Radiation Oncology Basics — MCQs

Radiation Oncology Basics Indian Medical PG Practice Questions and MCQs

Question 101: Which of the following tumors is associated with the abscopal effect?

A. Chronic myeloid leukemia
B. Chronic lymphocytic leukemia (Correct Answer)
C. Acute lymphoblastic leukemia
D. Acute myelogenous leukemia

Explanation: **Explanation:** The **Abscopal Effect** is a rare phenomenon in radiation oncology where localized radiation treatment to a primary tumor site results in the regression of distant, non-irradiated metastatic lesions. This effect is mediated by the **immune system**; radiation induces immunogenic cell death, releasing tumor-associated antigens that prime T-cells to mount a systemic anti-tumor response. **Why Chronic Lymphocytic Leukemia (CLL) is correct:** CLL is the classic example among the options provided. Historically, the abscopal effect was frequently documented in patients with CLL or low-grade lymphomas who received splenic irradiation, leading to a significant reduction in distant lymphadenopathy and an improvement in peripheral blood counts. Because CLL is a malignancy of mature B-cells that circulate through the lymphoid system, it is particularly susceptible to this immune-mediated systemic "bypass" effect. **Why other options are incorrect:** * **CML, ALL, and AML:** While theoretically possible, the abscopal effect is rarely reported in acute leukemias or CML. These are aggressive, rapidly proliferating myeloid or immature lymphoid malignancies where the primary treatment is systemic chemotherapy or targeted therapy (like TKIs in CML), rather than localized radiotherapy. The immune environment in acute leukemias is often too suppressive or the disease progression too rapid for the abscopal effect to manifest clinically. **NEET-PG High-Yield Pearls:** * **Mechanism:** Radiation + Immune System = Systemic Response. * **Commonly associated tumors:** Melanoma, Renal Cell Carcinoma (RCC), and Lymphomas (including CLL). * **Modern Context:** The interest in the abscopal effect has surged recently due to the use of **Checkpoint Inhibitors** (e.g., PD-1 inhibitors), which synergize with radiotherapy to enhance this systemic response.

Question 102: The important symptom of radiation proctitis is:

A. Bleeding per rectum (Correct Answer)
B. Weight loss
C. Loss of weight
D. Colicky abdominal pain

Explanation: **Explanation:** **Radiation proctitis** is a common complication following pelvic radiotherapy (for cancers of the cervix, prostate, or bladder). It occurs due to the proximity of the rectum to these pelvic organs, making it susceptible to radiation-induced mucosal damage. **Why "Bleeding per rectum" is correct:** The hallmark of chronic radiation proctitis is **painless rectal bleeding (hematochezia)**. Pathophysiologically, radiation causes obliterative endarteritis and mucosal ischemia, leading to the formation of fragile, superficial **telangiectasias**. These neovascular vessels bleed easily upon contact with stool. Other common symptoms include tenesmus and mucus discharge. **Why the other options are incorrect:** * **Weight loss (Options B & C):** While weight loss is a systemic sign of advanced malignancy or malabsorption, it is not a primary or specific symptom of radiation proctitis itself. Proctitis is a localized inflammatory/vascular process. * **Colicky abdominal pain (Option D):** This is more characteristic of intestinal obstruction or small bowel radiation enteritis. Radiation proctitis typically presents with pelvic discomfort or tenesmus rather than generalized colicky abdominal pain. **High-Yield Clinical Pearls for NEET-PG:** * **Acute vs. Chronic:** Acute proctitis occurs within 6 weeks (due to direct mucosal injury); Chronic proctitis occurs months to years later (due to ischemia and fibrosis). * **Endoscopic Finding:** The classic finding on sigmoidoscopy is **multiple telangiectasias** and pale, friable mucosa. * **Treatment:** The first-line treatment for symptomatic bleeding is often **Sucralfate enemas**. For refractory cases, **Argon Plasma Coagulation (APC)** is the gold standard for cauterizing telangiectasias.

Question 103: After how many days of radiotherapy, mucositis typically appears?

A. 7 days
B. 10 days
C. 14 days (Correct Answer)
D. 30 days

Explanation: **Explanation:** Oral mucositis is a common acute complication of radiotherapy, particularly in head and neck cancers. The timing of its onset is dictated by the **kinetics of the oral mucosal epithelium.** 1. **Why 14 days is correct:** The oral mucosa has a rapid cell turnover rate, typically renewing every 10–14 days. Radiotherapy causes DNA damage to the basal germinal cells, inhibiting their ability to proliferate. As the existing mature superficial cells are naturally shed and not replaced by new cells from the basal layer, the mucosal lining thins and eventually breaks down. This process clinically manifests as erythema and ulceration (mucositis) typically at the **end of the second week (14 days)** of standard fractionated radiotherapy (2 Gy/day). 2. **Analysis of Incorrect Options:** * **7 days:** While microscopic damage begins immediately, the superficial layer remains intact for the first week; only mild erythema may be seen. * **10 days:** This is the early transition phase, but frank mucositis usually peaks and becomes clinically significant around day 14. * **30 days:** By this time, mucositis is usually at its peak or beginning to heal if the treatment course is short. 30 days is too late for the *initial* appearance. **High-Yield Clinical Pearls for NEET-PG:** * **Definition of Acute vs. Late effects:** Acute effects (like mucositis) occur within **90 days** of starting therapy; late effects occur after 90 days. * **Grading:** The WHO or RTOG scales are used to grade mucositis (Grade 1: Erythema; Grade 2: Isolated ulcers; Grade 3: Confluent ulcers; Grade 4: Hemorrhage/Necrosis). * **Management:** "Magic mouthwash" (containing lidocaine, antacids, and diphenhydramine) and Palifermin (recombinant keratinocyte growth factor) are high-yield management options. * **Recovery:** Mucositis usually resolves 2–4 weeks after the completion of radiotherapy.

Question 104: What is the maximum radiation dose to point A for early and advanced Ca cervix?

A. 80-85 Gy and 85-90 Gy (Correct Answer)
B. 85-90 Gy and 90-95 Gy
C. 75-80 Gy and 80-85 Gy
D. 70-75 Gy and 75-80 Gy

Explanation: In Carcinoma Cervix, the total radiation dose is a combination of **External Beam Radiotherapy (EBRT)** and **Brachytherapy**. The target for dose prescription is **Point A**, located 2 cm superior to the lateral vaginal fornix and 2 cm lateral to the uterine canal. ### Why Option A is Correct The standard therapeutic window for Point A aims to achieve local control while minimizing toxicity to the rectum and bladder. * **Early-stage (IB1, IIA1):** A total dose of **80–85 Gy** is sufficient for smaller tumor volumes. * **Advanced-stage (IIB, III, IVA):** Due to larger tumor bulk and parametrial involvement, a higher dose of **85–90 Gy** is required to achieve optimal tumor regression. ### Explanation of Incorrect Options * **Option B (85–95 Gy):** These doses exceed the tolerance limits of the surrounding pelvic organs (Rectum and Bladder), significantly increasing the risk of radiation proctitis and fistulas. * **Options C & D (70–85 Gy):** These doses are generally considered sub-therapeutic for definitive management of advanced cervical cancer, leading to higher rates of local recurrence. ### High-Yield Clinical Pearls for NEET-PG * **Point A:** Represents the crossing of the **Ureter and Uterine Artery**. It is the primary point for dose prescription. * **Point B:** Located 3 cm lateral to Point A (5 cm from the midline). It represents the **Obturator nodes** and pelvic wall involvement. * **Manchester System:** The classic system used for cervical brachytherapy dosimetry. * **ICRU 38/89:** Modern guidelines emphasize GEC-ESTRO recommendations, moving from 2D points (Point A) to 3D volume-based planning (HR-CTV).

Question 105: Cobalt-60 is:

A. A naturally occurring radioisotope
B. An artificial radioisotope (Correct Answer)
C. A product of plutonium
D. A product of uranium

Explanation: **Explanation:** **Cobalt-60 ($^{60}$Co)** is the most widely used radioisotope in external beam radiotherapy (Teletherapy). It is an **artificial radioisotope** produced by the neutron activation of stable Cobalt-59 ($^{59}$Co) in a nuclear reactor. When $^{59}$Co is bombarded with thermal neutrons, it captures a neutron to become the unstable, radioactive $^{60}$Co. **Analysis of Options:** * **Option A (Incorrect):** Naturally occurring radioisotopes include Radium-226, Uranium-238, and Carbon-14. Cobalt-60 does not exist in nature and must be synthesized. * **Option C & D (Incorrect):** While Plutonium and Uranium are used in nuclear reactors, Cobalt-60 is not a "fission product" (waste product) of their decay. Instead, it is a "neutron activation product" created by intentionally placing stable cobalt targets inside the reactor. **Clinical Pearls for NEET-PG:** * **Decay Process:** $^{60}$Co undergoes **beta-minus ($\beta^-$) decay** to reach a stable state of Nickel-60 ($^{60}$Ni). * **Energy Emission:** During this decay, it emits two characteristic gamma-ray photons with energies of **1.17 MeV and 1.33 MeV** (Average energy = **1.25 MeV**). * **Half-life:** The half-life of $^{60}$Co is **5.26 years**. In clinical practice, the source output must be corrected monthly, and the source is typically replaced every 5–7 years. * **Penumbra:** Cobalt-60 machines have a larger **geometric penumbra** compared to Linear Accelerators (LINAC) because the source has a finite physical diameter (usually 1.5–2.0 cm).

Question 106: Which of the following is the most beneficial technique of using chemotherapy with a course of radiotherapy in head and neck malignancies?

A. Neo adjuvant chemotherapy
B. Adjuvant chemotherapy
C. Concurrent chemotherapy (Correct Answer)
D. Alternating chemotherapy and radiotherapy

Explanation: **Explanation:** In the management of locally advanced Head and Neck Squamous Cell Carcinomas (HNSCC), **Concurrent Chemoradiotherapy (CCRT)** is considered the gold standard. The primary medical concept behind this is **radiosensitization**. Chemotherapeutic agents (most commonly Cisplatin) act as "sensitizers" that inhibit the repair of sublethal radiation damage in tumor cells and promote synchronization of the cell cycle into the G2/M phase, which is the most radiosensitive phase. This synergy results in superior locoregional control and overall survival compared to radiotherapy alone. **Analysis of Incorrect Options:** * **Neo-adjuvant (Induction) Chemotherapy:** Given before radiotherapy to shrink the tumor. While it may reduce distant metastasis, it has not consistently shown an improvement in overall survival compared to CCRT and may delay definitive local treatment. * **Adjuvant Chemotherapy:** Given after the primary treatment (surgery or RT). In head and neck cancers, its role is limited as it does not significantly improve survival once the primary treatment is completed. * **Alternating Chemotherapy and Radiotherapy:** This involves giving cycles of CT and RT sequentially. It is logistically complex and has been largely superseded by concurrent protocols which offer better biological synergy. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** **Cisplatin** is the most common agent used concurrently with RT in head and neck cancers. * **Spatial Cooperation:** Chemotherapy treats micrometastases (systemic) while RT treats the primary site (local). * **P16 Status:** In Oropharyngeal cancers, HPV/p16 status is a crucial prognostic factor, though CCRT remains a mainstay for advanced stages. * **Toxicities:** While CCRT is most effective, it also increases acute toxicities like severe mucositis and dysphagia.

Question 107: What dose of radiation therapy is recommended for pain relief in bone metastases?

A. 8 Gy in one fraction (Correct Answer)
B. 20 Gy in 5 fractions
C. 30 Gy in 10 fractions
D. Above 70 Gy

Explanation: **Explanation:** **1. Why 8 Gy in one fraction is correct:** The primary goal of radiotherapy for bone metastases is **palliation** (pain relief and prevention of skeletal-related events). Multiple randomized controlled trials and international guidelines (ASTRO/ESTRO) have established that **8 Gy in a single fraction** is as effective as longer courses for pain control. It is the preferred regimen because it is convenient for the patient, cost-effective, and minimizes hospital visits for terminally ill patients. **2. Analysis of Incorrect Options:** * **B (20 Gy in 5 fractions) & C (30 Gy in 10 fractions):** These are "multi-fraction" palliative regimens. While they are frequently used in clinical practice (especially if there is an associated soft tissue mass or for spinal stability), they do not provide superior pain relief compared to the 8 Gy single dose. In the context of NEET-PG, 8 Gy is the "gold standard" answer for simple pain relief. * **D (Above 70 Gy):** This is a **radical/curative dose** used for primary epithelial tumors (like Head and Neck cancers). Such high doses would cause significant toxicity and are never used for palliative bone metastasis treatment. **3. Clinical Pearls for NEET-PG:** * **Pain Relief Onset:** Improvement usually begins within 1–2 weeks, with maximum relief at 4 weeks. * **Re-treatment:** Single-fraction (8 Gy) carries a higher rate of "re-treatment" compared to multi-fraction regimens, but the overall pain response rate is identical. * **Pathological Fractures:** If a fracture has already occurred, surgical fixation followed by multi-fraction RT (e.g., 30 Gy/10 fractions) is usually preferred over a single dose. * **Strontium-89 / Samarium-153:** These are systemic radiopharmaceuticals used for widespread, diffuse "blastic" bone metastases (e.g., Prostate cancer).

Question 108: High dose radiotherapy to the pancreas most commonly causes deficiency of which of the following structures?

A. Acinar cells (Correct Answer)
B. Islets of Langerhans
C. Both acinar cells and islets of Langerhans
D. None of the above

Explanation: **Explanation:** The pancreas consists of two distinct functional components: the **exocrine** portion (acinar cells) and the **endocrine** portion (islets of Langerhans). These components exhibit significantly different levels of radiosensitivity. **1. Why Acinar Cells are the Correct Answer:** Acinar cells are responsible for the secretion of digestive enzymes. In the hierarchy of radiosensitivity, the exocrine pancreas is much more sensitive to ionizing radiation than the endocrine portion. High-dose radiotherapy leads to the destruction of acinar tissue, resulting in **exocrine pancreatic insufficiency**. This clinically manifests as malabsorption and steatorrhea. Pathologically, this is characterized by atrophy of the acini and subsequent replacement by fibrous tissue. **2. Why the Other Options are Incorrect:** * **Islets of Langerhans:** The endocrine cells (Alpha, Beta, Delta) are remarkably **radioresistant**. Even after high doses of radiation that cause total acinar atrophy and extensive fibrosis, the islets often remain morphologically intact and functional. Therefore, radiation-induced diabetes mellitus is rare compared to exocrine failure. * **Both acinar cells and islets of Langerhans:** This is incorrect because the damage is disproportionate. While extreme doses might eventually affect the entire organ, the "most common" and primary deficiency is strictly exocrine. **High-Yield Clinical Pearls for NEET-PG:** * **Radiosensitivity Rule:** Cells that are rapidly dividing or less differentiated are generally more radiosensitive (Law of Bergonié and Tribondeau). However, the pancreas is a "stable" organ where the exocrine part is simply more prone to radiation-induced fibrotic changes than the endocrine part. * **Tolerance Dose (TD 5/5):** The whole pancreas has a tolerance dose of approximately **40-45 Gy**. Exceeding this significantly increases the risk of radiation pancreatitis. * **Clinical Presentation:** Patients post-radiotherapy for pancreatic or upper GI tumors should be monitored for **steatorrhea**, as they may require oral pancreatic enzyme replacement therapy (PERT).

Question 109: Mega voltage therapy consists of:

A. Greater than 1000 kV (Correct Answer)
B. 500-1000 kV
C. Less than 500 kV
D. More than 2000 kV

Explanation: **Explanation:** The classification of radiotherapy is primarily based on the energy (voltage) of the X-ray beams used. **Megavoltage therapy** refers to radiation treatment using photon beams with energies of **1 MeV (1000 kV) or higher**. 1. **Why Option A is correct:** By definition, megavoltage equipment (such as Linear Accelerators/LINAC and Cobalt-60 units) operates in the range of 1 MV to 25 MV. These high-energy beams are essential in modern oncology because they provide a **"skin-sparing effect,"** where the maximum dose is delivered at a specific depth below the skin surface (e.g., 1.5 cm for 6 MV), reducing the risk of severe radiation dermatitis. 2. **Why other options are incorrect:** * **Option B & C:** These fall under **Orthovoltage therapy** (typically 150–500 kV) or **Deep therapy**. These lower energies have poor penetration and cause maximum dose deposition on the skin surface, making them unsuitable for deep-seated tumors. * **Option D:** While 2000 kV is technically megavoltage, it is a subset of the "Greater than 1000 kV" category. Option A is the standard threshold definition used in radiological physics. **High-Yield Clinical Pearls for NEET-PG:** * **Grenz Rays:** Very low energy (<20 kV). * **Superficial Therapy:** 50–150 kV (used for skin lesions). * **Cobalt-60:** A common megavoltage source emitting gamma rays at **1.17 and 1.33 MeV** (Average: 1.25 MeV). * **Advantages of Megavoltage:** Greater penetration (depth dose), skin-sparing effect, and reduced bone absorption (less risk of osteoradionecrosis) compared to orthovoltage.

Question 110: Following surgical extraction, radiotherapy should be avoided for how long?

A. 7 days
B. 10-14 days (Correct Answer)
C. 15-20 days
D. 30 days

Explanation: **Explanation:** The correct answer is **10-14 days (Option B)**. This timeframe is critical in radiation oncology to ensure adequate **wound healing** before initiating radiotherapy. **1. Why 10-14 days is correct:** Radiotherapy (RT) works by inducing DNA damage and generating free radicals, which primarily target rapidly dividing cells. While this kills tumor cells, it also severely impairs the proliferation of fibroblasts and the formation of granulation tissue necessary for wound healing. If RT is started too early (before 10 days), it can lead to wound dehiscence, infection, and chronic non-healing ulcers. By 10-14 days, the proliferative phase of healing is sufficiently advanced, and sutures are typically removed, making it the safest window to begin treatment. **2. Why other options are incorrect:** * **7 days (Option A):** This is too early. The tensile strength of the wound is still very low, and the inflammatory phase may not have fully transitioned to the proliferative phase. * **15-20 days & 30 days (Options C & D):** While waiting longer ensures better healing, delaying radiotherapy beyond 3 weeks (21 days) in an oncology setting increases the risk of **repopulation** of residual microscopic tumor cells, potentially compromising the curative intent of the treatment. **Clinical Pearls for NEET-PG:** * **Osteoradionecrosis (ORN):** This is a dreaded complication of RT in head and neck cancers. To prevent ORN, all necessary dental extractions must be completed **at least 2 weeks before** starting radiotherapy. * **Post-RT Extractions:** If a tooth must be extracted *after* radiotherapy, it is generally advised to wait at least 6 months to 1 year, often requiring hyperbaric oxygen therapy to prevent bone necrosis. * **Rule of Thumb:** "Wait 2 weeks before, and avoid forever after" is a common clinical adage regarding extractions and radiation.

Practice by Chapter

Principles of Radiation Therapy

Practice Questions

Radiation Therapy Equipment

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Treatment Planning Process

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External Beam Radiation Therapy

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Brachytherapy

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3D Conformal Radiation Therapy

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Intensity-Modulated Radiation Therapy

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Image-Guided Radiation Therapy

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Stereotactic Radiosurgery

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Total Body Irradiation

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Palliative Radiation Therapy

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Combined Modality Treatments

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