Radiation Exposure — MCQs
A child undergoes prophylactic irradiation as preparation for bone marrow transplantation (BMT) for treatment of acute lymphoblastic leukemia (ALL). Which of the following cell types will be least affected by the radiation?
Principles used in Radio Therapy are:
Radiation causes cell death by:
Which of the following is a stochastic effect of radiation?
A 7 weeks pregnant lady has 1 accidental exposure to x-ray. Which of the following should be done?
Which of the following is/are most radioresistant?
A 10-year-old child with a history of frequent micturition and fever since 2 years presents to the pediatric OPD. On examination, it was normal. What would be the MOST APPROPRIATE diagnostic modality for this child?
Radiation exposure during infancy has been linked to which one of the following carcinoma?
A patient presents with a skin rash that is exaggerated on sun exposure. What is the repair mechanism involved in this condition?
In a child with rickets which part of the bone is affected?
Radiation Exposure Indian Medical PG Practice Questions and MCQs
Question 1: A child undergoes prophylactic irradiation as preparation for bone marrow transplantation (BMT) for treatment of acute lymphoblastic leukemia (ALL). Which of the following cell types will be least affected by the radiation?
- A. Spermatogonia
- B. Bone marrow
- C. Intestinal epithelial cells
- D. Neurons (Correct Answer)
Explanation: ***Neurons*** - **Neurons** are highly differentiated cells with very low rates of cell division in adults. As radiation primarily targets rapidly dividing cells [4], **neurons are least susceptible** to radiation damage. - While high doses of radiation can eventually damage neurons, their **radioresistance** is significantly higher compared to rapidly proliferating tissues. *Spermatogonia* - **Spermatogonia** are germ cells that undergo continuous and rapid division to produce sperm, making them **highly sensitive to radiation** [2]. - Radiation exposure can lead to **sterility** due to the destruction of these rapidly dividing cells [2]. *Bone marrow* - The **bone marrow** contains hematopoietic stem cells that are responsible for the continuous production of blood cells, involving **rapid cell division** [3]. - It is one of the most **radiosensitive tissues** [1], and radiation exposure can lead to **myelosuppression** and pancytopenia. *Intestinal epithelial cells* - **Intestinal epithelial cells** have a high turnover rate due to their constant shedding and replacement [5], making them **very sensitive to radiation** [1]. - Radiation damage to these cells can cause **mucositis, nausea, vomiting, and diarrhea**. **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. 112-113. [2] 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. 113-114. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 112-113. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Central Nervous System Synapse, pp. 436-437. [5] 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. 79-80.
Question 2: Principles used in Radio Therapy are:
- A. Ultrasonic effect
- B. Charring of nucleoprotein
- C. Infrared rays
- D. Ionizing radiation (Correct Answer)
Explanation: ***Ionizing radiation*** - Radiation therapy primarily utilizes **ionizing radiation** (e.g., X-rays, gamma rays, protons) to damage the **DNA** of cancer cells. - This damage prevents cancer cells from growing and dividing, leading to their death and tumor shrinkage. *Ultrasonic effect* - **Ultrasound** uses high-frequency sound waves for imaging (sonography) and, in some therapeutic applications, to generate heat or mechanically disrupt tissues. - It is not the primary principle for general **radiotherapy** which aims to destroy cancer cells via DNA damage. *Charring of nucleoprotein* - **Charring** refers to the severe burning of organic material, often resulting in carbonization. - While radiation can cause significant cellular damage, the primary mechanism is not macroscopic charring but rather precise **DNA damage** at a molecular level. *Infrared rays* - **Infrared rays** are a form of electromagnetic radiation associated with heat, used in some warming therapies or for imaging (thermography). - They lack the energy to cause **ionization** and significant DNA damage to effectively treat cancer in the manner of therapeutic radiation.
Question 3: Radiation causes cell death by:
- A. Charring of nucleoproteins
- B. Ionization (Correct Answer)
- C. Disruption of cytosol
- D. Destroying their mitochondria
Explanation: ***Ionization*** - Radiation, particularly **ionizing radiation**, causes cell death by directly or indirectly damaging cellular components through the process of **ionization**. [1] - This involves the removal of electrons from atoms or molecules, leading to the formation of highly reactive **free radicals** (especially hydroxyl radicals from water radiolysis) that can damage DNA, proteins, and lipids. [1] - The most critical lethal lesion is **DNA double-strand breaks**, which are difficult to repair and trigger apoptosis or mitotic catastrophe. [1] *Charring of nucleoproteins* - **Charring** typically refers to the combustion or burning of organic matter, which is not the mechanism of cell death caused by therapeutic radiation doses. - While radiation can cause protein denaturation, it does not lead to the macroscopic charring of nucleoproteins within cells. *Disruption of cytosol* - While severe radiation damage can impact the entire cell, direct and selective **disruption of the cytosol** is not the primary or most impactful mechanism of radiation-induced cell death. - The critical targets for radiation-induced cell death are primarily the **nucleus** and its DNA, not the cytoplasm. [2] *Destroying their mitochondria* - Although radiation can induce **mitochondrial dysfunction** and contribute to cell death through apoptosis, it is not the initial or primary mechanism of cell destruction. - The most critical and direct damage leading to cell death is inflicted upon the **DNA** in the nucleus, particularly causing double-strand breaks. [1] **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. 100-102. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Central Nervous System Synapse, pp. 438-439.
Question 4: Which of the following is a stochastic effect of radiation?
- A. Alopecia in the irradiated portal
- B. Local desquamation in the irradiated field
- C. Genetic mutation (Correct Answer)
- D. All of the options
Explanation: ***Genetic mutation*** - **Stochastic effects** are those for which the probability of occurrence, rather than the severity, is a function of radiation dose without a threshold. **Genetic mutations** are a classic example, as any dose carries some probability of inducing a change in DNA that can be passed to offspring. - The severity of a genetic mutation, if it occurs, is independent of the dose. It's the chance of it happening that increases with exposure. *Alopecia in the irradiated portal* - **Alopecia** (hair loss) due to radiation is a **deterministic effect**, meaning there is a threshold dose below which it does not occur, and above that threshold, the severity increases with dose. - It occurs locally in the **irradiated field** because it is a direct tissue reaction to cellular damage. *Local desquamation in the irradiated field* - **Desquamation** (skin peeling) is a **deterministic effect** that results from direct cell death and damage in the skin, a tissue reaction with a dose threshold. - Its occurrence and severity are directly related to the **radiation dose received** in the specific area. *All of the options* - This option is incorrect because **alopecia** and **desquamation** are deterministic effects, not stochastic effects. - Only **genetic mutation** falls under the category of stochastic effects among the choices provided.
Question 5: A 7 weeks pregnant lady has 1 accidental exposure to x-ray. Which of the following should be done?
- A. Continue the pregnancy with monitoring (Correct Answer)
- B. Perform chromosome analysis if needed
- C. Conduct pre-invasive diagnostic testing if indicated
- D. Consider termination of pregnancy
Explanation: ***Continue the pregnancy with monitoring*** - The risk of **fetal malformation** and **intellectual disability** from a single diagnostic X-ray exposure is generally considered very low, often below the threshold for clinical concern. - Current guidelines typically recommend continuing pregnancy with routine monitoring unless the estimated fetal dose exceeds a certain threshold (e.g., 50-100 mGy), which is unlikely with a single accidental exposure. *Perform chromosome analysis if needed* - **Chromosome analysis** is generally reserved for cases with suspected genetic anomalies or significant fetal exposure to radiation at doses known to induce chromosomal damage. - A single, accidental X-ray exposure is unlikely to cause clinically significant chromosomal aberrations requiring such invasive testing. *Conduct pre-invasive diagnostic testing if indicated* - **Pre-invasive diagnostic testing**, such as nuchal translucency scans or maternal serum screening, assesses risks for common aneuploidies and neural tube defects, not typically direct radiation effects. - While these tests are part of routine prenatal care, a single X-ray exposure does not, by itself, create a specific indication for additional pre-invasive testing beyond standard recommendations. *Consider termination of pregnancy* - **Termination of pregnancy** is usually considered only in cases of significant, confirmed fetal harm or very high radiation doses that unequivocally increase the risk of severe birth defects or intellectual disability. - A single accidental X-ray exposure almost certainly does not meet this threshold, as the associated risks to the fetus are minimal.
Question 6: 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 7: A 10-year-old child with a history of frequent micturition and fever since 2 years presents to the pediatric OPD. On examination, it was normal. What would be the MOST APPROPRIATE diagnostic modality for this child?
- A. 3D MCU (Correct Answer)
- B. MR UROGRAM
- C. 3D CT UROGRAM
- D. IVP
Explanation: ***3D MCU (Micturating Cystourethrogram)*** - **Gold standard** for diagnosing **vesicoureteral reflux (VUR)**, the most common cause of recurrent UTIs in children - In a child with **2-year history of recurrent UTIs** (fever + frequent micturition), VUR is the primary concern that needs to be ruled out - MCU provides **dynamic imaging** during bladder filling and voiding, allowing direct visualization of **reflux** and assessment of **bladder and urethral anatomy** - **Standard of care** recommended by IAP (Indian Academy of Pediatrics) and major pediatric nephrology guidelines - Though it involves ionizing radiation, the **diagnostic benefit far outweighs risks** in this clinical scenario - Cost-effective and widely available in Indian healthcare settings *MR Urogram* - Provides excellent anatomical detail of the **upper urinary tract** (kidneys, ureters) without radiation - However, it is **NOT the first-line investigation** for recurrent UTI workup in children - Does not adequately assess **dynamic VUR** like MCU does - More expensive, requires sedation in many children, and less accessible - Reserved for specific indications like suspected anatomical anomalies after initial screening *3D CT Urogram* - Excellent for detailed anatomical evaluation but involves **high radiation dose** - Not appropriate as first-line investigation in a **chronic, non-acute pediatric case** - Reserved for complex cases where MR is contraindicated or for acute complications *IVP (Intravenous Pyelogram)* - **Obsolete modality** that has been replaced by ultrasound, MCU, and modern cross-sectional imaging - Provides limited functional and anatomical information - Higher radiation exposure with inferior image quality compared to modern techniques - Not used in current pediatric practice
Question 8: Radiation exposure during infancy has been linked to which one of the following carcinoma?
- A. Thyroid (Correct Answer)
- B. Lung
- C. Breast
- D. Melanoma
Explanation: ***Thyroid*** - The **thyroid gland** is highly sensitive to radiation, particularly during childhood and infancy, making it susceptible to developing **carcinoma** after exposure [1]. - This increased sensitivity is due to the rapid cell division and growth of the thyroid gland in young individuals. - **Classic examples**: Children exposed after the **Chernobyl nuclear accident** showed markedly increased thyroid cancer rates; survivors of atomic bomb exposure in **Hiroshima and Nagasaki** demonstrated increased thyroid malignancies in those exposed during childhood [1]. - **Papillary thyroid carcinoma** is the most common type following radiation exposure [1], [2]. *Lung* - While **lung cancer** can be associated with radiation exposure, it is more commonly linked to adult exposures (e.g., occupational, smoking) and usually requires a higher dose over a longer period. - The risk for lung cancer linked specifically to **infancy radiation** is significantly lower compared to thyroid cancer. *Breast* - **Breast carcinoma** risk can be increased by radiation exposure, especially during adolescence and early adulthood due to the developing glandular tissue. - However, the sensitivity of breast tissue to radiation leading to cancer is generally lower in infancy compared to the **thyroid gland**. *Melanoma* - **Melanoma** is a skin cancer primarily caused by exposure to **ultraviolet (UV) radiation** from the sun or tanning beds. - While ionizing radiation can contribute to overall cancer risk, it is not a primary or significant risk factor for melanoma, especially from infancy exposure compared to UV radiation. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1098-1099. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 429-430.
Question 9: A patient presents with a skin rash that is exaggerated on sun exposure. What is the repair mechanism involved in this condition?
- A. Nucleotide excision repair (Correct Answer)
- B. Base excision repair
- C. Mismatch repair
- D. Double stranded DNA break repair
Explanation: ***Nucleotide excision repair*** - This mechanism is responsible for repairing **bulky lesions** in DNA, such as **pyrimidine dimers** caused by **UV radiation** from sun exposure. - Patients with defects in nucleotide excision repair (e.g., **xeroderma pigmentosum**) are highly sensitive to sunlight and develop skin rashes, pigment changes, and skin cancers. *Base excision repair* - This pathway primarily corrects **small damaged bases** that do not cause significant distortion of the DNA helix, such as deaminated, oxidized, or alkylated bases. - It does not primarily address the bulky lesions induced by UV light that cause exaggerated sun sensitivity. *Mismatch repair* - This system corrects errors, like **mismatched base pairs**, that are incorporated during DNA replication. - It is not directly involved in repairing DNA damage caused by environmental factors like UV radiation. *Double stranded DNA break repair* - This mechanism repairs **double-strand breaks** in DNA, which are highly deleterious lesions caused by ionizing radiation or oxidative stress. - While critical for genome stability, it is not the primary repair pathway for UV-induced DNA lesions or the direct cause of sun sensitivity.
Question 10: In a child with rickets which part of the bone is affected?
- A. A
- B. B
- C. C (Correct Answer)
- D. D
Explanation: ***C*** - C points to the **growth plate (physis) and metaphyseal region**, which is the **primary site of pathology in rickets**. - Rickets causes defective mineralization at the growth plate where endochondral ossification occurs, leading to accumulation of unmineralized osteoid and disorganized chondrocyte columns. - The **metaphysis** (the region including the growth plate) shows the characteristic radiological findings: widening, fraying, cupping, and loss of sharp margins. *A* - A indicates the **diaphysis** (shaft of the bone), which consists of mature cortical bone. - The diaphysis is **not primarily affected** in rickets, though severe cases may lead to bowing deformities due to bone softening. - The initial and primary pathological changes occur at the actively growing regions, not the shaft. *B* - B points to the **metaphysis**, which is the flared region of long bone adjacent to the growth plate. - The metaphysis is indeed significantly affected in rickets, showing widening and irregular mineralization. - However, if the image distinguishes between the broader metaphyseal region (B) and the specific growth plate zone (C), then C represents the more precise site where the pathological process of defective mineralization originates. *D* - D points to the **epiphysis**, the rounded end of the long bone that forms part of the joint. - The epiphysis consists of already-formed bone and is **not the primary site** of rickets pathology. - Rickets affects the zone of provisional calcification at the growth plate, not the pre-existing epiphyseal bone.
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