Design and Application of Acrylic Electron Wedge to Improve Dose Inhomogeneities at the Junction of Electron Fields

전자선 조사야 결합부분의 선량분포 개선을 위한 Acrylic Electron Wedge의 제작 및 사용

  • Kim Young Bum (Dept. of Radiation Oncology, Korea University Hospital) ;
  • Kwon Young Ho (Dept. of Radiation Oncology, Korea University Hospital) ;
  • Whang Woong Ku (Dept. of Radiation Oncology, Korea University Hospital) ;
  • Kim You Hyun (Dept. of Radiologic Technology, College of Health Sciences Korea University)
  • 김영범 (고려대학교 안암병원 치료방사선과) ;
  • 권영호 (고려대학교 안암병원 치료방사선과) ;
  • 황웅구 (고려대학교 안암병원 치료방사선과) ;
  • 김유현 (고려대학교 보건대학 방사선과)
  • Published : 1998.12.01

Abstract

Treatment of a large diseased area with electron often requires the use of two or more adjoining fields. In such cases, not only electron beam divergence and lateral scattering but also fields overlapping and separation may lead to significant dose inhomogeneities(${\pm}20\%$) at the field junction area. In this study, we made Acrylic Electron Wedges to improve dose homogeneities(${\pm}5\%$) in these junction areas and considered application it to clinical practices. All measurements were made using 6, 9, 12, 16, 20MeV Electron beams from a linear accelerator for a $10{\times}10cm$ field at 100cm SSD. Adding a 1 mm sheet of acryl gradually from 1 mm to 15 mm, We acquired central axis depth dose beam profile and isodose curves in water phantom. As a result, for all energies, the practical range was reduced by approximately the same distance as the thickness of the acryl insert, e.g. a 1 mm thick acryl insert reduce the practical range by approximately 1 mm. For every mm thickness of acryl inserted, the beam energy was reduced by approximately 0.2MeV. These effects were almost independent of beam energy and field size. The use of Acrylic Electron Wedges produced a small increase $(less\;than\;3\%)\;in\;the\;surface\;dose\;and\;a\;small\;Increase(less\;than\;1\%)$ in X-ray contamination. For acryl inserts, thickness of 3 mm or greater, the penumbra width increased nearly linear for all energies and isodose curves near the beam edge were nearly parallel with the incident beam direction, and penumbra width was $35\;mm{\sim}40\;mm$. We decide heel thickness and angle of the wedge at this point. These data provide the information necessary to design Acrylic Electron Wedge which can be use to improve dose uniformity at electron field junctions and it will be effectively applicated in clinical practices.

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