Radiation Oncology Basics Practice Questions

Q: Stereotactic surgery is used for the treatment of which of the following conditions?

Brain tumor. **Explanation:** Stereotactic surgery, specifically **Stereotactic Radiosurgery (SRS)**, is a highly precise form of radiation therapy that uses multiple convergent beams to deliver a single high dose of radiation to a specific target. The hallmark of SRS is the use of a **rigid coordinate system** (often involving a stereotactic frame) to immobilize the patient and ensure sub-millimeter accuracy. * **Why A is Correct:** SRS was originally developed by Lars Leksell specifically for **intracranial lesions**. Because the skull provides a fixed, rigid structure, it allows for the precise localization required to treat brain tumors (e.g., vestibular schwannomas, meningiomas, or solitary metastases) and functional disorders (e.g., trigeminal neuralgia) while sparing adjacent critical brain tissue. * **Why B, C, and D are Incorrect:** These organs are located in the thorax or abdomen and are subject to **respiratory motion** and physiological displacement. While a similar technique called **Stereotactic Body Radiotherapy (SBRT)** is used for lung or renal tumors, the term "Stereotactic Surgery" (SRS) classically refers to intracranial procedures where rigid immobilization is possible. Cervix cancer is primarily treated with external beam radiation and **brachytherapy**, not stereotactic surgery. **High-Yield Clinical Pearls for NEET-PG:** * **Gamma Knife:** A specialized SRS unit using Cobalt-60 sources, used exclusively for the brain. * **CyberKnife:** A robotic linear accelerator that can perform both SRS and SBRT without a rigid frame. * **Indication:** SRS is the treatment of choice for small, deep-seated brain tumors inaccessible by conventional open surgery. * **Dose:** Unlike conventional radiotherapy (fractionated), SRS delivers a massive dose in a **single session** (or up to 5 fractions).

Q: Conformation radiotherapy uses which of the following?

Multileaf collimator. **Explanation:** **Conformal Radiotherapy (3D-CRT)** is a technique designed to deliver a radiation dose that "conforms" precisely to the three-dimensional shape of the tumor, thereby sparing the surrounding healthy tissues. 1. **Why Multileaf Collimator (MLC) is correct:** The MLC is the key component of modern linear accelerators (LINACs) used to achieve this conformation. It consists of a large number of individual, computer-controlled tungsten "leaves" that can move independently. These leaves can be positioned to create a custom-shaped aperture that matches the projection of the tumor from any given angle, effectively shielding normal tissue while allowing the beam to hit the target. 2. **Why the other options are incorrect:** * **Single leaf collimator:** This does not exist in clinical practice. Standard collimators use two pairs of jaws (X and Y) to create rectangular fields, which cannot conform to irregular tumor shapes. * **Cone:** These are circular attachments used primarily in Stereotactic Radiosurgery (SRS) or electron therapy for small, circular fields. They lack the flexibility to conform to complex, irregular volumes. * **Cylinder:** These are typically used as applicators in brachytherapy (e.g., vaginal cylinders) rather than as beam-shaping devices in external beam radiotherapy. **High-Yield Clinical Pearls for NEET-PG:** * **IMRT (Intensity Modulated Radiotherapy):** An advanced form of conformal therapy where the MLC leaves move *during* treatment to vary the intensity of the beam. * **MLC Material:** Usually made of **Tungsten** due to its high atomic number and density, providing excellent radiation attenuation. * **Goal of Conformal Therapy:** To increase the **Therapeutic Index** (maximizing tumor kill while minimizing Normal Tissue Complication Probability).

Q: Which of the following statements is true about medulloblastoma?

Highly radiosensitive. **Explanation:** **Medulloblastoma** is a highly malignant Grade IV embryonal tumor arising from the cerebellum. It is one of the most **radiosensitive** tumors in the central nervous system. 1. **Why Option A is correct:** Medulloblastoma belongs to the "Small Round Blue Cell Tumor" family. These tumors are characterized by high cellularity and rapid cell division, making them exquisitely sensitive to ionizing radiation. Because of its tendency to spread via cerebrospinal fluid (CSF), the standard of care involves **Craniospinal Irradiation (CSI)** to treat the entire neuraxis. 2. **Why Option B is incorrect:** While surgery is the initial step for maximal safe resection and diagnosis, it is rarely curative alone. The primary treatment is a **multimodal approach** combining surgery, radiation, and chemotherapy. 3. **Why Option C is incorrect:** Medulloblastoma is a pediatric tumor. It is the most common malignant brain tumor in children, typically peaking between ages 3 and 9. It is rare in adults. 4. **Why Option D is incorrect:** While chemotherapy is used (especially in infants to delay radiation or in high-risk groups), it is an **adjunct**. The question asks for the most defining characteristic; its extreme radiosensitivity is a classic radiological and oncological hallmark. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Arises from the **roof of the 4th ventricle** (vermis) in children. * **Imaging:** Appears hyperdense on NCCT (due to high cellularity) and shows "drop metastases" in the spinal subarachnoid space. * **Homer-Wright Rosettes:** A classic histopathological finding. * **Zuckerman’s Point:** A critical area in radiation planning to avoid overlapping doses during CSI.

Q: What is the half-life of Cobalt-60?

5.2 years. **Explanation:** **Cobalt-60 ($^{60}$Co)** is a synthetic radioactive isotope produced by the neutron activation of Cobalt-59 in a nuclear reactor. It is the primary source used in conventional **Teletherapy** units for treating cancer. 1. **Why 5.2 years is correct:** The physical half-life of Cobalt-60 is approximately **5.26 years** (often rounded to 5.3 years in textbooks). This relatively short half-life means that the source loses about **1% of its activity per month**. Consequently, treatment times must be adjusted monthly to compensate for the decaying output, and the source typically requires replacement every 5 to 10 years. 2. **Analysis of Incorrect Options:** * **2.6 years:** This is the half-life of **Californium-252**, a neutron emitter used in some forms of brachytherapy. * **8 days (not years):** While "8" is a common number in radiology, **8 days** is the half-life of **Iodine-131**, used for thyroid imaging and therapy. * **1600/3200 years:** **Radium-226**, the historical standard for brachytherapy, has a half-life of **1600 years**. **High-Yield Clinical Pearls for NEET-PG:** * **Energy:** Cobalt-60 undergoes beta decay followed by the emission of two characteristic gamma photons with energies of **1.17 MeV and 1.33 MeV** (Average energy = **1.25 MeV**). * **D-max:** The depth of maximum dose (build-up region) for Cobalt-60 is **0.5 cm** below the skin, providing a modest skin-sparing effect. * **Penumbra:** Cobalt units have a larger **geometric penumbra** compared to Linear Accelerators (LINAC) because the source has a finite diameter (usually 1.5–2.0 cm).

Q: Recall phenomenon is seen in:

Chemotherapy following radiotherapy. **Explanation:** **Radiation Recall Phenomenon** is an acute inflammatory reaction that occurs in a previously irradiated area when a patient is subsequently administered certain systemic chemotherapy agents. **1. Why Option D is Correct:** The phenomenon is strictly defined by its sequence: **Chemotherapy following Radiotherapy**. After a patient has completed radiation and the initial skin reaction has healed, the administration of a "triggering" cytotoxic drug reactivates the inflammatory process in the exact same field that was irradiated. It is essentially a "latent" radiation injury being unmasked by chemotherapy. Common triggers include Doxorubicin, Paclitaxel, and Methotrexate. **2. Why Other Options are Incorrect:** * **Option A:** Radiotherapy following chemotherapy is not "recall"; it is simply standard sequential therapy. If chemotherapy sensitizes the tissue *during* radiation, it is called "radiosensitization." * **Options B & C:** Surgery does not trigger a "recall" of radiation effects. While radiotherapy can complicate surgical healing (due to fibrosis or poor vascularity), the specific inflammatory "recall" reaction is unique to pharmacological triggers. **3. Clinical Pearls for NEET-PG:** * **Most Common Site:** Skin (Radiation Recall Dermatitis), appearing like a severe sunburn or even blistering. * **Internal Organs:** It can also occur in the lungs (pneumonitis) or GI tract. * **Time Interval:** It can occur weeks, months, or even years after the original radiotherapy. * **Common Triggering Agents:** **Doxorubicin** (most common), Actinomycin-D, Gemcitabine, and Taxanes. * **Management:** Withdrawal of the triggering agent and administration of corticosteroids.

Q: Which of the following isotopes is used in Brachytherapy?

All of the above. **Explanation:** Brachytherapy is a form of radiotherapy where a sealed radioactive source is placed inside or in close proximity to the area requiring treatment. This allows for a high dose of radiation to be delivered locally to the tumor while sparing surrounding healthy tissues. **Why "All of the Above" is Correct:** All three isotopes listed are historically or currently significant in brachytherapy practice: * **Radium-226:** Historically, Radium was the first isotope used in brachytherapy (pioneered by Marie Curie). Although largely replaced by modern isotopes due to safety concerns (long half-life and radon gas production), it remains the "gold standard" against which other sources are compared. * **Iodine-125:** This is a low-energy gamma emitter commonly used for **permanent interstitial implants**, most notably in the treatment of **Prostate Cancer** (seed brachytherapy). * **Iridium-192:** This is the most widely used isotope in modern **High-Dose-Rate (HDR)** brachytherapy. It is preferred due to its high specific activity and small source size, making it ideal for temporary implants in breast, cervix, and head and neck cancers. **High-Yield Clinical Pearls for NEET-PG:** * **Cobalt-60:** Used in Teletherapy (External Beam Radiation) and Gamma Knife, but rarely in modern brachytherapy. * **Cesium-137:** Frequently used in the past for intracavitary brachytherapy in cervical cancer (Manual Afterloading). * **Gold-198:** Used for permanent implants (similar to I-125). * **Inverse Square Law:** The fundamental physical principle of brachytherapy, explaining why the dose falls off rapidly as distance from the source increases. * **Half-life (T 1/2) to remember:** Ir-192 (~74 days), I-125 (~60 days), Ra-226 (1600 years).

Q: What is true about the device shown below, except?

Indicated for only large tumor volumes.. ***Indicated for only large tumor volumes.*** - **Vaginal cylinders** are actually used for **microscopic or small-volume residual disease**, not large tumor volumes. - Large tumor volumes would require **external beam radiation therapy** or **interstitial brachytherapy**, not intracavitary cylinders. *Used for vaginal brachytherapy after surgery for uterine cancer.* - The **vaginal cylinder** is specifically designed for **intracavitary brachytherapy** following hysterectomy. - Commonly used in **endometrial cancer** patients to deliver targeted radiation to the vaginal cuff. *This treatment decreases the risk of vaginal cuff recurrence.* - **Adjuvant vaginal brachytherapy** significantly reduces the risk of **local recurrence** at the vaginal cuff. - Studies show a **reduction in vaginal recurrence rates** from approximately 7% to 2-3% with this treatment. *It is placed in the proximal vagina.* - The cylinder is positioned in the **upper third of the vagina** (proximal vagina) near the vaginal cuff. - Proper placement ensures optimal **dose distribution** to the surgical margin while sparing surrounding organs.

Q: What type of radiation is produced by a linear accelerator?

X-rays. **Explanation:** A **Linear Accelerator (LINAC)** is the most common device used for external beam radiation therapy in oncology. It functions by accelerating charged particles (usually electrons) to high speeds using radiofrequency electromagnetic waves. When these high-energy electrons strike a high-atomic-number target (like tungsten), their kinetic energy is converted into high-energy **X-rays** via the **Bremsstrahlung (braking radiation)** process. These X-rays are then shaped and directed to treat deep-seated tumors. **Analysis of Options:** * **A. X-rays (Correct):** LINACs produce "megavoltage" X-rays. They can also be used in "electron mode" to treat superficial tumors, but their primary output for deep radiotherapy is X-rays. * **B. Gamma rays:** These are emitted from the nucleus of unstable isotopes (e.g., Cobalt-60). Unlike X-rays produced by machines, gamma rays are a product of natural radioactive decay. * **C. Beta rays:** These are high-speed electrons or positrons emitted during radioactive decay. While LINACs use electrons internally, the therapeutic beam produced after hitting a target is X-ray radiation. * **D. Neutrons:** These are uncharged particles. While some high-energy LINACs (above 10 MV) can produce "contaminant" neutrons as a byproduct, they are not the intended therapeutic radiation. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** LINACs use **microwave technology** to accelerate electrons in a part called the "waveguide." * **Energy Range:** LINACs typically operate in the **4 to 25 MeV** range, providing much higher penetration than orthovoltage units. * **Advantage:** Unlike Cobalt-60 units, a LINAC can be turned off (no source decay), reducing the risk of accidental exposure when not in use. * **Skin Sparing Effect:** High-energy X-rays from a LINAC exhibit a "build-up" effect, where the maximum dose is delivered at a depth (e.g., 1.5 cm for 6 MV) rather than on the skin surface.

Question 1

Stereotactic surgery is used for the treatment of which of the following conditions?

Accepted Answer

Brain tumor

Answer

Lung carcinoma

Answer

Cervix cancer

Answer

Renal carcinoma

Question 2

Conformation radiotherapy uses which of the following?

Accepted Answer

Multileaf collimator

Answer

Single leaf collimator

Answer

Cone

Answer

Cylinder

Question 3

Which of the following statements is true about medulloblastoma?

Accepted Answer

Highly radiosensitive

Answer

Surgery is the primary treatment modality

Answer

Predominantly occurs in the adult age group

Answer

Chemotherapy is effective

Question 4

What is the half-life of Cobalt-60?

Accepted Answer

5.2 years

Answer

2.6 years

Answer

8 years

Answer

3200 years

Question 5

Recall phenomenon is seen in:

Accepted Answer

Chemotherapy following radiotherapy

Answer

Radiotherapy following chemotherapy

Answer

Surgery after radiotherapy

Answer

Radiotherapy after surgery

Question 6

Which of the following isotopes is used in Brachytherapy?

Accepted Answer

All of the above

Answer

Radium

Answer

Iodine-125

Answer

Iridium

Question 7

Regarding the Bragg peak effect of protons, all of the following are true, except:

Accepted Answer

It involves electromagnetic radiation.

Answer

It produces ionization in a biological system.

Answer

The dose of a single beam is 2-4 times greater than the path dose.

Answer

It is used in beam therapy for arteriovenous malformation of the brain.

Question 8

What is true about the device shown below, except?

Accepted Answer

Indicated for only large tumor volumes.

Answer

Used for vaginal brachytherapy after surgery for uterine cancer.

Answer

This treatment decreases the risk of vaginal cuff recurrence.

Answer

It is placed in the proximal vagina.

Question 9

What is the recommended treatment for post-radiation skin desquamation?

Accepted Answer

Observation alone

Answer

Petroleum jellies

Answer

Surgery

Answer

Antibiotic coverage

Question 10

What type of radiation is produced by a linear accelerator?

Accepted Answer

X-rays

Answer

Gamma rays

Answer

Beta rays

Answer

Neutrons

Radiation Oncology Basics — MCQs

Radiation Oncology Basics — MCQs

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