Radiation Oncology Basics — MCQs

Radiation Oncology Basics Indian Medical PG Practice Questions and MCQs

Question 61: Which of the following is NOT a permanent implant isotope used for brachytherapy?

A. Cesium-131
B. Gold-198
C. Radon-222
D. Iridium-192 (Correct Answer)

Explanation: **Explanation:** Brachytherapy involves placing radioactive sources directly into or near a tumor. These are classified into **temporary implants** (removed after the dose is delivered) and **permanent implants** (left in the body to decay completely). **Why Iridium-192 is the correct answer:** Iridium-192 ($^{192}Ir$) is the most commonly used isotope for **temporary brachytherapy**, particularly in High-Dose-Rate (HDR) systems. It has a relatively long half-life (approx. 74 days) and high specific activity, making it unsuitable for permanent implantation as it would deliver radiation for an excessively long period, posing a safety risk to the patient and the public. **Analysis of Incorrect Options:** * **Cesium-131 ($^{131}Cs$):** A modern isotope used for permanent seeds (e.g., prostate cancer) due to its short half-life (9.7 days), allowing for rapid dose delivery. * **Gold-198 ($^{198}Au$):** Historically used as permanent "seeds" for various tumors. It has a short half-life of 2.7 days. * **Radon-222 ($^{222}Rn$):** One of the earliest isotopes used for permanent interstitial implants (half-life 3.8 days). **High-Yield Clinical Pearls for NEET-PG:** * **Permanent Implants (LDR):** Usually involve isotopes with short half-lives like **Iodine-125** (60 days), **Palladium-103** (17 days), and **Cesium-131**. * **Prostate Brachytherapy:** Most common clinical application for permanent seed implantation. * **Iridium-192** is the "workhorse" of modern HDR brachytherapy (used in breast, cervix, and head/neck cancers). * **Cobalt-60** is used for Teletherapy, while **Iridium-192** and **Cesium-137** (now less common) are used for Brachytherapy.

Question 62: Which of the following is a late complication of radiotherapy?

A. Nausea
B. Erythema
C. Thrombocytopenia
D. Radiation pneumonitis (Correct Answer)

Explanation: **Explanation:** Radiation complications are classified based on the timing of their occurrence relative to the treatment course: **Acute** (during or within weeks of therapy) and **Late** (months to years after therapy). **Why Radiation Pneumonitis is correct:** Radiation pneumonitis is a classic **late-phase** complication, typically occurring **1 to 6 months** after the completion of thoracic radiotherapy. It is characterized by inflammation of the lung parenchyma due to damage to type II pneumocytes and vascular endothelial cells. If left untreated, it can progress to irreversible radiation fibrosis. **Analysis of Incorrect Options:** * **A. Nausea:** This is an **acute** complication, often part of "radiation sickness," occurring within hours or days of treatment, especially when the abdomen or brain is irradiated. * **B. Erythema:** This is an **acute** skin reaction (radiation dermatitis) occurring within days to weeks due to damage to the basal layer of the epidermis. * **C. Thrombocytopenia:** This is an **acute** hematological toxicity resulting from bone marrow suppression, typically seen when large volumes of bone-marrow-producing areas are included in the radiation field. **High-Yield Clinical Pearls for NEET-PG:** * **Acute Effects:** Occur in rapidly dividing tissues (Skin, Mucosa, Bone Marrow). * **Late Effects:** Occur in slowly proliferating tissues (Lung, Kidney, Heart, CNS). These are often permanent and progressive. * **Lhermitte’s Sign:** A transient late complication of spinal cord irradiation (electric shock sensation on neck flexion). * **Xerostomia:** Can be both acute (early onset) and late (permanent destruction of salivary glands).

Question 63: What is the standard radiation dose for treating Hodgkin lymphoma?

A. 20-30 Gy (Correct Answer)
B. 30-40 Gy
C. 40-50 Gy
D. 50-60 Gy

Explanation: **Explanation:** The treatment paradigm for Hodgkin Lymphoma (HL) has shifted significantly toward **Combined Modality Therapy (CMT)**, which utilizes chemotherapy followed by low-dose **Involved-Site Radiation Therapy (ISRT)**. **Why 20-30 Gy is correct:** Hodgkin Lymphoma is highly radiosensitive. Modern protocols (like ABVD chemotherapy followed by radiation) have shown that lower doses are sufficient for disease control while minimizing long-term toxicities. * For patients with **favorable early-stage HL** who achieve a complete response on PET scan, the standard dose is **20 Gy**. * For **unfavorable early-stage HL** or those with a partial response, the dose is typically **30 Gy**. Thus, the range of 20-30 Gy represents the current standard of care. **Why other options are incorrect:** * **30-40 Gy:** This was the historical standard (Extended Field Radiation) used before the era of modern chemotherapy. Currently, doses above 30 Gy are reserved only for bulky disease or salvage therapy. * **40-60 Gy:** These high doses are typically used for solid epithelial tumors (e.g., Squamous Cell Carcinoma of the head and neck). Using such doses in HL would lead to unacceptable risks of secondary malignancies and cardiovascular disease. **NEET-PG High-Yield Pearls:** * **Radiosensitivity:** Lymphocytes are among the most radiosensitive cells in the body (Law of Bergonie and Tribondeau). * **Field Evolution:** The field has evolved from **Mantle Field** (historical) → **Involved Field (IFRT)** → **Involved Site (ISRT)** (current standard). * **Late Complications:** The primary goal of using 20-30 Gy is to reduce the risk of secondary breast cancer, lung cancer, and coronary artery disease.

Question 64: For radiotherapy, an isotope is placed in or around the cancer site. What is this called?

A. Brachytherapy (Correct Answer)
B. Teletherapy
C. External beam therapy
D. Intensity modulated radiotherapy

Explanation: **Explanation:** The correct answer is **Brachytherapy**. This term is derived from the Greek word *'brachys'*, meaning 'short distance.' In this modality, radioactive sources (isotopes) are placed directly into (interstitial), inside a body cavity (intracavitary), or on the surface of the tumor. This allows for a high dose of radiation to be delivered to the tumor while rapidly sparing the surrounding healthy tissues due to the **Inverse Square Law**. **Analysis of Incorrect Options:** * **Teletherapy (Option B):** Derived from *'tele'*, meaning 'far.' This refers to radiation delivered from a source located at a distance from the body (usually 80–100 cm). * **External Beam Radiotherapy (EBRT) (Option C):** This is a synonym for Teletherapy. It uses machines like Linear Accelerators (LINAC) or Cobalt-60 to aim high-energy beams at the cancer from outside the body. * **Intensity Modulated Radiotherapy (IMRT) (Option D):** An advanced form of EBRT that manipulates the intensity of individual beams to conform precisely to the tumor shape, minimizing damage to adjacent organs at risk (OARs). **High-Yield Clinical Pearls for NEET-PG:** * **Common Isotopes:** Cesium-137 (Cervical cancer), Iridium-192 (Breast/Prostate), and Iodine-125 (Permanent seeds for Prostate). * **Manchester System:** A classic dosage system used specifically for Brachytherapy in Carcinoma Cervix. * **Advantage:** Brachytherapy provides a superior "biological dose" because the radiation source moves with the organ (e.g., the uterus), unlike external beams.

Question 65: Which of the following is true regarding brachytherapy?

A. Brachytherapy always gives homogeneous radiation.
B. Brachytherapy is the same as teletherapy.
C. Brachytherapy is used in carcinoma of the cervix. (Correct Answer)
D. All of the above.

Explanation: **Explanation:** **Brachytherapy** (derived from the Greek word *brachys*, meaning "short") is a form of radiotherapy where a sealed radioactive source is placed inside or in close proximity to the area being treated. **Why Option C is Correct:** Brachytherapy is a cornerstone in the management of **Carcinoma Cervix**. It allows for the delivery of a very high dose of radiation to the tumor (via intracavitary applicators like Tandem and Ovoids) while sparing adjacent critical organs like the bladder and rectum. It is typically used as a "boost" after External Beam Radiation Therapy (EBRT). **Why Other Options are Incorrect:** * **Option A:** Brachytherapy follows the **Inverse Square Law**, meaning the radiation intensity decreases rapidly as the distance from the source increases. This results in **highly non-homogeneous** dose distribution (high dose near the source, low dose further away), which is actually its primary clinical advantage. * **Option B:** Brachytherapy is distinct from **Teletherapy** (External Beam Radiation). In teletherapy, the radiation source is at a distance from the patient (e.g., Linear Accelerator or Cobalt-60 unit), whereas in brachytherapy, the source is internal. **High-Yield Clinical Pearls for NEET-PG:** * **Common Isotopes:** Iridium-192 (most common for HDR), Cesium-137, Iodine-125 (permanent seeds for prostate), and Cobalt-60. * **Types:** * *Intracavitary:* Cervix, Endometrium. * *Interstitial:* Breast, Soft tissue sarcoma, Tongue. * *Surface Mold:* Skin cancers. * *Intraluminal:* Esophagus, Bronchus. * **Advantage:** It provides a high "therapeutic ratio" by delivering a localized ablative dose with a rapid dose fall-off.

Question 66: Which types of beams can be used for cancer treatment?

A. Gamma rays
B. Alpha rays
C. Neutrons
D. All of the above (Correct Answer)

Explanation: **Explanation:** Radiation therapy utilizes ionizing radiation to destroy cancer cells by damaging their DNA. The correct answer is **"All of the above"** because clinical oncology employs various types of ionizing radiation, categorized into electromagnetic waves and particulate radiation. * **Gamma Rays (Option A):** These are high-energy electromagnetic photons emitted from radioactive isotopes. They are the mainstay of **Brachytherapy** (e.g., Iridium-192) and **Teletherapy** (e.g., Cobalt-60 machines). * **Alpha Rays (Option B):** These are heavy, positively charged particles (helium nuclei). Due to their high Linear Energy Transfer (LET) and short range (micrometers), they are highly effective for targeted therapy. A clinical example is **Radium-223**, used for treating bone metastases in prostate cancer. * **Neutrons (Option C):** These are uncharged particles used in **Neutron Beam Therapy** or **Boron Neutron Capture Therapy (BNCT)**. They have a high Relative Biological Effectiveness (RBE), making them useful for radioresistant tumors like salivary gland cancers or melanomas. **High-Yield Clinical Pearls for NEET-PG:** * **Linear Energy Transfer (LET):** Alpha particles and Neutrons are **High-LET** radiation (cause direct DNA damage), whereas X-rays and Gamma rays are **Low-LET** (cause indirect damage via free radicals). * **Most Common Source:** The most common beam used in modern radiotherapy (LINAC) is **Photons (X-rays)** and **Electrons**. * **Proton Therapy:** A rapidly emerging modality that utilizes the **Bragg Peak** phenomenon, allowing maximum dose delivery at a specific depth with minimal exit dose, sparing healthy tissue.

Question 67: All of the following are used in interstitial brachytherapy except?

A. Co-60 (Correct Answer)
B. Ir-192
C. Au-198
D. Cs-137

Explanation: **Explanation:** The core concept in interstitial brachytherapy is the placement of radioactive sources directly into the tumor tissue. This requires sources that are small, flexible, and have a high specific activity to deliver a localized dose while minimizing damage to surrounding healthy tissues. **Why Co-60 is the correct answer:** **Cobalt-60 (Co-60)** is primarily used in **External Beam Radiation Therapy (EBRT)** via Telecobalt units. It is generally **not used for interstitial brachytherapy** because it has a very high energy (mean 1.25 MeV), which makes shielding difficult within the body, and it has a relatively large source size. While Co-60 can be used in some Intracavitary applications (like modern HDR units), it is not a standard choice for interstitial implants. **Analysis of other options:** * **Ir-192 (Iridium):** The most commonly used isotope for temporary interstitial brachytherapy (HDR and LDR). Its high specific activity allows for very small source sizes (wires/seeds), making it ideal for breast, head, and neck cancers. * **Au-198 (Gold):** Historically used as permanent interstitial "seeds" (e.g., for prostate or tongue) due to its short half-life (2.7 days), allowing the source to be left in the body permanently. * **Cs-137 (Cesium):** Traditionally used for LDR interstitial and intracavitary (cervix) brachytherapy. While being phased out by Ir-192, it remains a classic example of a brachytherapy source. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for Brachytherapy:** Ir-192 is currently the most versatile and widely used isotope. * **Permanent Implants:** Iodine-125 (I-125) and Palladium-103 (Pd-103) are the modern choices for permanent prostate brachytherapy. * **Half-life Fact:** Ir-192 has a half-life of **74 days**, whereas Co-60 has a half-life of **5.26 years**. * **Ophthalmic Applicators:** Ruthenium-106 and Iodine-125 are used for choroidal melanoma (plaque brachytherapy).

Question 68: Which of the following is NOT a brachytherapy technique used for carcinoma of the cervix?

A. Paris technique
B. New York technique (Correct Answer)
C. Manchester technique
D. Stockholm technique

Explanation: **Explanation:** In the treatment of Carcinoma Cervix, **Brachytherapy** (internal radiation) is a cornerstone of therapy. Historically, three major classical systems were developed based on different dose distribution philosophies and loading patterns. 1. **Why Option B is Correct:** There is no established **"New York technique"** in the classical nomenclature of cervical brachytherapy. This is a distractor option. 2. **Why Other Options are Incorrect:** * **Stockholm Technique (Option D):** One of the oldest methods, it uses an "intermittent" high-intensity loading approach. It utilizes a central tandem and a flat vaginal applicator (box) with high doses delivered in 2–3 sessions over a few weeks. * **Paris Technique (Option A):** Developed at the Curie Institute, this technique uses a "continuous" low-dose-rate approach. It is characterized by using a tandem and two vaginal cylinders (colpostats) joined by a spacer (cork). * **Manchester Technique (Option C):** This is the most high-yield system for exams. It evolved from the Paris system and introduced the concept of **Point A and Point B** to standardize dosage. It uses a fixed relationship between the intrauterine tandem and vaginal ovoids. **High-Yield Clinical Pearls for NEET-PG:** * **Point A:** Located 2 cm superior to the lateral vaginal fornix and 2 cm lateral to the uterine canal. It represents where the uterine artery crosses the ureter. * **Point B:** Located 3 cm lateral to Point A (5 cm from the midline). It represents the pelvic wall and lymph nodes (Obturator nodes). * **ICRU 38/89:** Modern brachytherapy has shifted from these classical systems toward Image-Guided Adaptive Brachytherapy (IGABT) using MRI-based volume planning (HR-CTV).

Question 69: Intercavitatory radiotherapy is a treatment modality for which of the following conditions?

A. Carcinoma of the Cervix (Correct Answer)
B. Carcinoma of the Oesophagus
C. Carcinoma of the Stomach
D. Renal cell Carcinoma

Explanation: **Explanation:** **Brachytherapy** is a form of radiotherapy where the radiation source is placed within or in close proximity to the target tissue. It is broadly classified into Interstitial, Intercavitary, Intraluminal, and Surface mold therapy. **Why Carcinoma of the Cervix is Correct:** Intercavitary radiotherapy (ICRT) involves placing radioactive sources (like Cesium-137 or Iridium-192) into a pre-existing body cavity. In **Carcinoma of the Cervix**, sources are placed in the uterine cavity (tandem) and the vaginal fornices (ovoids/colpostats). This allows a very high dose of radiation to be delivered directly to the tumor while rapidly sparing adjacent critical organs like the bladder and rectum due to the inverse square law. **Why Other Options are Incorrect:** * **Carcinoma of the Oesophagus:** This is typically treated with **Intraluminal** brachytherapy (placing the source within the lumen of a tube) or external beam radiotherapy (EBRT). * **Carcinoma of the Stomach:** Primarily managed via surgery and adjuvant chemotherapy/EBRT; brachytherapy is not a standard modality here. * **Renal Cell Carcinoma:** This is a radioresistant tumor. The primary treatment is surgical (nephrectomy). Radiotherapy is generally reserved for palliation of bone metastases. **High-Yield Clinical Pearls for NEET-PG:** * **Manchester System:** The classic system used for Cervix Brachytherapy (Point A and Point B). * **Point A:** Located 2 cm superior to the lateral vaginal fornix and 2 cm lateral to the uterine canal. It represents where the uterine artery crosses the ureter. * **Most common source used today:** Iridium-192 (High Dose Rate brachytherapy). * **Interstitial Brachytherapy:** Used for Carcinoma of the Tongue, Lip, and Breast (source is placed directly into the tissue).

Question 70: Which of the following is used in External Beam Radiotherapy?

A. I-131
B. P-32
C. I-125
D. LINAC (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. LINAC** **Concept:** External Beam Radiotherapy (EBRT) involves delivering high-energy radiation from a source outside the patient’s body. The **Linear Accelerator (LINAC)** is the most commonly used device for EBRT. It uses microwave technology to accelerate electrons to near light speed, which then collide with a heavy metal target to produce high-energy X-rays (photons) or are used directly as electron beams to treat tumors. **Analysis of Incorrect Options:** * **A. I-131 (Iodine-131):** This is a radioisotope used primarily in **Systemic Radionuclide Therapy**. It is administered orally for the treatment of hyperthyroidism and differentiated thyroid cancer. * **B. P-32 (Phosphorus-32):** This is a pure beta-emitter used in **Internal Radiotherapy**. Historically, it was used for polycythemia vera and is currently used for intracavitary treatment (e.g., cystic brain tumors) or pleurodesis. * **C. I-125 (Iodine-125):** This is a low-energy gamma emitter used primarily in **Brachytherapy** (permanent seed implants), most commonly for localized prostate cancer. **Clinical Pearls for NEET-PG:** * **LINAC vs. Cobalt-60:** While Cobalt-60 was the traditional EBRT source (using Gamma rays), LINAC is now preferred because it provides higher energy, better skin-sparing effects, and does not involve a radioactive source that decays. * **Teletherapy:** EBRT is also known as Teletherapy (source-to-surface distance is usually 80–100 cm). * **Brachytherapy:** Treatment where the source is placed inside or in close proximity to the tumor (short distance). * **Common EBRT Modalities:** 3D-CRT, IMRT (Intensity Modulated Radiotherapy), and VMAT (Volumetric Modulated Arc Therapy) are all delivered via a LINAC.

Practice by Chapter

Principles of Radiation Therapy

Practice Questions

Radiation Therapy Equipment

Practice Questions

Treatment Planning Process

Practice Questions

External Beam Radiation Therapy

Practice Questions

Brachytherapy

Practice Questions

3D Conformal Radiation Therapy

Practice Questions

Intensity-Modulated Radiation Therapy

Practice Questions

Image-Guided Radiation Therapy

Practice Questions

Stereotactic Radiosurgery

Practice Questions

Total Body Irradiation

Practice Questions

Palliative Radiation Therapy

Practice Questions

Combined Modality Treatments

Practice Questions

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