Radiation Oncology Basics Practice Questions

Q: Taste loss due to radiation therapy is recovered in approximately what timeframe?

60 - 120 days. **Explanation:** Radiation-induced dysgeusia (taste loss) is a common side effect in patients receiving radiotherapy for head and neck cancers. The underlying mechanism involves damage to the rapidly dividing basal cells of the taste buds and the microvilli of gustatory cells, which have a high turnover rate. **Why 60 - 120 days is correct:** Taste buds are highly radiosensitive. While taste impairment typically begins within the first 1-2 weeks of treatment (at doses around 10-20 Gy), the recovery process begins after the completion of radiotherapy. It takes approximately **2 to 4 months (60 - 120 days)** for the taste bud cells to regenerate and for the neural pathways to stabilize, leading to a significant restoration of taste function in most patients. **Analysis of Incorrect Options:** * **A. 2 weeks:** This is too early. While acute mucosal inflammation (mucositis) may begin to subside, the regeneration of specialized gustatory cells takes longer. * **B. 60 - 120 weeks:** This represents a timeframe of over 1-2 years. While some patients experience long-term changes, the majority of clinical recovery occurs much sooner. * **D. Not reversible:** Radiation-induced taste loss is generally reversible. Permanent loss (ageusia) is rare unless very high doses are delivered directly to the tongue or if there is severe, permanent xerostomia (dry mouth), as saliva is essential for tasting. **High-Yield Clinical Pearls for NEET-PG:** * **Order of Taste Loss:** Sensitivity to **bitter and acid** flavors is usually lost first, while **salty and sweet** are lost later. * **Xerostomia Connection:** Damage to the salivary glands (especially the parotid) exacerbates taste loss because saliva acts as a solvent for food particles to reach taste receptors. * **Zinc Supplementation:** Some studies suggest that Zinc sulfate may help in the early recovery of taste post-radiation.

Q: Carcinoma responding maximally to radiotherapy is:

Small cell carcinoma. **Explanation:** The responsiveness of a tumor to radiotherapy is primarily determined by its **radiosensitivity**, which is closely linked to the **Bergonie-Tribondeau law**. This law states that cells are more radiosensitive if they have a high mitotic rate, a long mitotic future, and are undifferentiated. **1. Why Small Cell Carcinoma is Correct:** Small cell carcinoma (most commonly seen in the lung) is a highly undifferentiated, rapidly dividing neuroendocrine tumor. Due to its high growth fraction and rapid cell turnover, it is classified as **highly radiosensitive**. It shows a dramatic initial response to radiation (and chemotherapy), often leading to significant tumor shrinkage or "vanishing" on follow-up imaging. **2. Why Other Options are Incorrect:** * **Squamous Cell Carcinoma (SCC):** While SCC is considered **radiosensitive** and is frequently treated with radiotherapy (e.g., in head and neck or cervical cancers), its response is generally slower and less "maximal" compared to small cell variants. * **Adenocarcinoma:** These tumors are generally considered **radioresponsive to radioresistant**. They are more differentiated and have a slower cell cycle compared to small cell carcinoma, making them less susceptible to radiation-induced DNA damage. **High-Yield Clinical Pearls for NEET-PG:** * **Radiosensitivity Hierarchy:** * *Highly Radiosensitive:* Lymphoma, Leukemia, Seminoma, Dysgerminoma, Small Cell Carcinoma. * *Moderately Radiosensitive:* Squamous Cell Carcinoma. * *Radioresistant:* Osteosarcoma, Malignant Melanoma, Pancreatic Adenocarcinoma. * **Therapeutic Ratio:** The ratio of the maximum tolerated dose of normal tissue to the minimum dose required to kill the tumor. * **The 4 R’s of Radiobiology:** Repair, Reassortment, Repopulation, and Reoxygenation.

Q: Intraoperative radiation therapy is typically indicated for which of the following organs?

Pancreas. **Explanation:** **Intraoperative Radiation Therapy (IORT)** involves the delivery of a single, concentrated dose of ionizing radiation directly to the tumor bed during surgery, immediately after the tumor is resected. **Why Pancreas is the Correct Answer:** The primary advantage of IORT is the ability to physically displace or shield radiosensitive dose-limiting structures (like the small intestine, stomach, and liver) away from the radiation field. In **pancreatic adenocarcinoma**, achieving negative surgical margins is difficult due to proximity to major vessels. IORT is typically indicated here to sterilize microscopic residual disease in the retroperitoneum, where conventional external beam radiation (EBRT) would be limited by bowel toxicity. **Analysis of Incorrect Options:** * **Breast:** While IORT is an emerging option for early-stage breast cancer (e.g., TARGIT trials), it is considered an *alternative* to whole-breast irradiation in highly selected cases, rather than a "typical" or standard indication compared to its established role in deep-seated abdominal malignancies. * **Cervix:** Cervical cancer is primarily managed with EBRT and **Brachytherapy** (intracavitary). IORT is rarely used unless there is a specific pelvic sidewall recurrence. * **Thyroid:** Differentiated thyroid cancer is managed with surgery and **Radioactive Iodine (I-131) therapy**. Radiation is rarely used, and IORT has no standard role here. **High-Yield Clinical Pearls for NEET-PG:** * **Common IORT Indications:** Pancreatic cancer, locally advanced rectal cancer, and retroperitoneal sarcomas. * **Key Advantage:** Maximizes the "Therapeutic Ratio" by allowing a high dose to the target while sparing OARs (Organs at Risk). * **Radiation Type:** Usually delivered via mobile linear accelerators (electrons) or low-energy X-rays.

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: 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.

Question 1

Taste loss due to radiation therapy is recovered in approximately what timeframe?

Accepted Answer

60 - 120 days

Answer

2 weeks

Answer

60 - 120 weeks

Answer

Not reversible

Question 2

Carcinoma responding maximally to radiotherapy is:

Accepted Answer

Small cell carcinoma

Answer

Squamous cell carcinoma

Answer

Adenocarcinoma

Answer

None of the above

Question 3

Intraoperative radiation therapy is typically indicated for which of the following organs?

Accepted Answer

Pancreas

Answer

Breast

Answer

Cervix

Answer

Thyroid

Question 4

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 5

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 6

Which of the following is not a radiotherapy equipment?

Accepted Answer

Thimble chamber

Answer

Betatron

Answer

Telecurie-cobalt unit

Answer

Linear accelerator

Question 7

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 8

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 9

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 10

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

Radiation Oncology Basics — MCQs

Radiation Oncology Basics — MCQs

On this page

Practice by Chapter

Want unlimited practice?