Quantitative analysis of in-air output ratio

Hisayuki Miyashita, Shogo Hatanaka, Yukio Fujita, Shimpei Hashimoto, Atsushi Myojyoyama, Hidetoshi Saitoh

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


Output factor (Scp) is one of the important factors required to calculate monitor unit (MU), and is divided into two components: phantom scatter factor (Sp) and in-air output ratio (Sc). Generally, Sc for arbitrary fields are calculated using several methods based on Sc determined by the absorbed dose measurement for several square fields. However, there are calculation errors when the treatment field has a large aspect ratio and the opening of upper and lower collimator are exchanged. To determine Sc accurately, scattered photons from the treatment head and backscattered particles into the monitor chamber must be analyzed individually. In this report, a simulation model that agreed well with measured Sc was constructed and dose variation by scattered photons from the treatment head and by backscattered particles into the monitor chamber was analyzed quantitatively. The results showed that the contribution of scattered photons from the primary collimator was larger than that of the flattening filter, and backscattered particles were affected by not only the upper jaw but also the lower jaw. In future work, a new Sc determination algorism based on the result of this report will be proposed.

Original languageEnglish
Pages (from-to)553-560
Number of pages8
JournalJournal of radiation research
Issue number3
Publication statusPublished - 2013 May
Externally publishedYes


  • Backscattered particles
  • Collision water kerma
  • Monte Carlo method
  • Scattered photon
  • in-air output ratio

ASJC Scopus subject areas

  • Medicine(all)


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