Treatment - Radiation

Radiation Therapy

• Role of Radiation Therapy 
  • Cure
  • Control
  • Palliation
• Overview:  Radiation Therapy
  • Used for over 100 years (Mustard gas in World War I)
  • Since cancer cells grow at a faster rate than normal cells, radiation therapy can be very effective
  • Usually a local treatment (whole body not exposed)
  • About half of all people who are diagnosed with cancer undergo radiation  
• Mechanism of Cellular Damage
  • Direct damage to cell’s DNA/ chromosomal structures
  • Indirect effect causing toxic changes to cells

Cellular Death

• May be immediate
• May occur when cells attempt to divide
• May occur from cell degeneration
• Takes days to weeks

Sensitivity to Radiation Damage

• Fast growing
• Well oxygenated cells
• Phase of cell cycle
• Degree of cellular differentiation

Types and Sources of Radiation

• External (external beam, teletherapy)
• Electromagnetic sources
  • X-rays (photons)
  • Gamma rays
• Particle Sources
  • Electrons
  • Protons/neutrons
• Brachytherapy (internal)
  • Sealed radionuclides (implants)
  • Intracavity
  • Interstitial sources
• Types
  • High-dose rate (HDR) implants (tubes skin / breast)
  • Low-dose rate (LDR) permanent implants (prostate cancer – seeds)

Radiation Treatment Frequency

• Accelerated fractionation
• Larger daily or weekly doses to reduce number of weeks of treatment
• Hyperfractionation
• Smaller dose given more than once per day
• Hypofractionation
• Larger doses given once a day or less often to reduce number of treatments

Types and Sources of Radiation

• Internal – brachytherapy
  • Tandem and Ovoids (e.g., a small, round metal tube, which is placed inside the woman's uterus to treat cervical cancer)
  • 15-20 min dwell time – multiple days
  • Machine feeds source in, then removes
• Uterus/Cervix
  • Unsealed sources
• Oral; IV
  • Intraperitoneal; Intrapleural
• Episcleral
  • Source attached to eye – ocular melanoma

Steps in Radiation Therapy

• Consultation
• Treatment Planning
• Pretreatment studies
• Simulation
• Computer planning
• Construction of blocks
• Treatment Experience and Follow-up

Additional Radiation Techniques

• Stereotactic radiosurgery
• Gamma knife/CyberKnife
  • Non-surgical radiotherapy
  • Precisely targeted radiation
  • Preserves health tissue
• Intraoperative radiotherapy (IORT)
  • Single dose RT to tumor bed