Stereotactic Radiosurgery — MCQs
Radiation exposure can lead to which type of thyroid carcinoma?
All of the following are true about long-term sequelae of craniospinal radiotherapy for children with CNS tumors except:
The technique employed in radiotherapy to counteract the effect of tumour motion due to breathing is known as –
In which of the following conditions is Stereotactic Radiosurgery primarily indicated?
Which radiotherapy technique involves the use of remote afterloading to deliver radiation directly to the tumor?
Most radiosensitive tumor among the following is
Stereotactic Radiotherapy is used in:
What is the management of osteoradionecrosis?
Cranial irradiation is also indicated in the treatment of which variety of lung cancer?
Prophylactic cranial irradiation is indicated in the treatment of all of the following conditions, except:
Stereotactic Radiosurgery Indian Medical PG Practice Questions and MCQs
Question 1: Radiation exposure can lead to which type of thyroid carcinoma?
- A. Lymphoma
- B. Papillary carcinoma (Correct Answer)
- C. Medullary carcinoma
- D. Follicular carcinoma
Explanation: ***Papillary carcinoma*** - Papillary thyroid carcinoma is strongly associated with **radiation exposure**, particularly during childhood [1]. - It is the most prevalent type of thyroid cancer and typically has a **good prognosis** [1]. *Lymphoma* - Thyroid lymphoma is rare and generally not linked to **radiation exposure**; it often presents as a **rapidly enlarging goiter**. - It is more commonly associated with **autoimmune thyroiditis**, not primary radiation effects. *Follicular carcinoma* - Follicular carcinoma shows a correlation with **iodine deficiency** rather than radiation exposure [1]. - Its presentation is more subtle, compared to the classical association of **radiation with papillary carcinoma**. *Medullary carcinoma* - Medullary thyroid carcinoma is primarily linked to **familial syndromes** like MEN 2 and not radiation exposure. - It arises from **parafollicular C cells**, making it clinically distinct from radiation-related types. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1098-1099.
Question 2: All of the following are true about long-term sequelae of craniospinal radiotherapy for children with CNS tumors except:
- A. Musculoskeletal hypoplasia
- B. Neurocognitive dysfunction
- C. Endocrinologic dysfunction
- D. Neuropsychological sequelae are independent of radiation dose (Correct Answer)
Explanation: ***Neuropsychological sequelae are independent of radiation dose*** - This statement is incorrect; **neuropsychological sequelae** are **highly dependent on the radiation dose** received by the brain, with higher doses generally leading to more severe and frequent cognitive impairments. - The impact of radiation on developing neural tissue is dose-related, affecting **myelination**, **synaptogenesis**, and **neurogenesis**, leading to dose-dependent cognitive deficits. *Musculoskeletal hypoplasia* - **Craniospinal irradiation (CSI)** can lead to musculoskeletal hypoplasia, particularly affecting the **vertebrae** and **long bones**, resulting in **short stature** and **scoliosis**. - Radiation can damage growth plates and bone-forming cells, impairing normal bone development and leading to growth deficiencies. *Neurocognitive dysfunction* - **Radiation to the brain** in children, especially at a young age, can cause significant **neurocognitive dysfunction**, including deficits in **memory**, **attention**, **processing speed**, and **executive functions**. - Damage to **white matter**, particularly secondary to demyelination and vasculopathy, plays a significant role in these cognitive impairments. *Endocrinologic dysfunction* - **CSI** frequently affects the **hypothalamic-pituitary axis**, leading to various **endocrinologic dysfunctions** such as **growth hormone deficiency**, **thyroid dysfunction**, and **gonadal dysfunction**. - The developing endocrine glands and their regulatory centers are particularly sensitive to radiation, impacting hormonal production and regulation.
Question 3: 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 4: 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 5: 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 6: 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 7: 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 8: What is the management of osteoradionecrosis?
- A. Hyperbaric oxygen
- B. Removal of sequestrum
- C. Fluoride application
- D. All of the above (Correct Answer)
Explanation: **Explanation:** Osteoradionecrosis (ORN) is a serious late complication of radiotherapy, most commonly affecting the mandible. It is characterized by bone death due to radiation-induced **hypocellularity, hypovascularity, and hypoxia (Marx’s 3H theory)**, leading to non-healing exposed bone. The management of ORN is multifaceted, involving conservative, medical, and surgical interventions: 1. **Hyperbaric Oxygen (HBO):** This is a cornerstone of treatment. It increases dissolved oxygen levels in tissues, stimulating angiogenesis and fibroblastic activity, which helps reverse the radiation-induced hypoxic state. 2. **Removal of Sequestrum (Sequestrectomy):** Surgical intervention is required to remove necrotic, infected bone (sequestrum) that acts as a nidus for infection and prevents healing. 3. **Fluoride Application:** Preventive and supportive care is vital. Radiation damages salivary glands (xerostomia), increasing the risk of radiation caries. Daily topical fluoride application is essential to maintain dental integrity and prevent odontogenic infections that could trigger or worsen ORN. **Why "All of the above" is correct:** Effective management requires a combination of improving tissue oxygenation (HBO), surgical debridement of dead bone, and strict oral hygiene/caries prevention (Fluoride) to arrest the progression of the disease. **High-Yield Clinical Pearls for NEET-PG:** * **Most common site:** Mandible (due to lower vascularity compared to the maxilla). * **Marx’s Protocol:** Often involves 20–30 sessions of HBO before surgery and 10 sessions after. * **PENTOCLO Protocol:** A newer medical management involving Pentoxifylline, Tocopherol (Vitamin E), and Clodronate. * **Prevention:** All necessary dental extractions should ideally be completed **at least 2–3 weeks before** starting radiotherapy.
Question 9: Cranial irradiation is also indicated in the treatment of which variety of lung cancer?
- A. Squamous cell carcinoma
- B. Non small cell cancer
- C. Small cell cancer (Correct Answer)
- D. Adenocarcinoma
Explanation: ### Explanation **Correct Answer: C. Small Cell Cancer** The correct answer is **Small Cell Lung Cancer (SCLC)**. The underlying medical concept is **Prophylactic Cranial Irradiation (PCI)**. SCLC is a highly aggressive neuroendocrine tumor characterized by rapid doubling time and a high propensity for early micrometastasis. Even when systemic chemotherapy achieves a complete or good partial response, the blood-brain barrier often acts as a "sanctuary site," protecting sequestered tumor cells from systemic drugs. Without PCI, approximately 50–60% of SCLC patients develop brain metastases within two years. Clinical trials have shown that PCI significantly reduces the incidence of brain metastases and improves overall survival in patients with limited-stage SCLC who respond to initial therapy. **Why other options are incorrect:** * **A, B, and D (Squamous cell, Adenocarcinoma, and NSCLC):** These fall under the umbrella of **Non-Small Cell Lung Cancer (NSCLC)**. Unlike SCLC, NSCLC is less sensitive to radiation and has a lower rate of early occult brain involvement. While cranial irradiation is used *palliatively* if brain metastases are already present, it is not a standard prophylactic indication for all patients as it is in SCLC. **High-Yield Clinical Pearls for NEET-PG:** * **Indication:** PCI is indicated in both Limited-Stage (LS) and Extensive-Stage (ES) SCLC if there is a good response to first-line chemo-radiotherapy. * **Sanctuary Site:** The brain is the most common site of "isolated relapse" in SCLC due to the blood-brain barrier. * **Dose:** Standard PCI dose is typically **25 Gy in 10 fractions**. * **Side Effects:** The major concern with PCI is neurocognitive decline (memory loss), which is why it is reserved for patients with good performance status.
Question 10: Prophylactic cranial irradiation is indicated in the treatment of all of the following conditions, except:
- A. Small cell carcinoma of the lung
- B. Acute lymphoblastic leukemia
- C. Hodgkin's lymphoma (Correct Answer)
- D. Non-Hodgkin's lymphoma
Explanation: **Explanation:** The concept of **Prophylactic Cranial Irradiation (PCI)** is based on the "sanctuary site" principle. Certain malignancies have a high propensity to metastasize to the Central Nervous System (CNS), but many systemic chemotherapeutic agents cannot cross the blood-brain barrier in therapeutic concentrations. PCI is administered to eliminate occult micro-metastases in the brain before they become clinically evident. **Why Hodgkin’s Lymphoma (HL) is the correct answer:** Hodgkin’s Lymphoma is primarily a nodal disease that spreads predictably via contiguous lymphatic chains. It has an **extremely low incidence of CNS involvement** (less than 1%). Therefore, there is no clinical indication for prophylactic radiation to the brain in HL patients. **Analysis of Incorrect Options:** * **Small Cell Carcinoma of the Lung (SCLC):** This is the classic indication for PCI. SCLC is highly neurotropic; without PCI, up to 50% of patients develop brain metastases. PCI is indicated for patients with both limited and extensive-stage SCLC who achieve a good response to initial chemo-radiotherapy. * **Acute Lymphoblastic Leukemia (ALL):** The CNS is a major sanctuary site for leukemic cells. While intrathecal chemotherapy has largely replaced radiation in many protocols to reduce long-term toxicity, PCI remains a recognized component of treatment for high-risk ALL to prevent CNS relapse. * **Non-Hodgkin’s Lymphoma (NHL):** Certain aggressive subtypes of NHL (e.g., Burkitt’s lymphoma, Lymphoblastic lymphoma, or Diffuse Large B-cell Lymphoma with high-risk features) carry a significant risk of CNS spread, making CNS prophylaxis (either via intrathecal drugs or PCI) necessary. **High-Yield Clinical Pearls for NEET-PG:** * **Standard Dose for PCI in SCLC:** Usually 25 Gy in 10 fractions. * **Side Effects:** The most significant long-term concern of PCI is neurocognitive decline (memory loss and ataxia). * **Sanctuary Sites:** The two primary sanctuary sites in oncology are the **Brain** and the **Testes**.
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