Radiation Oncology Basics Practice Questions

Q: Low dose radiotherapy is indicated for which of the following conditions?

Seminoma. **Explanation:** The correct answer is **Seminoma**. This question tests the concept of **radiosensitivity**, which refers to how susceptible a specific tumor cell type is to ionizing radiation. **1. Why Seminoma is correct:** Seminoma (a germ cell tumor of the testis) is one of the most **radiosensitive** tumors in the human body. Because the cells are highly undifferentiated and have a high mitotic index, they undergo apoptosis even at low doses of radiation. In clinical practice, prophylactic or therapeutic nodal irradiation for Stage I/II seminoma typically requires doses as low as **20–30 Gy**, whereas most epithelial cancers require 60–70 Gy. **2. Why the other options are incorrect:** * **Malignant Melanoma:** Historically considered **radioresistant**. It has a high capacity for repairing sublethal radiation damage. While high-dose "hypofractionated" radiation is sometimes used for palliation, it does not respond to low doses. * **Osteosarcoma & Chondrosarcoma:** These are bone-forming and cartilage-forming tumors, respectively. They are characterized by slow growth fractions and dense extracellular matrices, making them highly **radioresistant**. Surgery is the primary treatment; radiation is rarely effective unless used in extremely high doses for unresectable cases. **Clinical Pearls for NEET-PG:** * **Highly Radiosensitive Tumors:** Seminoma, Dysgerminoma, Lymphoma, Ewing’s Sarcoma, and Wilms’ Tumor. * **Radioresistant Tumors:** Osteosarcoma, Chondrosarcoma, Malignant Melanoma, and Renal Cell Carcinoma (RCC). * **Bergonie-Tribondeau Law:** Cells are more radiosensitive if they have a high mitotic rate, a long mitotic future, and are least specialized (undifferentiated). * **Mnemonic for Radiosensitivity:** *"**S**ome **L**ittle **E**nglish **W**hite **D**ogs"* (Seminoma, Lymphoma, Ewing’s, Wilms, Dysgerminoma).

Q: What does a linear accelerator (LINAC) produce in radiation therapy?

X-rays and electrons. ***X-rays and electrons*** - A linear accelerator (LINAC) accelerates **electrons** to high energies, which can be used directly as an **electron beam** to treat superficial tumors. - To treat deeper tumors, these high-energy **electrons** are made to strike a heavy metal target (like tungsten), which then produces high-energy **X-rays** (photons) through a process called **bremsstrahlung**. *Alpha and beta rays* - **Alpha particles** (helium nuclei) and **beta particles** (electrons from nuclear decay) are forms of particulate radiation emitted by radioactive substances, not generated by a LINAC. - While the LINAC beam consists of electrons, it does not produce **alpha particles**, which have very low penetration and are not used in external beam radiotherapy. *X-rays and gamma rays* - A LINAC produces **X-rays**, but not **gamma rays**. Although both are high-energy photons, their origin differs. - **Gamma rays** are emitted from the nucleus of a decaying radioactive atom (e.g., Cobalt-60), whereas **X-rays** from a LINAC are produced extranuclearly when electrons interact with a target. *Neutrons and positrons* - **Neutron therapy** is a specialized form of radiation that requires different equipment, like a cyclotron, and is not a primary output of a standard medical LINAC. - **Positrons** are the antimatter counterpart of electrons and are used in diagnostic imaging (**Positron Emission Tomography or PET**), not for therapeutic purposes in a LINAC.

Q: A cancer patient undergoing radiotherapy is given a dose of 1.8 to 2 Gy once daily for 5 days per week for a duration of 6 to 8 weeks. What is this type of radiotherapy called?

Regular Fractionated radiotherapy. ***Regular Fractionated radiotherapy***- This schedule uses biologically effective doses typically between **1.8 to 2.0 Gy** delivered once per day, 5 days per week, which is the standard of care for many cancers.- This conventional fractionation regimen allows for optimal **tumor cell kill** while providing sufficient time for normal tissues to repair sublethal damage between fractions (the principle of **Repair**).*Hyper fractionated radiotherapy*- This involves giving smaller doses per fraction (typically **<1.8 Gy**) delivered **more than once a day**.- The goal is often to reduce **late toxicities** to normal tissues while sometimes escalating the total dose delivered.*Accelerated fractionation radiotherapy*- This approach delivers the total treatment dose over a **significantly shorter overall treatment time** than standard fractionation, often involving multiple fractions per day or higher daily doses.- It is primarily used to counteract the effects of **accelerated tumor cell repopulation** during the course of treatment.*Brachytherapy*- This is a type of radiotherapy where the radiation source (sealed isotopes) is placed **inside or next to the tumor** (internal radiation), which is a delivery technique, not an external fractionation schedule.- It can be delivered as **High Dose Rate (HDR)** or **Low Dose Rate (LDR)** therapy.

Q: Most favorable prognosis after radiotherapy is in -

Seminoma. ***Seminoma*** - **Seminoma** is highly **radiosensitive**, meaning it responds very well to radiation therapy, leading to excellent oncological outcomes. - Due to its sensitivity, even advanced seminomas can often be cured with radiotherapy, contributing to a **favorable prognosis**. *Teratoma* - **Teratomas** are generally **radioresistant**, meaning they do not respond well to radiation therapy. - Treatment for teratomas typically involves **surgical resection**, as radiation is largely ineffective. *Desmoid* - **Desmoid tumors** (aggressive fibromatosis) are locally aggressive but rarely metastasize, and their response to radiotherapy is variable. - While radiation can be used for local control, the prognosis is often complicated by **local recurrence** and challenging surgical margins. *Melanoma* - **Melanoma** is notoriously **radioresistant**, making radiation therapy a less effective primary treatment option. - It is often used for **palliative care** or in cases of local recurrence, but rarely leads to a cure or favorable prognosis when used alone.

Q: Principles used in Radio Therapy are:

Ionizing radiation. ***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.

Q: All of the following are indications for Gamma Knife Radiosurgery EXCEPT

Brain tumours or lesions 4 cm or larger in diameter. ***Brain tumours or lesions 4 cm or larger in diameter*** - **Gamma Knife radiosurgery** is typically used for **small to medium-sized lesions** (generally less than 3-4 cm in diameter). - Larger lesions carry a **higher risk of cerebral edema** and radiation necrosis when treated with radiosurgery, making conventional surgery or fractionated radiotherapy more appropriate. *Acoustic neuroma* - **Gamma Knife radiosurgery** is a well-established treatment option for **acoustic neuromas** (vestibular schwannomas). - It aims to control tumor growth and preserve hearing and facial nerve function with a high success rate. *Arteriovenous malformation* - **Arteriovenous malformations (AVMs)** are commonly treated with **Gamma Knife radiosurgery** to induce thrombosis and obliteration of the abnormal vascular nidus. - This treatment helps in preventing future hemorrhage and reducing seizure risk. *Trigeminal neuralgia* - **Gamma Knife radiosurgery** is an effective treatment for **refractory trigeminal neuralgia**. - It delivers a highly focused dose of radiation to the trigeminal nerve root, creating a lesion that disrupts the pain signals.

Q: Stereotactic Radiosurgery is a form of –

Radiotherapy. ***Radiotherapy*** - **Stereotactic radiosurgery** is a highly precise form of **radiotherapy** that delivers a single high dose or multiple fractionated high doses of radiation to a specific target area. - It uses focused **radiation beams** to treat tumors or other lesions, often as an alternative to conventional surgery, by causing damage to the DNA of target cells. *Radioiodine therapy* - **Radioiodine therapy** primarily uses **iodine-131** to treat thyroid conditions like hyperthyroidism or thyroid cancer. - This involves the patient ingesting a radioactive isotope, unlike the external radiation beams used in radiosurgery. *Cryo Surgery* - **Cryosurgery** involves the use of **extreme cold** to destroy abnormal tissues. - It is a physical method of tissue destruction and does not involve radiation. *Robotic Surgery* - **Robotic surgery** utilizes robotic systems to assist in performing surgical procedures, enhancing precision, and control for the surgeon. - This is a mode of performing traditional surgery and does not involve radiation as its primary therapeutic agent.

Q: What is the radiation tolerance of the whole liver?

30 Gy. ***30 Gy*** - The **whole liver** has a relatively low radiation tolerance, with a typical threshold for developing **radiation-induced liver disease (RILD)** around 30-35 Gy for conventional fractionation. - Exceeding this dose to a significant volume of the liver can lead to **hepatic dysfunction** and failure. *45 Gy* - This dose is generally too high for whole-liver irradiation and would significantly increase the risk of **severe liver toxicity** in many patients. - While small volumes might tolerate higher doses, the **mean dose to the entire organ** should remain much lower. *15 Gy* - This dose is typically considered well below the tolerance limit for the whole liver and is unlikely to cause significant complications. - It might be used for palliation or as a component of fractionated regimens with higher doses to smaller target volumes. *40 Gy* - This dose is generally considered above the safe limits for irradiating the **entire liver**, posing a substantial risk of **radiation-induced liver damage**. - While some highly conformal techniques might deliver this to very small, localized tumors, it is not the tolerance for the **whole organ**.

Q: In cervical cancer brachytherapy, the primary reference point for dose prescription is -

Point A. ***Point A*** - **Point A** is defined as 2 cm lateral to the central canal of the uterus and 2 cm superior to the external os, representing a dose estimation to the **parametrium** and a critical reference for tumoricidal dose. - This point serves as the **primary prescription and reporting point** for brachytherapy in cervical cancer, as it is highly correlated with treatment outcomes and complications. - Established by **ICRU Report 38** as the standard reference point for dose prescription. *Point B* - **Point B** is located 5 cm from the midline (3 cm lateral to Point A) at the level of Point A, and is primarily used to estimate the dose received by the **pelvic side wall** and regional lymphatics. - It provides an indication of dose to structures further from the applicator but is **not the primary prescription point** for the target volume in brachytherapy. *Side walls of pelvis* - The dose to the **side walls of the pelvis** is relevant for assessing potential toxicity to structures like the obturator nerve and external iliac vessels, and for ensuring adequate coverage of pelvic lymph nodes. - While critical for treatment planning, the side walls themselves are not a primary dose prescription point but rather a **region of interest** for dose constraints and coverage. *Point H* - **Point H** represents the reference point for estimating the dose to the **rectum** in brachytherapy, located at the posterior vaginal wall. - While important for assessing **rectal toxicity** and as a dose-limiting structure, Point H is used for reporting organ-at-risk doses, not for primary tumor dose prescription.

Question 1

Low dose radiotherapy is indicated for which of the following conditions?

Accepted Answer

Seminoma

Answer

Malignant melanoma

Answer

Osteosarcoma

Answer

Chondrosarcoma

Question 2

What is the advantage of brachytherapy?

Accepted Answer

Can be given in all malignancies

Answer

Non-invasive

Answer

Less radiation hazard to normal tissue

Answer

Maximum radiation to diseased tissue

Question 3

What does a linear accelerator (LINAC) produce in radiation therapy?

Accepted Answer

X-rays and electrons

Answer

Alpha and beta rays

Answer

X-rays and gamma rays

Answer

Neutrons and positrons

Question 4

A cancer patient undergoing radiotherapy is given a dose of 1.8 to 2 Gy once daily for 5 days per week for a duration of 6 to 8 weeks. What is this type of radiotherapy called?

Accepted Answer

Regular Fractionated radiotherapy

Answer

Hyper fractionated radiotherapy

Answer

Brachytherapy

Answer

Accelerated fractionation radiotherapy

Question 5

Most favorable prognosis after radiotherapy is in -

Accepted Answer

Seminoma

Answer

Teratoma

Answer

Desmoid

Answer

Melanoma

Question 6

Principles used in Radio Therapy are:

Accepted Answer

Ionizing radiation

Answer

Ultrasonic effect

Answer

Charring of nucleoprotein

Answer

Infrared rays

Question 7

All of the following are indications for Gamma Knife Radiosurgery EXCEPT

Accepted Answer

Brain tumours or lesions 4 cm or larger in diameter

Answer

Acoustic neuroma

Answer

Arteriovenous malformation

Answer

Trigeminal neuralgia

Question 8

Stereotactic Radiosurgery is a form of –

Accepted Answer

Radiotherapy

Answer

Radioiodine therapy

Answer

Cryosurgery

Answer

Robotic Surgery

Question 9

What is the radiation tolerance of the whole liver?

Accepted Answer

30 Gy

Answer

45 Gy

Answer

15 Gy

Answer

40 Gy

Question 10

In cervical cancer brachytherapy, the primary reference point for dose prescription is -

Accepted Answer

Point A

Answer

Point B

Answer

Side walls of pelvis

Answer

Point H

Radiation Oncology Basics — MCQs

Radiation Oncology Basics — MCQs

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