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 one of the following radioisotopes is not used as permanent implant in brachytherapy?
Which of the following radioactive isotopes is not used for brachytherapy?
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:
Osteoradionecrosis most commonly results from which combination of factors?
What is the standard treatment of whole-brain radiotherapy (WB) for brain Metastasis?
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 one of the following radioisotopes is not used as permanent implant in brachytherapy?
- A. Palladium-103
- B. Gold-198
- C. Iodine-125
- D. Caesium-137 (Correct Answer)
Explanation: ***Caesium-137*** - **Caesium-137** is primarily used in **high-dose-rate (HDR)** brachytherapy or external beam radiotherapy, where sources are temporarily placed. - Its relatively **long half-life** (30 years) and higher energy gamma emissions make it unsuitable for permanent implantation due to prolonged radiation exposure. *Palladium-103* - **Palladium-103** is a commonly used isotope for **permanent seed implants** in brachytherapy, particularly for prostate cancer. - It has a relatively short **half-life of 17 days** and low-energy photons, allowing for localized delivery with minimal exposure to surrounding healthy tissue. *Gold-198* - **Gold-198** was historically used for **permanent seed implants** due to its relatively short **half-life of 2.7 days** and medium-energy gamma emissions. - While less common today, its properties are consistent with permanent implantation, decaying away in a short period. *Iodine-125* - **Iodine-125** is a widely used radioisotope for **permanent seed implants** in brachytherapy for various cancers, including prostate and ocular melanoma. - It has a **half-life of 59.4 days** and low-energy photons, making it ideal for localized, long-term radiation delivery with a steep dose fall-off.
Question 5: 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 6: 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 7: 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 8: 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 9: 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 10: 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.
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