Radiotherapy

Radiotherapy (RT) is the use of ionizing radiation to destroy or damage cancer cells by inducing DNA damage, leading to cell death. It is a key modality in the treatment of solid tumors, often used alone or in combination with surgery, chemotherapy, or immunotherapy.

• External Beam Radiotherapy (EBRT):
  • Delivered from a machine (e.g., linear accelerator)
  • Includes techniques such as:
    • 3D conformal radiotherapy (3D-CRT)
    • Intensity-modulated radiotherapy (IMRT)
    • Image-guided radiotherapy (IGRT)
    • Stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT)

• Brachytherapy:
  • Internal radiation by placing radioactive sources inside or near the tumor

• Systemic Radiotherapy:
  • Use of radioactive isotopes (e.g., I-131 for thyroid cancer)

• Causes DNA single- and double-strand breaks
• Generates free radicals → cytotoxic effect
• Induces apoptosis, senescence, or mitotic catastrophe
• Preferential effect on rapidly dividing tumor cells

• Curative intent: e.g., localized prostate, head and neck, brain tumors
• Adjuvant/Neoadjuvant: Combined with surgery or chemotherapy
• Palliative: Symptom control (e.g., bone metastases, spinal cord compression)
• Radiosurgery: Precise, high-dose delivery to small targets (e.g., brain metastases)

• Acute:
  • Skin erythema, mucositis, fatigue, nausea
• Late:
  • Fibrosis, radiation necrosis, second malignancies, organ dysfunction

• Abscopal effect:
  • Systemic anti-tumor response after localized RT, often linked to immune activation
• Radiation-induced immunosuppression:
  • Some settings show paradoxical promotion of metastasis via immune cell reprogramming (e.g., AREG induction)
• Combination therapies:
  • RT + immunotherapy
  • RT + EGFR inhibitors

• Conventional: 1.8–2 Gy per day
• Hypofractionated: Larger doses over fewer sessions
• Hyperfractionated: Smaller doses given more than once daily

• Combination Therapy
• Abscopal Effect
• Radiation Necrosis
• SBRT vs SRS
• Radiotherapy Planning