Radiation Oncology Basics Practice Questions

Q: Which is the treatment of choice for irradiation in Chordoma?

Protons. ***Protons*** - **Proton therapy** is the treatment of choice for chordoma due to its ability to deliver a high dose of radiation precisely to the tumor while sparing surrounding healthy tissues, crucial for tumors located near critical structures like the brainstem or spinal cord. - The **Bragg peak** associated with proton beams allows for a sharp drop-off in dose beyond the target, minimizing damage to adjacent normal tissue. *Electron therapy* - **Electron beams** have a limited penetration depth and are primarily used for superficial tumors. - Chordomas are typically deep-seated tumors, making electron therapy ineffective for delivering a sufficient dose to the entire tumor volume. *Gamma knife surgery* - **Gamma knife surgery** is a form of stereotactic radiosurgery primarily used for small, well-defined tumors, often in the brain. - Chordomas are often larger, irregularly shaped, and can be located in areas not suitable for a single-fraction, high-dose treatment like Gamma Knife radiosurgery. *3D conformal radiation therapy* - While **3D conformal radiation therapy (3D-CRT)** can shape radiation beams to the tumor, it delivers a continuous dose through the entire path of the beam, leading to a higher dose to surrounding healthy tissues compared to proton therapy. - The limitations of 3D-CRT in sparing adjacent critical structures make it generally less favorable than proton therapy for chordomas, especially in complex anatomical locations.

Q: What is the primary indication for stereotactic radiosurgery?

Brain metastases. ***Brain metastases*** - Stereotactic radiosurgery (SRS) is a highly effective primary or adjuvant treatment for patients with a limited number of **brain metastases**, especially those smaller than 3-4 cm. - It offers precise, high-dose radiation to the tumor with minimal damage to surrounding healthy brain tissue, making it ideal for treating multiple lesions without whole-brain radiation side effects. *Primary brain tumors (general category)* - While SRS can be used for some primary brain tumors, the overarching category is too broad to be the *primary* indication, as many primary brain tumors, like **glioblastoma multiforme**, require more extensive treatment. - The use of SRS for primary tumors depends heavily on their type, size, location, and whether they are **recurrent** or **inoperable**. *Medulloblastoma (a type of brain tumor)* - Medulloblastoma is typically treated with a combination of **surgery, craniospinal radiation**, and **chemotherapy** due to its propensity for CSF spread. - SRS is not a primary treatment for medulloblastoma and is generally reserved for rare, localized recurrences rather than initial management. *Meningioma (a type of benign brain tumor)* - SRS is a viable option for **meningiomas**, particularly those that are small, inoperable, or recurrent after surgery. - However, brain metastases represent a more common and frequent indication where SRS is often the first-line radiation treatment due to their distinct characteristics and radioresponsiveness.

Q: In which of the following cancers is intraoperative radiotherapy (IORT) applicable?

All of the options. ***All of the options*** - **Intraoperative radiotherapy (IORT)** is applicable to all three cancers listed: gastric cancer, colon carcinoma, and pancreatic carcinoma. - IORT is a technique where a **single, high dose of radiation** is delivered to the tumor bed during surgery to improve local control and reduce late toxicity to surrounding healthy tissues. - All three cancers benefit from IORT due to their **high risk of local recurrence** and the ability to directly target the tumor bed while sparing adjacent critical organs. **Gastric cancer:** - IORT addresses **high rates of local recurrence** after conventional surgery, especially in locally advanced stages - Allows direct radiation of potentially involved regional lymph nodes or margins difficult to eradicate surgically - Particularly useful when complete surgical clearance carries excessive morbidity risk **Colon carcinoma:** - IORT considered in **locally advanced or recurrent disease**, particularly when tumors invade adjacent structures - Beneficial after resections with positive or close margins - Delivers high dose to microscopic residual disease in the tumor bed, avoiding damage to vital organs from external beam radiotherapy **Pancreatic carcinoma:** - High propensity for **local invasion and recurrence** makes IORT particularly relevant - Delivers high dose directly to tumor bed following resection when microscopic residual disease is suspected - Overcomes limitations of external beam radiation due to proximity of critical organs (duodenum, stomach, kidneys)

Q: Precisely directed high dose radiation is used in which of the following therapies?

Stereotactic radiosurgery. ***Stereotactic radiosurgery*** - **Stereotactic radiosurgery (SRS)** is a highly precise radiation therapy that uses focused, high-dose radiation beams to target small tumors or abnormalities with **sub-millimeter accuracy**. - It delivers **very high doses per fraction** (typically 15-24 Gy in a single session) using stereotactic guidance systems. - Commonly used for **brain metastases, AVMs, acoustic neuromas**, and other small intracranial targets. *IMRT* - **Intensity-modulated radiation therapy (IMRT)** is an advanced form of 3D-conformal radiation therapy that modulates beam intensity to conform to tumor shape. - While IMRT is precise, it uses **conventional fractionation** (1.8-2 Gy per fraction over many treatments), not the high-dose approach of SRS. *EBRT* - **External beam radiation therapy (EBRT)** is a general term for radiation delivered from outside the body. - It encompasses various techniques but *does not specifically indicate the **stereotactic precision and high-dose per fraction** characteristic of SRS*. *Brachytherapy* - **Brachytherapy** involves placing radioactive sources **directly inside or next to the tumor**. - While it delivers high doses locally, it is not "precisely directed high-dose radiation" from external beams like SRS.

Q: What is the standard radiation dose to point A in the cervix for brachytherapy in the treatment of cervical cancer?

8000 rad. ***8000 rad*** - The standard **total cumulative radiation dose** to **Point A** in the cervix for the treatment of cervical cancer is approximately **8000 rad (80 Gy)**. - This represents the **combined dose** from external beam radiation therapy (EBRT, typically 45-50 Gy) plus intracavitary brachytherapy (typically 30-40 Gy to Point A). - Point A is a classical reference point defined as **2 cm superior to the external cervical os and 2 cm lateral to the uterine canal**, representing the location where the uterine artery crosses the ureter. - This total dose aims to provide adequate tumor control while minimizing toxicity to surrounding organs like the bladder and rectum. *6000 rad* - A total dose of **6000 rad** is insufficient for definitive local control of cervical cancer. - This dose is below the therapeutic threshold and would result in significantly higher rates of local recurrence and treatment failure. - Adequate doses are essential for curative intent in cervical cancer management. *10000 rad* - A dose of **10000 rad** to Point A would be excessively high and significantly increase the risk of severe acute and late toxicities to surrounding tissues. - Such a high dose could lead to serious complications including **rectovaginal or vesicovaginal fistulas, proctitis, cystitis, bowel strictures, and tissue necrosis**. - The therapeutic window would be exceeded, causing more harm than benefit. *4000 rad* - A dose of **4000 rad** would be substantially lower than the standard therapeutic dose for cervical cancer. - This suboptimal dose would likely result in **inadequate tumor control and increased risk of local recurrence**. - It is far below the dose required for curative treatment of cervical cancer.

Q: For the treatment of deep-seated tumors, the following rays are used:

X rays and Gamma rays. ***X rays and Gamma rays*** - **X-rays** and **gamma rays** are high-energy electromagnetic radiation capable of penetrating deep into tissues to target deep-seated tumors. - They induce DNA damage in cancer cells, leading to cell death and tumor regression, making them mainstays in **radiation therapy**. *Alpha rays and Beta rays* - **Alpha particles** have a very short range and high linear energy transfer, making them suitable for superficial tumors or targeted internal delivery rather than deep-seated tumors. - **Beta particles** have a medium range in tissue but are generally less penetrating than X-rays or gamma rays, limiting their effectiveness for deep lesions. *Electrons and positrons* - **Electron beams** are used for superficial tumors due to their limited penetration depth, typically reaching only a few centimeters into tissue. - **Positrons** are used in imaging (PET scans) and are not directly used for therapeutic tumor ablation, as their annihilation with electrons produces gamma rays, but they themselves don't treat tumors. *High power laser beams* - **Laser beams** are primarily used for superficial tissue ablation, cutting, or coagulation in surgical procedures due to their limited direct penetration into deep tissues without significant scattering and absorption. - While lasers can be used in some interstitial tumor treatments, they are not a primary method for treating large, deep-seated tumors due to their localized effect and lack of volumetric penetration.

Q: Which of the following radioisotopes is commonly used as a source for external beam radiotherapy in the treatment of cancer patients?

Cobalt - 60. ***Cobalt - 60*** - **Cobalt-60** is a radioisotope that emits high-energy gamma rays, making it suitable for deep tissue penetration in **external beam radiotherapy**. - Its decay produces gamma rays of 1.17 and 1.33 MeV, which are effective in **damaging cancer cells' DNA**. *Strontium - 89* - **Strontium-89** is a **beta-emitter** primarily used for **palliative treatment of bone metastases**, not external beam radiotherapy. - It accumulates in areas of increased bone turnover, providing localized pain relief. *Radium - 226* - **Radium-226** was historically used in brachytherapy but is now largely replaced due to its long half-life and production of **alpha particles** and **radon gas**, posing significant safety concerns. - Its primary therapeutic use involved internal placement in tumors. *Cobalt - 59* - **Cobalt-59** is the only **stable isotope of cobalt** and is not radioactive, thus it cannot be used as a source for radiotherapy. - It is used in various applications, but not for radiation therapy.

Q: Which one of the following radioisotopes is not used as a permanent implant?

Caesium-137. ***Caesium-137*** - **Caesium-137** is primarily used in **high-dose-rate (HDR) brachytherapy** or teletherapy, where the source is temporarily placed to deliver a high dose over a short period. - Its **long half-life** (30.17 years) and high energy gamma emissions make it unsuitable for permanent implants, as it would expose patients to radiation for an extended and unsafe duration. *Iodine-125* - **Iodine-125** is a commonly used radioisotope for **permanent prostate brachytherapy implants** due to its relatively low energy and long half-life (59.4 days). - Its **low photon energy** allows for precise dose delivery within the target tissue with minimal dose to surrounding healthy tissues. *Palladium-103* - **Palladium-103** is another radioisotope frequently used in **permanent prostate brachytherapy implants**, similar to Iodine-125. - It has a shorter half-life (17 days) and lower energy compared to Iodine-125, making it suitable for treating **faster-growing tumors** that require a quicker dose delivery. *Gold-198* - **Gold-198** is a historical radioisotope used for **permanent interstitial implants**, particularly for head and neck cancers or sometimes prostate. - It has a relatively short half-life (2.7 days) and emits both beta particles and gamma rays, which can be useful for localized treatment but less commonly used now compared to Iodine-125 or Palladium-103.

Q: Which is used in both teletherapy and brachytherapy?

Cobalt 60. ***Cobalt 60*** - **Cobalt-60** is the correct answer as it is used in both **teletherapy and brachytherapy**. - **Teletherapy**: Cobalt-60 teletherapy machines (cobalt units) have been widely used for external beam radiation therapy and remain in use globally. - **Brachytherapy**: Cobalt-60 is used in both low-dose rate (LDR) and high-dose rate (HDR) brachytherapy applications, with Co-60 seeds and sources for various tumor sites. - Its high energy (1.17 and 1.33 MeV gamma rays) and suitable half-life (5.27 years) make it versatile for both modalities. *Iridium 192* - **Iridium-192** is predominantly used in **HDR brachytherapy** as a temporary implant source. - It is the most common radioisotope for modern HDR brachytherapy systems. - While it emits gamma radiation, it is **not routinely used for teletherapy** in clinical practice due to its lower energy and shorter half-life (74 days). *Palladium* - **Palladium-103** is used exclusively in **low-dose rate (LDR) brachytherapy**, particularly for permanent seed implants in prostate cancer. - Its lower energy photons and short half-life (17 days) make it unsuitable for teletherapy. *Iodine 131* - **Iodine-131** is primarily used in **nuclear medicine** for thyroid cancer treatment and hyperthyroidism (targeted radionuclide therapy). - It is not used for conventional external beam teletherapy or brachytherapy implants.

Q: The element used for intracavitary brachytherapy in carcinoma of the cervix is:

Caesium-137. ***Caesium-137*** - **Caesium-137** is the most commonly used radioisotope for **intracavitary brachytherapy** in cervical carcinoma due to its suitable half-life and gamma-ray energy. - It allows for effective localized radiation delivery to the tumor while minimizing exposure to surrounding healthy tissues. *Cobalt-60* - While **Cobalt-60** is a radioisotope used in radiation therapy, its higher energy and longer half-life make it more suitable for **external beam radiotherapy** rather than intracavitary brachytherapy. - Its use in brachytherapy is less common compared to Caesium-137 for cervical cancer. *Radio iodine* - **Radio iodine (Iodine-131)** is primarily used for the treatment of **thyroid cancers** and hyperthyroidism, as the thyroid gland selectively absorbs iodine. - It is not indicated for the treatment of **cervical carcinoma**. *Strontium* - **Strontium-90** is a beta-emitting radioisotope primarily used in **superficial brachytherapy** for conditions like pterygium, not deep-seated tumors like cervical cancer. - Its beta radiation has limited penetration depth, making it unsuitable for intracavitary treatment of the cervix.

Question 1

Which is the treatment of choice for irradiation in Chordoma?

Accepted Answer

Protons

Answer

Electron therapy

Answer

Gamma knife surgery

Answer

3D conformal radiation therapy

Question 2

What is the primary indication for stereotactic radiosurgery?

Accepted Answer

Brain metastases

Answer

Medulloblastoma

Answer

Primary brain tumors

Answer

Meningioma

Question 3

In which of the following cancers is intraoperative radiotherapy (IORT) applicable?

Accepted Answer

All of the options

Answer

Gastric cancer

Answer

Colon carcinoma

Answer

Pancreatic carcinoma

Question 4

Precisely directed high dose radiation is used in which of the following therapies?

Accepted Answer

Stereotactic radiosurgery

Answer

EBRT

Answer

IMRT

Answer

Brachytherapy

Question 5

What is the standard radiation dose to point A in the cervix for brachytherapy in the treatment of cervical cancer?

Accepted Answer

8000 rad

Answer

6000 rad

Answer

10000 rad

Answer

4000 rad

Question 6

For the treatment of deep-seated tumors, the following rays are used:

Accepted Answer

X rays and Gamma rays

Answer

Alpha rays and Beta rays

Answer

Electrons and positrons

Answer

High power laser beams

Question 7

Which of the following radioisotopes is commonly used as a source for external beam radiotherapy in the treatment of cancer patients?

Accepted Answer

Cobalt - 60

Answer

Cobalt - 59

Answer

Strontium - 89

Answer

Radium - 226

Question 8

Which one of the following radioisotopes is not used as a permanent implant?

Accepted Answer

Caesium-137

Answer

Iodine-125

Answer

Palladium-103

Answer

Gold-198

Question 9

Which is used in both teletherapy and brachytherapy?

Accepted Answer

Cobalt 60

Answer

Iodine 131

Answer

Iridium 192

Answer

Palladium

Question 10

The element used for intracavitary brachytherapy in carcinoma of the cervix is:

Accepted Answer

Caesium-137

Answer

Radio iodine

Answer

Cobalt-60

Answer

Strontium

Radiation Oncology Basics — MCQs

Radiation Oncology Basics — MCQs

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