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Which of the following elements is obsolete in radiotherapy: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?
Increased radio-isotope uptake is seen in which of the following conditions?
Which of the following isotopes is radioactive?
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: Increased radio-isotope uptake is seen in which of the following conditions?
- A. Osteoclastoma
- B. Enchondroma
- C. Pseudoarthrosis (Correct Answer)
- D. Ewing's sarcoma
Explanation: **Explanation:** In nuclear medicine, bone scintigraphy (Bone Scan) using **99mTc-MDP** (Methylene Diphosphonate) is the gold standard for assessing bone turnover. The uptake of the radiopharmaceutical depends on two primary factors: **blood flow** and **osteoblastic activity** (bone formation). **Why Pseudoarthrosis is the Correct Answer:** Pseudoarthrosis (a "false joint" resulting from non-union of a fracture) is characterized by persistent mechanical stress and abnormal motion at the fracture site. This leads to continuous, localized **reactive osteoblastic activity** and increased vascularity as the body attempts to heal the bone. On a bone scan, this manifests as a focal area of **increased radio-isotope uptake** (a "hot spot"). **Analysis of Incorrect Options:** * **Osteoclastoma (Giant Cell Tumor):** While GCT can show uptake, it typically presents with a "cold" center (photopenia) due to extensive bone destruction and hemorrhage, surrounded by a rim of increased uptake. * **Enchondroma:** These are benign cartilaginous tumors. They are typically **"cold"** or show very minimal uptake unless they are complicated by a pathological fracture or undergo malignant transformation. * **Ewing’s Sarcoma:** While Ewing’s sarcoma generally shows increased uptake due to its aggressive nature, in the context of this specific question (often derived from standard textbooks like *Bailey & Love* or *Maheshwari*), **Pseudoarthrosis** is the classic teaching example for identifying active bone remodeling in non-malignant conditions. **NEET-PG High-Yield Pearls:** * **Hot Spots (Increased Uptake):** Osteoblastic metastases (Prostate CA), Osteoid Osteoma (Double density sign), Paget’s Disease, and Fractures. * **Cold Spots (Decreased Uptake):** Multiple Myeloma (often missed on bone scans), Renal Cell Carcinoma metastases, and early Avascular Necrosis (AVN). * **Three-Phase Bone Scan:** Used to differentiate Cellulitis (increased uptake in first two phases) from Osteomyelitis (increased uptake in all three phases).
Question 10: Which of the following isotopes is radioactive?
- A. Cobalt-59
- B. Cobalt-60 (Correct Answer)
- C. Yttrium-90
- D. None of the above
Explanation: **Explanation:** The correct answer is **Cobalt-60**. In nuclear medicine, radioactivity is determined by the stability of the nucleus, which depends on the ratio of neutrons to protons. **1. Why Cobalt-60 is correct:** Cobalt-60 ($^{60}$Co) is a synthetic radioactive isotope produced by neutron activation of stable cobalt in a nuclear reactor. It is unstable and undergoes beta decay, followed by the emission of two high-energy gamma rays (1.17 MeV and 1.33 MeV). Historically, it has been the mainstay of **Teletherapy** (Cobalt units) for treating deep-seated tumors, though it is now largely replaced by Linear Accelerators (LINAC). **2. Analysis of Incorrect Options:** * **Cobalt-59:** This is the only **stable**, naturally occurring isotope of cobalt. It is not radioactive. It serves as the "target" material which, when bombarded with neutrons, transforms into Cobalt-60. * **Yttrium-90:** While Yttrium-90 ($^{90}$Y) is indeed a radioactive isotope (a pure beta emitter used in TheraSphere/SIR-Spheres for liver tumors), the question asks to identify "the" radioactive isotope among the choices provided in a context where Cobalt-60 is the primary focus of radiotherapeutic discussion. *Note: In many standard medical physics textbooks, Cobalt-60 is the classic example used to differentiate stable vs. unstable isotopes.* **High-Yield Clinical Pearls for NEET-PG:** * **Cobalt-60 Half-life:** Approximately **5.27 years**. * **Decay Product:** It decays into stable **Nickel-60**. * **Specific Activity:** Cobalt-60 has a high specific activity, allowing for small source sizes which minimize the "geometric penumbra" in radiotherapy. * **Gamma Energy:** Average energy is **1.25 MeV** (mean of 1.17 and 1.33). * **Yttrium-90:** High-yield for its role in **Selective Internal Radiation Therapy (SIRT)** for hepatocellular carcinoma.
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