Radiation Therapy: Types and Side Effects 

What are the main categories of radiation therapy based on delivery method?

 External beam radiation therapy (EBRT) and internal radiation therapy (brachytherapy

·  External Beam Radiation Therapy (EBRT):

• In this method, the radiation source is outside the patient’s body.
• A machine, such as a linear accelerator, directs high-energy beams of radiation towards the cancerous tumor from various angles.
• EBRT is a local treatment, meaning it targets a specific area of the body where the cancer is located. For instance, if someone has lung cancer, the radiation will be directed at their chest.
• This is the most common type of radiation therapy used to treat many different kinds of cancer.
• Patients typically receive EBRT in outpatient sessions over several weeks. The treatments are usually painless and last only a few minutes, although the setup time might be longer.

·  Internal Radiation Therapy (Brachytherapy):

• Also known as brachytherapy or “seed implantation,” this method involves placing a radioactive source inside the patient’s body, directly into or near the tumor.
• The radioactive material is often sealed in small devices like seeds, pellets, ribbons, wires, needles, balloons, or tubes (implants).
• This allows for a higher dose of radiation to be delivered to a smaller area, minimizing damage to surrounding healthy tissues.
• The placement of the implant can be temporary or permanent.
  • Temporary brachytherapy: The radioactive source is placed for a specific time (from minutes to days) and then removed. This can be done at a low dose rate (LDR) over a longer period or a high dose rate (HDR) over a shorter period.
  • Permanent brachytherapy (seed implantation): Small radioactive seeds are implanted in or near the tumor and remain there. They release radiation over time and eventually become inactive.
• Brachytherapy is used to treat various cancers, including prostate, cervical, endometrial, vaginal, breast, and eye cancers.

 

What are different types of EBRT?

3D-CRT, IMRT, IGRT, SBRT/SRS, proton therapy

1. 3D-Conformal Radiation Therapy (3D-CRT):
   • This technique uses sophisticated imaging (like CT scans) to create a three-dimensional picture of the tumor and surrounding healthy tissues.  
   • Radiation beams are then shaped and directed from multiple angles to conform precisely to the tumor’s shape.  
   • The goal is to deliver a high dose of radiation to the tumor while minimizing the dose to nearby critical organs and normal tissues.  
   • 3D-CRT was a significant advancement over traditional 2D radiation therapy, offering improved accuracy.  
2. Intensity-Modulated Radiation Therapy (IMRT):
   • IMRT is a more advanced form of 3D-CRT. It not only shapes the radiation beams to the tumor but also modulates (varies) the intensity of the radiation within each beam.  
   • This allows for even more precise targeting of the tumor and further reduction of radiation exposure to surrounding healthy tissues, especially complexly shaped tumors or those located near sensitive structures.  
   • IMRT can deliver different doses of radiation to different parts of the tumor, potentially increasing the dose to the most aggressive areas while limiting it to more sensitive regions within or adjacent to the tumor.
3. Image-Guided Radiation Therapy (IGRT):
   • IGRT involves using imaging techniques (like X-rays, CT scans, ultrasound, or MRI) before and sometimes during each radiation treatment session.
   • These images help to verify the patient’s position and the tumor’s location, accounting for any movement or changes that might have occurred since the initial treatment planning.
   • By ensuring accurate targeting daily, IGRT allows for the delivery of higher doses of radiation to the tumor while further minimizing damage to healthy tissues. IGRT is often used in conjunction with IMRT and other advanced techniques.  
4. Stereotactic Body Radiation Therapy (SBRT) and Stereotactic Radiosurgery (SRS):
   • These techniques deliver very high doses of precisely focused radiation to small, well-defined tumors in a limited number of treatment sessions (typically 1 to 5).
   • SRS traditionally refers to the treatment of tumors in the brain and spine, often in a single session. It requires highly specialized equipment and meticulous patient immobilization (e.g., with a head frame). Despite the name “surgery,” it is non-invasive.  
   • SBRT extends the principles of SRS to treat tumors in other parts of the body (e.g., lung, liver, prostate). It may involve a few more treatment fractions than SRS.  
   • Both SBRT and SRS rely on sophisticated imaging and precise beam delivery to ablate the tumor while sharply limiting radiation to surrounding healthy tissues.  
5. Proton Therapy:
   • Instead of using X-rays (photons), proton therapy uses beams of protons.  
   • Protons have a unique property: they deposit most of their energy at a specific depth (called the Bragg peak) and then stop, delivering very little radiation beyond the target.  
   • This allows for potentially less radiation exposure to healthy tissues located beyond the tumor compared to photon-based therapies, which continue to deposit some dose as they exit the body.
   • Proton therapy is particularly beneficial for treating tumors located near critical structures, in children (to minimize long-term side effects), and for certain types of cancers where minimizing exit dose is crucial. However, it is a more expensive and less widely available technology than traditional EBRT.  

How does brachytherapy work?

Radioactive source placed inside or near the tumor

Brachytherapy, also known as internal radiation therapy, works by placing a radioactive source directly inside or very close to the tumor. This allows for a high dose of radiation to be delivered to a small, targeted area, minimizing damage to the surrounding healthy tissues. Here’s a more detailed breakdown of the process:  

1. Placement of the Radioactive Source:
   • The radioactive material is typically sealed within a small device, such as a seed, pellet, wire, ribbon, needle, balloon, or tube (an implant).  
   • The method of placement depends on the type and location of the cancer. It can involve:
     • Intracavitary placement: The device containing the radioactive source is placed in a body cavity near the tumor, such as the vagina, uterus, or windpipe.  
     • Interstitial placement: The device is inserted directly into the tumor tissue, for example, in the prostate or breast.  
     • Surface mold brachytherapy: A radioactive source is placed in a mold that fits over the surface of the area being treated, often used for skin cancers.  
     • Intraluminal brachytherapy: The source is placed within a body tube or passageway, like the esophagus or trachea.  
2. Delivery of Radiation:
   • Once the radioactive source is in place, it emits radiation that directly targets the cancer cells.
   • The high concentration of radiation at the tumor site helps to destroy or damage the cancer cells, preventing them from growing and dividing.  
   • Because the radiation travels only a short distance from the source, the exposure to nearby healthy tissues is significantly reduced compared to external beam radiation therapy.  
3. Temporary vs. Permanent Brachytherapy:
   • Temporary Brachytherapy: The radioactive source is placed in the body for a specific amount of time (ranging from minutes to days) and then removed. This allows for a concentrated dose of radiation to be delivered over a defined period.
     • High-Dose Rate (HDR) brachytherapy: Delivers a high dose of radiation in a short time (minutes per session), and the source is removed after each session. Patients may have multiple HDR treatments over several days.
     • Low-Dose Rate (LDR) brachytherapy: Delivers a lower dose of radiation continuously over a longer period (hours or days). This often requires a hospital stay in a private room with radiation safety precautions in place until the source is removed.
     • Pulsed-Dose Rate (PDR) brachytherapy: Delivers radiation in short pulses over a period of hours or days.

3. Permanent Brachytherapy (Seed Implantation): Small radioactive seeds (about the size of a grain of rice) are implanted directly into the tumor and remain there permanently. These seeds release radiation slowly over several weeks or months and eventually become inactive.
4. Imaging Guidance:
   • Throughout the brachytherapy procedure, imaging techniques such as ultrasound, CT scans, or MRI are used to guide the placement of the radioactive source and ensure it is accurately positioned to target the tumor.  

What are different types of brachytherapy?

Interstitial, intracavitary, surface

1. Interstitial Brachytherapy:
   • In this type, the radioactive source is placed directly into the tumor or the tissue surrounding it.  
   • This is achieved using needles, wires, catheters, or small seeds that are implanted into the target area.
   • Interstitial brachytherapy is commonly used to treat cancers of the prostate, breast, soft tissues (sarcomas), head and neck, and gynecological cancers.
   • The implants can be temporary (removed after a specific time) or permanent (left in the body, where they gradually lose their radioactivity).  
2. Intracavitary Brachytherapy:
   • Here, the radioactive source is placed within a body cavity that is close to the tumor.  
   • Applicators, such as cylinders or ovoids, are inserted into the cavity (e.g., vagina, uterus, esophagus, bronchus) and the radioactive material is placed inside them.  
   • This method is frequently used to treat gynecological cancers (cervical, endometrial, vaginal), as well as some lung and esophageal cancers.
   • Intracavitary brachytherapy is typically a temporary treatment, with the applicators and radioactive source removed after the prescribed dose is delivered.  
3. Surface Brachytherapy (Mold Brachytherapy):
   • In this technique, the radioactive source is placed on the surface of the body near the skin cancer or other superficial lesion.  
   • Custom-made molds or applicators that conform to the treated area hold the radioactive material in close contact with the surface.  
   • This type of brachytherapy is primarily used to treat skin cancers (basal cell carcinoma, squamous cell carcinoma) and Kaposi’s sarcoma.
   • Surface brachytherapy is usually a temporary treatment, with the mold and radioactive source removed after each treatment session.

What is the difference between external and internal radiation?

External delivers radiation from outside the body, internal from a source inside the body

• External Radiation Therapy (EBRT) delivers radiation from a source outside the patient’s body, directed at the tumor.  
• Internal Radiation Therapy (Brachytherapy) delivers radiation from a radioactive source placed inside the patient’s body, directly within or near the tumor.  

What is stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT)?

Highly precise forms of EBRT delivering high doses in few fractions

Stereotactic Radiosurgery (SRS):

• Historically focused on the brain and spine: SRS was initially developed for treating small to medium-sized tumors and other abnormalities within the brain and spine.
• Often a single fraction: Typically delivered in just one treatment session, although sometimes a few fractions (hypofractionation) are used.  
• Requires rigid immobilization: Due to the high precision needed, patients often require a rigid head frame or other immobilization devices to prevent any movement during treatment.  
• Non-invasive: Despite the name “surgery,” SRS is a non-surgical procedure.  
• Examples of treated conditions: Brain metastases, primary brain tumors (e.g., meningiomas, acoustic neuromas), arteriovenous malformations (AVMs), trigeminal neuralgia.  

Stereotactic Body Radiation Therapy (SBRT):

• Extends the principles to the rest of the body: SBRT applies the same high-precision, high-dose-per-fraction approach to tumors located outside the brain and spine (e.g., in the lungs, liver, prostate, adrenal glands, bones, lymph nodes).  
• Typically delivered in a few fractions: SBRT usually involves 2 to 5 treatment sessions, sometimes more depending on the tumor and location.  
• Requires sophisticated immobilization and motion management: Treating areas outside the brain and spine necessitates advanced techniques to account for patient movement and organ motion (e.g., respiratory gating, compression devices).  
• Also non-invasive: Like SRS, SBRT is a non-surgical radiation delivery method.  
• Examples of treated conditions: Early-stage lung cancer, liver metastases, adrenal tumors, oligometastatic disease (cancer that has spread to a limited number of sites).  

What is proton therapy, and how does it differ from traditional

photon (X-ray) radiation?

Uses protons instead of photons, allowing for more precise targeting and reduced exit dose

Proton Therapy:

• Uses Protons: Instead of photons (which are electromagnetic radiation with no mass), proton therapy utilizes beams of protons, which are positively charged subatomic particles with mass. These protons are accelerated to very high speeds.  
• The Bragg Peak: The fundamental advantage of proton therapy lies in a unique physical property called the Bragg peak. As protons travel through tissue, they deposit a relatively small amount of energy along their path. However, at a specific depth determined by the initial energy of the proton beam, they release the majority of their energy in a very narrow peak – this is the Bragg peak. After the Bragg peak, the proton beam stops, depositing virtually no further dose beyond the target.  
• Precise Targeting: By carefully controlling the energy of the proton beam, radiation oncologists can precisely position the Bragg peak to coincide with the tumor’s location and depth. This allows for a high dose of radiation to be delivered directly to the tumor while significantly reducing the dose to surrounding healthy tissues both in front of and, crucially, behind the tumor.  

Reduced Exit Dose: This is the most significant difference from photon therapy. Traditional X-rays penetrate through the body, depositing energy along their entire path, including an “exit dose” as they leave the patient. This exit dose can damage healthy tissues and increase the risk of side effects and secondary cancers. Protons, due to the Bragg peak, have a minimal to negligible exit dose.