Radiobiology Practice Questions

Q: Most common acute skin manifestation of radiotherapy:

Erythema. ***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.

Q: Cancer patient undergoes radiotherapy, pick the true statement for radiosensitivity of tissues?

Small blood vessels are radiosensitive tissues. ***Small blood vessels are radiosensitive tissues*** - **Endothelial cells** lining small blood vessels are actively dividing and have a relatively short lifespan, making them susceptible to radiation-induced damage. - Damage to these vessels can lead to **fibrosis** and **tissue hypoxia**, contributing to late radiation effects. *GI mucosa is one of the most radioresistant tissues in the body* - The **GI mucosa** is one of the **most radiosensitive** tissues due to its rapid cell turnover and high proliferative capacity, leading to symptoms like mucositis and diarrhea after radiation. - The constant renewal of epithelial cells makes them highly vulnerable to the **cytotoxic effects** of radiation. *Rapidly dividing cells are resistant to radiation* - **Rapidly dividing cells**, such as those in the bone marrow, GI crypts, and hair follicles, are generally **most sensitive** to radiation. - This forms the basis of radiation therapy, as cancer cells often have a higher proliferative rate than many normal tissues, making them a target. *The intensity of radiation is inversely proportional to the square of distance from the source* - This statement describes the **inverse square law** for radiation intensity, which is true, but it is a principle of radiation physics, not a statement about the radiosensitivity of tissues. - The inverse square law dictates how radiation dose **attenuates with distance**, which is critical for dose calculation but not directly about biological radiosensitivity.

Q: Even conventional radiological procedures are contraindicated in which neurological disease?

Ataxia telangiectasia. ***Ataxia telangiectasia*** - Patients with **ataxia telangiectasia** have a defect in the **ATM gene**, leading to extreme sensitivity to **ionizing radiation**, making conventional radiological procedures unsafe. - This increased radiosensitivity can result in severe adverse reactions, including increased risk of **malignancy** and neurological damage if exposed to routine diagnostic radiation. *Cockayne Syndrome* - **Cockayne Syndrome** is characterized by a defect in **DNA repair**, specifically **transcription-coupled repair**, leading to pronounced sun sensitivity and premature aging. - While these patients are sensitive to UV radiation, they do not have the profound hypersensitivity to **ionizing radiation** that contraindicates conventional X-ray imaging, distinguishing them from ataxia telangiectasia. *Gorlin Syndrome* - **Gorlin Syndrome** (Nevoid Basal Cell Carcinoma Syndrome) is associated with an increased risk of developing various cancers, including **basal cell carcinomas**, and is linked to the **PTCH1 gene**. - Although individuals with Gorlin Syndrome have an increased lifetime risk of developing tumors with **ionizing radiation exposure**, it does not typically contraindicate conventional diagnostic imaging, unlike the extreme radiosensitivity seen in ataxia telangiectasia. *All of the options* - This option is incorrect because while Cockayne Syndrome and Gorlin Syndrome involve heightened cancer risks or sensitivities, only **ataxia telangiectasia** presents a direct and severe contraindication to conventional radiological procedures due to extreme **radiosensitivity**.

Q: Which of the following is most radioresistant?

Cartilage. ***Cartilage*** - **Cartilage** is a connective tissue with a relatively **low metabolic rate** and **avascular nature**, making its cells (chondrocytes) less susceptible to rapid turnover and DNA damage from radiation. - Its **dense extracellular matrix** and limited cellular division contribute to its inherent resistance to ionizing radiation, requiring higher doses to induce significant damage. *Ewing's sarcoma* - **Ewing's sarcoma** is a highly **malignant bone tumor** that is generally considered **radiosensitive** and often treated with radiation therapy. - Its cells are rapidly dividing, making them more vulnerable to the DNA-damaging effects of radiation. *GIT epithelium* - The **gastrointestinal tract (GIT) epithelium** is characterized by **rapid cell turnover** and high mitotic activity to constantly replace damaged cells and absorb nutrients. - This high proliferative rate makes the GIT epithelium highly **radiosensitive**, leading to common side effects like mucositis and diarrhea during radiation therapy. *Gonadal tumours* - Tumors of the **gonads** (e.g., testicular seminoma, ovarian dysgerminoma) are often highly **radiosensitive** and respond well to radiation therapy due to the germ cell origin and rapid proliferation of tumor cells. - The germ cells themselves are very sensitive to radiation, leading to concerns about **fertility preservation** in patients undergoing treatment.

Q: Which of the following cells are most radiosensitive?

Cells of hematopoietic series. ***Cells of hematopoietic series*** - Among the **hematopoietic cells**, **lymphocytes** are the **most radiosensitive cells** in the human body, susceptible to damage at doses as low as 2 Gy. - The hematopoietic series includes highly radiosensitive cells like lymphocytes, bone marrow stem cells, and various precursor cells that are actively dividing. - According to the **Bergonié-Tribondeau law**, cells that are rapidly dividing, undifferentiated, and have a long mitotic future are most radiosensitive. *Cells of erythroblastic series* - While **erythroblasts** are radiosensitive due to their high proliferation rate, they are **not the most radiosensitive** cells. - **Lymphocytes** (part of the broader hematopoietic series) are significantly more radiosensitive than erythroblastic cells. - Erythroblastic cells require higher radiation doses for damage compared to lymphocytes. *Fibroblasts* - **Fibroblasts** are relatively radioresistant because they are generally quiescent with low mitotic activity. - Their primary function in producing **collagen** and structural components means they are less affected by radiation unless the dose is very high. *Erythrocytes* - **Mature erythrocytes (red blood cells)** are highly radioresistant because they are terminally differentiated, anucleated, and no longer divide. - They lack the cellular machinery for division and repair that would make them susceptible to radiation damage.

Q: Radiosensitizers are all Except

Amifostine. ***Amifostine*** - Amifostine is a **radioprotector**, meaning it helps protect healthy tissues from the damaging effects of radiation. - It does this by selectively scavenging **free radicals** in normal cells, reducing radiation-induced toxicity. *Metronidazole* - **Metronidazole** is a well-known **radiosensitizer**, particularly effective in hypoxic (low-oxygen) tumor environments. - It enhances the effectiveness of radiation therapy by forming **toxic free radicals** when metabolized in hypoxic cells, thereby increasing DNA damage. *Nimorazole* - **Nimorazole** is another **nitroimidazole radiosensitizer**, similar in action to metronidazole. - It is used to improve the outcome of radiation therapy in certain cancers, especially in **hypoxic tumors**, by increasing their sensitivity to radiation. *Cisplatin* - **Cisplatin** is a platinum-based **chemotherapeutic agent** that also acts as a potent **radiosensitizer**. - It enhances the cytotoxic effects of radiation by interfering with **DNA repair mechanisms** and inducing DNA damage more effectively when combined with radiation.

Q: The least radiosensitive tissue is:

Nervous tissue. ***Nervous tissue*** - **Nervous tissue** is considered the least radiosensitive due to its **highly differentiated state**, low mitotic activity, and limited capacity for cell division. - Mature neurons are post-mitotic and therefore much less susceptible to radiation-induced cell death compared to rapidly dividing cells. *Thyroid* - The **thyroid gland** is relatively radiosensitive, particularly in children, and exposure to radiation can increase the risk of developing **thyroid cancer** or hypothyroidism. - It contains cells with moderate mitotic activity and is an **endocrine gland** with active metabolic processes sensitive to radiation damage. *Kidney* - The **kidney** is moderately radiosensitive, with radiation damage potentially leading to **renal fibrosis**, impaired kidney function, and hypertension. - While cells do not divide rapidly, they are susceptible to damage from radiation, which can affect the **glomeruli** and tubules. *Bone* - **Bone tissue**, especially red bone marrow within the bone, is considered radiosensitive due to the presence of **hematopoietic stem cells** with high mitotic activity. - Radiotherapy to bone can lead to **osteoradionecrosis** and damage to blood-forming elements within the marrow.

Q: Which ocular structure is the most radiosensitive?

Lens. ***Lens*** - The **lens** is the most radiosensitive structure of the eye, particularly its **equatorial epithelial cells**. - Radiation exposure can lead to the development of **cataracts**, a common long-term complication in individuals exposed to ionizing radiation. *Cornea* - The **cornea** is relatively radioresistant compared to the lens. - While high doses of radiation can cause corneal damage such as **keratitis**, it is less susceptible to radiation-induced pathology at doses that affect the lens. *Retina* - The **retina** is also relatively radioresistant compared to the lens, although very high doses can cause **retinopathy**. - Symptoms of radiation retinopathy include **microaneurysms**, hemorrhages, and eventually vision loss, but these require significantly higher doses than those causing cataracts. *All of the options* - This option is incorrect because while all mentioned structures can be affected by radiation, they exhibit different sensitivities. - The **lens** stands out as uniquely vulnerable, making it the most radiosensitive among them.

Q: Which of the following is/are most radioresistant?

Erythrocytes. ***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 1

Most common acute skin manifestation of radiotherapy:

Accepted Answer

Erythema

Answer

Dermatitis

Answer

Atopy

Answer

Hyperpigmentation

Question 2

Cancer patient undergoes radiotherapy, pick the true statement for radiosensitivity of tissues?

Accepted Answer

Small blood vessels are radiosensitive tissues

Answer

GI mucosa is one of the most radioresistant tissues in the body

Answer

Rapidly dividing cells are resistant to radiation

Answer

The intensity of radiation is inversely proportional to the square of distance from the source

Question 3

Even conventional radiological procedures are contraindicated in which neurological disease?

Accepted Answer

Ataxia telangiectasia

Answer

Cockayne Syndrome

Answer

Gorlin Syndrome

Answer

All of the options

Question 4

Which of the following is most radioresistant?

Accepted Answer

Cartilage

Answer

Ewing's sarcoma

Answer

GIT epithelium

Answer

Gonadal tumours

Question 5

Which of the following cells are most radiosensitive?

Accepted Answer

Cells of hematopoietic series

Answer

Fibroblasts

Answer

Erythrocytes

Answer

Cells of erythroblastic series

Question 6

Radiosensitizers are all Except

Accepted Answer

Amifostine

Answer

Metronidazole

Answer

Nimorazole

Answer

Cisplatin

Question 7

The least radiosensitive tissue is:

Accepted Answer

Nervous tissue

Answer

Thyroid

Answer

Kidney

Answer

Bone

Question 8

Which ocular structure is the most radiosensitive?

Accepted Answer

Lens

Answer

Cornea

Answer

Retina

Answer

All of the options

Question 9

Which type of radiation effect results in radiation induced thyroid cancer?

Accepted Answer

Somatic

Answer

Teratogenic

Answer

Genetic

Answer

Deterministic

Question 10

Which of the following is/are most radioresistant?

Accepted Answer

Erythrocytes

Answer

Neurons

Answer

Muscle cells

Answer

All of the options

Radiobiology — MCQs

Radiobiology — MCQs

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