Radiation Oncology Basics — MCQs

Radiation Oncology Basics Indian Medical PG Practice Questions and MCQs

Question 21: Whole body electron therapy is useful in the management of which of the following conditions?

A. Nodular Lymphocyte Predominant Hodgkin Lymphoma
B. Sezary syndrome
C. Mycosis fungoides (Correct Answer)
D. Hodgkin's disease

Explanation: **Explanation:** **Total Skin Electron Beam Therapy (TSEBT)** is a specialized form of radiotherapy that utilizes the unique physical properties of electrons to treat superficial skin malignancies. Unlike X-rays, electrons have a limited range and a rapid "fall-off" in tissue, meaning they deliver a high dose to the skin surface (dermis and epidermis) while sparing deeper internal organs. **Why Mycosis Fungoides (MF) is the correct answer:** Mycosis Fungoides is the most common form of **Cutaneous T-Cell Lymphoma (CTCL)**. Since the disease often involves large areas of the skin surface but remains superficial for a long period, TSEBT is the treatment of choice for extensive plaque or erythrodermic stages. It provides excellent symptom relief and high complete remission rates by targeting the malignant T-cells infiltrating the skin. **Analysis of Incorrect Options:** * **Sezary Syndrome (B):** While related to MF, Sezary Syndrome is the leukemic (systemic) phase characterized by erythroderma and malignant cells in the peripheral blood. Treatment is primarily systemic (e.g., extracorporeal photopheresis, chemotherapy) rather than localized skin radiation. * **Hodgkin’s Disease & NLPHL (A & D):** These are nodal lymphomas. They require systemic chemotherapy and/or Involved Site Radiation Therapy (ISRT) using high-energy Photons (X-rays) to reach deep-seated lymph nodes. Electron therapy is too superficial for these conditions. **High-Yield Clinical Pearls for NEET-PG:** * **Energy used:** Typically low-energy electrons (6–9 MeV) are used to treat the skin up to a depth of approximately 5–10 mm. * **Stanford Technique:** The most common clinical method for delivering TSEBT, involving the patient standing in six different positions to ensure uniform skin coverage. * **Side Effects:** Acute effects include erythema, alopecia, and nail loss (onycholysis); long-term risks include secondary skin cancers and chronic xerosis.

Question 22: Which of the following statements about Gamma Knife is FALSE?

A. Focused radiation is delivered to the tumor.
B. It provides equal exposure to surrounding healthy tissue. (Correct Answer)
C. It is a type of stereotactic surgery.
D. It is primarily used for small brain tumors.

Explanation: **Explanation:** The **Gamma Knife** is a specialized form of **Stereotactic Radiosurgery (SRS)**. The fundamental principle of SRS is to deliver a high dose of radiation to a precisely defined target while ensuring a **steep dose gradient**. This means the radiation dose drops off rapidly outside the target area, thereby **sparing surrounding healthy tissue** from significant exposure. Therefore, Option B is false because the goal is the exact opposite of "equal exposure." * **Option A is correct:** Gamma Knife uses approximately 192–201 cobalt-60 sources. These beams converge at a single point (the isocenter), delivering a highly focused, lethal dose to the lesion. * **Option C is correct:** It is considered "surgery" without a scalpel. It uses a rigid stereotactic frame (or mask-based systems) to provide sub-millimeter accuracy, allowing for a single-fraction treatment. * **Option D is correct:** Due to its precision and the physical constraints of the machine, it is primarily indicated for small, well-defined intracranial lesions (typically <3–4 cm), such as acoustic neuromas, meningiomas, pituitary adenomas, and brain metastases. **High-Yield Clinical Pearls for NEET-PG:** * **Source:** Uses **Cobalt-60** ($^{60}$Co) which emits Gamma rays. * **Targeting:** Best for **intracranial** lesions; it cannot be used for extracranial (body) tumors (CyberKnife is used for those). * **Precision:** It offers the highest mechanical accuracy (0.15 mm) among all SRS platforms. * **Indications:** Arteriovenous Malformations (AVM), Trigeminal Neuralgia, and small brain tumors.

Question 23: A patient with a history of radiation therapy requires special consideration because:

A. The vascularity of the bone may be disrupted. (Correct Answer)
B. Salivary function may be increased.
C. Plaque accumulation greater than normal can be expected.
D. The potential for periodontal disease is greatly increased.

Explanation: **Explanation:** **Correct Option: A (The vascularity of the bone may be disrupted)** Radiation therapy, particularly for head and neck cancers, induces long-term changes in the microvasculature. High-dose radiation leads to **endarteritis obliterans**, a process characterized by the narrowing and occlusion of small blood vessels. This results in a state of **hypovascularity, hypocellularity, and hypoxia (the 3-H principle)**. When bone vascularity is compromised, its ability to repair and mount an immune response is severely diminished, leading to a high risk of **Osteoradionecrosis (ORN)** following invasive procedures like dental extractions. **Incorrect Options:** * **B:** Radiation to the head and neck typically causes **xerostomia** (dry mouth) due to irreversible damage to the acinar cells of the salivary glands, leading to *decreased*, not increased, salivary function. * **C & D:** While plaque accumulation and periodontal disease can occur due to poor oral hygiene and xerostomia, they are secondary effects. The most critical "special consideration" from a surgical and pathological standpoint in radiation oncology is the permanent alteration of bone vitality and blood supply. **High-Yield Clinical Pearls for NEET-PG:** * **Osteoradionecrosis (ORN):** Most commonly affects the **mandible** (due to its higher density and lower baseline vascularity compared to the maxilla). * **Threshold Dose:** The risk of ORN increases significantly when the radiation dose exceeds **60 Gy**. * **Management:** Hyperbaric Oxygen (HBO) therapy is often used to stimulate angiogenesis in irradiated tissues before surgical interventions (Marx Protocol). * **Radiation Caries:** A rapid form of tooth decay occurring post-radiation due to changes in salivary pH and flow.

Question 24: Prophylactic intracranial radiation is indicated in which of the following malignancies?

A. Small cell carcinoma (Correct Answer)
B. Testicular carcinoma
C. Breast carcinoma
D. Gastric carcinoma

Explanation: **Explanation:** **1. Why Small Cell Carcinoma (SCLC) is correct:** Small cell lung carcinoma is highly aggressive and has a strong predilection for early hematogenous spread to the brain. Even when systemic chemotherapy achieves a complete response, the **Blood-Brain Barrier (BBB)** often acts as a "pharmacological sanctuary," preventing drugs from reaching micrometastases in the CNS. Without intervention, approximately 50–60% of SCLC patients develop brain metastases within two years. **Prophylactic Cranial Irradiation (PCI)** is indicated in patients with Limited-Stage SCLC who achieve a good response to initial therapy, as it significantly reduces the incidence of brain metastases and improves overall survival. **2. Why the other options are incorrect:** * **Testicular Carcinoma:** While it can metastasize to the brain (especially choriocarcinoma), the primary treatment is surgery and platinum-based chemotherapy. PCI is not a standard protocol. * **Breast Carcinoma:** Brain metastases are common in HER2+ and Triple-Negative subtypes, but they usually occur in the setting of advanced systemic disease. Screening and targeted therapies are preferred over prophylactic radiation. * **Gastric Carcinoma:** This malignancy primarily spreads via the lymphatic system or to the liver/peritoneum. Brain involvement is rare, making PCI unnecessary. **Clinical Pearls for NEET-PG:** * **Standard Dose for PCI:** Usually 25 Gy in 10 fractions. * **Other indications for PCI:** Occasionally used in **Acute Lymphoblastic Leukemia (ALL)** in pediatric patients (though largely replaced by intrathecal chemotherapy to avoid neurotoxicity). * **SCLC Hallmark:** It is a neuroendocrine tumor associated with paraneoplastic syndromes (e.g., SIADH, Lambert-Eaton Syndrome). * **Radiosensitivity:** SCLC is highly radiosensitive, which is why PCI is effective even at relatively low doses.

Question 25: Prophylactic craniospinal irradiation is indicated in which of the following conditions?

A. Medulloblastoma (Correct Answer)
B. Meningoma
C. Oligodendroglioma
D. All of the above

Explanation: **Explanation:** **Medulloblastoma** is the correct answer because it is a highly malignant primitive neuroectodermal tumor (PNET) with a notorious tendency for **leptomeningeal dissemination**. The tumor cells frequently "drop down" through the cerebrospinal fluid (CSF) to seed the spinal cord. Therefore, even if imaging shows a localized posterior fossa mass, the entire neuraxis is considered at risk. **Craniospinal Irradiation (CSI)** is the standard of care post-resection to treat potential microscopic disease throughout the brain and spinal canal. **Why the other options are incorrect:** * **Meningioma:** These are typically benign, slow-growing tumors arising from the arachnoid cap cells. They are localized and do not spread via the CSF; treatment is usually surgical resection or localized radiotherapy. * **Oligodendroglioma:** These are primary glial tumors. While they can be infiltrative, they generally do not exhibit the high rate of diffuse neuraxial seeding seen in Medulloblastoma. Treatment focuses on the primary tumor bed using localized radiation and chemotherapy (PCV regimen). **High-Yield Clinical Pearls for NEET-PG:** * **Indications for CSI:** Medulloblastoma, Ependymoma (if disseminated), Germinoma (CNS Germ Cell Tumors), and occasionally in high-risk CNS Leukemia. * **Medulloblastoma "Drop Metastasis":** Always look for the "sugar coating" (leptomeningeal enhancement) on spinal MRI. * **Radiotherapy Technique:** CSI is technically challenging because it requires "matching" brain and spine fields to avoid overdosing or underdosing the spinal cord. * **Age Factor:** In children under 3 years, radiation is often delayed or avoided due to severe neurocognitive side effects, opting for intensive chemotherapy instead.

Question 26: Which of the following is the most radiosensitive?

A. Carcinoma of the cervix
B. Carcinoma of the kidney
C. Carcinoma of the ovary (Correct Answer)
D. Carcinoma of the pancreas

Explanation: **Explanation:** The radiosensitivity of a tumor is primarily determined by its cell of origin and its rate of proliferation (Law of Bergonié and Tribondeau). Tumors derived from germ cells or lymphoid tissue are generally highly radiosensitive. **1. Why Carcinoma of the Ovary is correct:** Ovarian cancers, particularly **Dysgerminomas** (the most common germ cell tumor of the ovary), are exquisitely radiosensitive. Even epithelial ovarian cancers show moderate sensitivity compared to solid visceral adenocarcinomas. In the context of the given options, ovarian malignancies represent the most responsive group to ionizing radiation. **2. Analysis of Incorrect Options:** * **Carcinoma of the Cervix (Option A):** Squamous cell carcinoma of the cervix is considered **radiocurable** and moderately radiosensitive. While radiation is a primary treatment modality, it requires much higher doses to achieve control compared to ovarian germ cell tumors. * **Carcinoma of the Kidney (Option B):** Renal Cell Carcinoma (RCC) is traditionally classified as **radioresistant**. It typically requires high-dose stereotactic radiation (SBRT) because standard fractionation is largely ineffective. * **Carcinoma of the Pancreas (Option D):** Pancreatic adenocarcinoma is highly **radioresistant** and carries a poor prognosis. Radiation is used mainly for local control or palliation, but the tumor cells themselves do not respond readily to standard doses. **High-Yield Clinical Pearls for NEET-PG:** * **Most Radiosensitive Tumor:** Seminoma (Male) / Dysgerminoma (Female). * **Most Radiosensitive Normal Cell:** Lymphocyte (exception to the rule as it is a non-dividing cell). * **Most Radiosensitive Phase of Cell Cycle:** **M phase** (Mitosis), followed by G2. * **Most Radioresistant Phase:** **S phase** (DNA synthesis). * **Order of Radiosensitivity (High to Low):** Lymphoma/Leukemia > Germ cell tumors > Squamous cell carcinoma > Adenocarcinoma > Sarcomas > Melanoma/Glioma.

Question 27: Brachytherapy is used in which of the following conditions?

A. Stage Ib Ca cervix (Correct Answer)
B. Ovarian Ca
C. Stage IV Ca vagina
D. Stage II fallopian tube Ca

Explanation: **Explanation:** **Brachytherapy** involves placing a radioactive source directly into or near a tumor, allowing for a high dose of radiation to the target tissue while sparing surrounding healthy organs (inverse square law). 1. **Why Stage Ib Ca Cervix is Correct:** In Carcinoma Cervix, brachytherapy is a cornerstone of treatment. For early stages like **Stage Ib**, it is often used as a boost following External Beam Radiotherapy (EBRT) or as part of definitive chemoradiotherapy. It provides a concentrated dose to the cervix and paracervical tissues, which is essential for local tumor control and achieving high cure rates. 2. **Why the Incorrect Options are Wrong:** * **Ovarian Ca:** The primary treatment is surgical debulking followed by systemic chemotherapy (Taxanes/Platinum). Brachytherapy is not used because ovarian cancer typically spreads via peritoneal seeding, requiring whole-abdomen coverage rather than localized radiation. * **Stage IV Ca Vagina:** While brachytherapy is used in early-stage vaginal cancer, Stage IV involves distant metastasis or extension to the bladder/rectal mucosa. At this advanced stage, systemic therapy or palliative EBRT is preferred over localized brachytherapy. * **Stage II Fallopian Tube Ca:** Similar to ovarian cancer, fallopian tube malignancies are managed with surgery and systemic chemotherapy due to their pattern of intraperitoneal spread. **Clinical Pearls for NEET-PG:** * **Manchester System:** Uses Point A (2cm superior and 2cm lateral to the external os) and Point B (3cm lateral to Point A) for dosing in Ca Cervix. * **Common Isotopes:** Iridium-192 (most common for HDR), Cesium-137 (LDR), and Cobalt-60. * **Rule of Thumb:** Brachytherapy is ideal for accessible, localized tumors (Cervix, Endometrium, Prostate, Tongue).

Question 28: Which of the following statements is true regarding medulloblastoma?

A. It is primarily seen in individuals over 50 years of age.
B. It is a radiosensitive tumor. (Correct Answer)
C. The sole treatment modality is surgical resection.
D. It is typically found in the anterior cranial fossa.

Explanation: **Explanation:** **1. Why Option B is Correct:** Medulloblastoma is a highly cellular, primitive neuroectodermal tumor (PNET) that exhibits high mitotic activity. In radiobiology, the **Law of Bergonié and Tribondeau** states that cells that are rapidly dividing and undifferentiated are more sensitive to radiation. Consequently, medulloblastoma is considered a **highly radiosensitive tumor**. Radiation therapy, typically delivered via Craniospinal Irradiation (CSI), is a cornerstone of management to address its tendency for leptomeningeal seeding. **2. Why the Other Options are Incorrect:** * **Option A:** Medulloblastoma is primarily a **pediatric tumor**, representing the most common malignant brain tumor in children (peak incidence: 3–8 years). It is rare in adults over 50. * **Option C:** Treatment is **multimodal**. While maximal safe surgical resection is the first step, it is almost always followed by adjuvant radiotherapy and/or chemotherapy due to the high risk of recurrence and neuraxial spread. * **Option D:** It is a tumor of the **posterior cranial fossa**, typically arising from the roof of the fourth ventricle (cerebellar vermis) in children. **3. Clinical Pearls for NEET-PG:** * **Imaging:** On CT, it appears as a hyperdense midline mass in the posterior fossa. On MRI, it shows restricted diffusion (low ADC values) due to high cellularity. * **Drop Metastasis:** It has a high propensity for CSF dissemination; hence, imaging of the **entire neuraxis** (spine) is mandatory. * **Homer-Wright Rosettes:** A classic histopathological finding (though seen in only ~40% of cases). * **Zuckerguss:** A term used to describe the "icing-like" appearance of leptomeningeal metastases on the brain surface.

Question 29: Stereotactic surgery is used for the treatment of which of the following conditions?

A. Brain tumor (Correct Answer)
B. Lung carcinoma
C. Cervix cancer
D. Renal carcinoma

Explanation: **Explanation:** Stereotactic surgery, specifically **Stereotactic Radiosurgery (SRS)**, is a highly precise form of radiation therapy that uses multiple convergent beams to deliver a single high dose of radiation to a specific target. The hallmark of SRS is the use of a **rigid coordinate system** (often involving a stereotactic frame) to immobilize the patient and ensure sub-millimeter accuracy. * **Why A is Correct:** SRS was originally developed by Lars Leksell specifically for **intracranial lesions**. Because the skull provides a fixed, rigid structure, it allows for the precise localization required to treat brain tumors (e.g., vestibular schwannomas, meningiomas, or solitary metastases) and functional disorders (e.g., trigeminal neuralgia) while sparing adjacent critical brain tissue. * **Why B, C, and D are Incorrect:** These organs are located in the thorax or abdomen and are subject to **respiratory motion** and physiological displacement. While a similar technique called **Stereotactic Body Radiotherapy (SBRT)** is used for lung or renal tumors, the term "Stereotactic Surgery" (SRS) classically refers to intracranial procedures where rigid immobilization is possible. Cervix cancer is primarily treated with external beam radiation and **brachytherapy**, not stereotactic surgery. **High-Yield Clinical Pearls for NEET-PG:** * **Gamma Knife:** A specialized SRS unit using Cobalt-60 sources, used exclusively for the brain. * **CyberKnife:** A robotic linear accelerator that can perform both SRS and SBRT without a rigid frame. * **Indication:** SRS is the treatment of choice for small, deep-seated brain tumors inaccessible by conventional open surgery. * **Dose:** Unlike conventional radiotherapy (fractionated), SRS delivers a massive dose in a **single session** (or up to 5 fractions).

Question 30: Radiotherapy is used in the treatment of angiofibroma when it involves which of the following structures?

A. Cheek
B. Orbit
C. Middle cranial fossa (Correct Answer)
D. Cavernous sinus

Explanation: **Explanation:** Juvenile Nasopharyngeal Angiofibroma (JNA) is a benign but locally aggressive, highly vascular tumor. The primary treatment modality is **surgical excision** (typically via endoscopic or open approaches). However, radiotherapy plays a critical role in specific scenarios. **Why Middle Cranial Fossa is Correct:** Radiotherapy is indicated for JNA when the tumor is **unresectable** or involves vital structures where surgery would carry unacceptable morbidity. Extension into the **middle cranial fossa** (intracranial extension) often involves the skull base and dural attachments, making complete surgical clearance difficult and risky. In such cases, external beam radiotherapy (EBRT) is used to induce endarteritis obliterans, leading to tumor regression and vascular fibrosis. **Analysis of Incorrect Options:** * **A. Cheek:** Extension into the cheek (infratemporal fossa/buccal space) is common but surgically accessible. These are typically managed with preoperative embolization followed by surgical resection. * **B. Orbit:** While orbital extension (via the inferior orbital fissure) occurs, it is generally managed surgically unless it involves the optic chiasm or bilateral cavernous sinuses. * **D. Cavernous Sinus:** While this is a site of intracranial extension, the standard teaching and most common indication cited in textbooks for radiotherapy in JNA is extensive **middle cranial fossa** involvement or recurrent disease that is surgically inaccessible. **Clinical Pearls for NEET-PG:** * **Classic Presentation:** Adolescent male with painless, progressive epistaxis and nasal obstruction (Holman-Miller sign: anterior bowing of the posterior wall of the maxillary sinus). * **Diagnosis:** Contrast-enhanced CT/MRI is diagnostic. **Biopsy is contraindicated** due to the risk of torrential hemorrhage. * **Radiotherapy Dose:** Usually 30–35 Gy over 3 weeks (lower than doses for malignancies). * **Gold Standard:** Surgery remains the first-line treatment for most stages (Fisch or Radkowski classifications).

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

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free