Radiation Oncology Basics Practice Questions

Q: Which of the following tumors is least sensitive to radiotherapy?

Osteosarcoma. In radiation oncology, tumors are classified based on their **radiosensitivity**, which refers to the relative susceptibility of cells and tissues to the ionizing effects of radiation. ### **Why Osteosarcoma is the Correct Answer** **Osteosarcoma** is a primary bone malignancy characterized by the production of osteoid (bone matrix) by malignant cells. It is classically considered a **radioresistant** tumor. Because its cells have robust DNA repair mechanisms and the dense osteoid matrix may contribute to a hypoxic microenvironment (making it less susceptible to free radical damage), radiotherapy is rarely used as a primary treatment. The mainstay of management is surgical resection combined with chemotherapy. ### **Explanation of Incorrect Options** * **Ewing’s Sarcoma:** Unlike osteosarcoma, this is a highly **radiosensitive** small round blue cell tumor. Radiotherapy is a standard component of management, especially when surgical margins are close or the tumor is unresectable. * **Wilms’ Tumor (Nephroblastoma):** This pediatric renal tumor is very sensitive to radiation. Radiotherapy is frequently used in advanced stages (Stage III and IV) to treat the flank or whole abdomen. * **Neuroblastoma:** Another small round blue cell tumor of childhood that is highly radiosensitive. Radiation is often used for local control in high-risk cases. ### **NEET-PG High-Yield Pearls** * **Most Radiosensitive Tumor:** Seminoma (Dysgerminoma in females). * **Radiosensitive "Small Round Blue Cell" Group:** Includes Ewing’s, Neuroblastoma, Wilms’ tumor, and Lymphoma. * **Highly Radioresistant Tumors:** Osteosarcoma, Malignant Melanoma, Renal Cell Carcinoma (RCC), and Pancreatic Adenocarcinoma. * **Bergonie-Tribondeau Law:** Cells are more radiosensitive if they have a high mitotic rate, a long mitotic future, and are undifferentiated.

Q: Radiotherapy is the treatment of choice for which one of the following tumors?

Rodent ulcer. **Explanation:** **Rodent Ulcer (Basal Cell Carcinoma - BCC):** Rodent ulcer is the clinical term for Basal Cell Carcinoma (BCC). It is highly **radiosensitive**. While surgical excision is often the primary treatment for small lesions, radiotherapy is considered a **treatment of choice**, especially in elderly patients or for lesions located in areas where surgery would be disfiguring (e.g., medial canthus of the eye, nose, or ear). It provides excellent cosmetic results and high cure rates for superficial and nodular variants. **Why the other options are incorrect:** * **Verrucous Carcinoma:** This is a well-differentiated variant of Squamous Cell Carcinoma (SCC). It is notoriously **radioresistant**. Importantly, radiotherapy is contraindicated because it can trigger **anaplastic transformation** into a highly aggressive, metastatic spindle cell carcinoma. * **Malignant Melanoma:** Melanoma is traditionally considered **radioresistant**. The primary treatment is wide local excision with adequate margins. Radiotherapy is generally reserved for palliation or specific adjuvant settings (e.g., brain metastases). * **Marjolin’s Ulcer:** This is an aggressive SCC arising in chronic scars or non-healing wounds. It is relatively **radioresistant** and has a high risk of metastasis. The treatment of choice is wide local excision with a 2-cm margin; radiotherapy is only used if surgery is not possible. **High-Yield Clinical Pearls for NEET-PG:** * **BCC (Rodent Ulcer):** Most common skin cancer; characterized by "pearly" borders and telangiectasia; rarely metastasizes but is locally invasive. * **Radiosensitivity Rule:** BCC is more radiosensitive than SCC. * **Marjolin’s Ulcer:** Most common site is the lower limb; characterized by a long latent period (average 30 years). * **Verrucous Carcinoma:** Also known as **Ackerman’s tumor**; common in the oral cavity (tobacco chewers) and glans penis (Buschke-Löwenstein tumor).

Q: Whole body electron therapy is useful in the management of which of the following conditions?

Mycosis fungoides. **Explanation:** **Total Skin Electron Beam Therapy (TSEBT)** is a specialized form of radiotherapy that utilizes the unique physical properties of electrons to treat superficial skin malignancies. Unlike X-rays, electrons have a limited range and a rapid "fall-off" in tissue, meaning they deliver a high dose to the skin surface (dermis and epidermis) while sparing deeper internal organs. **Why Mycosis Fungoides (MF) is the correct answer:** Mycosis Fungoides is the most common form of **Cutaneous T-Cell Lymphoma (CTCL)**. Since the disease often involves large areas of the skin surface but remains superficial for a long period, TSEBT is the treatment of choice for extensive plaque or erythrodermic stages. It provides excellent symptom relief and high complete remission rates by targeting the malignant T-cells infiltrating the skin. **Analysis of Incorrect Options:** * **Sezary Syndrome (B):** While related to MF, Sezary Syndrome is the leukemic (systemic) phase characterized by erythroderma and malignant cells in the peripheral blood. Treatment is primarily systemic (e.g., extracorporeal photopheresis, chemotherapy) rather than localized skin radiation. * **Hodgkin’s Disease & NLPHL (A & D):** These are nodal lymphomas. They require systemic chemotherapy and/or Involved Site Radiation Therapy (ISRT) using high-energy Photons (X-rays) to reach deep-seated lymph nodes. Electron therapy is too superficial for these conditions. **High-Yield Clinical Pearls for NEET-PG:** * **Energy used:** Typically low-energy electrons (6–9 MeV) are used to treat the skin up to a depth of approximately 5–10 mm. * **Stanford Technique:** The most common clinical method for delivering TSEBT, involving the patient standing in six different positions to ensure uniform skin coverage. * **Side Effects:** Acute effects include erythema, alopecia, and nail loss (onycholysis); long-term risks include secondary skin cancers and chronic xerosis.

Q: Which of the following statements about Gamma Knife is FALSE?

It provides equal exposure to surrounding healthy tissue.. **Explanation:** The **Gamma Knife** is a specialized form of **Stereotactic Radiosurgery (SRS)**. The fundamental principle of SRS is to deliver a high dose of radiation to a precisely defined target while ensuring a **steep dose gradient**. This means the radiation dose drops off rapidly outside the target area, thereby **sparing surrounding healthy tissue** from significant exposure. Therefore, Option B is false because the goal is the exact opposite of "equal exposure." * **Option A is correct:** Gamma Knife uses approximately 192–201 cobalt-60 sources. These beams converge at a single point (the isocenter), delivering a highly focused, lethal dose to the lesion. * **Option C is correct:** It is considered "surgery" without a scalpel. It uses a rigid stereotactic frame (or mask-based systems) to provide sub-millimeter accuracy, allowing for a single-fraction treatment. * **Option D is correct:** Due to its precision and the physical constraints of the machine, it is primarily indicated for small, well-defined intracranial lesions (typically <3–4 cm), such as acoustic neuromas, meningiomas, pituitary adenomas, and brain metastases. **High-Yield Clinical Pearls for NEET-PG:** * **Source:** Uses **Cobalt-60** ($^{60}$Co) which emits Gamma rays. * **Targeting:** Best for **intracranial** lesions; it cannot be used for extracranial (body) tumors (CyberKnife is used for those). * **Precision:** It offers the highest mechanical accuracy (0.15 mm) among all SRS platforms. * **Indications:** Arteriovenous Malformations (AVM), Trigeminal Neuralgia, and small brain tumors.

Q: A patient with a history of radiation therapy requires special consideration because:

The vascularity of the bone may be disrupted.. **Explanation:** **Correct Option: A (The vascularity of the bone may be disrupted)** Radiation therapy, particularly for head and neck cancers, induces long-term changes in the microvasculature. High-dose radiation leads to **endarteritis obliterans**, a process characterized by the narrowing and occlusion of small blood vessels. This results in a state of **hypovascularity, hypocellularity, and hypoxia (the 3-H principle)**. When bone vascularity is compromised, its ability to repair and mount an immune response is severely diminished, leading to a high risk of **Osteoradionecrosis (ORN)** following invasive procedures like dental extractions. **Incorrect Options:** * **B:** Radiation to the head and neck typically causes **xerostomia** (dry mouth) due to irreversible damage to the acinar cells of the salivary glands, leading to *decreased*, not increased, salivary function. * **C & D:** While plaque accumulation and periodontal disease can occur due to poor oral hygiene and xerostomia, they are secondary effects. The most critical "special consideration" from a surgical and pathological standpoint in radiation oncology is the permanent alteration of bone vitality and blood supply. **High-Yield Clinical Pearls for NEET-PG:** * **Osteoradionecrosis (ORN):** Most commonly affects the **mandible** (due to its higher density and lower baseline vascularity compared to the maxilla). * **Threshold Dose:** The risk of ORN increases significantly when the radiation dose exceeds **60 Gy**. * **Management:** Hyperbaric Oxygen (HBO) therapy is often used to stimulate angiogenesis in irradiated tissues before surgical interventions (Marx Protocol). * **Radiation Caries:** A rapid form of tooth decay occurring post-radiation due to changes in salivary pH and flow.

Q: Brachytherapy is used in which of the following conditions?

Stage Ib Ca cervix. **Explanation:** **Brachytherapy** involves placing a radioactive source directly into or near a tumor, allowing for a high dose of radiation to the target tissue while sparing surrounding healthy organs (inverse square law). 1. **Why Stage Ib Ca Cervix is Correct:** In Carcinoma Cervix, brachytherapy is a cornerstone of treatment. For early stages like **Stage Ib**, it is often used as a boost following External Beam Radiotherapy (EBRT) or as part of definitive chemoradiotherapy. It provides a concentrated dose to the cervix and paracervical tissues, which is essential for local tumor control and achieving high cure rates. 2. **Why the Incorrect Options are Wrong:** * **Ovarian Ca:** The primary treatment is surgical debulking followed by systemic chemotherapy (Taxanes/Platinum). Brachytherapy is not used because ovarian cancer typically spreads via peritoneal seeding, requiring whole-abdomen coverage rather than localized radiation. * **Stage IV Ca Vagina:** While brachytherapy is used in early-stage vaginal cancer, Stage IV involves distant metastasis or extension to the bladder/rectal mucosa. At this advanced stage, systemic therapy or palliative EBRT is preferred over localized brachytherapy. * **Stage II Fallopian Tube Ca:** Similar to ovarian cancer, fallopian tube malignancies are managed with surgery and systemic chemotherapy due to their pattern of intraperitoneal spread. **Clinical Pearls for NEET-PG:** * **Manchester System:** Uses Point A (2cm superior and 2cm lateral to the external os) and Point B (3cm lateral to Point A) for dosing in Ca Cervix. * **Common Isotopes:** Iridium-192 (most common for HDR), Cesium-137 (LDR), and Cobalt-60. * **Rule of Thumb:** Brachytherapy is ideal for accessible, localized tumors (Cervix, Endometrium, Prostate, Tongue).

Q: Which of the following statements is true regarding medulloblastoma?

It is a radiosensitive tumor.. **Explanation:** **1. Why Option B is Correct:** Medulloblastoma is a highly cellular, primitive neuroectodermal tumor (PNET) that exhibits high mitotic activity. In radiobiology, the **Law of Bergonié and Tribondeau** states that cells that are rapidly dividing and undifferentiated are more sensitive to radiation. Consequently, medulloblastoma is considered a **highly radiosensitive tumor**. Radiation therapy, typically delivered via Craniospinal Irradiation (CSI), is a cornerstone of management to address its tendency for leptomeningeal seeding. **2. Why the Other Options are Incorrect:** * **Option A:** Medulloblastoma is primarily a **pediatric tumor**, representing the most common malignant brain tumor in children (peak incidence: 3–8 years). It is rare in adults over 50. * **Option C:** Treatment is **multimodal**. While maximal safe surgical resection is the first step, it is almost always followed by adjuvant radiotherapy and/or chemotherapy due to the high risk of recurrence and neuraxial spread. * **Option D:** It is a tumor of the **posterior cranial fossa**, typically arising from the roof of the fourth ventricle (cerebellar vermis) in children. **3. Clinical Pearls for NEET-PG:** * **Imaging:** On CT, it appears as a hyperdense midline mass in the posterior fossa. On MRI, it shows restricted diffusion (low ADC values) due to high cellularity. * **Drop Metastasis:** It has a high propensity for CSF dissemination; hence, imaging of the **entire neuraxis** (spine) is mandatory. * **Homer-Wright Rosettes:** A classic histopathological finding (though seen in only ~40% of cases). * **Zuckerguss:** A term used to describe the "icing-like" appearance of leptomeningeal metastases on the brain surface.

Question 1

Which of the following tumors is least sensitive to radiotherapy?

Accepted Answer

Osteosarcoma

Answer

Ewing's sarcoma

Answer

Wilms' tumor

Answer

Neuroblastoma

Question 2

Which isotope is most commonly used in brachytherapy for carcinoma of the cervix?

Accepted Answer

Cesium-137

Answer

Radium-226

Answer

Cobalt-60

Answer

Gold-198

Question 3

Radiotherapy is the treatment of choice for which one of the following tumors?

Accepted Answer

Rodent ulcer

Answer

Verrucous carcinoma

Answer

Malignant melanoma

Answer

Marjolin's ulcer

Question 4

Whole body electron therapy is useful in the management of which of the following conditions?

Accepted Answer

Mycosis fungoides

Answer

Nodular Lymphocyte Predominant Hodgkin Lymphoma

Answer

Sezary syndrome

Answer

Hodgkin's disease

Question 5

Which of the following statements about Gamma Knife is FALSE?

Accepted Answer

It provides equal exposure to surrounding healthy tissue.

Answer

Focused radiation is delivered to the tumor.

Answer

It is a type of stereotactic surgery.

Answer

It is primarily used for small brain tumors.

Question 6

A patient with a history of radiation therapy requires special consideration because:

Accepted Answer

The vascularity of the bone may be disrupted.

Answer

Salivary function may be increased.

Answer

Plaque accumulation greater than normal can be expected.

Answer

The potential for periodontal disease is greatly increased.

Question 7

Brachytherapy is used in which of the following conditions?

Accepted Answer

Stage Ib Ca cervix

Answer

Ovarian Ca

Answer

Stage IV Ca vagina

Answer

Stage II fallopian tube Ca

Question 8

The best method to reduce radiation caries is application of viscous:

Accepted Answer

1% neutral sodium fluoride gel

Answer

0.5% neutral sodium fluoride gel

Answer

0.5% stannous fluoride gel

Answer

1% stannous fluoride gel

Question 9

A 49-year-old computer technician receives irradiation to the pelvis for cervical cancer. Three months after irradiation, severe rectal proctitis may be shown by the presence of which of the following?

Accepted Answer

Ulcers

Answer

Strictures at anal verge

Answer

Mucosa prolapse

Answer

Multiple telangiectasis and polypoid tumor

Question 10

Which of the following statements is true regarding medulloblastoma?

Accepted Answer

It is a radiosensitive tumor.

Answer

It is primarily seen in individuals over 50 years of age.

Answer

The sole treatment modality is surgical resection.

Answer

It is typically found in the anterior cranial fossa.

Radiation Oncology Basics — MCQs

Radiation Oncology Basics — MCQs

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