Radionuclide Therapy — MCQs
A 60-year-old man with advanced prostate cancer presents with severe, constant back pain. X-ray reveals vertebral metastases. What is the most appropriate management?
Radioisotope used for thyroid treatment of metastasis/ablation
Which of the following conditions is the most common complication of radioiodine treatment for Graves' disease?
Which of the following elements is obsolete in radiotherapy:
Which radioisotope is used for treating bone cancer?
All the following radioisotopes are used in painful body metastasis except
Which of the following tumours is radiosensitive?
Which artificial radioisotopes are used in nuclear medicine?
Which radiopharmaceutical is used for a liver scan?
What is the investigation of choice for whole-body imaging in metastasis?
Radionuclide Therapy Indian Medical PG Practice Questions and MCQs
Question 1: A 60-year-old man with advanced prostate cancer presents with severe, constant back pain. X-ray reveals vertebral metastases. What is the most appropriate management?
- A. Chemotherapy
- B. Surgical decompression
- C. Radiation therapy (Correct Answer)
- D. NSAIDs
Explanation: ***Radiation therapy*** - **Radiation therapy** is highly effective for localized pain control in **vertebral metastases** and can prevent further spinal cord compression [1]. - It works by shrinking the tumor, thereby alleviating pain and restoring neurological function in many cases. *Chemotherapy* - While chemotherapy is a systemic treatment for prostate cancer, its **pain-relieving effects are often slower** and less immediate compared to radiation for localized bone pain. - It may be used in conjunction with radiation, but it is typically not the **most appropriate initial management** for severe, constant pain due to vertebral metastases. *Surgical decompression* - **Surgical decompression** is primarily considered for patients with **spinal cord compression** leading to neurological deficits or intractable pain unresponsive to radiation [1]. - The patient's presentation of severe, constant back pain due to vertebral metastases, without mentioned neurological compromise, makes **radiation therapy a more appropriate first-line treatment** in this context [1]. *NSAIDs* - **NSAIDs** might provide some mild pain relief, but they are **insufficient for severe pain** caused by progressive vertebral metastases. - They also carry risks like **gastrointestinal complications** and **renal impairment**, especially in elderly patients with advanced cancer.
Question 2: Radioisotope used for thyroid treatment of metastasis/ablation
- A. I-90
- B. I-131 (Correct Answer)
- C. I-83
- D. I-123
Explanation: ***I-131*** - **Iodine-131** is widely used for **thyroid cancer treatment** due to its ability to emit both **beta particles** (for therapeutic ablation) and **gamma rays** (for imaging). - Its therapeutic effect relies on its uptake by thyroid cells and metastatic lesions, leading to **localized radiation damage** and destruction. - **I-131** has a half-life of **8 days**, making it ideal for both treatment and post-therapy imaging. *I-90* - **I-90 is not a recognized or clinically used iodine isotope** in nuclear medicine. - This is not a standard radioisotope for any medical application, including thyroid treatment. *I-83* - **I-83** is not a commonly used or recognized radioisotope in clinical nuclear medicine, particularly not for thyroid treatment. - There is no significant clinical application for this specific iodine isotope in thyroid disease. *I-123* - **Iodine-123** is a **diagnostic radioisotope** used for thyroid imaging (**scans**) due to its **gamma emission** and shorter half-life (13 hours). - It is not used for treatment or ablation of thyroid cancer as it lacks the therapeutic beta particle emission of **I-131**. - **I-123** provides excellent imaging quality with lower radiation dose to the patient compared to I-131.
Question 3: Which of the following conditions is the most common complication of radioiodine treatment for Graves' disease?
- A. Hypothyroidism (Correct Answer)
- B. Thyroid cancer
- C. Thyroid storm
- D. Subacute thyroiditis
Explanation: ***Hypothyroidism*** - **Radioiodine (RAI) therapy** destroys overactive thyroid cells, making it highly effective for Graves' disease but often leading to a permanent state of **hypothyroidism** post-treatment. - The goal of RAI is to eliminate the source of excess hormone production, and while effective, it frequently necessitates lifelong **thyroid hormone replacement**. *Thyroid storm* - **Thyroid storm** is a rare, life-threatening complication, usually seen in untreated or undertreated hyperthyroidism or during acute stress, not typically a direct outcome of effective RAI. - While a transient increase in thyroid hormones can occur shortly after RAI, a full-blown thyroid storm is infrequent with proper preparation and management. *Thyroid cancer* - There is no significant evidence to suggest an increased risk of **thyroid cancer** in adults following therapeutic doses of radioiodine for Graves' disease [1]. - The radiation dose is targeted primarily at the thyroid gland, and studies have shown no clear link to increased malignancy [1]. *Subacute thyroiditis* - **Subacute thyroiditis** (also known as de Quervain's thyroiditis) is typically a post-viral inflammatory condition of the thyroid, characterized by pain and tenderness in the thyroid gland [2]. - It does not directly result from radioiodine treatment; however, some patients may experience a transient inflammatory response (radiation thyroiditis) after RAI, which is usually mild and self-limiting, not true subacute thyroiditis.
Question 4: Which of the following elements is obsolete in radiotherapy:
- A. Iridium 192
- B. Cesium 137
- C. Cobalt 60
- D. Radium 226 (Correct Answer)
Explanation: ***Radium 226*** - **Radium 226** was one of the earliest radioactive sources used in brachytherapy but has largely been replaced due to its decay products producing **radon gas**, a toxic noble gas. - Its high **gamma energy** and long half-life made it difficult to shield and handle, leading to significant radiation safety concerns. *Iridium 192* - **Iridium 192** is a widely used radioisotope in **HDR (High-Dose Rate) brachytherapy** due to its relatively short half-life and suitable gamma energy for dose delivery. - It allows for flexible treatment planning and precise targeting in various cancer sites. *Cesium 137* - **Cesium 137** is commonly used in **LDR (Low-Dose Rate) brachytherapy** and some teletherapy units, offering a longer half-life than Iridium-192. - Its gamma energy is lower than that of Radium-226, making it safer to handle and shield. *Cobalt 60* - **Cobalt 60** was historically and is still used in **teletherapy units (gamma knives)** for external beam radiotherapy, especially for brain tumors. - Its high-energy gamma rays provide excellent dose penetration, though it has largely been replaced by linear accelerators in conventional external beam radiotherapy.
Question 5: Which radioisotope is used for treating bone cancer?
- A. I-123
- B. Sr-89 (Correct Answer)
- C. Ga-67
- D. Tc-99m
Explanation: ***Sr-89*** - **Strontium-89** (Sr-89) is a **beta-emitting radioisotope** commonly used for the palliative treatment of **bone pain** in patients with metastatic bone cancer. - It is chemically similar to **calcium** which allows it to be preferentially incorporated into areas of increased bone turnover, such as **bone metastases**, delivering therapeutic radiation directly to the cancerous sites. *I-123* - **Iodine-123** (I-123) is a **gamma-emitting radioisotope** primarily used in **diagnostic imaging**, particularly for **thyroid scans** and functional brain imaging. - It is not used therapeutically for bone cancer. *Ga-67* - **Gallium-67** (Ga-67) is a **gamma-emitting radioisotope** used in **diagnostic imaging** to detect **inflammation**, infection, and certain types of cancer, including lymphoma. - It is not a primary treatment agent for bone cancer. *Tc-99m* - **Technetium-99m** (Tc-99m) is the most common **diagnostic radioisotope** used in nuclear medicine, primarily for **bone scans** (when complexed with diphosphonates), cardiac imaging, and various other organ studies. - While integral for diagnosing bone metastases, it is **not used therapeutically** to treat bone cancer.
Question 6: All the following radioisotopes are used in painful body metastasis except
- A. Tin-117
- B. Samarium-153
- C. Strontium-89
- D. Yttrium (Correct Answer)
Explanation: ***Yttrium*** - **Yttrium-90 (⁹⁰Y)** is a pure **beta-emitter** primarily used for **radioembolization of liver tumors** (selective internal radiation therapy) and **radiosynovectomy** for joint inflammation. - It is **NOT a standard radioisotope for treating painful bone metastases**, unlike the other options listed. - Its high-energy beta particles and specific applications make it unsuitable for the palliative treatment of bone pain from metastases. *Tin-117* - **Tin-117m (¹¹⁷ᵐSn-DTPA)** is a **conversion electron emitter** that has been studied and used for palliation of painful bone metastases. - It localizes to areas of increased osteoblastic activity and provides localized radiation therapy. - Though less commonly used than Samarium-153 or Strontium-89, it is still a therapeutic option for bone pain. *Samarium-153* - **Samarium-153 (¹⁵³Sm-EDTMP)** is a commonly used **beta-emitting radioisotope** for the treatment of painful bone metastases. - It selectively binds to areas of increased bone turnover, such as metastases, and its beta emissions provide **localized pain relief**. - FDA-approved and widely used for bone pain palliation. *Strontium-89* - **Strontium-89 (⁸⁹Sr)** is another highly effective **beta-emitting radioisotope** used for palliation of painful bone metastases. - It is a **calcium analog** and is preferentially incorporated into bone mineral at sites of increased osteoblastic activity. - FDA-approved and considered a gold standard for bone pain treatment.
Question 7: Which of the following tumours is radiosensitive?
- A. Ewing's sarcoma (Correct Answer)
- B. Osteosarcoma
- C. Hepatocellular carcinoma
- D. Malignant melanoma
Explanation: ***Ewing's sarcoma*** - **Ewing's sarcoma** is highly radiosensitive, meaning radiation therapy is an effective treatment modality, often used as a primary or adjuvant therapy. - Its high responsiveness to radiation helps control local disease and improve patient outcomes, especially when combined with chemotherapy. *Osteosarcoma* - **Osteosarcoma** is generally considered radioresistant, meaning it responds poorly to radiation therapy. - While radiation may be used in specific palliative settings, it is not a primary curative treatment for osteosarcoma, which primarily relies on surgery and chemotherapy. *Hepatocellular carcinoma* - **Hepatocellular carcinoma (HCC)** is largely radioresistant, and external beam radiation therapy has limited efficacy as a stand-alone treatment. - While certain advanced techniques like stereotactic body radiation therapy (SBRT) can be used for localized control, it is not considered broadly radiosensitive. *Malignant melanoma* - **Malignant melanoma** is historically considered highly radioresistant, requiring very high doses of radiation for any significant tumor control. - In recent years, high-dose, hypofractionated radiation therapy has shown some promise for local control, but it is not a universally radiosensitive tumor.
Question 8: Which artificial radioisotopes are used in nuclear medicine?
- A. Radium
- B. Uranium
- C. Plutonium (Correct Answer)
- D. Iridium
Explanation: ### Explanation **Correct Answer: C. Plutonium** In nuclear medicine, radioisotopes are categorized as either **natural** (found in nature) or **artificial** (man-made via nuclear reactors or cyclotrons). **Plutonium (specifically Pu-238)** is an artificial radioisotope produced in nuclear reactors. While not used as a diagnostic tracer or therapeutic agent for internal administration, it has a significant historical and niche clinical application as a power source for **Radioisotope Thermoelectric Generators (RTGs)** in long-lived **cardiac pacemakers**. Its high energy density and long half-life made it ideal for devices requiring decades of operation without battery replacement. **Analysis of Incorrect Options:** * **A. Radium:** This is a **naturally occurring** radioactive metal found in uranium ores. While Radium-223 is used in treating bone metastases (Xofigo), the element itself is classified as natural. * **B. Uranium:** This is a **naturally occurring** heavy metal. It is the raw material used to produce artificial isotopes but is not used directly in clinical nuclear medicine. * **C. Iridium:** While Iridium-192 is used in Brachytherapy, it is generally classified as a transition metal used in "sealed sources" for radiotherapy rather than being the classic example of an "artificial radioisotope" in the context of general nuclear medicine tracers (like Technetium-99m). However, in the context of this specific question, Plutonium is the most distinct "artificial/man-made" element. **High-Yield Clinical Pearls for NEET-PG:** * **Technetium-99m (Tc-99m):** The most commonly used artificial radioisotope in diagnostic nuclear medicine (produced in a Mo-99/Tc-99m generator). * **Cyclotron-produced isotopes:** Include F-18 (used in PET scans), I-123, and Thallium-201. * **Reactor-produced isotopes:** Include I-131, Mo-99, and Xenon-133. * **Therapeutic Alpha Emitter:** Radium-223 is the first alpha-emitting radiopharmaceutical approved to improve survival in castration-resistant prostate cancer with bone metastases.
Question 9: Which radiopharmaceutical is used for a liver scan?
- A. Tc-99m sulphur colloid (Correct Answer)
- B. Tc-99m mebrofenin
- C. Tc-99m MIBI
- D. Tc-99m DTPA
Explanation: **Explanation:** The correct answer is **Tc-99m sulphur colloid**. The underlying principle for a liver-spleen scan is the **phagocytic activity of the Reticuloendothelial System (RES)**. When Tc-99m sulphur colloid is injected intravenously, the particles (sized 0.1–1.0 μm) are cleared from the blood by Kupffer cells in the liver (80–90%), splenic macrophages (5–10%), and bone marrow. This scan is primarily used to evaluate functional liver anatomy and detect "cold nodules" (e.g., abscesses or tumors) or "hot spots" (e.g., Focal Nodular Hyperplasia). **Analysis of Incorrect Options:** * **Tc-99m Mebrofenin:** This is an IDA (Iminodiacetic acid) derivative used for **HIDA scans**. It evaluates the **hepatobiliary system** (hepatocyte uptake and biliary excretion) and is the gold standard for diagnosing Acute Cholecystitis. * **Tc-99m MIBI:** Primarily used for **Myocardial Perfusion Imaging** and Parathyroid imaging. It is taken up by mitochondria. * **Tc-99m DTPA:** A chelating agent cleared by glomerular filtration, used for **Renal Dynamic Scans** to assess GFR and obstructive uropathy. **High-Yield Clinical Pearls for NEET-PG:** 1. **Colloid Shift:** In portal hypertension or cirrhosis, there is decreased liver uptake and increased uptake in the spleen and bone marrow. 2. **Focal Nodular Hyperplasia (FNH):** This is the only liver lesion that typically appears "hot" or "isointense" on a sulphur colloid scan due to the presence of Kupffer cells. 3. **Hot Spot on Liver Scan:** Classically seen in **Superior Vena Cava (SVC) Obstruction** (due to collateral flow via the vein of Sappey).
Question 10: What is the investigation of choice for whole-body imaging in metastasis?
- A. Magnetic Resonance Imaging
- B. Radiography
- C. Bone scan (Correct Answer)
- D. CT Scan
Explanation: **Explanation:** **Bone Scan (Technetium-99m MDP)** is the investigation of choice for screening whole-body skeletal metastases because of its high sensitivity and ability to image the entire skeleton in a single session. It works on the principle of detecting increased osteoblastic activity (bone remodeling) at sites of tumor infiltration. Its primary advantage is the ability to detect "hot spots" weeks or months before structural changes become visible on conventional X-rays. **Why other options are incorrect:** * **Radiography (X-ray):** It has low sensitivity for early metastasis. A bone lesion only becomes visible on an X-ray after **30-50% of bone mineral density is lost**. It is, however, the best modality to confirm a finding seen on a bone scan. * **CT Scan:** While excellent for evaluating cortical bone and detailed anatomy, it is not practical for whole-body screening due to high radiation doses and lower sensitivity for early marrow-based lesions compared to nuclear imaging. * **MRI:** MRI is the most sensitive modality for detecting **bone marrow infiltration**. However, it is not typically the first-line "investigation of choice" for whole-body screening due to high costs, long scan times, and limited availability of whole-body MRI protocols. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Tc-99m MDP (Methylene Diphosphonate) adsorbs onto the **hydroxyapatite crystals** of the bone. * **The "Cold Scan" Exception:** Highly aggressive or purely osteolytic tumors (e.g., Multiple Myeloma, Renal Cell Carcinoma, or Thyroid Cancer) may show as "cold" or false-negative on a bone scan because they do not trigger an osteoblastic response. * **Flare Phenomenon:** An apparent increase in tracer uptake seen shortly after starting chemotherapy, which actually represents healing bone rather than disease progression. * **Superscan:** A bone scan showing intense, uniform skeletal uptake with **absent renal/bladder activity**, typically seen in diffuse metastatic prostate cancer or hyperparathyroidism.
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