Brachytherapy — MCQs
Radiation exposure can lead to which type of thyroid carcinoma?
Which of the following is most radioresistant?
A 26-year-old male presents to the outpatient department with a discrete thyroid swelling. On neck ultrasound, an isolated cystic swelling of the gland is seen. What is the risk of malignancy associated with this finding?
Which of the following radioactive isotopes is not used for brachytherapy?
What is the management of osteoradionecrosis?
Prophylactic cranial irradiation is indicated in the treatment of all of the following conditions, except:
Osteoradionecrosis most commonly results from which combination of factors?
What is the standard treatment of whole-brain radiotherapy (WB) for brain Metastasis?
Maximum damage to the skin is caused by which type of radiation therapy?
Brachytherapy is an internal radiation therapy procedure for treating tumors. Which of the following isotopes is NOT used in brachytherapy?
Brachytherapy 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: Which of the following is most radioresistant?
- A. Cartilage (Correct Answer)
- B. Ewing's sarcoma
- C. GIT epithelium
- D. Gonadal tumours
Explanation: ***Cartilage*** - **Cartilage** is a connective tissue with a relatively **low metabolic rate** and **avascular nature**, making its cells (chondrocytes) less susceptible to rapid turnover and DNA damage from radiation. - Its **dense extracellular matrix** and limited cellular division contribute to its inherent resistance to ionizing radiation, requiring higher doses to induce significant damage. *Ewing's sarcoma* - **Ewing's sarcoma** is a highly **malignant bone tumor** that is generally considered **radiosensitive** and often treated with radiation therapy. - Its cells are rapidly dividing, making them more vulnerable to the DNA-damaging effects of radiation. *GIT epithelium* - The **gastrointestinal tract (GIT) epithelium** is characterized by **rapid cell turnover** and high mitotic activity to constantly replace damaged cells and absorb nutrients. - This high proliferative rate makes the GIT epithelium highly **radiosensitive**, leading to common side effects like mucositis and diarrhea during radiation therapy. *Gonadal tumours* - Tumors of the **gonads** (e.g., testicular seminoma, ovarian dysgerminoma) are often highly **radiosensitive** and respond well to radiation therapy due to the germ cell origin and rapid proliferation of tumor cells. - The germ cells themselves are very sensitive to radiation, leading to concerns about **fertility preservation** in patients undergoing treatment.
Question 3: A 26-year-old male presents to the outpatient department with a discrete thyroid swelling. On neck ultrasound, an isolated cystic swelling of the gland is seen. What is the risk of malignancy associated with this finding?
- A. 48%
- B. 12%
- C. 24%
- D. 3% (Correct Answer)
Explanation: ***3%*** - **Purely cystic thyroid nodules** (as described in this case with "isolated cystic swelling") have a **very low risk of malignancy**, typically **2-3%** or less. - According to **ATA guidelines** and **TIRADS classification**, purely cystic nodules are considered **low suspicion** lesions. - The cystic nature suggests a **benign process** such as a degenerated adenoma, colloid cyst, or simple cyst. - **Fine needle aspiration (FNA)** may still be considered if the nodule is >2 cm or has any suspicious solid components, but is often not required for purely cystic lesions. *48%* - This percentage is **significantly higher** than the actual malignancy risk for a purely cystic thyroid swelling. - Such a **high risk** would typically be associated with **solid nodules** exhibiting highly suspicious ultrasound features such as: - Microcalcifications - Irregular or spiculated margins - Taller-than-wide shape - Marked hypoechogenicity - Extrathyroidal extension *24%* - This percentage represents a **moderate to high risk** of malignancy, which is **not characteristic** of an isolated purely cystic thyroid swelling. - A risk in this range might be seen with: - **Mixed solid-cystic nodules** with predominantly solid components - Solid nodules with **intermediate suspicious features** on ultrasound *12%* - While lower than 24% or 48%, 12% is still **considerably higher** than the generally accepted malignancy risk for purely cystic thyroid nodules. - This risk level could be plausible for: - **Predominantly cystic nodules** with some eccentric solid components - Solid nodules with **mildly suspicious** features on ultrasound
Question 4: 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 5: 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 6: 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**.
Question 7: Osteoradionecrosis most commonly results from which combination of factors?
- A. Infection, trauma, and radiation
- B. Radiation, trauma, and infection (Correct Answer)
- C. Trauma, radiation, and infection
- D. None of the above
Explanation: ### Explanation **Osteoradionecrosis (ORN)** is a serious complication of radiation therapy, most commonly affecting the mandible. The pathophysiology is traditionally explained by the **Marx Theory (3-H Principle)**: Hypoxia, Hypocellularity, and Hypovascularity. **1. Why Option B is Correct:** The classic triad responsible for the development of ORN is **Radiation, Trauma, and Infection**. * **Radiation:** Causes endarteritis obliterans, leading to a permanent state of hypoxia and reduced bone vitality. * **Trauma:** Often in the form of a tooth extraction or ill-fitting dentures, it acts as the inciting event that breaks the mucosal barrier. * **Infection:** Once the barrier is breached, secondary infection and microbial colonization occur in the non-vital bone, leading to non-healing necrosis. **2. Why Other Options are Incorrect:** While Options A and C contain the same three elements, the sequence in Option B reflects the **chronological pathophysiology** generally accepted in clinical oncology: Radiation therapy creates the vulnerable environment, Trauma provides the trigger, and Infection complicates the healing process. In the context of NEET-PG, the "Radiation-Trauma-Infection" sequence is the standard academic description of the triad. **3. High-Yield Clinical Pearls for NEET-PG:** * **Most Common Site:** The **Mandible** (due to its higher bone density and lower vascularity compared to the maxilla). * **Marx Classification:** Used to stage ORN based on response to Hyperbaric Oxygen (HBO) therapy. * **Prevention:** All necessary dental extractions should be completed at least **2–3 weeks before** starting radiation therapy. * **Treatment:** Management includes antibiotics, debridement, and **Hyperbaric Oxygen (HBO)** therapy to stimulate angiogenesis.
Question 8: What is the standard treatment of whole-brain radiotherapy (WB) for brain Metastasis?
- A. 20 grays (Gy) in 10 fractions
- B. 30 grays (Gy) in 10 fractions (Correct Answer)
- C. 30 grays (Gy) in 5 fractions
- D. 15 grays (Gy) in 10 fractions
Explanation: ### Explanation **Standard Treatment Protocol** Whole-brain radiotherapy (WBRT) is a cornerstone in the palliative management of multiple brain metastases. The goal is to achieve a balance between tumor control and the preservation of neurocognitive function. The **standard fractionation schedule is 30 Gy delivered in 10 fractions** (3 Gy per fraction) over two weeks. This regimen is preferred because it provides an optimal therapeutic ratio, effectively reducing intracranial pressure and neurological symptoms while minimizing long-term radiation-induced leukoencephalopathy. **Analysis of Options** * **Option A (20 Gy in 10 fractions):** This dose is sub-therapeutic for most solid tumor metastases. While it uses a standard number of fractions, the total dose is insufficient for durable local control. * **Option C (30 Gy in 5 fractions):** This represents "hypofractionation" (6 Gy per fraction). While sometimes used in patients with a very poor prognosis (short life expectancy), it carries a significantly higher risk of acute and late neurological toxicity due to the high dose per fraction. * **Option D (15 Gy in 10 fractions):** This dose is far below the clinical threshold required to treat metastatic disease and is not a recognized standard protocol. **High-Yield Clinical Pearls for NEET-PG** * **Indications:** WBRT is typically indicated for patients with >3–4 metastases or those not suitable for Stereotactic Radiosurgery (SRS). * **Hippocampal Sparing:** Modern WBRT techniques often use "Hippocampal Sparing" to reduce memory decline. * **Steroid Adjunct:** Dexamethasone is usually administered alongside WBRT to reduce vasogenic edema caused by the tumors and the radiation itself. * **Alternative Schedule:** 20 Gy in 5 fractions is another accepted short-course regimen for patients with poor performance status.
Question 9: Maximum damage to the skin is caused by which type of radiation therapy?
- A. Super voltage X-ray therapy
- B. Mega voltage X-ray
- C. Orthovoltage X-ray (Correct Answer)
- D. Cobalt-60
Explanation: **Explanation:** The degree of skin damage in radiation therapy is primarily determined by the **"Skin Sparing Effect."** This phenomenon depends on the energy of the radiation beam and the depth at which the maximum dose ($D_{max}$) is deposited. **Why Orthovoltage is the Correct Answer:** Orthovoltage X-rays operate at a relatively low energy range (typically **200–500 kV**). Because of this low energy, the maximum dose ($D_{max}$) is deposited almost immediately at the **skin surface**. Since the skin receives 100% of the prescribed dose, it suffers the most significant damage, leading to side effects like erythema, desquamation, and permanent scarring. **Analysis of Incorrect Options:** * **Supervoltage (500–1000 kV) & Megavoltage (>1 MV) X-rays:** As the energy of the X-ray increases, the $D_{max}$ shifts deeper into the tissues (e.g., for a 6 MV beam, $D_{max}$ is at 1.5 cm). This results in a lower dose at the surface, providing a significant skin-sparing effect. * **Cobalt-60:** This is a form of megavoltage therapy (average energy 1.25 MeV). Its $D_{max}$ occurs at **0.5 cm** below the skin surface, meaning it spares the skin significantly more than orthovoltage. **High-Yield Clinical Pearls for NEET-PG:** * **Skin Sparing Effect:** The higher the energy of the photon beam, the deeper the $D_{max}$, and the greater the skin sparing. * **$D_{max}$ Values to Remember:** * **Orthovoltage:** 0.0 cm (Surface) * **Cobalt-60:** 0.5 cm * **4 MV:** 1.0 cm * **6 MV:** 1.5 cm * **10 MV:** 2.5 cm * **Clinical Use:** Orthovoltage is now rarely used except for very superficial lesions (e.g., skin cancers) precisely because it lacks skin sparing.
Question 10: Brachytherapy is an internal radiation therapy procedure for treating tumors. Which of the following isotopes is NOT used in brachytherapy?
- A. Iodine-125
- B. Iodine-131 (Correct Answer)
- C. Cesium-137
- D. Iridium-192
Explanation: **Explanation:** The core principle of **Brachytherapy** is the placement of radioactive sources either inside or in close proximity to the tumor. This allows for a high dose of radiation to the target tissue with a rapid dose fall-off, sparing surrounding healthy organs. **Why Iodine-131 is the correct answer:** Iodine-131 (I-131) is primarily used in **Systemic Radionuclide Therapy**, not brachytherapy. It is administered orally or intravenously (unsealed source) for the treatment of differentiated thyroid cancer and hyperthyroidism. Because it is distributed through the bloodstream to target thyroid tissue globally, it does not fit the definition of "brachy" (short-distance) localized source therapy. **Analysis of other options:** * **Iridium-192 (Option D):** The most commonly used isotope in modern clinical brachytherapy, especially for High Dose Rate (HDR) procedures (e.g., cervical and breast cancer). It has a high specific activity and a half-life of ~74 days. * **Iodine-125 (Option A):** A low-energy gamma emitter used for **permanent seed implants**, most commonly in prostate cancer (LDR brachytherapy). * **Cesium-137 (Option C):** Historically the gold standard for Low Dose Rate (LDR) brachytherapy in cervical cancer (e.g., Manchester system). While largely replaced by Iridium-192, it remains a classic brachytherapy isotope. **High-Yield Clinical Pearls for NEET-PG:** * **Cobalt-60:** Used in Teletherapy (Bhabhatron/Gamma Knife) and occasionally in HDR brachytherapy. * **Palladium-103:** Another common isotope for permanent prostate seeds. * **Strontium-90:** A pure beta emitter used for superficial brachytherapy (e.g., pterygium in the eye). * **Gold-198:** Historically used as permanent grains/seeds.
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