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Characterisation of Dosimetry in Electron Radiotherapy under different Bolus Applications.

Author: Lindsay James Tremethick

Field: Master of Applied Science (Medical and Health Physics)

Document Content:

This thesis investigates the dosimetry of electron beams in radiotherapy, specifically examining the impact of different bolus applications. Radiation therapy, a technique utilizing ionizing radiation for cancer treatment, relies on precise dose delivery. Electron beams, characterized by their build-up and rapid dose fall-off, offer advantages in treating lesions while sparing deeper normal tissues. The study explores three general methods for modulating electron beams: Intensity Modulated Electron Therapy, Segmented-field Electron Conformal Therapy, and Bolus Electron Conformal Therapy. These methods aim to level irregular surfaces, improve dose distributions, and increase surface dose at lower energies. The research focuses on the common practice of applying tissue-like materials (bolus) to the skin surface to modify electron beams. While this method has limitations, such as hygiene concerns and difficulties in precise contouring, moving the bolus to the applicator level presents new challenges in understanding its effect on electron beam dosimetry. This thesis aims to provide insights into these challenges.

Detailed Table of Contents:

  • Declaration
  • Acknowledgement
  • Illustration Index
  • Index of Tables
  • 0. ABSTRACT
  • 1. INTRODUCTION
    • 1.1 Radiotherapy
    • 1.2 Electron Interactions
      • 1.2.1 Stopping Powers
    • 1.3 Electron Beam Therapy
    • 1.4 Modulated Electron Radiotherapy
    • 1.5 Aims
  • 2 METHODOLOGICAL DESIGN
    • 2.1 Equipment & General Data Collection Conditions
    • 2.2 Clinical Electron Beam Characteristics
      • 2.2.1 Central Axis Percentage Depth Dose
        • 2.2.1.1 PDD Dependence on Energy
        • 2.2.1.2 PDD Dependence on Field Size
        • 2.2.1.3 PDD Dependence on Angle of incidence
    • 2.3 Ionisation Chambers
      • 2.3.1 Thimble Chambers
      • 2.3.2 Parallel Plate Chambers
    • 2.4 Data Collection
      • 2.4.1 Depth Ionisation to Depth Dose Conversion
    • 2.5 Specific Measurement Conditions
      • 2.5.1 Effective Point of Measurement (EPOM)
    • 2.6 Bolus Materials
    • 2.7 Smoothing Algorithms
  • 3. RESULTS
    • 3.1 Beam Quality Comparison
    • 3.2 Spatial resolution as a function of chamber IC-15, CC-04 and PPC-40(Roos Type)
    • 3.3 Bolus on the Applicator
      • 3.3.1 Full Bolus
        • 3.3.1.1 Full Bolus Perspex
        • 3.3.1.2 Full Bolus Teflon
        • 3.3.1.3 Full Bolus Aluminium
      • 3.3.2 Partial Bolus
        • 3.3.2.1 Partial Bolus Perspex
        • 3.3.2.2 Partial Bolus Teflon
        • 3.3.2.3 Partial Bolus Aluminium
      • 3.3.3 Strip Bolus
        • 3.3.3.1 Strip Bolus Teflon
      • 3.3.4 Higher Z Grids
        • 3.3.4.1 Aluminium Mesh
        • 3.3.4.2 Stainless Steel Mesh
    • 3.4 Bolus on Surface
      • 3.4.1 Perspex
      • 3.4.2 Teflon
  • 4. DISCUSSION
    • 4.1 Beam Quality
    • 4.3 Bolus on Applicator
      • 4.3.1 Full Bolus
      • 4.3.2 Partial Bolus
      • 4.3.3 Strip Bolus
      • 4.3.4 Higher Z Grids
    • 4.4 Bolus on Surface
  • 5. CONCLUSION
  • 6. BIBLIOGRAPHY
  • APPENDIX