The Study of Shielding Effect on Ovoids of Three Different Gynecological Applicator Sets in microSelectron-HDR System

microSelectron-HDR System에서 부인암 강내조사에 쓰이는 세 가지 Applicator Set들의 Ovoids에 대한 차폐효과 연구

  • Cho, Young-K. (Department of Radiation Oncology, Inha University Medical College, Inha University Hospital) ;
  • Park, Sung-Y. (Department of Radiation Oncology, Inha University Medical College, Inha University Hospital) ;
  • Choi, Jin-H. (Department of Radiation Oncology, Gachon Medical College, Ghil Medical Center) ;
  • Kim, Hung-J. (Department of Radiation Oncology, Inha University Medical College, Inha University Hospital) ;
  • Kim, Woo-C. (Department of Radiation Oncology, Inha University Medical College, Inha University Hospital) ;
  • Loh, John-J.K. (Department of Radiation Oncology, Inha University Medical College, Inha University Hospital) ;
  • Kim, Joo-Y. (Department of Radiation Oncology, Gachon Medical College, Ghil Medical Center)
  • 조영갑 (인하대병원 방사선종양학과) ;
  • 박성용 (인하대병원 방사선종양학과) ;
  • 최진호 (길병원 방사선종양학과) ;
  • 김헌정 (인하대병원 방사선종양학과) ;
  • 김우철 (인하대병원 방사선종양학과) ;
  • 노준규 (인하대병원 방사선종양학과) ;
  • 김주영 (길병원 방사선종양학과)
  • Published : 1998.12.30

Abstract

There are three different types of gynecological applicator sets available in microSelectron-high dose-rate(HDR) System by Nucletron; standard applicator set(SAS), standard shielded applicator set(SSAS), and Fletcher-Williamson applicator set(FWAS). Shielding effect of a SAS without shielding material was compared with that of a SSAS with shielding material made of stainless steel(density ${\varrho}=8,000kg/m^3$) at the top and bottom of each ovoid, and of a FWAS with shielding material made of tungsten alloy(density ${\varrho}=14,000kg/m^3$ at the top and bottom of each ovoid. The shielding effects to the rectum and bladder of these two shielded applicator sets were to be measured at reference points with an ion chamber and specially designed supporting system for applicator ovoids inside of the computerized 3-dimensional water phantom. To determine the middle point of two ovoids the measurement was performed with the reference tip of ion chamber placed at the same level and at the middle point from the two ovoids, while scanning the dose with the ion chamber on each side of ovoids. The doses to the reference points of rectum were measured at 20(Rl), 25(R2), 30(R3), 40(R4), 50(R5), and 60(R6) mm located posteriorly on the vertical line drawn from M5(the middle dwell position of ovoid), and the doses to the bladder were measured at 20(Bl), 30(B2), 40(B3), 50(B4), and 60(B5) mm located anteriorly on the vertical line drawn from M5. The same technique was employed to measure the doses on each reference point of both SSAS and FWAS. The differences of measured rectal doses at 25 mm(R2) and 30 mm(R3) between SAS and SSAS were 8.0 % and 6.0 %: 25.0% and 23.0 % between SAS and FWAS. The differences of measured bladder doses at 20 mm(Bl) and 30 mm(B2) between SAS and SSAS were 8.0 % and 3.0 %: 23.0 % and 17.0 % between SAS and FWAS. The maximum shielding effects to the rectum and bladder of SSAS were 8.0 % and 8.0 %, whereas those of FWAS were 26.0 % and 23.0 %, respectively. These results led to the conclusion that FWAS has much better shielding effect than SSAS does, and when SSAS and FWAS were used for gynecological intracavitary brachytherapy in microSelectron-HDR system, the dose to the rectum and bladder was significantly reduced to optimize the treatment outcome and to lower the complication rates in the rectum and bladder.