Radiological Physics and Technology

, Volume 10, Issue 1, pp 33–40 | Cite as

Evaluation of beam modeling for small fields using a flattening filter-free beam

  • Daisuke KawaharaEmail author
  • Shuichi Ozawa
  • Takeo Nakashima
  • Masamichi Aita
  • Shintaro Tsuda
  • Yusuke Ochi
  • Takuro Okumura
  • Hirokazu Masuda
  • Yoshimi Ohno
  • Yuji Murakami
  • Yasushi Nagata


The characteristics of a flattening filter-free (FFF) beam are different from those of a beam with a flattening filter. For small-field dosimetry, the beam data needed by the radiation treatment planning system (RTPS) includes the percent depth dose (PDD), off-center ratio (OCR), and output factor (OPF) for field sizes down to 3 × 3 cm2 to calculate the beam model. The purpose of this study was to evaluate the accuracy of calculations for the FFF beam by the Eclipse treatment planning system for field sizes smaller than 3 × 3 cm2 (2 × 2 and 1 × 1 cm2). We used 6X and 10X FFF beams by the Varian TrueBeam to produce. The AAA and AXB algorithms of the Eclipse were used to compare the Monte Carlo (MC) calculation and the measurements from three dosimeters, a diode detector, a PinPoint dosimeter, and EBT3 film. The PDD curves and the penumbra width in the OCR calculated by the Eclipse, measured data, and those from the MC calculations were in good agreement to within ±2.8 % and ±0.6 mm, respectively. However, the difference in the OPF values between AAA and AXB for a field size of 1 × 1 cm2 was 5.3 % for the 6X FFF beam and 7.6 % for the 10X FFF beam. Therefore, we have to confirm the small field data that is included for the RTPS commission procedures.


Small field Flattening filter-free (FFF) beam Monte Carlo Output factor 


Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.


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Copyright information

© Japanese Society of Radiological Technology and Japan Society of Medical Physics 2016

Authors and Affiliations

  • Daisuke Kawahara
    • 1
    • 2
    Email author
  • Shuichi Ozawa
    • 3
  • Takeo Nakashima
    • 1
  • Masamichi Aita
    • 1
  • Shintaro Tsuda
    • 1
  • Yusuke Ochi
    • 1
  • Takuro Okumura
    • 1
  • Hirokazu Masuda
    • 1
  • Yoshimi Ohno
    • 1
  • Yuji Murakami
    • 3
  • Yasushi Nagata
    • 3
  1. 1.Section of Radiation Therapy, Department of Clinical SupportHiroshima University HospitalHiroshimaJapan
  2. 2.Course of Medical and Dental Sciences, Graduate School of Biomedical and Health SciencesHiroshima UniversityHiroshimaJapan
  3. 3.Department of Radiation Oncology, Institute of Biomedical and Health SciencesHiroshima UniversityHiroshimaJapan

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