Master’s thesis of Applied Physics (Medical & Health Physics) : The reduction of dose to breast tissue during multi-slice CT examinations using bismuth breast shields and dose modulation technologies

The Reduction of Dose to Breast Tissue During Multi-slice CT Examinations Using Bismuth Breast Shields and Dose Modulation Technologies

Author: Cameron Storm

Field: Applied Physics (Medical & Health Physics)

Document Content:
This thesis investigates methods to reduce radiation dose to breast tissue during multi-slice CT examinations, a critical concern due to the increasing number of CT scans performed worldwide and the associated risk of induced breast cancer. The study employed a novel geometric phantom to assess various dose reduction techniques, including bismuth breast shields and dose modulation. Doses were measured using over 300 TLD crystals, generating comprehensive dose contour maps. The research found that bismuth breast shields can achieve significant dose reductions, ranging from 21% for smaller breasts to 44% for larger breasts, with a maximum observed reduction of 57%. However, these shields also introduced additional quantitative and qualitative noise in diagnostic regions. Dose modulation techniques on the Philips 64 CT scanner were also found effective, offering 40-50% dose reduction, and when combined with breast shields, potentially up to 80% reduction, albeit with increased noise. The study concludes that further analysis on acceptable noise levels is necessary before definitive clinical recommendations can be made regarding bismuth breast shields, noting that other methods exist which offer comparable dose reduction with lower noise.

Detailed Table of Contents:

• ABSTRACT
• INTRODUCTION
  • Aim
  • Radiation and Cancer
    • Ionising Radiation
    • Biological Damage from Ionising Radiation
    • Accuracy of the LNT Theory
    • Recommendations of the ICRP
    • Breast Cancer
    • Trends in modern women
  • CT – Basic principles
    • Doses from CT
    • Noise (and Image Quality) in CT
  • Methods to Reduce Dose
    • General methods
    • Dose Reduction technologies
    • Patient Shields
    • Effectiveness of Dose Reduction Techniques
  • Paediatric Considerations
• METHODS & EQUIPMENT
  • CT Scanner
  • The Phantom
    • Material Selection
    • Size Selections
    • Additional Design Considerations
    • Phantom Summary
  • Thermoluminescent Dosimetry
    • TLD Theory
    • TLD Materials
    • Checklist for Reporting of TLD Results
    • Procedure details
  • Energy Response and water equivalence of the TLDs
    • Introduction
    • Methods
    • Dose Analysis
    • Conclusions
• RESULTS AND DISCUSION
  • Breast shield lead equivalence
    • Introduction
    • Equipment
    • Methods
    • Results and Discussion
  • Initial TLD Exposures
    • Introduction
    • Aim
    • Methods & Materials
    • Results & Discussion
  • Depth of Dose
    • Background
    • Aim
    • Methods & Materials
    • Results & Discussion
  • Breast Shield Effectiveness – Geometric Phantom
    • Background
    • Aim
    • Methods & Materials
    • Results & Discussion
  • Breast Size Dose Analysis
    • Background
    • Aim
    • Methods & Materials
    • Results & Discussion
  • Manually reducing mA
    • Background
    • Aim
    • Methods & Materials
    • Results & Discussion
  • Dose Modulation
    • Background
    • Aim
    • Methods & Materials
    • Results & Discussion
• FINAL CONLCUSIONS
  • Summary Comparison Tables
  • Future Work
    • Maximum Noise Values
    • Paediatric Comparison
  • Limitations of this work
• REFERENCES
• Appendices
  • Comparison of breast shield studies
  • Problems/Issues
    • TLD batch dependencies
    • Repeating experiments
    • Collimator Size Effects