Radiological Physics and Technology

, Volume 11, Issue 2, pp 192–201 | Cite as

Output factor determination based on Monte Carlo simulation for small cone field in 10-MV photon beam

  • Kyohei Fukata
  • Satoru Sugimoto
  • Chie Kurokawa
  • Akito Saito
  • Tatsuya Inoue
  • Keisuke Sasai


The difficulty of measuring output factor (OPF) in a small field has been frequently discussed in recent publications. This study is aimed to determine the OPF in a small field using 10-MV photon beam and stereotactic conical collimator (cone). The OPF was measured by two diode detectors (SFD, EDGE detector) and one micro-ion chamber (PinPoint 3D chamber) in a water phantom. A Monte Carlo simulation using simplified detector model was performed to obtain the correction factor for the detector measurements. About 12% OPF difference was observed in the measurement at the smallest field (7.5 mm diameter) for EDGE detector and PinPoint 3D chamber. By applying the Monte Carlo-based correction factor to the measurement, the maximum discrepancy among the three detectors was reduced to within 3%. The results indicate that determination of OPF in a small field should be carefully performed. Especially, detector choice and appropriate correction factor application are very important in this regard.


Dosimetry Monte Carlo SRS Small field 



The authors would like to thank the radiotherapy-related staffs in Juntendo University Hospital for giving us the opportunity for fruitful measurement.

Compliance with ethical standards

Conflict of interest

We have no conflicts of interest to declare for this study.

Statement of human and animal rights

There is no animal or humans involved in this study.

Informed consent

There are no human subjects involved in this work.


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Copyright information

© Japanese Society of Radiological Technology and Japan Society of Medical Physics 2018

Authors and Affiliations

  1. 1.Cancer CenterKeio University School of MedicineTokyoJapan
  2. 2.Graduate School of MedicineJuntendo UniversityTokyoJapan
  3. 3.Department of Radiation OncologyHiroshima University HospitalHiroshimaJapan
  4. 4.Department of RadiologyJuntendo University Urayasu HospitalTomioka 2-1-1, Urayasu-shi, ChibaJapan

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