Theranostics — MCQs
Cardiotoxicity caused by radiotherapy & chemotherapy is best detected by
Which phase of the cell cycle is most sensitive to radiotherapy?
Radiation exposure can lead to which type of thyroid carcinoma?
Gold standard investigation for breast carcinoma screening in a patient with silicone breast implants
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?
'Gamma knife' is a term used to denote which of the methods of treatment?
For which malignancy is intensity-modulated radiotherapy (IMRT) the most suitable?
Distant bone metastases can be best detected by which of the following imaging techniques?
A research team is developing a new radiotracer for imaging hypoxia in tumors. They need to select between 18F-labeled and 64Cu-labeled versions of the same molecule. Considering half-lives (18F: 110 min, 64Cu: 12.7 hours), positron ranges, and clinical applicability, which choice and rationale is most appropriate?
In designing a clinical protocol for PSMA PET imaging in prostate cancer, which combination of factors would provide optimal image quality while minimizing radiation exposure?
Theranostics Indian Medical PG Practice Questions and MCQs
Question 1: Cardiotoxicity caused by radiotherapy & chemotherapy is best detected by
- A. ECHO (Correct Answer)
- B. Endomyocardial Biopsy
- C. ECG
- D. Radionuclide Scan
Explanation: ***ECHO*** - **Echocardiography (ECHO)** is the primary and most widely used non-invasive method for detecting cardiotoxicity due to its ability to assess **left ventricular ejection fraction (LVEF)**, a key indicator of cardiac function, and structural changes. - It is crucial for **baseline assessment**, monitoring during treatment, and follow-up, identifying both systolic and diastolic dysfunction effectively. *Endomyocardial Biopsy* - While **endomyocardial biopsy** is considered the gold standard for definitive diagnosis of some cardiomyopathies (e.g., myocarditis), it is **invasive** and carries risks such as perforation, tamponade, and arrhythmias. - It is usually reserved for cases where other non-invasive tests are inconclusive and there's a strong clinical suspicion of severe cardiac disease, or for research, not routine monitoring of cardiotoxicity. *ECG* - An **ECG** can detect arrhythmias and ischemic changes but is **not sensitive or specific** enough to reliably detect early or subtle changes in cardiac function characteristic of cardiotoxicity. - It may show changes secondary to heart failure, but it does not directly measure ejection fraction or assess overall cardiac mechanical function. *Radionuclide Scan* - **Radionuclide scans**, specifically **MUGA (Multigated Acquisition)** scans, can accurately measure **LVEF** and are an alternative to ECHO, particularly when ECHO images are suboptimal [1]. - However, they involve **radiation exposure**, making them less ideal for frequent monitoring compared to echocardiography, especially in cancer patients who are already exposed to radiation.
Question 2: Which phase of the cell cycle is most sensitive to radiotherapy?
- A. M phase (Correct Answer)
- B. G1 phase
- C. S phase
- D. G2 phase
Explanation: ***M phase*** - Cells in the **M phase** (mitosis) are generally the most sensitive to radiation-induced damage due to their condensed chromosomes and active processes of chromosome segregation [2]. - DNA in the M phase is highly accessible and vulnerable to breaks, making it difficult for the cell to repair damage before division. *G1 phase* - The **G1 phase** is relatively radioresistant because the cell has ample time to repair DNA damage before DNA replication [1]. - Cells are actively growing and performing normal functions, with chromosomes in a decondensed state. *S phase* - The **S phase**, during which DNA synthesis occurs, is intermediate in terms of radiosensitivity. - While DNA is being replicated, there are active repair mechanisms, making it more resistant than M phase but less than G1. *G2 phase* - The **G2 phase** is generally considered the second most radiosensitive phase, as DNA has been replicated but the cell is preparing for mitosis and has less time for repair before division. - Radiation damage during G2 can disrupt the fidelity of chromosome distribution in the upcoming M phase. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 302-303. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 112-113.
Question 3: 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 4: Gold standard investigation for breast carcinoma screening in a patient with silicone breast implants
- A. Mammography
- B. CT scan
- C. USG
- D. MRI (Correct Answer)
Explanation: ***MRI*** - **MRI** is considered the **gold standard** for breast cancer screening in patients with silicone breast implants due to its superior ability to visualize breast tissue through the implant and detect subtle lesions. - It offers **high sensitivity** in detecting both implant rupture and early malignancies, often providing better clarity than mammography in augmented breasts where implants can obscure tissue. *Mammography* - While a standard screening tool, **mammography** can be limited in patients with silicone implants because the implants can **obscure adjacent breast tissue**, making detection of small masses challenging. - Special views (e.g., **Eklund views**) can be used, but sensitivity is still reduced compared to MRI in augmented breasts. *CT scan* - **CT scans** are not routinely used for primary breast cancer screening due to their use of **ionizing radiation** and lower sensitivity for detecting early breast lesions compared to MRI. - CT is more commonly used for **staging** advanced cancers or evaluating complex masses detected by other modalities. *USG* - **Ultrasound (USG)** is a valuable complementary tool, especially for evaluating palpable lumps or clarifying findings from mammography, but it is **operator-dependent** and has a lower overall sensitivity for general screening compared to MRI. - It is particularly useful for differentiating between **cystic and solid masses** and detecting implant ruptures but is not the gold standard for comprehensive screening in augmented breasts.
Question 5: 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 6: 'Gamma knife' is a term used to denote which of the methods of treatment?
- A. Radiotherapy (Correct Answer)
- B. Chemotherapy
- C. Radioisotope scan
- D. Nuclear medicine
Explanation: ***Radiotherapy*** - The **gamma knife** is a highly precise form of **stereotactic radiosurgery** that delivers many small beams of gamma radiation to a target. - It is used to treat conditions like **brain tumors**, arteriovenous malformations, and trigeminal neuralgia without open surgery. *Chemotherapy* - **Chemotherapy** involves the use of drugs to destroy cancer cells, often affecting the entire body. - It does not involve focused radiation beams and is fundamentally different from a gamma knife. *Radioisotope scan* - A **radioisotope scan** (or nuclear scan) uses radioactive tracers to image the function and structure of organs. - It is a diagnostic imaging technique, not a method of treatment like the gamma knife. *Nuclear medicine* - **Nuclear medicine** is a branch of medicine dealing with the use of radioactive substances in diagnosis and treatment. - While gamma knife uses gamma radiation, the term nuclear medicine encompasses a broader range of diagnostic and therapeutic applications, and "gamma knife" specifically refers to a **radiotherapy technique**.
Question 7: For which malignancy is intensity-modulated radiotherapy (IMRT) the most suitable?
- A. Lung
- B. Prostate (Correct Answer)
- C. Leukemias
- D. Stomach
Explanation: ***Prostate*** - **IMRT** is highly suitable for prostate cancer due to the prostate's proximity to critical organs like the **rectum and bladder**. - Its ability to conform the **radiation dose tightly** to the tumor while sparing adjacent healthy tissue significantly reduces side effects like **rectal bleeding** or **urinary dysfunction** [1]. *Lung* - While IMRT is used in lung cancer, especially for complex tumors near vital structures, **stereotactic body radiation therapy (SBRT)** is often preferred for early-stage lung cancer due to its high dose delivery over fewer fractions. - The **motion of the lung** during respiration can make precise IMRT delivery challenging without specialized techniques like **gating or tracking**. *Leukemias* - **Leukemias** are systemic diseases involving blood and bone marrow, making localized radiation therapies like IMRT generally unsuitable as a primary treatment. - Treatment for leukemias primarily involves **chemotherapy, targeted therapy, or stem cell transplant**. *Stomach* - **Stomach cancer** often requires larger radiation fields due to tumor spread and nodal involvement, making the precise dose sculpting of IMRT less advantageous compared to its benefits in smaller, well-defined tumors. - The **mobility of the stomach** and surrounding organs can also present challenges for highly conformal radiation delivery.
Question 8: Distant bone metastases can be best detected by which of the following imaging techniques?
- A. Bone scan (Correct Answer)
- B. CT
- C. Intravenous venogram
- D. PET scan
Explanation: ***Bone scan*** - A **bone scan** is highly sensitive for detecting **osteoblastic activity**, which is characteristic of most bone metastases. - It involves injecting a **radioactive tracer** (usually technetium-99m methylene diphosphonate) that accumulates in areas of increased bone turnover, making it excellent for surveying the entire skeletal system. *PET scan* - While a **PET scan** (Positron Emission Tomography) can detect bone metastases, especially with **FDG-PET**, it is generally more expensive and may not be as sensitive for purely **osteoblastic lesions** as a bone scan. - Its primary role is often in assessing metabolic activity of the primary tumor and other distant soft tissue metastases. *CT* - **CT scans** (Computed Tomography) are excellent for assessing bone anatomy, cortical destruction, and soft tissue involvement, but they are generally less sensitive for detecting early or widespread **osseous metastatic disease** compared to a bone scan. - CT provides detailed anatomical information but may miss early **marrow involvement** that alters bone metabolism. *Intravenous venogram* - An **intravenous venogram** is an imaging technique used to visualize veins, primarily for detecting **thrombosis** or venous insufficiency. - It has no role in the detection of **bone metastases**, as it provides no information about bone structure or metabolic activity.
Question 9: A research team is developing a new radiotracer for imaging hypoxia in tumors. They need to select between 18F-labeled and 64Cu-labeled versions of the same molecule. Considering half-lives (18F: 110 min, 64Cu: 12.7 hours), positron ranges, and clinical applicability, which choice and rationale is most appropriate?
- A. 64Cu for longer imaging window despite inferior image quality
- B. 64Cu because shorter positron range improves resolution
- C. 18F for better spatial resolution despite requiring on-site cyclotron (Correct Answer)
- D. 18F because longer half-life allows delayed imaging
Explanation: ***18F for better spatial resolution despite requiring on-site cyclotron*** - **18F** has a shorter **positron range** compared to **64Cu**, which minimizes the distance the positron travels before annihilation, leading to superior **spatial resolution**. - While it necessitates proximity to a **cyclotron** due to a 110-minute half-life, this timeframe is sufficient for most **hypoxia imaging** tracers to reach a high **target-to-background ratio**. *64Cu for longer imaging window despite inferior image quality* - **64Cu** provides a longer imaging window due to its **12.7-hour half-life**, but its longer **positron range** leads to increased **blurring** and poorer resolution. - For diagnostic **tumor hypoxia**, the extra-long window is often unnecessary and leads to a higher **absorbed radiation dose** for the patient. *64Cu because shorter positron range improves resolution* - This statement is factually incorrect as **64Cu** actually has a significantly longer **effective positron range** than **18F**. - Higher **energy positrons** travel further in tissue, which degrades the **image quality** by misplacing the site of annihilation relative to the source. *18F because longer half-life allows delayed imaging* - This is incorrect as **18F** has a much shorter half-life (**110 minutes**) compared to the **12.7 hours** of **64Cu**. - The shorter half-life of **18F** prevents very late delayed imaging but helps in keeping the total **patient radiation exposure** lower.
Question 10: In designing a clinical protocol for PSMA PET imaging in prostate cancer, which combination of factors would provide optimal image quality while minimizing radiation exposure?
- A. 18F-PSMA with 4 hour delayed imaging
- B. 68Ga-PSMA with 3 hour uptake time without furosemide
- C. 68Ga-PSMA with 1 hour uptake time and furosemide administration (Correct Answer)
- D. 18F-PSMA with 30 minutes uptake time and forced hydration
Explanation: ***68Ga-PSMA with 1 hour uptake time and furosemide administration*** - An **uptake time of 60 minutes** is the standard for **68Ga-PSMA**, providing an optimal **target-to-background ratio** (TBR) while maintaining efficient clinical workflow. - The administration of **furosemide** (a loop diuretic) promotes **urinary washout** of the tracer, reducing interfering **bladder activity** and lowering the radiation dose to the urinary tract. *18F-PSMA with 4 hour delayed imaging* - While **18F-labeled tracers** have a longer half-life, a 4-hour delay is excessive and leads to significant **decay of activity**, potentially requiring higher initial doses and increasing **radiation exposure**. - Such long delays are not practical for routine clinical protocols and do not provide a significant clinical advantage over standard 1-2 hour imaging for most **PSMA** ligands. *68Ga-PSMA with 3 hour uptake time without furosemide* - **68Ga** has a short physical half-life (68 minutes), so a 3-hour wait significantly reduces the **count rate**, leading to poor **image quality** due to increased noise. - Omitting **furosemide** results in high tracer concentration in the **bladder**, which can obscure local recurrence in the **prostate bed** or nearby pelvic lymph nodes via **halo artifacts**. *18F-PSMA with 30 minutes uptake time and forced hydration* - A **30-minute uptake time** is generally insufficient for optimal **tracer internalization** into prostate cancer cells, resulting in a lower **tumor-to-background ratio**. - Although **forced hydration** helps, it is less effective than **furosemide** at rapidly clearing the high-intensity tracer from the **distal ureters** and bladder during the peak imaging window.
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