Oncology: Radiation Therapy (RT/XRT)

Radiation Therapy (RT/XRT)

Target

  • Primary Target: DNA
  • Most Vulnerable Stage: M Phase (Mitosis)
    • High Mitotic Rates are More Sensitive
  • Most Damaging Effect: Oxygen Radicals Cause Apoptosis
    • Effect Maximal with High O2 Levels – Therefore More Effective Preop
    • Large Tumors Less Effective (Less O2)

Use

  • Higher Energy = Skin-Preserving Effect (Maximal Potential at Deeper Structures)
  • Given in Multiple Fractions to a Total Dose
  • Fractionate Dosing
    • Allows Repair of Normal Cells
    • Allows Re-Oxygenation & Cell-Cycle Redistribution of CA Cells
  • Chemotherapy May Be Used as a “Radiosensitizer” (Not Considered True Chemotherapy)
  • Preoperative XRT Can Cause Increased Risk of Wound Healing Complications
  • Most Sensitive Tumor: Seminoma

Radioactive Particle Used

  • Photons (No Electric Charge)
    • Radiation Beams Travel Deep into the Body
    • Beams Will Scatter a Little Along Their Path
    • They Do Not Stop at the Tumor but Pass Through the Body
    • Used in X-Ray Machines at Lower Doses
  • Protons (Positive Charge)
    • Radiation Beams Travel Deep into the Body
    • Deposit Majority of Energy at the End of Their Path
    • Minimal Effect on Tissue They Pass Through & Do Not Exit the Body
  • Electrons (Negative Charge)
    • Deposit Majority of Energy at the Tissue Surface
    • Used for Skin & Superficial Tumors

Radiation Dermatitis

  • Cause: Radiation Induces DNA Breakage Causing Apoptosis, Cellular Necrosis & Dermal Fibrosis
  • Very Common After Radiation (95%)
  • Risk Factors:
    • Elderly
    • Female
    • Obesity
    • Body Site
  • Treatment:
    • Grade 1 (Dry Desquamation): General Skin Care & Moisturizers
    • Grade 2-3 (Moist Desquamation): Soft Absorbent Dressings
    • Grade 4 (Full-Thickness Necrosis): May Require Surgical Debridement & Stopping Radiation

Radiation-Induced Angiosarcoma (RIAS)

  • Rare Late Complication (0.05-0.3%)
  • Majority Present with Localized Disease Amenable to Surgery
  • Primary Treatment: Surgical Resection
    • May Consider Neoadjuvant Chemotherapy to Downstage Locally Advanced Tumors
  • Stewart-Treves Syndrome

Types of Radiation Therapy

Types of Radiation Therapy

  • External Beam Radiation Therapy (EBRT/Teletherapy) – Radiation Delivered from Outside of the Body
    • Most Common
  • Internal Radiotherapy – Radiation Delivered from Inside of the Body

External Beam Radiation Therapy (EBRT/Teletherapy)

  • Three-Dimensional Conformal Radiation Therapy (3DCRT) – Uses Imaging to Plan a “Simulation” (Treatment Approach) for Radiation Beams to Conform to the Tumor Shape from Several Directions
    • Most Common
  • Intensity-Modulated Radiation Therapy (IMRT) – Uses Smaller Beams of Radiation with Varying Strengths to Give Higher Doses in Selected Areas of the Tumor
    • A Type of 3DCRT
    • Volumetric Modulated Arc Radiation Therapy (VMAT) – Radiotherapy Machine Rotates Around the Patient During a Beam in an Arc Shape
      • A Type of IMRT
      • Used for Areas Near Sensitive Body Organs
    • Image-Guided Radiation Therapy (IGRT) – Uses Imaging During Radiation Therapy Sessions to Make Adjustments, Not Just in Planning
      • A Type of IMRT
      • Used for Tissues that May Move Significantly (Lungs)
  • Stereotactic Radiation Therapy (SRT) – Uses Focused High-Energy Beams to Treat Small Tumors
    • Stereotactic Radiosurgery (SRS) – SRT Used on the Brain or CNS
      • Ex: GammaKnife
    • Stereotactic Body Radiation Therapy (SBRT) – SRT Used Outside of the Brain or CNS (Liver, Lung, etc)

Internal Radiotherapy

  • Radioactive Implant (Brachytherapy/Seed Implantation) – Radioactive Material (“Seeds”) are Implanted Next to the Tumor & Slowly Release Highly-Concentrated Doses of Radiation Over Months
  • Radioactive Liquid Treatment (Radioisotope) – Radioactive Liquid is Ingested or Injected & Collects in Cancerous Areas with Smaller Effects on Healthy Tissue
    • Ex: Iodine-131 for Thyroid Cancer