Radiation Therapy: Overview and Types

Radiation Therapy is a type of cancer treatment that uses high doses of radiation to kill cancer cells or shrink tumors. It works by damaging the DNA of cancer cells, which prevents them from dividing and growing. Normal cells can also be affected, but they typically recover better than cancer cells.

Radiation therapy can be used in different scenarios:

• Curative Treatment: To eliminate cancer and prevent recurrence.
• Adjuvant Therapy: After surgery or chemotherapy to destroy any remaining cancer cells.
• Neoadjuvant Therapy: Before surgery to shrink a tumor.
• Palliative Treatment: To relieve symptoms in advanced cancer cases.

Types of Radiation Therapy

1. External Beam Radiation Therapy (EBRT): Most Common Type: Uses a machine (like a LINAC) to deliver high-energy rays directly to the tumor from outside the body.

Types of EBRT:

• 3D Conformal Radiation Therapy (3D-CRT): Uses 3D imaging to shape the radiation beams precisely around the tumor.
• Intensity-Modulated Radiation Therapy (IMRT): Varies the intensity of the radiation beams, allowing higher doses to the tumor while sparing nearby normal tissues.
• Volumetric Modulated Arc Therapy (VMAT): Delivers radiation in a continuous arc, reducing treatment time and increasing precision.
• Stereotactic Radiosurgery (SRS): Delivers a high dose of radiation in a single session to small, precise areas (commonly used for brain tumors).
• Stereotactic Body Radiation Therapy (SBRT): Similar to SRS but used for tumors in the body (e.g., lung, liver).

2. Internal Radiation Therapy (Brachytherapy)

• Involves placing radioactive sources inside or near the tumor.
• Commonly used for cancers like cervical, prostate, breast, and skin cancer.

Types of Brachytherapy:

• High-Dose Rate (HDR): Delivers a high dose of radiation in a short time.
• Low-Dose Rate (LDR): Delivers radiation over a longer period, sometimes requiring a hospital stay.

Advantages: Direct delivery of radiation minimizes exposure to surrounding healthy tissues.

3. Systemic Radiation Therapy: Uses radioactive substances (e.g., radioisotopes) that are swallowed, injected, or infused into the bloodstream.

Common Agents:

• Radioactive Iodine (I-131): Used for thyroid cancer.
• Radium-223 (Xofigo): Used for metastatic prostate cancer affecting the bones.

Benefits: Allows the radiation to travel throughout the body, targeting specific cancer cells.

Different Types of Radiation Used

1. Photon Radiation:

• Most common type used in LINACs (linear accelerators).
• Deeply penetrates tissues, making it effective for tumors located deep within the body.

Typical energies: 6 MV, 10 MV, 15 MV.

2. Electron Beam Radiation:

• Used for tumors located near the surface of the body (e.g., skin cancer, head and neck tumors).
• Limited penetration depth (2-5 cm), reducing damage to deeper tissues.

3. Proton Beam Therapy: Uses protons instead of photons. Protons have a unique property called the Bragg peak, where the maximum energy is deposited at a specific depth.

Advantages: Minimizes damage to surrounding healthy tissues, making it ideal for pediatric cancers and tumors near critical organs (e.g., brain, spine).

4. Neutron and Carbon Ion Therapy: Less common but used in certain cases for radio-resistant tumors.

• Neutron Therapy: Highly effective but also more damaging to normal tissue.
• Carbon Ion Therapy: Offers better precision and is used in specialized centers.

How Radiation Therapy is Administered

• Simulation and Planning: Before treatment, a simulation session is conducted using CT or MRI scans to map out the tumor. Treatment planning software is used to design the precise delivery of radiation.
• Daily Treatment: Patients typically undergo daily sessions (fractions) over several weeks. Each session is short (15-30 minutes), with the actual radiation delivery lasting only a few minutes.
• Follow-Up: Regular imaging and blood tests are conducted to monitor the effectiveness and adjust the treatment plan as needed.

Side Effects of Radiation Therapy

• Short-Term: Skin irritation, fatigue, nausea, and temporary hair loss (in treated areas).
• Long-Term: Potential damage to nearby organs, fibrosis, and risk of secondary cancers.

Radiation therapy is a powerful tool in the fight against cancer, offering different modalities and technologies tailored to specific types of cancer. Advances in precision and targeting have significantly improved outcomes while reducing side effects. The choice of therapy depends on the tumor type, location, and patient health, highlighting the importance of a multidisciplinary approach.

What is Chemo-Radiation?

Chemo-radiation (or chemoradiotherapy) is a cancer treatment approach that combines chemotherapy and radiation therapy simultaneously. The aim is to enhance the effectiveness of both treatments by using chemotherapy to sensitize cancer cells, making them more vulnerable to the radiation. This approach can increase the overall response rate and improve the chances of controlling the cancer.

Mechanism of Action

1. Chemotherapy as a Radiosensitizer:

• Certain chemotherapy drugs (e.g., cisplatin, 5-fluorouracil) act as radiosensitizers, increasing the sensitivity of cancer cells to radiation damage.
• By damaging the DNA and impairing the repair mechanisms of cancer cells, chemotherapy makes them more susceptible to the lethal effects of radiation.

2. Concurrent Treatment:

• Instead of administering chemotherapy and radiation sequentially, they are given at the same time, which can lead to better local control of the tumor.

3. Higher Efficacy:

• This combined approach can be more effective than either treatment alone, especially in cancers that are locally advanced and difficult to treat with a single modality.

Types of Cancers Treated with Chemo-Radiation

Chemo-radiation is often used for cancers that are locally advanced, meaning the cancer has spread locally but not to distant organs. Some common cancers treated with this approach include:

1. Head and Neck Cancers:

• Cancers of the oral cavity, oropharynx, larynx, and nasopharynx often respond well to chemo-radiation.
• Standard chemotherapy agents: Cisplatin or 5-fluorouracil.

2. Cervical Cancer:

• For locally advanced cervical cancer (stage II, III, or IVA), concurrent chemo-radiation is the standard of care.
• Cisplatin is the most commonly used radiosensitizing agent.

3. Lung Cancer:

• For non-small cell lung cancer (NSCLC), especially in stages IIIA and IIIB, concurrent chemo-radiation is often recommended.
• Common agents: Cisplatin and etoposide.

4. Esophageal Cancer:

• Chemo-radiation is used for squamous cell carcinoma and adenocarcinoma of the esophagus, either as a definitive treatment or as a neoadjuvant approach before surgery.
• Common drugs: 5-fluorouracil and cisplatin.

5. Anal Cancer:

• The standard treatment for anal squamous cell carcinoma is chemo-radiation, typically using mitomycin-C and 5-fluorouracil.

6. Rectal Cancer:

• For locally advanced rectal cancer, chemo-radiation is often given preoperatively (neoadjuvant therapy) to shrink the tumor and improve surgical outcomes.

7. Glioblastoma (Brain Tumor):

• In aggressive brain tumors like glioblastoma, chemo-radiation with the drug temozolomide is part of the standard treatment protocol.

Benefits of Chemo-Radiation

• Higher Treatment Efficacy: The combined effect of chemotherapy and radiation leads to improved tumor control.
• Organ Preservation: In certain cancers (e.g., laryngeal cancer, anal cancer), chemo-radiation can help preserve organ function and avoid surgery.
• Better Local Control: Effective in managing tumors that are localized but inoperable or too large for surgery.

Risks and Side Effects

While chemo-radiation can be more effective, it also increases the risk of side effects, as both treatments can be toxic:

• Increased Toxicity: Higher rates of side effects such as nausea, fatigue, and low blood counts.
• Mucositis: Inflammation of the mucous membranes, common in head and neck cancers.
• Gastrointestinal Issues: Diarrhea, abdominal pain, and rectal bleeding in pelvic cancers.
• Radiation Pneumonitis: Inflammation of the lungs when treating lung or chest tumors.

Chemo-radiation is a powerful approach in cancer treatment, particularly for locally advanced cancers. By combining the DNA-damaging effects of both chemotherapy and radiation, it increases the likelihood of tumor control and survival. However, it requires careful patient selection and monitoring due to the potential for increased toxicity.

A side note for those interested in the physics of radiation therapy:

In radiation therapy and medical physics, MV and MeV are units used to describe energy levels, particularly in linear accelerators (LINACs).

1. MV (Megavolts)

• MV stands for megavolts, which is a unit of electric potential or voltage.
• In the context of radiation therapy, it refers to the photon beam energy produced by the linear accelerator.
• For example, a 6 MV photon beam indicates that the x-rays generated have an energy equivalent to 6 megavolts of electric potential. The actual average energy of the photons is typically about one-third of the stated MV, so a 6 MV beam has an average photon energy of approximately 2 MeV.

2. MeV (Mega-electron Volts)

• MeV stands for mega-electron volts, a unit of energy used to describe the kinetic energy of particles such as electrons or protons.
• In the context of a LINAC, it refers to the energy of electron beams. For example, a 12 MeV electron beam has electrons with an energy of 12 million electron volts.
• Higher MeV values indicate higher penetration and energy, which determines the depth of treatment and the type of tissues that can be targeted effectively.

Differences:

• MV (Megavolts) is used to describe photon beam energy, often in x-ray or gamma-ray treatments.
• MeV (Mega-electron Volts) is used for particle beam energy, such as electron or proton beams.

Applications:

• Lower energies like 6 MV are typically used for superficial tumors or areas close to the skin.
• Higher energies like 15 MV or 18 MeV electrons can penetrate deeper into the body, making them suitable for treating larger or deeper tumors.

These distinctions are important when selecting the appropriate energy level for different cancer treatments, balancing the need for deeper tissue penetration against the risk of damage to surrounding healthy tissues.