Transmission Dose Estimation Algorithm for in vivo Dosimetry

  • Yun, Hyong-Geun (Department of Therapeutic Radiology, Dankook University College of Medicine) ;
  • Huh, Soon-Nyung (Department of Therapeutic Radiology, Seoul National University College of Medicine) ;
  • Lee, Hyoung-Koo (Department of Biomedical Engineering, Catholic University College of Medicine) ;
  • Woo, Hong-Gyun (Department of Therapeutic Radiology, Seoul National University College of Medicine) ;
  • Shin, Kyo-Chul (Department of Therapeutic Radiology, Dankook University College of Medicine) ;
  • Ha, Sung-Whan (Department of Therapeutic Radiology, Seoul National University College of Medicine)
  • Published : 2003.03.30

Abstract

Purpose : Measurement of transmission dose is useful for in vivo dosimetry of QA purpose. The objective of this study is to develope an algorithm for estimation of tumor dose using measured transmission dose for open radiation field. Materials and Methods : Transmission dose was measured with various field size (FS), phantom thickness (Tp), and phantom chamber distance (PCD) with a acrylic phantom for 6 MV and 10 MV X-ray Source to chamber distance (SCD) was set to 150 cm. Measurement was conducted with a 0.6 cc Farmer type ion chamber. Using measured data and regression analysis, an algorithm was developed for estimation of expected reading of transmission dose. Accuracy of the algorithm was tested with flat solid phantom with various settings. Results : The algorithm consisted of quadratic function of log(A/P) (where A/P is area-perimeter ratio) and tertiary function of PCD. The algorithm could estimate dose with very high accuracy for open square field, with errors within ${\pm}0.5%$. For elongated radiation field, the errors were limited to ${\pm}1.0%$. Conclusion : The developed algorithm can accurately estimate the transmission dose in open radiation fields with various treatment settings.

References

  1. Millwater cJ, MacLeod AS, Thwaites DI, In vivo semiconductor dosimetry as part of routine quality assurance, Br. J. Radiol., 71:661-668(1998)
  2. Adeyemi A, Lord J, In audit of radiotherapy patient doses measured with in vivo semiconductor detectors, Br. J. Radiol., 70:399-408(1997)
  3. Urie MM, Goiten M, Loppke K, The role of uncertainty analysis in treatment plannning, Int. J. Radiat. Oncol. Biol Phys., 21:91-107(1991)