25 MV X-ray beam characteristics from a 35 MeV linear accelerator

James A. Purdy, David J. Keys, Fred G. Abrath

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


This manuscript presents characteristic dosimetry measurements for the 25 MV X-ray beam from the Varian Associates Clinac® 35 linear accelerator. The quality of the beam is expressed by its attenuation as a narrow beam in lead. Percentage depth dose tables are given as a function of field size for square fields. Tissue-phantom ratios are tabulated for square field sizes. A study of the variation of the dose in the buildup region demonstrates that surface dose and the depth of maximum dose is a strong function of the field size. Other beam parameters measured and discussed include field flatness and symmetry, penumbra, and applicability of inverse square law.

Original languageEnglish
Pages (from-to)337-343
Number of pages7
JournalInternational journal of radiation oncology, biology, physics
Issue number3-4
StatePublished - 1978


  • Dosimetry
  • Linear accelerator
  • Measurement techniques


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