Radiation Oncology Basics Practice Questions

Q: What is the dose of radiation that leads to mucositis?

3500-4000 rads. **Explanation:** Radiation-induced mucositis is a common acute complication of radiotherapy, particularly in head and neck cancers. It occurs due to the depletion of the basal cell layer of the oral mucosa, leading to inflammation, ulceration, and pain. **Why Option D is Correct:** The threshold for clinically significant mucositis typically begins after the third or fourth week of conventional fractionation (2 Gy/day). By this time, the cumulative dose reaches **3500–4000 rads (35–40 Gy)**. At this dosage, the rate of cell death in the mucosal epithelium exceeds the rate of regeneration, resulting in denudation and the formation of pseudomembranes. **Analysis of Incorrect Options:** * **Option A (1000 rads):** This is a low dose. While it may cause mild erythema, it is insufficient to cause the structural breakdown of the mucosa. * **Option B (1500–2000 rads):** At this stage (end of week 2), patients may experience "patchy mucositis" or soreness, but the classic confluent mucositis associated with the question's threshold is not yet fully established. * **Option C (2500–3000 rads):** This is an intermediate dose where symptoms intensify, but the peak incidence and severity of confluent mucositis are more characteristically seen at the 3500–4000 rads mark. **NEET-PG High-Yield Pearls:** * **Unit Conversion:** 100 rads = 1 Gray (Gy). Therefore, 4000 rads = 40 Gy. * **Early vs. Late Effects:** Mucositis is an **acute effect** (occurs during or within 90 days of treatment). Late effects include xerostomia and osteoradionecrosis. * **Management:** Treatment is primarily supportive (salt-soda rinses, topical anesthetics, and "Magic Mouthwash"). * **Radiosensitivity:** The oral mucosa is highly radiosensitive because it consists of rapidly dividing labile cells.

Q: Which of the following tumors is most radiosensitive?

Carcinoma of the nasopharynx. **Explanation:** The radiosensitivity of a tumor is generally determined by its histological type, degree of differentiation, and the rate of cell division (Law of Bergonie and Tribondeau). **Why Carcinoma of the Nasopharynx is correct:** Nasopharyngeal carcinoma (NPC), particularly the **undifferentiated subtype (WHO Type 3)**, is highly radiosensitive. This is due to its high mitotic index and its frequent association with lymphoid stroma (lymphoepithelioma). Because the nasopharynx is surgically inaccessible, **Radiotherapy (RT)** is the primary treatment of choice for all stages of NPC, often yielding excellent local control. **Analysis of Incorrect Options:** * **Carcinoma of the Glottis:** While early-stage glottic cancer is responsive to radiation, it is generally less sensitive than the undifferentiated cells of the nasopharynx. It is often treated with RT to preserve voice function, but the intrinsic sensitivity is lower. * **Carcinoma of the Subglottic Area:** These tumors are often detected late, tend to be more keratinizing/differentiated, and frequently involve the underlying cartilage, making them less responsive to radiation compared to NPC. * **Carcinoma of the Thyroid:** Most thyroid cancers (Papillary and Follicular) are **radioresistant** to external beam radiation. They are primarily managed surgically and with Radioactive Iodine (I-131) therapy, not standard external beam RT. **High-Yield Clinical Pearls for NEET-PG:** * **Most Radiosensitive Tumor:** Seminoma (Male) and Dysgerminoma (Female). * **Most Radiosensitive Normal Cell:** Lymphocyte (exception to the rule that mature cells are resistant). * **Radiosensitivity Scale:** Lymphoma/Leukemia > Squamous Cell Carcinoma > Adenocarcinoma > Sarcoma > Osteosarcoma (highly resistant). * **Nasopharyngeal Ca:** Strongly associated with **EBV (Epstein-Barr Virus)**; the most common site of origin is the **Fossa of Rosenmüller**.

Q: Which radioactive element is no longer used in current medical practice?

Radium 226. **Explanation:** **Radium-226 (Option A)** is the correct answer because it has been entirely phased out of modern clinical practice. Historically, Radium-226 was the first isotope used in brachytherapy (discovered by Marie Curie). However, it is no longer used due to significant safety concerns: it has an extremely long half-life (1,600 years), decays into a hazardous daughter product (**Radon-222 gas**), and is a "bone-seeker," posing a high risk of bone marrow toxicity and osteosarcoma if accidental internal exposure occurs. **Why the other options are incorrect:** * **Cobalt-60 (Option B):** Still used in external beam radiotherapy (Telecobalt units) and Gamma Knife surgery, particularly in developing countries, due to its high-energy gamma emission. * **Cesium-137 (Option C):** While its use in brachytherapy has decreased, it is still utilized in blood irradiators and some manual afterloading systems. It replaced Radium because it is safer to handle. * **Iridium-192 (Option D):** This is currently the **most commonly used** isotope for High-Dose-Rate (HDR) brachytherapy due to its high specific activity and small source size. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for HDR Brachytherapy:** Iridium-192 (Half-life: 74 days). * **Permanent Implants (Prostate Cancer):** Iodine-125 or Palladium-103 are preferred. * **Historical Context:** Radium-226 was replaced by Cesium-137, which has since been largely replaced by Iridium-192. * **Safety:** The "Radon hazard" is unique to Radium-226, requiring hermetically sealed containers that are no longer standard in modern oncology.

Q: What is the quantum of radiation advocated at point A in carcinoma cervix?

8000 cGy. ***8000 cGy*** - Point A in the **Manchester system** refers to a reference point 2 cm lateral and 2 cm superior to the cervical os, representing the **paracervical tissues** and **uterine vessels**. - The total dose of **8000 cGy** is achieved through a combination of **external beam radiotherapy (EBRT)** (~4500 cGy) and **low-dose rate (LDR) brachytherapy** (~3500 cGy). *1000 cGy* - This dose is significantly **underdosed** for carcinoma cervix and would result in **poor tumor control** and high recurrence rates. - Such low doses are typically used for **palliative treatments** or **benign conditions**, not curative intent in cervical cancer. *2000 cGy* - This dose is still **inadequate** for achieving local control in cervical carcinoma and would lead to **treatment failure**. - It represents less than 25% of the required therapeutic dose for **curative treatment** of cervical cancer. *5000 cGy* - While closer to therapeutic levels, this dose is still **suboptimal** for point A in cervical cancer treatment protocols. - It falls short of the **internationally accepted standard** of 8000 cGy and may result in **suboptimal outcomes** and higher recurrence rates.

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

Iridium-192. **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.

Q: Which of the following is a late complication of radiotherapy?

Radiation pneumonitis. **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 1

Which type of lung tumour responds best to radiotherapy?

Accepted Answer

Small cell carcinoma

Answer

Squamous cell carcinoma

Answer

Adenocarcinoma

Answer

All respond equally well

Question 2

What is the dose of radiation that leads to mucositis?

Accepted Answer

3500-4000 rads

Answer

1000 rads

Answer

1500-2000 rads

Answer

2500-3000 rads

Question 3

Which of the following is not a radiotherapy equipment?

Accepted Answer

Thimble chamber

Answer

Betatron

Answer

Telecurie-cobalt unit

Answer

Linear accelerator

Question 4

Which of the following is the most radiosensitive tumor?

Accepted Answer

Ewing tumor

Answer

Hodgkin's disease

Answer

Carcinoma cervix

Answer

Malignant fibrous histiocytoma

Question 5

Emergency radiotherapy is indicated in which of the following conditions?

Accepted Answer

Superior vena cava syndrome

Answer

Pericardial tamponade

Answer

Increased intracranial pressure

Answer

Spinal cord compression

Question 6

Which of the following tumors is most radiosensitive?

Accepted Answer

Carcinoma of the nasopharynx

Answer

Carcinoma of the glottis

Answer

Carcinoma of the subglottic area

Answer

Carcinoma of the thyroid

Question 7

Which radioactive element is no longer used in current medical practice?

Accepted Answer

Radium 226

Answer

Cobalt 60

Answer

Cesium 137

Answer

Iridium 192

Question 8

What is the quantum of radiation advocated at point A in carcinoma cervix?

Accepted Answer

8000 cGy

Answer

1000 cGy

Answer

2000 cGy

Answer

5000 cGy

Question 9

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

Accepted Answer

Iridium-192

Answer

Cesium-131

Answer

Gold-198

Answer

Radon-222

Question 10

Which of the following is a late complication of radiotherapy?

Accepted Answer

Radiation pneumonitis

Answer

Nausea

Answer

Erythema

Answer

Thrombocytopenia

Radiation Oncology Basics — MCQs

Radiation Oncology Basics — MCQs

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