ABSORBED DOSE TO WATER REFERENCE DOSIMETRY USING VARIOUS WATER-EQUIVALENT SOLID PHANTOMS IN HIGH-ENERGY PHOTON BEAMS

DOI 13 References
  • ARAKI Fujio
    Department of Radiological Technology, Kumamoto University School of Health Sciences
  • HANYU Yuji
    Division of Radiation Oncology, Tokyo Women's Medical University Hospital
  • OKUMURA Masahiko
    Department of Central Radiology, Kinki University Hospital
  • YOSHIURA Takao
    Department of Radiology, University Hospital of Occupational and Environmental Health
  • ANAI Shigeo
    Department of Radiation Therapy, National Hospital Organization Kyushu Cancer Center
  • OHURA Hiroki
    Department of Radiology, Kyushu University Hospital
  • NAMBU Hidekazu
    Department of Radiology, Nara Hospital Kinki University Medical School
  • FUKUGAMI Satoshi
    Department of Radiology, Nara Hospital University Medical School
  • KAWAMORITA Ryu
    Department of Radiology, Tenri Hospital
  • YAMAMOTO Toshijiro
    Department of Radiology, Hyogo Medical College Hospital
  • AKITA Kazuhiko
    Department of Radiology, Osaka Medical College Hospital

Bibliographic Information

Other Title
  • 光子ビームにおける水等価固体ファントムを用いた水吸収線量の評価

Search this article

Description

Most recent megavoltage dosimetry protocols (e.g., the Japan Society of Medical Physics (JSMP) (JSMP-01), the American Association of Physicists in Medicine (AAPM) (TG-51), and the International Atomic Energy Agency (IAEA) (TRS-398)) have limited to the use of liquid water as a phantom material for reference dose measurements. This is because water is well-defined and reproducibly available compared to water-equivalent solid phantoms. This study presents methods to determine absorbed dose to water using ionization chambers calibrated in terms of absorbed dose to water but irradiated in solid phantoms. Achieving solid phantom measurements on an absolute basis has distinct advantages in verification measurements and quality assurance. We provide a depth scaling factor that transfers a depth in the solid phantom to a water equivalent depth and an ionization conversion factor (ionization ratio) that converts a chamber reading in the solid phantom to that in water. The absorbed dose to water under reference conditions can be obtained from the solid phantom measurements by using the two factors. We calculated the depth scaling factor for four solid phantoms (Solid Water RMI457, Tough Water WE211, RW3, and MixDP) for photon energies between 4 and 18 MV. The calculated average scaling factor for each phantom agreed within 1.5% compared with the relative electron density. For various Farmer-type cylindrical chambers, we also calculated and measured the ionization conversion factor for the four solid phantoms. The solid phantom measurements were performed at many hospitals. For RMI457 and WE211, the differences between measured and calculated factors varied between -0.5% and 0.7% with the average ionization conversion factor 0.3% lower than the calculation, whereas RW3 agreed within 0.5% after one phantom examination. Similarly, the differences for MixDP ranged from -0.2% to -1.5% with the average 1.0% lower than the calculation. The composition of commercial plastic phantoms and their homogeneity may not always be reproducible and consistent with assumed composition like MixDP used in this study. By comparing measured and calculated ionization conversion factors at the calibration depth, the findings of this study provide methods to verify the consistency of a given plastic for the purpose of clinical reference dosimetry.

Journal

  • The Journal of JASTRO

    The Journal of JASTRO 19 (2), 99-107, 2007

    Japanese Society for Therapeutic Radiology and Oncology

References(13)*help

See more

Related Projects

See more

Keywords

Details 詳細情報について

Report a problem

Back to top