Radiotherapy

Definition:

• Radiotherapy (RT) is the therapeutic use of ionizing radiation to destroy cancer cells while minimizing damage to normal tissues.
• Can be used as curative, adjuvant, neoadjuvant, or palliative therapy.

Types of Radiotherapy

1. External Beam Radiotherapy (EBRT)
   • Radiation delivered from outside the body using linear accelerators
   • Techniques:
     • 3D conformal RT (3D-CRT)
     • Intensity-modulated RT (IMRT) – precise targeting
     • Stereotactic radiosurgery (SRS) – high-dose focused radiation (e.g., brain metastases)
2. Brachytherapy
   • Internal radiation placed close to or inside the tumor
   • Examples: cervical, prostate, head & neck cancers
3. Systemic Radiotherapy
   • Radioisotopes administered systemically
   • Examples: I-131 for thyroid cancer, radium-223 for bone metastases

Mechanism of Action

• Ionizing radiation → DNA damage (single- and double-strand breaks)
• Tumor cells are less efficient at DNA repair → apoptosis or mitotic death
• Fractionation allows normal tissues to repair between doses

Clinical Uses

1. Curative – primary treatment for localized tumors (e.g., head & neck, prostate, breast)
2. Adjuvant – after surgery to reduce recurrence (e.g., breast cancer, sarcomas)
3. Neoadjuvant – to shrink tumors pre-surgery (e.g., rectal cancer, sarcomas)
4. Palliative – symptom control (e.g., bone pain, brain metastases, airway obstruction)

Pharmacist Considerations

• Not a drug therapy, but RT interacts with systemic therapies:
  • Chemotherapy: radiosensitizers (cisplatin, 5-FU, capecitabine) enhance tumor kill
  • Targeted therapies / immunotherapy: may increase toxicity when combined
• Supportive care: manage acute RT side effects based on site:
  • Skin: dermatitis → topical steroids, gentle skin care
  • GI tract: mucositis, diarrhea → antiemetics, antidiarrheals, hydration
  • Bone marrow suppression when RT includes large marrow volume → monitor CBC
• Long-term / late toxicities:
  • Secondary malignancies
  • Fibrosis, organ dysfunction (heart, lungs, kidneys)
  • Endocrine deficits (especially in pediatric patients)

High-Yield Pharmacist Pearls

• Fractionation is key: total dose divided into multiple fractions to spare normal tissue
• Combination with chemo: drugs like cisplatin, 5-FU, gemcitabine can be radiosensitizers
• Patient counseling: acute side effects are site-specific, usually self-limited; long-term effects may be delayed
• Pediatric patients require special attention to growth, neurocognitive development, endocrine function