High-resolution computed tomography*** - **HRCT** is the gold standard for diagnosing and assessing the extent of radiation-induced lung injury (**RILI**) due to its superior spatial resolution. - It can identify subtle interstitial changes, **ground-glass opacities**, **consolidation**, and **fibrosis** that are characteristic of RILI. *Standard chest radiograph* - A standard chest radiograph has limited sensitivity in detecting early interstitial changes or mild forms of **RILI**. - It can miss subtle findings and often shows abnormalities only in advanced stages. *Magnetic resonance imaging* - While MRI can provide functional information and assess soft tissue involvement, it has limitations in imaging lung parenchyma due to **motion artifacts** and low signal intensity from air. - Its role in the routine diagnosis of **RILI** is secondary to HRCT. *Thoracic ultrasound* - Thoracic ultrasound is useful for identifying **pleural effusions**, **pneumothorax**, and peripheral lung consolidations. - However, it has very limited penetration and is not suitable for evaluating deeper lung parenchyma or diffuse interstitial lung disease like **RILI**.

Question 156: Gamma knife utilizes which radioactive isotope?

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

Explanation: ***Cobalt-60*** - The **Gamma Knife** employs multiple sources of **cobalt-60** to deliver highly focused beams of gamma radiation. - These beams converge at precise intracranial targets to treat various conditions like **tumors** and **vascular malformations**. *Strontium 89* - **Strontium-89** is a beta-emitting isotope used primarily in the palliation of **bone pain** from metastatic cancer. - It is not used in the **Gamma Knife** for focused intracranial radiation therapy. *I-131* - **Iodine-131** is a beta and gamma-emitting isotope used mainly in the treatment of **thyroid cancer** and hyperthyroidism. - Its application is systemic or targeted to the thyroid gland, not via the **Gamma Knife**. *P-32* - **Phosphorus-32** is a beta-emitting isotope historically used in applications like treating polycythemia vera and sometimes for intracavitary radiation. - It is not a component of the **Gamma Knife** system.

Question 157: Radiation used most commonly for pain management due to bone metastasis is?

A. Cobalt-60
B. Strontium-89 (Correct Answer)
C. Iridium-192
D. Tritium

Explanation: ***Strontium-89*** - **Strontium-89** is a **beta-emitting radiopharmaceutical** specifically approved for **palliation of painful bone metastases** - Administered **intravenously**, it preferentially localizes to areas of increased osteoblastic activity in **metastatic bone lesions** - Provides effective pain relief in **70-80% of patients** with widespread bone metastases, particularly from prostate and breast cancer - It is one of the **most commonly used** radiation modalities specifically indicated for bone metastasis pain management *Cobalt-60* - **Cobalt-60** was historically used in **external beam radiotherapy (EBRT)** teletherapy units for treating bone metastases - In modern practice, Cobalt-60 has been largely **replaced by linear accelerators (LINAC)** for EBRT - While EBRT is used for localized bone metastases, for the specific indication of widespread bone pain, radiopharmaceuticals are preferred *Iridium-192* - **Iridium-192** is primarily used in **brachytherapy** for localized tumor treatment - Not typically used for **bone metastases pain management** - More commonly employed for gynecological, prostate, and other site-specific cancers *Tritium* - **Tritium** (Hydrogen-3) is a low-energy beta-emitter used in **research and diagnostics** - Not used for **therapeutic radiation** - Its low energy and short range make it unsuitable for treating bone lesions

Question 158: In which of the following conditions is Stereotactic Radiosurgery primarily indicated?

A. Ependymoma
B. Arteriovenous malformation of the brain (Correct Answer)
C. Medulloblastoma of the spinal cord
D. Glioblastoma multiforme

Explanation: ***Arteriovenous malformation of the brain*** - **Stereotactic Radiosurgery (SRS)** is a highly effective treatment for brain AVMs, particularly those that are **small to medium-sized** and located in eloquent brain regions. - SRS delivers a **highly focused dose of radiation** directly to the AVM, causing the abnormal blood vessels to gradually close off over time, reducing the risk of hemorrhage. *Medulloblastoma of the spinal cord* - Medulloblastoma is a **highly aggressive malignant brain tumor** that often metastasizes to the spinal cord via cerebrospinal fluid. - Treatment for spinal medulloblastoma typically involves **cranio-spinal irradiation with chemotherapy**, and SRS is generally not the primary treatment modality for diffuse spinal disease. *Ependymoma* - Ependymomas are tumors arising from the **ependymal cells** lining the ventricles and spinal cord. - While surgery is the primary treatment, radiotherapy, including **conventional fractionated external beam radiation**, is often used as adjuvant therapy, but SRS is less commonly the sole primary indication. *Glioblastoma multiforme* - Glioblastoma multiforme (GBM) is the **most aggressive primary brain tumor** and is typically treated with **maximal surgical resection followed by concurrent chemoradiotherapy**. - While SRS may be used in carefully selected cases for **recurrent GBM** or as a boost in primary treatment, it is not the primary solitary indication for initial management.

Question 159: Commonly used type of radiation in radiotherapy is:

A. Alpha rays
B. Beta rays
C. Gamma rays
D. X-rays (Correct Answer)

Explanation: ***X-rays*** - **X-rays** are the most commonly used type of radiation in external beam radiotherapy due to their ability to penetrate tissues and deliver precise doses to tumors. - Modern radiotherapy devices, such as **linear accelerators**, generate high-energy X-rays for cancer treatment. *Alpha rays* - **Alpha particles** have a very limited penetration range in tissue, making them unsuitable for treating deep-seated tumors with external beam radiotherapy. - Their primary use is in targeted internal radiation therapies, such as **alpha-emitting radioisotopes** in specific radiopharmaceuticals. *Beta rays* - **Beta particles** have a slightly greater penetration than alpha particles but are still generally limited for superficial treatment or internal applications rather than external beam therapy for most cancers. - They are used in certain types of **brachytherapy** or in radioisotope treatments. *Gamma rays* - **Gamma rays** are used in radiotherapy, particularly in older cobalt-60 teletherapy units, but less frequently than X-rays generated by linear accelerators today. - While possessing good penetration, their energy spectrum is fixed by the isotope, offering less flexibility in treatment planning than variable-energy X-rays.

Question 160: What is the standard radiation dose delivered to Point A in the treatment of cervical cancer?

A. 3000 cGy
B. 5000 cGy
C. 8500 cGy
D. 7000 cGy (Correct Answer)

Explanation: ***7000 cGy*** - The standard radiation dose delivered to **Point A** in the treatment of cervical cancer, when combined with external beam radiation therapy and brachytherapy, typically totals around **7000-8000 cGy**. This dose aims to achieve tumor control while minimizing toxicity to surrounding organs. - **Point A** is a defined anatomical reference point used in brachytherapy planning for cervical cancer, representing the approximate location of the **uterine arteries** and the site of potential tumor recurrence. *3000 cGy* - A dose of **3000 cGy** is too low for definitive treatment of cervical cancer. Such a dose might be used as a palliative measure or part of a more extensive treatment regimen, but not as the total dose to Point A. - Inadequate dosing increases the risk of **local failure** and recurrence of the cancer. *5000 cGy* - While **5000 cGy** is a commonly used dose for external beam radiation therapy (EBRT) in cervical cancer, it is typically supplemented with brachytherapy to boost the dose to Point A and the tumor. - This dose alone would likely be insufficient to achieve adequate tumor control at **Point A** and the whole tumor volume. *8500 cGy* - A dose of **8500 cGy** to Point A might be considered in some highly selected and advanced cases, but it generally approaches the upper limits of tolerance for surrounding critical structures. - Doses this high carry an increased risk of **severe late toxicities** to organs such as the bladder, rectum, and small bowel.

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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