Use of diverging apertures to minimize the edge scatter in passive scattering proton therapy

Tianyu Zhao, Bin Cai, Baozhou Sun, Kevin Grantham, Sasa Mutic, Eric Klein

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


The purpose of this study was to evaluate the use of diverging-cut aperture to minimize collimator contamination in proton therapy. Two sets of apertures with nondivergent and divergent edge were fabricated to produce a 10cm × 10cm field at the radiation isocenter of a single-room proton therapy unit. Transverse profiles were acquired in a scanning water tank with both aperture sets. Up to 9.5% extra dose was observed from aperture scattering near the field edges with the nondivergent aperture set at 2cm above the water surface and remained 3.0% at depth of 10cm. For the divergent set, the contamination was reduced to less than 3.5% and 1.3%, respectively. Our study demonstrated that scattering from apertures contaminated the dose distribution near the field edge at shallow depth. A diverging-cut aperture was capable of reducing the contamination and is recommended for use in passive scattering proton therapy, especially when critical organs are lateral and proximal to the target at shallow depth.

Original languageEnglish
Pages (from-to)367-372
Number of pages6
JournalJournal of applied clinical medical physics
Issue number5
StatePublished - 2015


  • Aperture
  • Edge scatter
  • Passive scattering
  • Proton


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