Radiation Therapy Equipment — MCQs
Precisely directed high dose radiation is used in which of the following therapies?
A pregnant woman with head trauma requires a CT scan of the head. What is the most effective radiation protection measure for the fetus?
Principles used in Radio Therapy are:
Which of the following is not an artificial radio isotope element?
Which of the following radioactive isotopes is not used for brachytherapy?
In cervical cancer brachytherapy, the primary reference point for dose prescription is -
Which is the treatment of choice for irradiation in Chordoma?
Which radioisotope is commonly used in teletherapy?
An elderly male presents with T3N0 laryngeal carcinoma. Treatment is:
Which of the following statements about hypernephroma is true?
Radiation Therapy Equipment Indian Medical PG Practice Questions and MCQs
Question 1: Precisely directed high dose radiation is used in which of the following therapies?
- A. EBRT
- B. IMRT
- C. Brachytherapy
- D. Stereotactic radiosurgery (Correct Answer)
Explanation: ***Stereotactic radiosurgery*** - **Stereotactic radiosurgery (SRS)** is a highly precise radiation therapy that uses focused, high-dose radiation beams to target small tumors or abnormalities with **sub-millimeter accuracy**. - It delivers **very high doses per fraction** (typically 15-24 Gy in a single session) using stereotactic guidance systems. - Commonly used for **brain metastases, AVMs, acoustic neuromas**, and other small intracranial targets. *IMRT* - **Intensity-modulated radiation therapy (IMRT)** is an advanced form of 3D-conformal radiation therapy that modulates beam intensity to conform to tumor shape. - While IMRT is precise, it uses **conventional fractionation** (1.8-2 Gy per fraction over many treatments), not the high-dose approach of SRS. *EBRT* - **External beam radiation therapy (EBRT)** is a general term for radiation delivered from outside the body. - It encompasses various techniques but *does not specifically indicate the **stereotactic precision and high-dose per fraction** characteristic of SRS*. *Brachytherapy* - **Brachytherapy** involves placing radioactive sources **directly inside or next to the tumor**. - While it delivers high doses locally, it is not "precisely directed high-dose radiation" from external beams like SRS.
Question 2: A pregnant woman with head trauma requires a CT scan of the head. What is the most effective radiation protection measure for the fetus?
- A. Using MRI instead
- B. Lead apron over abdomen
- C. Avoid CT, rely on clinical assessment
- D. Reduced mA and kVp (Correct Answer)
Explanation: ***Reduced mA and kVp*** - **Optimizing scan parameters** (reducing mA and kVp) is the most effective way to minimize radiation dose during head CT in pregnancy. - Modern CT scanners with **iterative reconstruction** allow significant dose reduction without compromising diagnostic image quality. - The fetal dose from head CT is already negligible (< 0.01 mGy), but dose optimization further reduces any potential risk. - This directly addresses the radiation source rather than attempting to shield scatter radiation. *Lead apron over abdomen* - Lead shielding provides **minimal to no benefit** during head CT as the fetus is far from the primary beam. - Scatter radiation reaching the pelvis from head CT is negligible. - Lead aprons can interfere with **automatic exposure control (AEC)**, potentially increasing rather than decreasing dose. - Modern radiology guidelines (ACR, ICRP) no longer routinely recommend gonadal shielding for most CT examinations. *CT not recommended* - Withholding indicated imaging in trauma is **inappropriate and potentially dangerous**. - The diagnostic benefit of head CT in trauma far outweighs the negligible fetal risk. - **Maternal well-being** is the priority, and missing a critical head injury poses greater risk to both mother and fetus. *Using MRI instead* - While MRI has no ionizing radiation, it is **not appropriate for acute trauma** evaluation. - MRI takes longer to perform, requires patient cooperation, and is less readily available in emergency settings. - CT remains the **gold standard** for acute head trauma assessment.
Question 3: Principles used in Radio Therapy are:
- A. Ultrasonic effect
- B. Charring of nucleoprotein
- C. Infrared rays
- D. Ionizing radiation (Correct Answer)
Explanation: ***Ionizing radiation*** - Radiation therapy primarily utilizes **ionizing radiation** (e.g., X-rays, gamma rays, protons) to damage the **DNA** of cancer cells. - This damage prevents cancer cells from growing and dividing, leading to their death and tumor shrinkage. *Ultrasonic effect* - **Ultrasound** uses high-frequency sound waves for imaging (sonography) and, in some therapeutic applications, to generate heat or mechanically disrupt tissues. - It is not the primary principle for general **radiotherapy** which aims to destroy cancer cells via DNA damage. *Charring of nucleoprotein* - **Charring** refers to the severe burning of organic material, often resulting in carbonization. - While radiation can cause significant cellular damage, the primary mechanism is not macroscopic charring but rather precise **DNA damage** at a molecular level. *Infrared rays* - **Infrared rays** are a form of electromagnetic radiation associated with heat, used in some warming therapies or for imaging (thermography). - They lack the energy to cause **ionization** and significant DNA damage to effectively treat cancer in the manner of therapeutic radiation.
Question 4: Which of the following is not an artificial radio isotope element?
- A. CO 60
- B. Ra226 (Correct Answer)
- C. 1-125
- D. Tc-99m
Explanation: ***Ra-226*** * **Radium-226** (Ra-226) is a **naturally occurring radioactive isotope** of radium, found in the uranium decay chain. * It is not artificially produced but rather exists in nature as a product of the **radioactive decay of uranium-238**. *Co-60* * **Cobalt-60** is a **synthetic radioactive isotope** produced by neutron activation of cobalt-59. * It is widely used in **radiation therapy** and industrial applications, making it an artificial radioisotope. *I-125* * **Iodine-125** is an **artificially produced radioisotope** commonly used in brachytherapy and diagnostic imaging. * It is created in a nuclear reactor by bombarding tellurium-124 with neutrons, making it not naturally occurring. *Tc-99m* * **Technetium-99m** is the most widely used **artificial radioisotope** in nuclear medicine for diagnostic imaging. * It is produced artificially from molybdenum-99 generators and does not occur naturally, making it an ideal choice for medical imaging due to its short half-life and gamma emission.
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: In cervical cancer brachytherapy, the primary reference point for dose prescription is -
- A. Point A (Correct Answer)
- B. Point B
- C. Side walls of pelvis
- D. Point H
Explanation: ***Point A*** - **Point A** is defined as 2 cm lateral to the central canal of the uterus and 2 cm superior to the external os, representing a dose estimation to the **parametrium** and a critical reference for tumoricidal dose. - This point serves as the **primary prescription and reporting point** for brachytherapy in cervical cancer, as it is highly correlated with treatment outcomes and complications. - Established by **ICRU Report 38** as the standard reference point for dose prescription. *Point B* - **Point B** is located 5 cm from the midline (3 cm lateral to Point A) at the level of Point A, and is primarily used to estimate the dose received by the **pelvic side wall** and regional lymphatics. - It provides an indication of dose to structures further from the applicator but is **not the primary prescription point** for the target volume in brachytherapy. *Side walls of pelvis* - The dose to the **side walls of the pelvis** is relevant for assessing potential toxicity to structures like the obturator nerve and external iliac vessels, and for ensuring adequate coverage of pelvic lymph nodes. - While critical for treatment planning, the side walls themselves are not a primary dose prescription point but rather a **region of interest** for dose constraints and coverage. *Point H* - **Point H** represents the reference point for estimating the dose to the **rectum** in brachytherapy, located at the posterior vaginal wall. - While important for assessing **rectal toxicity** and as a dose-limiting structure, Point H is used for reporting organ-at-risk doses, not for primary tumor dose prescription.
Question 7: Which is the treatment of choice for irradiation in Chordoma?
- A. Protons (Correct Answer)
- B. Electrons
- C. Gamma radiation
- D. 3D - CRT
Explanation: ***Protons*** - Proton therapy is the treatment of choice for **chordoma** due to its ability to deliver a high dose of radiation directly to the tumor while minimizing dose to surrounding healthy tissues. - This precision is critical for tumors located near **sensitive structures**, such as the brainstem, spinal cord, or optic nerves, common sites for chordomas. *Electrons* - **Electron therapy** is typically used for superficial tumors because electrons rapidly deposit their energy within the first few centimeters of tissue. - Chordomas are often deeply seated tumors, making electron therapy an unsuitable option for comprehensive treatment. *Gamma radiation* - **Gamma radiation**, as delivered by techniques like **Gamma Knife radiosurgery**, is primarily used for smaller, well-circumscribed intracranial lesions. - While precise, it may not be ideal for the larger, often irregularly shaped chordomas found in the skull base or sacrum, and it lacks the dose-sparing capabilities of proton beams at depth. *3D - CRT* - **3D Conformal Radiation Therapy (3D-CRT)** uses multiple beams to shape the radiation dose to the tumor, offering better conformity than conventional radiation. - However, compared to proton therapy, 3D-CRT still deposits a significant amount of radiation in tissues both distal and proximal to the tumor, leading to a higher risk of side effects, which is particularly concerning for chordomas given their proximity to critical structures.
Question 8: Which radioisotope is commonly used in teletherapy?
- A. Ra-226
- B. Cs-137
- C. Co-60 (Correct Answer)
- D. Ir-192
Explanation: ***Co-60*** - **Cobalt-60** is a widely used radioisotope in teletherapy (external beam radiotherapy) due to its high-energy gamma emissions (1.17 and 1.33 MeV). - Its relatively long half-life of **5.27 years** makes it practical for sustained clinical use in **teletherapy units**. *Ra-226* - **Radium-226** was historically used in brachytherapy but has largely been replaced due to its alpha emissions, which are difficult to shield, and its long-lived radioactive decay products. - Its use for teletherapy is **not common** because of these safety concerns and the availability of more suitable isotopes. *Cs-137* - **Cesium-137** is primarily used in **brachytherapy** and some low-dose rate teletherapy machines for specific applications, but not as commonly as Co-60 for general teletherapy. - Its lower gamma energy (0.662 MeV) and shorter half-life than Co-60 (30.17 years) make it less ideal for the widespread **deep penetration** required in many teletherapy treatments. *Ir-192* - **Iridium-192** is predominantly used in **high-dose-rate (HDR) brachytherapy** for temporary implants, delivering radiation over short periods. - Its relatively short half-life of **73.8 days** and lower average gamma energy make it unsuitable for typical long-term teletherapy external beam applications.
Question 9: An elderly male presents with T3N0 laryngeal carcinoma. Treatment is:
- A. Radical radiotherapy followed by chemotherapy
- B. Concurrent chemoradiotherapy (Correct Answer)
- C. Neo-adjuvant chemotherapy followed by radiotherapy
- D. Radical radiotherapy without chemotherapy
Explanation: ***Concurrent chemoradiotherapy*** - For **T3N0 laryngeal carcinoma**, concurrent chemoradiotherapy is the **preferred organ preservation treatment** in appropriate candidates, offering comparable oncologic outcomes to total laryngectomy. - The combination of **chemotherapy (typically cisplatin) and radiation** works synergistically to enhance tumor cell kill, with chemotherapy acting as a **radiosensitizer**. - This approach achieves **local control rates of 60-70%** while preserving laryngeal function and voice quality. - Standard protocols include **radiation (70 Gy) with concurrent cisplatin** (100 mg/m² on days 1, 22, 43). *Radical radiotherapy without chemotherapy* - **Radiation therapy alone** is an alternative organ preservation approach for selected T3N0 cases, particularly in **elderly patients** with comorbidities who cannot tolerate chemotherapy. - However, multiple studies show that **concurrent chemoradiotherapy provides superior local control** and survival compared to radiation alone for T3 laryngeal cancer. - RT alone may achieve **local control in 50-60%** of T3 cases, which is lower than concurrent chemoRT. *Radical radiotherapy followed by chemotherapy* - Sequential therapy is **less effective** than concurrent administration because chemotherapy's primary role is as a **radiosensitizer** during radiation. - Delivering chemotherapy after radiation loses the **synergistic effect** crucial for tumor control. - This sequence is not a standard treatment approach for T3 laryngeal cancer. *Neo-adjuvant chemotherapy followed by radiotherapy* - **Induction chemotherapy** followed by radiation is used in some organ preservation protocols, particularly for advanced disease. - However, this approach is typically reserved for **T4 disease** or for tumor downstaging assessment. - Current evidence favors **concurrent chemoradiotherapy over sequential induction-radiation** for T3 laryngeal cancer in terms of organ preservation rates and survival.
Question 10: Which of the following statements about hypernephroma is true?
- A. May present with rapidly developing varicocele
- B. Usually an adenocarcinoma
- C. Not radiosensitive (Correct Answer)
- D. Arises from the cortex, usually from a pre-existing adenoma
Explanation: ***Radiosensitive*** - Hypernephroma, or renal cell carcinoma, is typically resistant to **radiation therapy**, making this statement false. - It is generally treated with **surgery** and targeted therapies rather than radiation. *Usually adenocarcinoma* - Hypernephroma is indeed a type of **adenocarcinoma**, as it originates from the renal tubular epithelium [1]. - It is the most common form of **kidney cancer**, supporting this as a true statement. *May present with rapidly developing varicocele* - Rapidly developing **varicocele** can occur due to **renal vein obstruction** associated with renal tumors [2], so this statement is true. - Varicocele is a recognized clinical feature in renal cell carcinoma due to its anatomical relationships. *Arise from cortex usually from pre existing adenoma* - Hypernephroma does arise from the **renal cortex**, often from pre-existing renal adenomas or other lesions. - This establishes its origin, making the statement accurate. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Kidney, pp. 959-961. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Diseases Of The Urinary And Male Genital Tracts, pp. 492-493.
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