A method for increased dose conformity and segment reduction for sMLC delivered IMRT treatment of the prostate

Robert A. Price, Scott Murphy, Shawn W. McNeeley, C. M.Charlie Ma, Eric Horwitz, Benjamin Movsas, Adam Raben, Alan Pollack

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


Purpose: The focus of this work is to develop a practical planning method that results in increased dose conformity and reduced treatment time for segmental multileaf collimation (sMLC) based intensity-modulated radiation therapy (IMRT) delivery. Methods and Materials: Additional regions for dose constraint are introduced within the normal tissue during the planning process by designing a series of concentric ellipsoids around the target. A dose gradient is then defined by assigning dose constraints to each concentric region. The technique was tested at two centers and data for 26 and 10 patients, respectively, are presented allowing for differences in treatment technique, beam energy, ellipsoid definition, and prescription dose. At both centers, a series of patients previously treated for prostate cancer with IMRT were selected, and comparisons were made between the original and new plans. Results: While meeting target dose specifications and normal tissue constraints, the average number of beam directions decreased by 1.6 with a standard error (SE) of 0.1. The average time for delivery at center 1 decreased by 29.0% with an SE of 2.0%, decreasing from 17.5 min to 12.3 min. The average time for delivery at center 2 decreased by 29.9% with an SE of 3.8%, decreasing from 11 min to 7.7 min. The amount of nontarget tissue receiving D100 decreased by 15. 7% with an SE of 2.4%. Nontarget tissue receiving D95, D 90, and D50 decreased by 16.3, 15.1, and 19.5%, respectively, with SE values of approximately 2% at center 1. Corresponding values for D100, D95, D90, and D50 decreased by 13.5, 16.7, 17.1, and 5.1%, respectively, with SE values of less than 3% at center 2. Conclusions: By designating subsets of tissue as concentric regions around the target(s) and carefully defining each region's dose constraints, we have gained an increased measure of control over the region outside the target boundaries. This increased control manifests as two distinct endpoints that are beneficial to the IMRT process: increased dose conformity and decreased treatment time.

Original languageEnglish (US)
Pages (from-to)843-852
Number of pages10
JournalInternational Journal of Radiation Oncology Biology Physics
Issue number3
StatePublished - Nov 1 2003
Externally publishedYes


  • Conformal prostate irradiation
  • IMRT
  • sMLC

ASJC Scopus subject areas

  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Radiation


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