Treatment planning and delivery of IMRT using 6 and 18 MV photon beams without flattening filter

Sotirios Stathakis, Carlos Esquivel, Alonso Gutierrez, Courtney R. Buckey, Niko Papanikolaou

Research output: Contribution to journalArticlepeer-review

55 Scopus citations


In light of the increasing use of intensity modulated radiation therapy (IMRT) in modern radiotherapy practice, the use of a flattening filter may no longer be necessary. Commissioning data have been measured for a Varian 23EX linear accelerator with 6 and 18 MV photon energies without a flattening filter. Measurements collected for the commissioning of the linac included percent depth dose curves and profiles for field sizes ranging from 2×2 to 40×40 cm2 as defined by the jaws and multileaf collimator. Machine total scatter factors were measured and calculated. Measurements were used to model the unflattened beams with the Pinnacle3 treatment planning system. IMRT plans for prostate, lung, brain and head and neck cancer cases were generated using the flattening filter and flattening filter-free beams. From our results, no difference in the quality of the treatment plans between the flat and unflattened photon beams was noted. There was however a significant decrease in the number of monitor units required for unflattened beam treatment plans due to the increase in linac output-approximately two times and four times higher for the 6 and 18 MV, respectively.

Original languageEnglish (US)
Pages (from-to)1629-1637
Number of pages9
JournalApplied Radiation and Isotopes
Issue number9
StatePublished - Sep 2009


  • Flattening filter free linac
  • Intensity modulated radiation therapy
  • Photons
  • Radiation therapy

ASJC Scopus subject areas

  • Radiation


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