Radiation Oncology Basics Practice Questions

Q: What is the standard treatment of whole-brain radiotherapy (WB) for brain Metastasis?

30 grays (Gy) in 10 fractions. ### Explanation **Standard Treatment Protocol** Whole-brain radiotherapy (WBRT) is a cornerstone in the palliative management of multiple brain metastases. The goal is to achieve a balance between tumor control and the preservation of neurocognitive function. The **standard fractionation schedule is 30 Gy delivered in 10 fractions** (3 Gy per fraction) over two weeks. This regimen is preferred because it provides an optimal therapeutic ratio, effectively reducing intracranial pressure and neurological symptoms while minimizing long-term radiation-induced leukoencephalopathy. **Analysis of Options** * **Option A (20 Gy in 10 fractions):** This dose is sub-therapeutic for most solid tumor metastases. While it uses a standard number of fractions, the total dose is insufficient for durable local control. * **Option C (30 Gy in 5 fractions):** This represents "hypofractionation" (6 Gy per fraction). While sometimes used in patients with a very poor prognosis (short life expectancy), it carries a significantly higher risk of acute and late neurological toxicity due to the high dose per fraction. * **Option D (15 Gy in 10 fractions):** This dose is far below the clinical threshold required to treat metastatic disease and is not a recognized standard protocol. **High-Yield Clinical Pearls for NEET-PG** * **Indications:** WBRT is typically indicated for patients with >3–4 metastases or those not suitable for Stereotactic Radiosurgery (SRS). * **Hippocampal Sparing:** Modern WBRT techniques often use "Hippocampal Sparing" to reduce memory decline. * **Steroid Adjunct:** Dexamethasone is usually administered alongside WBRT to reduce vasogenic edema caused by the tumors and the radiation itself. * **Alternative Schedule:** 20 Gy in 5 fractions is another accepted short-course regimen for patients with poor performance status.

Q: Maximum damage to the skin is caused by which type of radiation therapy?

Orthovoltage X-ray. **Explanation:** The degree of skin damage in radiation therapy is primarily determined by the **"Skin Sparing Effect."** This phenomenon depends on the energy of the radiation beam and the depth at which the maximum dose ($D_{max}$) is deposited. **Why Orthovoltage is the Correct Answer:** Orthovoltage X-rays operate at a relatively low energy range (typically **200–500 kV**). Because of this low energy, the maximum dose ($D_{max}$) is deposited almost immediately at the **skin surface**. Since the skin receives 100% of the prescribed dose, it suffers the most significant damage, leading to side effects like erythema, desquamation, and permanent scarring. **Analysis of Incorrect Options:** * **Supervoltage (500–1000 kV) & Megavoltage (>1 MV) X-rays:** As the energy of the X-ray increases, the $D_{max}$ shifts deeper into the tissues (e.g., for a 6 MV beam, $D_{max}$ is at 1.5 cm). This results in a lower dose at the surface, providing a significant skin-sparing effect. * **Cobalt-60:** This is a form of megavoltage therapy (average energy 1.25 MeV). Its $D_{max}$ occurs at **0.5 cm** below the skin surface, meaning it spares the skin significantly more than orthovoltage. **High-Yield Clinical Pearls for NEET-PG:** * **Skin Sparing Effect:** The higher the energy of the photon beam, the deeper the $D_{max}$, and the greater the skin sparing. * **$D_{max}$ Values to Remember:** * **Orthovoltage:** 0.0 cm (Surface) * **Cobalt-60:** 0.5 cm * **4 MV:** 1.0 cm * **6 MV:** 1.5 cm * **10 MV:** 2.5 cm * **Clinical Use:** Orthovoltage is now rarely used except for very superficial lesions (e.g., skin cancers) precisely because it lacks skin sparing.

Q: Which of the following is the most radiosensitive ovarian tumor?

Dysgerminoma. **Explanation:** **Dysgerminoma** is the most common malignant germ cell tumor of the ovary and is characterized by its extreme **radiosensitivity**. This property is a hallmark of germ cell tumors (similar to its male counterpart, the seminoma). While surgery is the primary treatment to preserve fertility, radiotherapy is highly effective in treating recurrences or metastatic disease because these cells undergo rapid apoptosis when exposed to ionizing radiation. **Analysis of Incorrect Options:** * **Dermoid Cyst (Mature Cystic Teratoma):** This is a benign germ cell tumor containing mature tissues (hair, teeth, sebum). These mature tissues are differentiated and **radioresistant**. * **Serous Cystadenoma:** This is a benign epithelial tumor. Epithelial tumors, in general, are less radiosensitive than germ cell tumors, and benign versions do not require radiation therapy. * **Endodermal Sinus Tumor (Yolk Sac Tumor):** While this is a malignant germ cell tumor, it is highly aggressive and primarily treated with **chemotherapy** (BEP regimen). It is not as exquisitely radiosensitive as Dysgerminoma. **Clinical Pearls for NEET-PG:** * **Tumor Marker:** Dysgerminoma is associated with elevated **LDH** (and occasionally hCG), whereas Endodermal Sinus Tumor is associated with high **AFP**. * **Radiosensitivity Rule:** In the context of "Most Radiosensitive," always look for **Dysgerminoma** (Ovary), **Seminoma** (Testis), or **Ewing’s Sarcoma** (Bone). * **Histology:** Dysgerminoma shows large cells with clear cytoplasm and central nuclei, separated by fibrous septa containing lymphocytes.

Q: Mould therapy is used in the treatment of:

Skin cancer. **Explanation:** **Mould therapy** is a form of **surface brachytherapy** where radioactive sources are placed in a customized applicator (the "mould") that is applied directly to the surface of the body. 1. **Why Skin Cancer is Correct:** Mould therapy is specifically designed for treating superficial lesions. The radioactive sources (commonly Iridium-192 or Cesium-137) are held at a short, fixed distance from the skin. This allows for a high dose of radiation to be delivered to the tumor while ensuring a rapid dose fall-off, which protects the deeper, healthy underlying tissues. It is most commonly used for cancers of the **skin (e.g., Basal Cell Carcinoma, Squamous Cell Carcinoma)**, lip, or hard palate. 2. **Why Other Options are Incorrect:** * **Pelvic and Prostate Cancer:** These involve deep-seated tumors. They are typically treated with **Intracavitary brachytherapy** (e.g., cervical cancer), **Interstitial brachytherapy** (needles inserted into the prostate), or External Beam Radiation Therapy (EBRT). Moulds cannot reach these depths. * **Lung Cancer:** This requires EBRT or occasionally **Intraluminal brachytherapy** (via bronchoscopy). A surface mould would be ineffective for internal thoracic structures. **High-Yield Clinical Pearls for NEET-PG:** * **Brachytherapy Types:** * **Surface (Moulds):** Skin, ear, eye. * **Interstitial:** Breast, Prostate, Tongue (using needles/wires). * **Intracavitary:** Cervix, Endometrium (using Tandem and Ovoids). * **Intraluminal:** Esophagus, Bronchus. * **Inverse Square Law:** The rapid dose fall-off in mould therapy is governed by the inverse square law, making it ideal for superficial treatment. * **Customization:** Moulds are often made of dental acrylic or thermoplastic materials to fit the patient's specific anatomy perfectly.

Q: Hyperfractionated radiotherapy is primarily used in which of the following conditions?

Lung cancer. **Explanation:** **Hyperfractionated radiotherapy** involves delivering a higher total dose of radiation by using smaller-than-standard doses (fractions) multiple times a day (usually twice). The primary goal is to exploit the difference in repair capacity between rapidly dividing tumor cells and late-responding normal tissues. 1. **Why Lung Cancer is Correct:** Small Cell Lung Cancer (SCLC) is the classic indication for hyperfractionation (e.g., the Turrisi regimen). Because lung tumors have a high growth fraction, giving two fractions a day minimizes "tumor repopulation" during the treatment course. Smaller doses per fraction also spare late-responding normal tissues like the lungs and spinal cord, allowing for a higher total curative dose. 2. **Why Other Options are Incorrect:** * **Melanomas and Soft Tissue Sarcomas:** These are considered **radioresistant** tumors with a low alpha/beta ratio. They respond better to **Hypofractionation** (larger doses per fraction given fewer times). Large fractions are needed to overcome their inherent repair mechanisms and slow cell cycling. * **All of the above:** Incorrect because the biological rationale for hyperfractionation (sparing late tissues while hitting fast-growing tumors) does not apply to slow-growing, radioresistant sarcomas or melanomas. **Clinical Pearls for NEET-PG:** * **Hyperfractionation:** Increased number of fractions, decreased dose per fraction, total dose increased. Best for **rapidly proliferating tumors** (e.g., SCLC, Head and Neck cancers). * **Hypofractionation:** Decreased number of fractions, increased dose per fraction. Best for **slowly proliferating tumors** (e.g., Prostate, Melanoma, Breast). * **Accelerated Fractionation:** Reducing the overall treatment time without changing the dose per fraction (to counter rapid tumor repopulation).

Q: Radiation caries is an example of:

Rampant caries.. **Explanation:** **Radiation caries** is a highly destructive form of dental decay that occurs in patients receiving radiotherapy for head and neck cancers. It is classified as a type of **Rampant Caries** because of its rapid onset, widespread involvement of multiple teeth, and progression to surfaces usually resistant to decay (such as incisal edges and cervical margins). The underlying mechanism is primarily indirect: radiation causes fibrosis and atrophy of the salivary glands (especially the parotid), leading to severe **xerostomia** (dry mouth). The loss of the buffering capacity, minerals, and antimicrobial properties of saliva results in a shift toward acidogenic flora, leading to the rapid "rampant" destruction of tooth structure. **Analysis of Options:** * **Option B (Correct):** Rampant caries refers to a sudden, widespread outbreak of dental caries affecting many teeth. Radiation caries fits this definition perfectly due to its aggressive nature post-irradiation. * **Option A (Incorrect):** Early childhood caries (nursing bottle syndrome) is specific to infants and toddlers, usually due to prolonged exposure to sugary liquids in bottles. * **Option C (Incorrect):** Exposure caries is not a standard clinical classification; while radiation "exposes" the teeth to risk, the clinical manifestation is categorized under rampant caries. **High-Yield Clinical Pearls for NEET-PG:** * **Critical Dose:** Salivary gland dysfunction can occur at doses as low as **20-30 Gy**. * **Clinical Presentation:** Typically starts at the **cervical (neck) region** of the teeth. * **Management:** Pre-radiation dental clearance, lifelong topical fluoride application, and meticulous oral hygiene. * **Osteoradionecrosis (ORN):** A more severe complication of radiation involving bone (usually the mandible), often triggered by post-radiation tooth extractions.

Q: What is the conventional daily dose regimen in external beam radiotherapy?

180-200 cGy. ### Explanation **1. Understanding the Correct Answer (C: 180-200 cGy)** In conventional external beam radiotherapy (EBRT), the total dose required to kill a tumor is divided into small daily increments called **fractions**. The standard or "conventional" fractionation schedule is **180 to 200 cGy (1.8–2.0 Gy) per day**, administered five days a week for 5 to 7 weeks. The underlying radiobiological principle is the **"4 Rs" of Radiobiology**: Repair, Re-oxygenation, Redistribution, and Repopulation. This specific dose range (1.8–2.0 Gy) is the "sweet spot" that maximizes damage to tumor cells while allowing normal surrounding tissues to **repair** sublethal DNA damage between treatments, thereby minimizing late-term complications. **2. Why Other Options are Incorrect** * **Options A & B (100-170 cGy):** These doses are considered **Hyperfractionation**. While smaller doses per fraction are gentler on normal tissues, they require treating the patient multiple times a day to reach the therapeutic threshold, which is not the "conventional" standard. * **Option D (225-250 cGy):** Doses above 200 cGy per fraction are termed **Hypofractionation**. While used in specific scenarios (like palliative care or stereotactic treatments), higher daily doses increase the risk of late-tissue toxicity (fibrosis, necrosis) in standard curative settings. **3. High-Yield Clinical Pearls for NEET-PG** * **Standard Unit:** 1 Gray (Gy) = 100 centiGray (cGy) = 1 Joule/kg. * **Hyperfractionation:** Smaller dose per fraction ( 2.2 Gy), fewer fractions. Aim: Convenience or for slow-growing tumors (e.g., Prostate). * **Accelerated Fractionation:** Same dose per fraction, but total treatment time is reduced (e.g., treating 6 days a week). Aim: Overcome tumor repopulation.

Q: What is the recommended quantum of radiation at point B in carcinoma of the cervix?

5000 cGy. ### Explanation In the Manchester System for Brachytherapy in cervical cancer, **Point B** is defined as a point **2 cm superior** to the external cervical os and **5 cm lateral** to the midline. **Why 5000 cGy is correct:** Point B represents the **pelvic side wall**, specifically the location of the obturator lymph nodes. The goal of radiation at Point B is to treat potential regional lymphatic spread. While Point A (the paracervical triangle) receives a high curative dose of approximately 7500–8000 cGy, the dose at Point B is typically **one-third to two-thirds** of the Point A dose. In standard clinical practice, the cumulative dose (External Beam Radiation + Brachytherapy) to Point B is approximately **5000–5500 cGy**. **Why incorrect options are wrong:** * **1000 cGy & 2000 cGy:** These doses are sub-therapeutic for cervical malignancy and would fail to control microscopic nodal disease. * **8000 cGy:** This is the typical total dose delivered to **Point A**. Delivering 8000 cGy to Point B would exceed the tolerance of surrounding normal tissues (rectum and bladder) and is physically impossible with standard brachytherapy pear-shaped distributions without causing severe necrosis. **High-Yield Clinical Pearls for NEET-PG:** * **Point A:** 2 cm superior to the external os and 2 cm lateral to the uterine canal. It represents the crossing of the **uterine artery and the ureter**. * **Point B:** 5 cm lateral to the midline (3 cm lateral to Point A). It represents the **obturator nodes**. * **Tolerance Doses (TD 5/5):** Bladder (65 Gy), Rectum (60 Gy). * **ICRU 38:** Modern reporting has shifted from Point A/B to volume-based assessments (GEC-ESTRO guidelines), but Point A/B remains a frequent examiner favorite.

Q: Which of the following malignancies responds best to radiotherapy?

Cervical Carcinoma. **Explanation:** The radiosensitivity of a tumor depends on its histological origin, degree of differentiation, and oxygenation. In clinical oncology, tumors are classified as radiosensitive, radioresponsive, or radioresistant. **1. Why Cervical Carcinoma is Correct:** Cervical carcinoma (most commonly Squamous Cell Carcinoma) is highly **radioresponsive**. Radiotherapy (both External Beam Radiation and Brachytherapy) is a primary treatment modality for locally advanced stages. Squamous cells generally have a high turnover rate and a predictable response to ionizing radiation, which induces DNA damage and subsequent apoptosis in these rapidly dividing cells. **2. Why the Other Options are Incorrect:** * **Renal Cell Carcinoma (RCC):** Classically considered **radioresistant**. While SBRT is sometimes used for palliation, RCC does not respond well to standard fractionation. Surgery remains the mainstay of treatment. * **Adenocarcinoma of the Colon:** Generally shows **poor radiosensitivity**. Surgery and chemotherapy are the primary treatments; radiation is rarely used for colon cancer (unlike rectal cancer, where it is used pre-operatively). * **Malignant Melanoma:** Notoriously **radioresistant** due to efficient DNA repair mechanisms and high levels of melanin, which may provide some radioprotection. It requires very high doses per fraction (hypofractionation) to see a response. **Clinical Pearls for NEET-PG:** * **Most Radiosensitive Tumor:** Seminoma (followed by Lymphoma and Wilms tumor). * **Most Radiosensitive Cell in the Body:** Lymphocyte (exception to the Law of Bergonie and Tribondeau). * **Most Radiosensitive Phase of Cell Cycle:** **M phase** (followed by G2). * **Most Radioresistant Phase:** **S phase** (specifically late S phase). * **Law of Bergonie and Tribondeau:** Radiosensitivity is directly proportional to the reproductive rate and inversely proportional to the degree of differentiation.

Q: All are true about stereotactic radiosurgery except?

Damage to nearby structures is significant. **Explanation:** Stereotactic Radiosurgery (SRS) is a highly precise form of radiation therapy designed to deliver a single, high dose of ionizing radiation to a specific target while minimizing exposure to surrounding healthy tissues. **Why Option D is the Correct Answer (The "Except" statement):** The hallmark of SRS is its **steep dose gradient**. Because it uses multiple convergent beams and rigid immobilization (stereotactic frames or image guidance), the radiation dose drops off rapidly outside the target volume. This ensures that **damage to nearby structures is minimal**, not significant. This precision allows for the treatment of lesions located near critical structures like the brainstem or optic nerves. **Analysis of Incorrect Options:** * **Option A (X-rays are used):** This is true. Linear accelerators (LINAC) use high-energy X-rays (photons) to perform SRS. (Note: Gamma Knives use Gamma rays, and CyberKnives use X-rays). * **Option B (A form of radiotherapy):** This is true. Despite the name "surgery," no incision is made; it is a specialized non-invasive radiation technique. * **Option C (Used in AV malformation):** This is true. SRS is a gold-standard treatment for small-to-medium Arteriovenous Malformations (AVMs), especially those in surgically inaccessible areas. **High-Yield Clinical Pearls for NEET-PG:** * **Definition:** SRS is typically delivered in a **single fraction** (or up to 5 fractions, termed Stereotactic Radiotherapy). * **Common Indications:** Vestibular Schwannomas (Acoustic Neuroma), Meningiomas, Brain Metastases, Trigeminal Neuralgia, and AVMs. * **Key Modalities:** Gamma Knife (Cobalt-60 source), LINAC-based (X-rays), and CyberKnife (robotic arm). * **Radiobiology:** Unlike conventional radiotherapy which relies on the "4 Rs," SRS works primarily through direct vascular damage and cellular necrosis.

Question 1

What is the standard treatment of whole-brain radiotherapy (WB) for brain Metastasis?

Accepted Answer

30 grays (Gy) in 10 fractions

Answer

20 grays (Gy) in 10 fractions

Answer

30 grays (Gy) in 5 fractions

Answer

15 grays (Gy) in 10 fractions

Question 2

Maximum damage to the skin is caused by which type of radiation therapy?

Accepted Answer

Orthovoltage X-ray

Answer

Super voltage X-ray therapy

Answer

Mega voltage X-ray

Answer

Cobalt-60

Question 3

Which of the following is the most radiosensitive ovarian tumor?

Accepted Answer

Dysgerminoma

Answer

Dermoid cyst

Answer

Serous cystadenoma

Answer

Endodermal sinus tumor

Question 4

Mould therapy is used in the treatment of:

Accepted Answer

Skin cancer

Answer

Pelvic cancer

Answer

Lung cancer

Answer

Prostate cancer

Question 5

Hyperfractionated radiotherapy is primarily used in which of the following conditions?

Accepted Answer

Lung cancer

Answer

Melanomas

Answer

Soft tissue sarcomas

Answer

All the above

Question 6

Radiation caries is an example of:

Accepted Answer

Rampant caries.

Answer

Early childhood caries.

Answer

Exposure caries.

Answer

None of the above.

Question 7

What is the conventional daily dose regimen in external beam radiotherapy?

Accepted Answer

180-200 cGy

Answer

100-150 cGy

Answer

150-170 cGy

Answer

225-250 cGy

Question 8

What is the recommended quantum of radiation at point B in carcinoma of the cervix?

Accepted Answer

5000 cGy

Answer

1000 cGy

Answer

2000 cGy

Answer

8000 cGy

Question 9

Which of the following malignancies responds best to radiotherapy?

Accepted Answer

Cervical Carcinoma

Answer

Renal Cell Carcinoma

Answer

Adenocarcinoma Colon

Answer

Malignant Melanoma

Question 10

All are true about stereotactic radiosurgery except?

Accepted Answer

Damage to nearby structures is significant

Answer

X-rays are used

Answer

A form of radiotherapy

Answer

Used in AV malformation

Radiation Oncology Basics — MCQs

Radiation Oncology Basics — MCQs

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