What are the different types of radiation therapy?

Types of Radiation Therapy

Radiation therapy can be broadly categorized into external beam radiation therapy (EBRT) and internal radiation therapy (brachytherapy), with multiple advanced techniques available within each category to optimize tumor control while minimizing damage to healthy tissues.

External Beam Radiation Therapy (EBRT)

External beam radiation therapy delivers radiation from outside the body, focusing high-energy beams onto the tumor. The main types include:

• Three-Dimensional Conformal Radiation Therapy (3D-CRT): Uses photon energy equal or superior to 10 MV to deliver radiation precisely shaped to match the tumor's dimensions 1

• Intensity Modulated Radiation Therapy (IMRT): An advanced form of 3D-CRT that uses inverse treatment planning with beams from different angles shaped according to the target form, with intensity adjusted throughout treatment to optimize dose to the target while limiting dose to surrounding normal tissues 1

• Volumetric Modulated Arc Therapy (VMAT): A form of IMRT where the radiation source rotates around the patient in one or more arcs while continuously delivering radiation 1

• Stereotactic Body Radiation Therapy (SBRT)/Stereotactic Ablative Radiotherapy (SABR): Uses focused beams of high-dose radiation (typically 6-18 Gy) delivered in fewer sessions (usually 2-8) compared to conventional radiotherapy, achieving high biological effectiveness while sparing surrounding tissues 1, 2

• Proton Therapy: Uses proton particles instead of photons, allowing for more precise dose delivery with minimal exit dose beyond the tumor 3

• Carbon Ion Therapy: Uses carbon ions which have higher biological effectiveness than photons or protons, particularly effective against radioresistant tumors 3

Internal Radiation Therapy (Brachytherapy)

Internal radiation therapy involves placing radioactive sources directly into or near the tumor. Types include:

• Low Dose Rate (LDR) Brachytherapy: Radioactive sources are placed permanently or temporarily in the body, delivering radiation at a low dose rate over time 1

• High Dose Rate (HDR) Brachytherapy: Delivers higher doses of radiation in a shorter time period using temporarily placed radioactive sources 1

• Endocavitary Brachytherapy: Radiation sources are placed in body cavities near the tumor, commonly used in cervical cancer 1

• Interstitial Brachytherapy: Radiation sources are placed directly into the tumor tissue 1

Specialized Radiation Techniques

• Image-Guided Radiation Therapy (IGRT): Incorporates imaging during radiation delivery to improve precision, allowing for reduction of safety margins around the tumor 4

• Adaptive Radiation Therapy: Modifies the treatment plan during the course of treatment based on changes in tumor size, shape, or position 1

• Transarterial Radioembolization (TARE): Delivers radioactive microspheres (usually containing yttrium-90) through the hepatic artery to treat liver tumors 1

Clinical Applications Based on Cancer Type

• Lung Cancer:

  • Early-stage NSCLC: SBRT is preferred for inoperable patients 1
  • Locally advanced NSCLC: IMRT with concurrent or sequential chemotherapy 1
  • Central lung tumors: Modified SBRT dosing (50 Gy in 5 fractions) to minimize toxicity 2

• Prostate Cancer:

  • Options include EBRT, brachytherapy alone, or combination therapy depending on risk stratification 1
  • IMRT is commonly used to minimize urinary and rectal toxicity 1

• Liver Cancer:

  • SBRT for early-stage disease or oligometastases 1
  • IMRT or image-guided RT for larger tumors 4

• Cervical Cancer:

  • Combination of external beam radiotherapy and brachytherapy 1
  • Standard dosimetry according to International Commission of Radiation Units recommendations 1

Emerging Trends and Future Directions

• Combined Modality Approaches: Integration of internal and external radiation therapy for synergistic effects 5

• Biological Response Modifiers: Use of agents that enhance radiation sensitivity of tumors 3

• Personalized Radiation Therapy: Tailoring radiation approach based on tumor genomics and radiobiology 3

• Advanced Imaging Integration: Further development of real-time imaging during treatment delivery 4

Important Considerations

• Radiation therapy contributes to approximately 40% of curative cancer treatments 6

• The goal of radiation therapy is to deliver adequate dose to the tumor while minimizing exposure to surrounding healthy tissues 6, 3

• Selection of radiation technique depends on tumor location, size, histology, patient comorbidities, and available technology 1

• Newer technologies continue to improve the therapeutic ratio by increasing precision and reducing toxicity 3, 4