Radiobiology Practice Questions

Q: Which of the following is a stochastic effect of radiation?

Genetic mutation. ***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.

Q: Most sensitive structure in the cell for radiotherapy is

DNA. ***DNA*** - **DNA** is the most sensitive structure to radiotherapy because radiation primarily induces damage through **direct ionization and free radical formation**, which critically affects **DNA integrity**. - Damage to **DNA** can lead to **strand breaks, base modifications, and cross-links**, ultimately impairing cell division and triggering **apoptosis** or **reproductive cell death**. *Mitochondrial membrane* - While radiation can damage mitochondrial membranes, leading to **oxidative stress** and release of pro-apoptotic factors, it is less critical for immediate cell survival compared to **DNA**. - **Mitochondrial damage** often contributes to the overall cell death pathway but is not the primary target for the cytotoxic effects of radiation. *Enzymes* - **Enzymes** can be damaged by radiation, leading to a loss of catalytic activity, but the cell has mechanisms to repair or replace damaged enzymes. - While enzyme damage can disrupt cellular processes, it is usually not the direct cause of cell death unless essential enzymes involved in **DNA repair** or *cell cycle regulation* are severely compromised. *Cell membrane* - The **cell membrane** can be damaged by radiation, affecting its permeability and signaling, but this damage is generally less detrimental and more repairable than **DNA damage**. - Significant cell membrane damage usually requires higher doses of radiation and is often secondary to more fundamental damage within the cell.

Q: Osteoradionecrosis occurs at a dose of:

> 60 Gy. ***> 60 Gy*** - **Osteoradionecrosis (ORN)** is a severe complication of radiation therapy characterized by devitalized bone tissue that fails to heal over a period of 3-6 months in the absence of tumor recurrence. - The critical threshold for ORN development is **> 60 Gy**, as this dose causes significant damage to bone vascularity and osteocytes, leading to impaired healing capacity and potential bone necrosis. - Risk factors include mandibular location, poor oral hygiene, dental extractions post-radiation, and cumulative doses exceeding this threshold. *> 10 Gy* - A radiation dose of **10 Gy** is too low to cause osteoradionecrosis as it does not produce sufficient vascular and cellular damage to bone tissue. - Such doses are typically used in palliative radiation therapy where the goal is symptom relief rather than definitive treatment. *> 30 Gy* - While **30 Gy** represents a moderate radiation dose, it remains below the established threshold for significant ORN risk. - Though some soft tissue changes may occur at this dose level, the vascular compromise and osteocyte death required for ORN typically require higher cumulative doses. *> 70 Gy* - While ORN certainly occurs at doses **> 70 Gy**, this represents the higher end of the risk spectrum rather than the threshold dose. - The established threshold in radiobiology literature is **60 Gy**, with risk increasing progressively beyond this point.

Q: Most radiosensitive tumor of the following is?

Dysgerminoma. ***Dysgerminoma*** - **Dysgerminomas** are highly **radiosensitive germ cell tumors**, making radiation therapy an effective treatment option, particularly for localized disease or residual masses after chemotherapy. - This high sensitivity is attributed to the tumor cells' **undifferentiated nature** and rapid proliferation. *Melanoma* - **Melanoma** is generally considered a **radioresistant** tumor, meaning high doses of radiation are often required to achieve local control. - Its resistance is thought to be due to efficient DNA repair mechanisms and intrinsic cellular resistance. *Thyroid carcinoma* - While some forms of thyroid carcinoma, particularly **papillary and follicular thyroid cancer**, are treatable with **radioactive iodine (I-131)**, this is a very specific type of internal radiation. - **External beam radiotherapy** is typically reserved for aggressive, anaplastic, or recurrent thyroid cancers that do not respond to I-131, and these forms are often less radiosensitive than dysgerminoma. *Renal cell carcinoma* - **Renal cell carcinoma (RCC)** is largely considered to be **radioresistant**, with radiation therapy playing a limited role in primary treatment. - Radiation is primarily used for **palliative care** to manage symptoms like bone pain or for local control of metastatic disease.

Q: Which of the following tumors is radio-resistant? a) Melanoma b) Hodgkin's Disease (HD) c) Seminoma d) Ewing's Sarcoma e) Chondrosarcoma

Chondrosarcoma. ***Chondrosarcoma*** - **Chondrosarcomas** are notoriously **radio-resistant** due to their low metabolic activity and the presence of a cartilaginous matrix that impairs oxygen delivery and DNA damage by radiation. - Due to their radio-resistance, **surgical resection** is the primary treatment for chondrosarcomas. *Hodgkin's Disease (HD)* - **Hodgkin's Disease** is known to be **highly radio-sensitive**, and radiation therapy is a cornerstone of its treatment, often used in conjunction with chemotherapy. - The excellent response to radiation is one of the reasons for the high cure rates associated with early-stage Hodgkin's lymphoma. *Ewing's sarcoma* - **Ewing's sarcoma** is a **highly radio-sensitive** tumor, and radiation therapy plays a crucial role in its local control, often used after or with chemotherapy. - It is frequently treated with a combination of chemotherapy, surgery, and radiation to achieve optimal outcomes. *Seminoma* - **Seminomas** are among the most **radio-sensitive** solid tumors, making radiation therapy a very effective treatment modality, particularly for localized disease. - Even at low doses, radiation can induce a significant response and achieve high cure rates in seminoma. *Melanoma* - While traditionally considered radio-resistant, **melanoma** can sometimes respond to high-dose or fractionated radiation therapy, particularly in palliative settings or for specific subtypes. - However, compared to the other options, its general sensitivity to conventional radiation doses is lower, and immunotherapy and targeted therapy are often preferred.

Q: Which of the following is most harmful to an individual cell?

Alpha particles. ***Alpha particles*** - **Alpha particles** have a **high linear energy transfer (LET)**, meaning they deposit a large amount of energy over a very short distance within a cell. - Due to their size and double positive charge, they cause dense ionization tracks, leading to **complex and irreparable DNA damage**, making them highly harmful to individual cells despite their limited penetrating power. *X-rays* - **X-rays** are a form of **electromagnetic radiation** with lower LET than alpha particles, causing more scattered ionization events. - While X-rays can cause DNA damage, it is often less complex and more amenable to cellular repair mechanisms compared to alpha particle damage. *Beta particles* - **Beta particles** are high-energy electrons with a **lower mass and charge** than alpha particles. - They have an intermediate LET, causing less concentrated ionization than alpha particles, making them less damaging to an individual cell compared to alpha particles. *Gamma rays* - **Gamma rays** are **electromagnetic radiation** with the **lowest LET** among the options, traveling long distances and causing sparse ionization within tissue. - Although highly penetrating, the energy deposition is spread out, resulting in less concentrated damage to individual cells compared to alpha particles.

Q: Most radiosensitive tumor among the following is

Dysgerminoma. ***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 1

Which of the following is a stochastic effect of radiation?

Accepted Answer

Genetic mutation

Answer

Alopecia in the irradiated portal

Answer

Local desquamation in the irradiated field

Answer

All of the options

Question 2

Most sensitive structure in the cell for radiotherapy is

Accepted Answer

DNA

Answer

Mitochondrial membrane

Answer

Enzymes

Answer

Cell membrane

Question 3

Which of the following is most sensitive to radiation

Accepted Answer

Lymphocyte

Answer

Stem cells

Answer

Skin

Answer

Bone

Question 4

Osteoradionecrosis occurs at a dose of:

Accepted Answer

> 60 Gy

Answer

> 10 Gy

Answer

> 70 Gy

Answer

> 30 Gy

Question 5

Most radiosensitive tumor of the following is?

Accepted Answer

Dysgerminoma

Answer

Melanoma

Answer

Thyroid carcinoma

Answer

Renal cell carcinoma

Question 6

Which of the following tumors is radio-resistant? a) Melanoma b) Hodgkin's Disease (HD) c) Seminoma d) Ewing's Sarcoma e) Chondrosarcoma

Accepted Answer

Chondrosarcoma

Answer

Hodgkin's Disease (HD)

Answer

Ewing's sarcoma

Answer

Seminoma

Answer

Melanoma

Question 7

Radioresistant tumour is

Accepted Answer

Malignant melanoma

Answer

Osteosarcoma

Answer

Multiple myeloma

Answer

Glioblastoma

Answer

Chondrosarcoma

Answer

Ewing's sarcoma

Answer

Wilms tumour

Answer

Seminoma

Answer

Lymphoma

Question 8

Which of the following is most harmful to an individual cell?

Accepted Answer

Alpha particles

Answer

X-rays

Answer

Beta particles

Answer

Gamma rays

Question 9

Most radiosensitive tumor among the following is

Accepted Answer

Dysgerminoma

Answer

Osteogenic sarcoma

Answer

Parotid carcinoma

Answer

Bronchogenic carcinoma

Question 10

Which of the following is a FALSE statement regarding radiation?

Accepted Answer

Small blood vessels are relatively resistant to radiation compared to other tissues

Answer

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

Answer

Rapidly dividing cells are highly sensitive to Radiation

Answer

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

Radiobiology — MCQs

Radiobiology — MCQs

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