Radiation Oncology Basics

Radiation Oncology Basics Indian Medical PG Question 1: A 55 year old woman diagnosed with ca cervix stage IIb is advised for chemoradiation. Which of the following is the true statement regarding radiation use?

• A. Rapidly proliferating cells are less affected by radiation
• B. The small bowel is not significantly affected by radiation
• C. Dose/Intensity of radiation is inversely proportional to the square of distance of source (Correct Answer)
• D. Small blood vessels are unaffected by radiation

Radiation Oncology Basics Explanation: ***Dose/Intensity of radiation is inversely proportional to the square of distance of source*** - This statement accurately describes the **inverse square law** which governs radiation intensity. As the distance from the radiation source increases, the dose or intensity of radiation decreases proportionally to the square of that distance. - This principle is crucial in **radiation safety** and treatment planning to ensure appropriate dose delivery and minimize exposure to non-target tissues. *Rapidly proliferating cells are less affected by radiation* - This is incorrect; **rapidly proliferating cells** are generally **more sensitive to radiation** because radiation primarily targets cells undergoing division, causing DNA damage. - Tissues with high cellular turnover, like bone marrow and gastrointestinal lining, are highly susceptible to radiation-induced damage. *The small bowel is not significantly affected by radiation* - This is incorrect; the **small bowel** is one of the most **radiosensitive organs** due to its rapidly proliferating epithelial cells. - Radiation to the abdomen and pelvis, common in cervical cancer treatment, frequently causes symptoms such as **nausea, vomiting, diarrhea**, and long-term complications like enteritis and strictures. *Small blood vessels are unaffected by radiation* - This is incorrect; **small blood vessels**, particularly the **endothelium**, are quite susceptible to radiation damage. - Radiation can cause **endothelial cell swelling**, damage, and sclerosis, leading to vascular insufficiency, fibrosis, and impaired tissue healing.

Radiation Oncology Basics Indian Medical PG Question 2: The technique employed in radiotherapy to counteract the effect of tumour motion due to breathing is known as –

• A. Tracking
• B. Gating (Correct Answer)
• C. Modulation
• D. Arc technique

Radiation Oncology Basics Explanation: ***Gating*** - **Respiratory gating** involves delivering radiation only during specific phases of the patient's breathing cycle when the tumor is within a defined target window. - This technique helps to **minimize the irradiated volume** of healthy tissue by avoiding treatment when the tumor moves out of the planned treatment field. *Tracking* - **Respiratory tracking** involves actively adjusting the radiation beam in real-time to follow the motion of the tumor during breathing. - While it aims to compensate for motion, it is a different mechanism from gating, which involves turning the beam on and off. *Modulation* - **Intensity-modulated radiation therapy (IMRT)** and similar techniques focus on varying the intensity of the radiation beam across the treatment field to conform the dose to the tumor shape. - Modulation addresses dose distribution within a target, rather than directly managing tumor motion due to respiration. *Arc technique* - **Arc therapy** (e.g., VMAT) involves continuous delivery of radiation as the treatment machine rotates around the patient. - This technique optimizes dose delivery angles and conformity but does not inherently counteract tumor motion, although it can be combined with motion management.

Radiation Oncology Basics Indian Medical PG Question 3: For which malignancy is intensity-modulated radiotherapy (IMRT) the most suitable?

• A. Lung
• B. Prostate (Correct Answer)
• C. Leukemias
• D. Stomach

Radiation Oncology Basics Explanation: ***Prostate*** - **IMRT** is highly suitable for prostate cancer due to the prostate's proximity to critical organs like the **rectum and bladder**. - Its ability to conform the **radiation dose tightly** to the tumor while sparing adjacent healthy tissue significantly reduces side effects like **rectal bleeding** or **urinary dysfunction** [1]. *Lung* - While IMRT is used in lung cancer, especially for complex tumors near vital structures, **stereotactic body radiation therapy (SBRT)** is often preferred for early-stage lung cancer due to its high dose delivery over fewer fractions. - The **motion of the lung** during respiration can make precise IMRT delivery challenging without specialized techniques like **gating or tracking**. *Leukemias* - **Leukemias** are systemic diseases involving blood and bone marrow, making localized radiation therapies like IMRT generally unsuitable as a primary treatment. - Treatment for leukemias primarily involves **chemotherapy, targeted therapy, or stem cell transplant**. *Stomach* - **Stomach cancer** often requires larger radiation fields due to tumor spread and nodal involvement, making the precise dose sculpting of IMRT less advantageous compared to its benefits in smaller, well-defined tumors. - The **mobility of the stomach** and surrounding organs can also present challenges for highly conformal radiation delivery.

Radiation Oncology Basics Indian Medical PG Question 4: Which one of the following imaging techniques gives the maximum radiation exposure to the patient?

• A. Chest X-ray
• B. MRI
• C. CT scan (Correct Answer)
• D. Bone scan

Radiation Oncology Basics Explanation: ***CT scan*** - **CT scans** involve multiple X-ray projections and computer processing, resulting in a significantly higher radiation dose compared to conventional X-rays. - The effective dose from a single chest or abdominal CT scan can be equivalent to hundreds of standard chest X-rays, making it the highest radiation contributor among the options listed. *Chest X-ray* - A **chest X-ray** uses a very small amount of ionizing radiation, typically one of the lowest doses among diagnostic imaging techniques that involve radiation. - While it uses radiation, its contribution to overall exposure is minimal, especially compared to CT scans. *MRI* - **MRI (Magnetic Resonance Imaging)** uses strong magnetic fields and radio waves to create detailed images of organs and soft tissues, not ionizing radiation. - Therefore, it involves **no radiation exposure** to the patient. *Bone scan* - A **bone scan** uses a small amount of **radioactive tracer** (radionuclide) injected into the bloodstream, which is then detected by a special camera. - While it involves radiation, the dose is generally lower than that of a CT scan and is comparable to or slightly higher than a series of X-rays.

Radiation Oncology Basics Indian Medical PG Question 5: Which of the following is an inappropriate indication for concomitant chemotherapy in cases of head and neck cancer?

• A. Metastatic advanced head and neck cancer (Correct Answer)
• B. As an organ-preserving method of treatment
• C. Primary treatment for patients with unresectable disease
• D. Postoperative case of intermediate stage resectable tumor

Radiation Oncology Basics Explanation: ***Metastatic advanced head and neck cancer*** - While chemotherapy is used in metastatic head and neck cancer, the term "concomitant chemotherapy" implies simultaneous administration with radiation therapy. For **metastatic disease**, the primary treatment strategy is usually **systemic chemotherapy** or targeted therapy, not necessarily concomitant with radiation to a local site with curative intent. - Concomitant chemoradiation is primarily used for **locally advanced, non-metastatic disease** to improve local control and survival, not typically for systemic metastatic disease where the goal is palliation or systemic control. *As an organ-preserving method of treatment* - Concomitant chemoradiation is a well-established strategy for organ preservation, particularly in advanced laryngeal and pharyngeal cancers, allowing patients to avoid **laryngectomy** or extensive surgical resections while achieving similar oncologic outcomes. - This approach aims to maintain **swallowing and speech function** by reducing tumor burden and eradicating microscopic disease. *Primary treatment for patients with unresectable disease* - For **unresectable locally advanced head and neck cancers**, concomitant chemoradiation is often considered the **definitive primary treatment** to achieve local control and improve survival outcomes. - Surgery is not feasible in these cases due to tumor extent or involvement of critical structures, making chemoradiation the best curative option. *Postoperative case of intermediate stage resectable tumor* - **Adjuvant concomitant chemoradiation** is indicated postoperatively for resected tumors with high-risk features such as **extracapsular extension (ECE)** or positive surgical margins, even in intermediate stages. - This is done to eradicate microscopic residual disease and reduce the risk of **local-regional recurrence**.

Radiation Oncology Basics Indian Medical PG Question 6: What is the most likely diagnosis based on the chest radiographs shown below?

• A. Lung abscess
• B. Lobar emphysema
• C. Segmental collapse (Correct Answer)
• D. Bronchiectasis

Radiation Oncology Basics Explanation: ***Segmental collapse*** - The frontal image shows a **wedge-shaped opacity** in the right upper lobe, and the lateral view reveals a **triangular area of increased density** consistent with collapsed lung tissue. - This pattern, particularly the triangular density on the lateral view and volume loss indicated by the position of the **minor fissure (white arrow)**, points towards segmental collapse. *Lung abscess* - A lung abscess typically presents as a **cavity with an air-fluid level**, which is not depicted in these images. - The lesion shown is mostly **solid and dense**, unlike the characteristic appearance of an abscess. *Lobar emphysema* - Lobar emphysema involves **overinflation of a lung lobe**, characterized by increased lucency and vascular attenuation, which is the opposite of the findings here. - There is no evidence of **air trapping** or **hyperinflation** in the images provided. *Bronchiectasis* - Bronchiectasis is characterized by **permanent abnormal dilation of the bronchi**, often seen as "tram tracks" or "ring" opacities on imaging. - The images do not show these specific findings; instead, they indicate a loss of lung volume.

Radiation Oncology Basics Indian Medical PG Question 7: What does this CT chest image show?

• A. Consolidation
• B. Pneumothorax
• C. Pleural effusion
• D. Segmental collapse (Correct Answer)

Radiation Oncology Basics Explanation: ***Segmental collapse*** - The CT image shows loss of lung volume in a specific segment, indicated by the **crowding of bronchi and vessels in the affected area**, which is suggestive of atelectasis or collapse. - The black arrow points to the collapsed segment, which appears as a **densified, airless region within the lung parenchyma**, consistent with segmental collapse. *Consolidation* - **Consolidation** typically presents as an area of increased opacification due to alveolar filling with exudate or fluid, but without significant loss of lung volume. - Unlike collapse, consolidation generally **retains the lung architecture** and does not show crowding of vessels and bronchi. *Pneumothorax* - A **pneumothorax** is characterized by the presence of air in the pleural space, which would appear as a dark, air-filled space between the lung and the chest wall. - This typically leads to a **collapsed lung that is displaced medially** and no longer touches the chest wall, which is not seen here. *Pleural effusion* - **Pleural effusion** is the accumulation of fluid in the pleural space, presenting as a homogenous, gravity-dependent opacity that obscures lung parenchyma. - It would typically cause **blunting of the costophrenic angles** and a meniscus sign, which are not the primary findings indicated by the arrow.

Radiation Oncology Basics Indian Medical PG Question 8: Investigation of choice for vascular ring around airway:

• A. PET
• B. Catheter directed angiography
• C. MRI
• D. CT (Correct Answer)

Radiation Oncology Basics Explanation: ***CT*** - **CT angiography (CTA)** is the **investigation of choice** for diagnosing vascular rings due to its ability to provide detailed anatomical visualization of the great vessels and their relationship to the trachea and esophagus. - It offers high spatial resolution, allowing precise identification of the type of vascular anomaly, the degree of **airway and esophageal compression**, and guiding surgical planning. *PET* - **PET scans** are primarily used for assessing **metabolic activity**, particularly in oncology or to evaluate organ function, and do not provide sufficient anatomical detail for vascular rings. - While it can detect metabolically active lesions, it is **not suitable** for visualizing the structural abnormalities of blood vessels and their compressive effects on the airway. *Catheter directed angiography* - **Catheter-directed angiography** is an **invasive procedure** involving radiation and contrast, primarily used for assessing blood flow dynamics, identifying stenosis, or guiding interventions. - While it can visualize vessels, CTA is **less invasive**, provides comparable or superior anatomical detail for vascular rings, and is generally preferred for initial diagnosis. *MRI* - **MRI** can provide good soft tissue contrast and visualize vascular structures without radiation, but it is often **less readily available** and can be more challenging for pediatric patients due to the need for sedation and longer scan times. - For comprehensive anatomical detail including bone and calcifications, and in patients who might struggle with breath-holding, **CT angiography** often offers clearer and more consistent images of complex vascular anatomy.

Radiation Oncology Basics Indian Medical PG Question 9: What is the management of osteoradionecrosis?

• A. Hyperbaric oxygen
• B. Removal of sequestrum
• C. Fluoride application
• D. All of the above (Correct Answer)

Radiation Oncology Basics Explanation: **Explanation:** Osteoradionecrosis (ORN) is a serious late complication of radiotherapy, most commonly affecting the mandible. It is characterized by bone death due to radiation-induced **hypocellularity, hypovascularity, and hypoxia (Marx’s 3H theory)**, leading to non-healing exposed bone. The management of ORN is multifaceted, involving conservative, medical, and surgical interventions: 1. **Hyperbaric Oxygen (HBO):** This is a cornerstone of treatment. It increases dissolved oxygen levels in tissues, stimulating angiogenesis and fibroblastic activity, which helps reverse the radiation-induced hypoxic state. 2. **Removal of Sequestrum (Sequestrectomy):** Surgical intervention is required to remove necrotic, infected bone (sequestrum) that acts as a nidus for infection and prevents healing. 3. **Fluoride Application:** Preventive and supportive care is vital. Radiation damages salivary glands (xerostomia), increasing the risk of radiation caries. Daily topical fluoride application is essential to maintain dental integrity and prevent odontogenic infections that could trigger or worsen ORN. **Why "All of the above" is correct:** Effective management requires a combination of improving tissue oxygenation (HBO), surgical debridement of dead bone, and strict oral hygiene/caries prevention (Fluoride) to arrest the progression of the disease. **High-Yield Clinical Pearls for NEET-PG:** * **Most common site:** Mandible (due to lower vascularity compared to the maxilla). * **Marx’s Protocol:** Often involves 20–30 sessions of HBO before surgery and 10 sessions after. * **PENTOCLO Protocol:** A newer medical management involving Pentoxifylline, Tocopherol (Vitamin E), and Clodronate. * **Prevention:** All necessary dental extractions should ideally be completed **at least 2–3 weeks before** starting radiotherapy.

Radiation Oncology Basics Indian Medical PG Question 10: Cranial irradiation is also indicated in the treatment of which variety of lung cancer?

• A. Squamous cell carcinoma
• B. Non small cell cancer
• C. Small cell cancer (Correct Answer)
• D. Adenocarcinoma

Radiation Oncology Basics Explanation: ### Explanation **Correct Answer: C. Small Cell Cancer** The correct answer is **Small Cell Lung Cancer (SCLC)**. The underlying medical concept is **Prophylactic Cranial Irradiation (PCI)**. SCLC is a highly aggressive neuroendocrine tumor characterized by rapid doubling time and a high propensity for early micrometastasis. Even when systemic chemotherapy achieves a complete or good partial response, the blood-brain barrier often acts as a "sanctuary site," protecting sequestered tumor cells from systemic drugs. Without PCI, approximately 50–60% of SCLC patients develop brain metastases within two years. Clinical trials have shown that PCI significantly reduces the incidence of brain metastases and improves overall survival in patients with limited-stage SCLC who respond to initial therapy. **Why other options are incorrect:** * **A, B, and D (Squamous cell, Adenocarcinoma, and NSCLC):** These fall under the umbrella of **Non-Small Cell Lung Cancer (NSCLC)**. Unlike SCLC, NSCLC is less sensitive to radiation and has a lower rate of early occult brain involvement. While cranial irradiation is used *palliatively* if brain metastases are already present, it is not a standard prophylactic indication for all patients as it is in SCLC. **High-Yield Clinical Pearls for NEET-PG:** * **Indication:** PCI is indicated in both Limited-Stage (LS) and Extensive-Stage (ES) SCLC if there is a good response to first-line chemo-radiotherapy. * **Sanctuary Site:** The brain is the most common site of "isolated relapse" in SCLC due to the blood-brain barrier. * **Dose:** Standard PCI dose is typically **25 Gy in 10 fractions**. * **Side Effects:** The major concern with PCI is neurocognitive decline (memory loss), which is why it is reserved for patients with good performance status.

Radiation Oncology Basics Flashcard 1 of 9

Question: _____ is the most commonly used radioactive agent for brachytherapy in carcinoma cervix.

Answer: Cesium

Radiation Oncology Basics Flashcard 2 of 9

Question: _____ is the treatment of choice for nasopharyngeal cancer stage I and II

Answer: Radiotherapy

Radiation Oncology Basics Flashcard 3 of 9

Question: In radiotherapy for carcinoma cervix, point A recieves _____ cGy of radiation dose

Answer: 7000-8000

Radiation Oncology Basics Flashcard 4 of 9

Question: Mechanism used to counteract respiratory movement in radiotherapy is called _____

Answer: gating

Radiation Oncology Basics Flashcard 5 of 9

Question: _____ fractionated radiotherapy is given once daily for 5 days/ week, with no more than 2 Gy/ fraction(fx).

Answer: Conventional

Radiation Oncology Basics Flashcard 6 of 9

Question: _____ is a radiosensitive tumor and responds very well to radiotherapy.

Answer: Medulloblastoma (CNS tumor)

Radiation Oncology Basics Flashcard 7 of 9

Question: _____ is Stereotactic Radiosurgery of the Brain.

Answer: Gamma Knife

Radiation Oncology Basics Flashcard 8 of 9

Question: In radiotherapy for carcinoma cervix, point A is _____cm above and 2cm lateral to external os

Answer: 2

Radiation Oncology Basics Flashcard 9 of 9

Question: What are the 5Rs of radiotherapy?_____ReassortmentRepopulationReoxygenationRadiosensitivity

Answer: Repair