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 Flashcard 1 of 5

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

Answer: Cesium

Radiation Oncology Basics Flashcard 2 of 5

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

Answer: Radiotherapy

Radiation Oncology Basics Flashcard 3 of 5

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

Answer: 7000-8000

Radiation Oncology Basics Flashcard 4 of 5

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

Answer: gating

Radiation Oncology Basics Flashcard 5 of 5

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

Answer: Conventional