Principles of Radiation Therapy — MCQs
Which of the following statements about thyroid eye disease is false?
What is the most effective management strategy for osteoradionecrosis?
A radioisotope used in both teletherapy and brachytherapy is
Principles used in Radio Therapy are:
Treatment of resectable T4N0M0 stage of head and neck carcinoma is?
Which of the following is NOT used for internal radiotherapy?
Which one of the following radioisotopes is not used as permanent implant in brachytherapy?
Which of the following is not a cause of oropharyngeal carcinoma?
Trismus in carcinoma of the temporal bone occurs due to involvement of:
Epithelioid hemangioendothelioma of the nose is classified as which of the following?
Principles of Radiation Therapy Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following statements about thyroid eye disease is false?
- A. NOSPECS score is used to classify thyroid eye disease
- B. The management corresponds to improvement in thyrotoxic state (Correct Answer)
- C. Can lead to visual loss
- D. Seen in more than 10% of patients with hyperthyroidism
Explanation: ***The management corresponds to improvement in thyrotoxic state*** - Thyroid eye disease (TED) is an **autoimmune condition** that runs independently of the thyroid's hormonal status [1]. While hyperthyroidism can trigger or worsen TED, treating the hyperthyroidism does not necessarily resolve or improve the eye symptoms [2]. - The disease course of TED is often **biphasic**, with an active inflammatory phase followed by a quiescent phase. Treatment decisions for TED are based on the severity and activity of the eye disease itself, not solely on the thyroid hormone levels. *NOSPECS score is used to classify thyroid eye disease* - The **NOSPECS classification system** is a well-established method for grading the severity of thyroid eye disease. - This acronym stands for **N**o signs or symptoms, **O**nly signs (e.g., lid retraction) no symptoms, **S**oft tissue involvement, **P**roptosis, **E**xtraocular muscle involvement, **C**orneal involvement, and **S**ight loss (optic neuropathy). *Can lead to visual loss* - Thyroid eye disease can cause **optic nerve compression** due to enlarged extraocular muscles or increased orbital fat, leading to **compressive optic neuropathy** and potentially irreversible visual loss. - Severe **corneal exposure** from proptosis and lid retraction can also lead to corneal ulceration, infection, and scaring, affecting vision. *Seen in more than 10% of patients with hyperthyroidism* - Thyroid eye disease is the **most common extrathyroidal manifestation** of Graves' disease, occurring in approximately 25-50% of patients with Graves' hyperthyroidism [1]. - While it is less common in other forms of hyperthyroidism or euthyroid individuals, the prevalence in Graves' disease alone is significantly higher than 10%.
Question 2: What is the most effective management strategy for osteoradionecrosis?
- A. Hyperbaric oxygen therapy
- B. Fluoride treatment
- C. Combination of hyperbaric oxygen therapy and surgical removal of necrotic bone (Correct Answer)
- D. Surgical removal of necrotic bone
Explanation: ***Combination of hyperbaric oxygen therapy and surgical removal of necrotic bone*** - This combined approach is the most effective strategy for **osteoradionecrosis** as it addresses both the underlying tissue damage and the removal of compromised bone. - **Hyperbaric oxygen therapy** promotes angiogenesis and increases oxygenation in damaged tissues, while **surgical debridement** removes non-viable bone to facilitate healing. *Hyperbaric oxygen therapy* - While beneficial for promoting tissue healing and angiogenesis, **hyperbaric oxygen therapy alone** may not be sufficient to resolve established osteoradionecrosis, particularly in cases with significant bone sequestration. - It works by increasing the **partial pressure of oxygen** in tissues, which can improve blood supply and support cellular repair, but often needs debridement of necrotic tissue to be fully effective. *Fluoride treatment* - **Fluoride treatment** is primarily used to prevent dental caries and manage **dentin hypersensitivity**, not to treat established osteoradionecrosis. - It has no direct therapeutic role in revascularizing necrotic bone or promoting the healing of radiation-damaged tissue. *Surgical removal of necrotic bone* - **Surgical debridement** is crucial for removing non-viable bone tissue, which acts as a barrier to healing and can harbor infection. - However, without adjunctive therapies like **hyperbaric oxygen**, simple debridement may not adequately address the underlying **hypoxia and hypovascularity** of the irradiated tissue, leading to persistent or recurrent necrosis.
Question 3: A radioisotope used in both teletherapy and brachytherapy is
- A. Gold-198
- B. Iodine-125
- C. Cesium-137 (Correct Answer)
- D. Radium-226
Explanation: ***Cesium-137*** - Cesium-137 is used in both **teletherapy (external beam radiation)** units, particularly older ones, and in **brachytherapy sources** for interstitial or intracavitary applications. - It emits **gamma rays** with an energy suitable for both types of therapy, giving it versatility. *Gold-198* - **Gold-198** is primarily used in **brachytherapy** as temporary or permanent implants, particularly for conditions like prostate cancer. - Its short half-life and primary emission of **beta particles** with accompanying gamma rays make it less suitable for external teletherapy applications. *Iodine-125* - **Iodine-125** is almost exclusively used in **low-dose-rate (LDR) brachytherapy**, commonly for prostate cancer and ocular melanomas. - It emits **low-energy gamma and X-rays**, which have a very limited range, making it unsuitable for teletherapy. *Radium-226* - **Radium-226** was historically one of the first radioisotopes used in brachytherapy but has largely been replaced due to its strong **gamma emissions** and the associated safety risks. - It was never widely adopted for teletherapy machines because its decay products include gaseous **radon**, posing significant handling and safety challenges.
Question 4: 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 5: Treatment of resectable T4N0M0 stage of head and neck carcinoma is?
- A. Radiotherapy alone
- B. Surgery and Radiotherapy (Correct Answer)
- C. Chemoradiation
- D. Surgery alone
Explanation: ***Surgery and Radiotherapy*** - For **resectable T4N0M0 head and neck carcinoma**, the standard treatment is **surgical resection** of the primary tumor followed by **adjuvant radiotherapy**. - This approach achieves optimal **local control** for advanced primary tumors without nodal involvement. - **Adjuvant radiotherapy** is essential for T4 tumors due to high risk of microscopic residual disease and local recurrence. - Surgery allows for complete tumor removal with negative margins, while radiotherapy addresses subclinical disease. *Radiotherapy alone* - Radiotherapy alone is **insufficient as monotherapy** for T4 tumors due to the large tumor burden and extensive local invasion. - Single modality radiation cannot reliably achieve adequate tumor control for advanced primary lesions. - Generally reserved for early-stage disease or patients unfit for surgery. *Chemoradiation* - **Definitive chemoradiation** is an alternative for **unresectable T4 tumors** or when organ preservation is desired (e.g., laryngeal cancer). - For **resectable** T4N0M0 disease, surgery with adjuvant RT is preferred as it provides better local control and allows pathological staging. - Chemoradiation may be used postoperatively if high-risk features are found (positive margins, perineural invasion, extranodal extension). - In this **N0 case with resectable tumor**, upfront surgery is the preferred initial approach. *Surgery alone* - While surgical resection is crucial for T4 tumors, **surgery alone is inadequate** due to high risk of locoregional recurrence. - T4 classification indicates extensive local invasion, necessitating **adjuvant radiotherapy** to eradicate microscopic disease. - Combined modality treatment (surgery + RT) significantly improves local control and survival compared to surgery alone.
Question 6: Which of the following is NOT used for internal radiotherapy?
- A. Iridium-192
- B. Iodine-125
- C. Cobalt-60 (Correct Answer)
- D. Iodine-131
Explanation: ***Cobalt-60*** - **Cobalt-60** is primarily used for **external beam radiotherapy** (teletherapy) due to its high-energy gamma emissions (1.17 and 1.33 MeV). - Its large size and significant shielding requirements make it unsuitable for direct internal placement. *Iridium-192* - **Iridium-192** is a common radionuclide used for **brachytherapy** (internal radiotherapy), often in high-dose rate (HDR) applications. - It emits medium-energy gamma rays and electrons, suitable for temporary implantations in various cancers. *Iodine-125* - **Iodine-125** is widely used in **low-dose rate (LDR) brachytherapy**, particularly for **prostate cancer**, as permanent implants. - It emits low-energy gamma rays and X-rays with a relatively long half-life, allowing localized treatment with minimal dose to surrounding healthy tissue. *Iodine-131* - **Iodine-131** is a radiopharmaceutical used for **systemic internal radiotherapy**, especially in the treatment of **thyroid cancers** and hyperthyroidism. - It is administered orally or intravenously and selectively absorbed by thyroid tissue, delivering therapeutic beta particles and diagnostic gamma rays.
Question 7: Which one of the following radioisotopes is not used as permanent implant in brachytherapy?
- A. Palladium-103
- B. Gold-198
- C. Iodine-125
- D. Caesium-137 (Correct Answer)
Explanation: ***Caesium-137*** - **Caesium-137** is primarily used in **high-dose-rate (HDR)** brachytherapy or external beam radiotherapy, where sources are temporarily placed. - Its relatively **long half-life** (30 years) and higher energy gamma emissions make it unsuitable for permanent implantation due to prolonged radiation exposure. *Palladium-103* - **Palladium-103** is a commonly used isotope for **permanent seed implants** in brachytherapy, particularly for prostate cancer. - It has a relatively short **half-life of 17 days** and low-energy photons, allowing for localized delivery with minimal exposure to surrounding healthy tissue. *Gold-198* - **Gold-198** was historically used for **permanent seed implants** due to its relatively short **half-life of 2.7 days** and medium-energy gamma emissions. - While less common today, its properties are consistent with permanent implantation, decaying away in a short period. *Iodine-125* - **Iodine-125** is a widely used radioisotope for **permanent seed implants** in brachytherapy for various cancers, including prostate and ocular melanoma. - It has a **half-life of 59.4 days** and low-energy photons, making it ideal for localized, long-term radiation delivery with a steep dose fall-off.
Question 8: Which of the following is not a cause of oropharyngeal carcinoma?
- A. Occupational exposure to hydrochloric acid (Correct Answer)
- B. Smoking
- C. Human Papilloma Virus infection
- D. Occupational exposure to isopropyl oil
Explanation: **Explanation:** The primary risk factors for oropharyngeal carcinoma (OPC) are lifestyle-related and viral, rather than chemical or industrial. **1. Why Option A is the Correct Answer:** Occupational exposure to **hydrochloric acid (HCl)** is primarily associated with dental erosion and irritation of the upper respiratory tract, but it is **not** a recognized carcinogen for the oropharynx. In contrast, exposure to strong inorganic acid mists (like sulfuric acid) is linked specifically to **laryngeal cancer**, not oropharyngeal cancer. **2. Analysis of Other Options:** * **Smoking (Option B):** Tobacco use is a classic risk factor. Carcinogens like nitrosamines and polycyclic aromatic hydrocarbons cause field cancerization, leading to squamous cell carcinoma (SCC) of the entire aerodigestive tract. * **Human Papilloma Virus (Option C):** HPV (specifically **Type 16**) is now the leading cause of oropharyngeal cancer globally, especially involving the palatine tonsils and base of tongue. HPV-positive tumors have a better prognosis than tobacco-related ones. * **Isopropyl Oil (Option D):** Occupational exposure to the manufacture of isopropyl alcohol (specifically the "strong acid process" involving isopropyl oil) is a documented risk factor for cancers of the **paranasal sinuses and the oropharynx**. **Clinical Pearls for NEET-PG:** * **Most Common Site:** The **palatine tonsil** is the most common site for oropharyngeal SCC. * **HPV Marker:** **p16** immunohistochemistry is used as a surrogate marker for HPV-associated oropharyngeal cancer. * **Plummer-Vinson Syndrome:** Associated with post-cricoid (hypopharyngeal) carcinoma, not primarily oropharyngeal. * **Diet:** Deficiencies in Vitamin A and C are also implicated in the development of oral and pharyngeal malignancies.
Question 9: Trismus in carcinoma of the temporal bone occurs due to involvement of:
- A. Dura
- B. Temporomandibular joint (Correct Answer)
- C. Mastoid
- D. Eustachian tube
Explanation: **Explanation:** In the context of temporal bone carcinoma (most commonly Squamous Cell Carcinoma), **Trismus** (inability to open the mouth) is a significant clinical sign indicating **anterior extension** of the tumor. **Why the Temporomandibular Joint (TMJ) is correct:** The anterior wall of the external auditory canal (EAC) is in direct anatomical proximity to the glenoid fossa and the TMJ. When a malignancy breaches the anterior bony or cartilaginous wall of the EAC, it invades the TMJ and the associated pterygoid muscles. This infiltration leads to pain and mechanical restriction of mandibular movement, resulting in trismus. This finding usually signifies an advanced stage (T3 or T4) and a poorer prognosis. **Why other options are incorrect:** * **Dura:** Involvement of the dura (superior extension through the tegmen) leads to neurological complications, CSF otorrhea, or meningitis, but does not mechanically restrict jaw movement. * **Mastoid:** Posterior extension into the mastoid air cells causes retroauricular pain and swelling, but the mastoid process does not interface with the muscles of mastication. * **Eustachian tube:** While the tumor can involve the Eustachian tube leading to middle ear effusion and conductive hearing loss, it does not cause the muscular or joint fixation required for trismus. **High-Yield NEET-PG Pearls:** * **Most common site:** The External Auditory Canal is the most common site for temporal bone malignancy. * **Most common histology:** Squamous Cell Carcinoma. * **Clinical Red Flag:** Chronic otorrhea that becomes **blood-stained** or is associated with **deep-seated ear pain** should always be suspicious of malignancy. * **Staging:** Facial nerve palsy and Trismus are indicators of advanced disease (T4 in the modified Pittsburgh staging system).
Question 10: Epithelioid hemangioendothelioma of the nose is classified as which of the following?
- A. Carcinoma
- B. Sarcoma (Correct Answer)
- C. Carcinosarcoma
- D. Hamartoma
Explanation: **Explanation:** **Epithelioid Hemangioendothelioma (EHE)** is a rare vascular neoplasm of intermediate malignancy. The correct classification is **Sarcoma** because it originates from mesenchymal tissue (specifically vascular endothelial cells). 1. **Why Sarcoma is Correct:** By definition, a sarcoma is a malignant tumor arising from mesenchymal cells (bone, cartilage, fat, muscle, or blood vessels). EHE is characterized by "epithelioid" endothelial cells that mimic epithelial cells in appearance but are positive for vascular markers like **CD31, CD34, and Factor VIII-related antigen**. It is considered an intermediate-grade vascular sarcoma, falling between a benign hemangioma and a highly aggressive angiosarcoma. 2. **Why Other Options are Incorrect:** * **Carcinoma:** These are malignant tumors of **epithelial** origin (e.g., Squamous Cell Carcinoma). While EHE has "epithelioid" features histologically, its lineage is endothelial (mesenchymal). * **Carcinosarcoma:** This is a true "mixed" tumor containing both malignant epithelial and malignant mesenchymal components. * **Hamartoma:** This is a benign, disorganized growth of mature native tissue. EHE is a neoplastic process with metastatic potential, not a developmental malformation. **High-Yield Clinical Pearls for NEET-PG:** * **Histology:** Look for "intracytoplasmic vacuoles" (lumina) containing red blood cells within epithelioid cells. * **Genetics:** Often associated with a specific translocation: **t(1;3)(p36;q25)** resulting in the **WWTR1-CAMTA1** fusion gene. * **Behavior:** It is locally invasive and has a metastatic rate of approximately 20-30%. * **Treatment:** Wide surgical excision is the primary modality; it is generally resistant to radiotherapy and chemotherapy.
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