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