Radiotherapy

Definition

  • Use of ionising radiation to damage DNA in order to prevent cell replication
  • Most rapidly replicating cells affected most
  • 100 Centigray = 100 Rads = 1 Gy (J/kg)

Types

  • Gamma rays
    • Radium – now obsolete
    • Cobolt 60 – almost obsolete
    • Iridium – used occasionally for brachytherapy
    • Caesium – used for gynae tumours
  • X Rays
    • Diagnostic – 50-150 kV
    • Deep XR Therapy (DXRT) – 300 kV
    • Linear accelerators – 4-24 MV
  • Electrons
    • Linear accelerators
  • Beta Rays
    • Electrons given off by ionised material
    • Injected locally
    • Strotium, Yittrium & Samarium

Mechanism of >Mechanism of Action

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  • Produce free radicals by breakup of H2O
  • Need Oxygen for DXRT to work
    • Hyperbaric better
    • Unoperated bed better
  • ? Haematology substitutes

    • Fractionation>Fractionation

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  • 1 large dose vs 60 small doses
  • Curative DXRT » Fractionation +++
  • Palliative DXRT » Minimal Fractionation

    • Timing

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  • Preoperative or Postoperative Radiotherapy
  • Preoperative radiotherapy is to ↓ size of tumour to improve survival following excision
  • There is NO role for preoperative radiotherapy to allow closer margins (ie. if plan wide margins for excision then still need wide margins after preoperative radiotherapy)

    • Radio-sensitive T>Radio-sensitive Tissue

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  • High turnover tissue
  • High blood supply

    • Technique

    >Techniqueblock-heading">Curative >Curativeblock-list">
  • Maximum dose with acceptable damage to normal tissue
  • 60 Gy in 30 fractions over 6 weeks
    • Equivalent to 18 Gy in one dose
  • Fractionation decreases late effects on normal tissue
    • Increases differential between tumour & tissue damage
    • Allows repair between treatments
  • Usually 2-3 weeks post-op
    • Allows wound healing
    • Minimises delay as tumour interference activates latent cells
  • Careful planning
    • Multiple fields
    • Minimises normal tissue damage

    • Palliative

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  • Shorter course with reduced total dose
  • 30 Gy in 10 fractions
  • Simple field set ups
  • Late morbidity less of issue
  • Delays callus formation if pathological fracture

    • Morbidity

    >Morbidityblock-heading">Early
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    • Erythema
    • Dry desquamation
    • Ulceration
    • Lymphopaenia
    • Telangiectasia
    • Myelosuppression
    • GIT effects

    Late

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    • Fibrosis
    • Contracture
    • Atrophy
    • Lymphoedema
    • Osteoradionecrosis
      • AVN of femoral head
    • Transverse myelitis
    • Pulmonary fibrosis
    • Soft tissue & Bony hypoplasia (in children)
    • Endocrine suppression
    • Infertility
    • Skin cancer
    • Sarcomatous change

    Specific Tumours<>Specific Tumours

    >Osteosarcomas

    • No indications pre-op
    • Used for
      • Unresectable tumours
      • Palliation for metastatic disease

    Ewings Sarcoma

    • Very radiosensitive but low curability
    • Effective combined with chemo
    • Surgery + Chemo have better results

    Chondrosarcoma

    • Relatively radioresistant
    • Used for
      • Recurrence
      • Inoperable disease

    Myeloma

    • Effective for Plasmacytoma
    • Chemo + Radio for Myeloma

    Soft tissue sarcoma

    • Where doubt regarding surgical margins
    • NV structures close
    • 50 Gy DXRT pre-op
    • 10 Gy Brachytherapy post-op