Radiation Oncology Basics — MCQs
Precisely directed high dose radiation is used in which of the following therapies?
A 55 year old woman diagnosed with ca cervix stage IIb is advised for chemoradiation. Which of the following is the true statement regarding radiation use?
For the treatment of deep-seated tumors, the following rays are used:
Most common acute skin manifestation of radiotherapy:
Radiosensitivity of tumour depends on:
Most radiosensitive tumor among the following is
Which of the following is/are most radioresistant?
Most sensitive tissue to Radiation is
Late effects of radiation therapy include:
Vitamin B12 deficiency can give rise to all of the following, except which of the following?
Radiation Oncology Basics Indian Medical PG Practice Questions and MCQs
Question 1: Precisely directed high dose radiation is used in which of the following therapies?
- A. EBRT
- B. IMRT
- C. Brachytherapy
- D. Stereotactic radiosurgery (Correct Answer)
Explanation: ***Stereotactic radiosurgery*** - **Stereotactic radiosurgery (SRS)** is a highly precise radiation therapy that uses focused, high-dose radiation beams to target small tumors or abnormalities with **sub-millimeter accuracy**. - It delivers **very high doses per fraction** (typically 15-24 Gy in a single session) using stereotactic guidance systems. - Commonly used for **brain metastases, AVMs, acoustic neuromas**, and other small intracranial targets. *IMRT* - **Intensity-modulated radiation therapy (IMRT)** is an advanced form of 3D-conformal radiation therapy that modulates beam intensity to conform to tumor shape. - While IMRT is precise, it uses **conventional fractionation** (1.8-2 Gy per fraction over many treatments), not the high-dose approach of SRS. *EBRT* - **External beam radiation therapy (EBRT)** is a general term for radiation delivered from outside the body. - It encompasses various techniques but *does not specifically indicate the **stereotactic precision and high-dose per fraction** characteristic of SRS*. *Brachytherapy* - **Brachytherapy** involves placing radioactive sources **directly inside or next to the tumor**. - While it delivers high doses locally, it is not "precisely directed high-dose radiation" from external beams like SRS.
Question 2: A 55 year old woman diagnosed with ca cervix stage IIb is advised for chemoradiation. Which of the following is the true statement regarding radiation use?
- A. Rapidly proliferating cells are less affected by radiation
- B. The small bowel is not significantly affected by radiation
- C. Dose/Intensity of radiation is inversely proportional to the square of distance of source (Correct Answer)
- D. Small blood vessels are unaffected by radiation
Explanation: ***Dose/Intensity of radiation is inversely proportional to the square of distance of source*** - This statement accurately describes the **inverse square law** which governs radiation intensity. As the distance from the radiation source increases, the dose or intensity of radiation decreases proportionally to the square of that distance. - This principle is crucial in **radiation safety** and treatment planning to ensure appropriate dose delivery and minimize exposure to non-target tissues. *Rapidly proliferating cells are less affected by radiation* - This is incorrect; **rapidly proliferating cells** are generally **more sensitive to radiation** because radiation primarily targets cells undergoing division, causing DNA damage. - Tissues with high cellular turnover, like bone marrow and gastrointestinal lining, are highly susceptible to radiation-induced damage. *The small bowel is not significantly affected by radiation* - This is incorrect; the **small bowel** is one of the most **radiosensitive organs** due to its rapidly proliferating epithelial cells. - Radiation to the abdomen and pelvis, common in cervical cancer treatment, frequently causes symptoms such as **nausea, vomiting, diarrhea**, and long-term complications like enteritis and strictures. *Small blood vessels are unaffected by radiation* - This is incorrect; **small blood vessels**, particularly the **endothelium**, are quite susceptible to radiation damage. - Radiation can cause **endothelial cell swelling**, damage, and sclerosis, leading to vascular insufficiency, fibrosis, and impaired tissue healing.
Question 3: For the treatment of deep-seated tumors, the following rays are used:
- A. X rays and Gamma rays (Correct Answer)
- B. Alpha rays and Beta rays
- C. Electrons and positrons
- D. High power laser beams
Explanation: ***X rays and Gamma rays*** - **X-rays** and **gamma rays** are high-energy electromagnetic radiation capable of penetrating deep into tissues to target deep-seated tumors. - They induce DNA damage in cancer cells, leading to cell death and tumor regression, making them mainstays in **radiation therapy**. *Alpha rays and Beta rays* - **Alpha particles** have a very short range and high linear energy transfer, making them suitable for superficial tumors or targeted internal delivery rather than deep-seated tumors. - **Beta particles** have a medium range in tissue but are generally less penetrating than X-rays or gamma rays, limiting their effectiveness for deep lesions. *Electrons and positrons* - **Electron beams** are used for superficial tumors due to their limited penetration depth, typically reaching only a few centimeters into tissue. - **Positrons** are used in imaging (PET scans) and are not directly used for therapeutic tumor ablation, as their annihilation with electrons produces gamma rays, but they themselves don't treat tumors. *High power laser beams* - **Laser beams** are primarily used for superficial tissue ablation, cutting, or coagulation in surgical procedures due to their limited direct penetration into deep tissues without significant scattering and absorption. - While lasers can be used in some interstitial tumor treatments, they are not a primary method for treating large, deep-seated tumors due to their localized effect and lack of volumetric penetration.
Question 4: Most common acute skin manifestation of radiotherapy:
- A. Dermatitis
- B. Erythema (Correct Answer)
- C. Atopy
- D. Hyperpigmentation
Explanation: ***Erythema*** - **Erythema** (redness) is the most immediate and common acute cutaneous reaction to radiotherapy due to **vasodilation** and inflammation of the skin in the irradiated area. - It often appears within days to weeks of starting radiation treatment and is a direct consequence of cell damage and the body's inflammatory response to it. *Dermatitis* - While radiation dermatitis is a broader term encompassing various skin changes from radiotherapy, **erythema** is the initial and most prevalent component of this dermatological spectrum, making it a more specific answer for the "most common" manifestation. - Dermatitis can also include later-stage problems like **dry desquamation** and **moist desquamation**, which are more severe reactions. *Atopy* - **Atopy** refers to a genetic predisposition to develop allergic diseases like asthma, allergic rhinitis, or atopic dermatitis. - It is an **intrinsic immune predisposition** and not a direct skin manifestation caused by radiotherapy itself. *Hyperpigmentation* - While **hyperpigmentation** can occur in the irradiated area, it is typically a **subacute or chronic** reaction, often appearing weeks to months after the onset of erythema or after the completion of treatment. - It is not the most immediate or common acute manifestation compared to erythema.
Question 5: Radiosensitivity of tumour depends on:
- A. Nucleus atypia
- B. Histology (Correct Answer)
- C. Blood supply
- D. Number of cells
Explanation: ***Histology*** - The **histological type** of a tumor is the **PRIMARY and fundamental determinant** of its radiosensitivity, as different cell types have varying inherent responses to radiation based on their cellular characteristics and DNA repair mechanisms [1]. - For example, **lymphomas** and **seminomas** are typically highly radiosensitive, while **sarcomas** and **melanomas** are often radioresistant [1]. - This intrinsic property is determined by the cell of origin and tissue type, making histology the most important factor [1]. *Nucleus atypia* - While **nuclear atypia** indicates malignancy and often correlates with aggressive behavior, it does not directly determine radiosensitivity. - It reflects cellular morphology and differentiation status rather than the intrinsic ability to repair radiation-induced damage. *Blood supply* - **Blood supply** influences the delivery of oxygen to tumor cells, and well-oxygenated cells are generally more radiosensitive (**oxygen effect**). - However, blood supply is a **modifying factor** for radiosensitivity, not the fundamental determinant like histology. - It enhances or reduces the effectiveness of radiation but doesn't define the inherent sensitivity of the tumor type. *Number of cells* - The **number of cells** in a tumor affects the overall dose required for tumor control but is not a primary factor in the intrinsic radiosensitivity of individual cells or the tumor type itself. - A larger tumor burden might require higher total doses and potentially harbors more resistant clones, but this doesn't change the inherent radiobiological properties determined by histology. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 204-209.
Question 6: Most radiosensitive tumor among the following is
- A. Dysgerminoma (Correct Answer)
- B. Osteogenic sarcoma
- C. Parotid carcinoma
- D. Bronchogenic carcinoma
Explanation: ***Dysgerminoma*** - **Dysgerminomas** are highly **radiosensitive** tumors, meaning they respond very well to radiation therapy. - This characteristic is often exploited in their treatment, especially for widespread disease or as adjuvant therapy. *Osteogenic sarcoma* - **Osteogenic sarcomas** (osteosarcomas) are generally **radioresistant**, requiring high doses of radiation for local control, often with limited success. - Treatment primarily relies on **surgery** and **chemotherapy**. *Parotid carcinoma* - **Parotid carcinomas** exhibit variable radiosensitivity depending on their histology, but generally are not considered among the most radiosensitive tumors. - Postoperative **radiotherapy** is often used for high-risk features rather than as primary monotherapy. *Bronchogenic carcinoma* - **Bronchogenic carcinomas** (lung cancers) show variable radiosensitivity. **Small cell lung carcinoma** is more radiosensitive than **non-small cell lung carcinoma**, but neither is considered as radiosensitive as dysgerminoma. - Treatment often involves **multimodality therapy** including chemotherapy, surgery, and radiation, with radiation efficacy depending on tumor type and stage.
Question 7: Which of the following is/are most radioresistant?
- A. Neurons
- B. Muscle cells
- C. Erythrocytes (Correct Answer)
- D. All of the options
Explanation: ***Erythrocytes*** - Erythrocytes are **anucleated** and terminally differentiated cells, meaning they do not divide. Cells that do not divide are generally **radioresistant**. - Their primary function is oxygen transport, and they have a limited metabolic capacity, making them less susceptible to the genetic damage that typically leads to radiation-induced cell death. *Neurons* - While neurons are **post-mitotic** and generally radioresistant compared to rapidly dividing cells, they are still more susceptible than mature erythrocytes. - High doses of radiation can lead to neuronal damage and death through mechanisms like **apoptosis** and indirect effects from damage to surrounding glial cells and vasculature. *Muscle cells* - Muscle cells (myocytes) are **terminally differentiated** and have a low mitotic rate, making them relatively radioresistant. - However, they are still more sensitive to radiation than erythrocytes, and high doses can cause muscle degeneration and fibrosis. *All of the options* - This option is incorrect because while neurons and muscle cells are relatively radioresistant, **erythrocytes are demonstrably the most radioresistant** among the choices due to their complete lack of a nucleus and inability to divide.
Question 8: Most sensitive tissue to Radiation is
- A. Skin
- B. Gonads (Correct Answer)
- C. Spleen
- D. Liver
Explanation: ***Gonads*** - **Gonadal cells (spermatogonia and oocytes)** are highly radiosensitive due to their rapid proliferation and differentiation, making them very vulnerable to radiation-induced damage. - Exposure to radiation can lead to **sterility** or genetic mutations in germ cells, which can be passed on to future generations. *Skin* - While skin is a moderately radiosensitive tissue, showing effects like **erythema** and desquamation at certain doses, it is not the most sensitive. - Its regenerative capacity allows for recovery from moderate radiation damage, unlike germ cells. *Spleen* - The **spleen**, as a lymphoid organ, contains rapidly dividing cells, particularly lymphocytes, which are radiosensitive. - However, its sensitivity is generally lower than that of germ cells in the gonads. *Liver* - The **liver** is generally considered a radioresistant organ, requiring much higher doses of radiation to exhibit significant damage. - Hepatocytes have a relatively slow turnover rate compared to other tissues like gonads or bone marrow.
Question 9: Late effects of radiation therapy include:
- A. Mucositis, Enteritis, Nausea and vomiting, Pneumonitis
- B. Enteritis, Nausea and vomiting, Pneumonitis, Somatic mutations
- C. Mucositis, Nausea and vomiting, Pneumonitis, Somatic mutations
- D. Mucositis, Enteritis, Pneumonitis, Somatic mutations (Correct Answer)
Explanation: ***Mucositis, Enteritis, Pneumonitis, Somatic mutations*** - **Somatic mutations** leading to **secondary malignancies** are a classic late effect of radiation (occurs years after exposure due to DNA damage) [1] - **Radiation pneumonitis** progressing to **pulmonary fibrosis** is a well-recognized late complication (typically 1-3 months to years post-treatment) [1] - **Chronic radiation enteritis** with fibrosis and vascular damage can occur months to years after abdominal/pelvic radiation [1] - **Chronic mucositis** with fibrosis can persist as a late effect, though mucositis is more commonly acute - This option represents the **most comprehensive list of late effects** among the choices *Mucositis, Enteritis, Nausea and vomiting, Pneumonitis* - **Nausea and vomiting** are predominantly **acute side effects** occurring during or immediately after radiation therapy, not late effects - While mucositis and enteritis can have chronic forms, including nausea/vomiting makes this option incorrect *Enteritis, Nausea and vomiting, Pneumonitis, Somatic mutations* - Incorrectly includes **nausea and vomiting** as a late effect - Though it includes somatic mutations (correct late effect), the presence of an acute symptom invalidates this choice *Mucositis, Nausea and vomiting, Pneumonitis, Somatic mutations* - Incorrectly includes **nausea and vomiting** as a late effect - Omits enteritis, which can manifest as chronic radiation enteritis with fibrosis and strictures **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Central Nervous System Synapse, pp. 437-439.
Question 10: Vitamin B12 deficiency can give rise to all of the following, except which of the following?
- A. Optic atrophy
- B. Peripheral neuropathy
- C. Myopathy (Correct Answer)
- D. Myelopathy.
Explanation: ***Myopathy*** - **Myopathy**, or muscle disease, is not a direct consequence of **Vitamin B12 deficiency**. - **Vitamin B12 deficiency** primarily affects neurological and hematological systems due to its role in myelin synthesis and DNA production. [1] *Myelopathy* - **Myelopathy**, specifically subacute combined degeneration of the spinal cord, is a classic neurological complication of **Vitamin B12 deficiency**. - This involves demyelination of the posterior and lateral columns, leading to symptoms like **ataxia** and **sensory deficits**. *Optic atrophy* - **Optic atrophy** or **toxic amblyopia** can occur in severe cases of **Vitamin B12 deficiency**. - This damage to the **optic nerve** results in progressive vision loss. *Peripheral neuropathy* - **Peripheral neuropathy**, characterized by symptoms like **paresthesias**, numbness, and weakness, is a common neurological manifestation of **Vitamin B12 deficiency**. - It results from **demyelination** and axonal degeneration of peripheral nerves.
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