title: Investigation of the added value of high-energy electrons in intensity-modulated radiotherapy: four clinical cases.
abstract: OBJECTIVE
  Intensity-modulated radiotherapy (IMRT) with photon beams is currently pursued in many clinics. Theoretically, inclusion of intensity- and energy-modulated high-energy electron beams (15-50 MeV) offers additional possibilities to improve radiotherapy treatments of deep-seated tumors. In this study the added value of high-energy electron beams in IMRT treatments was investigated.
  
  
  METHODS
  In a comparative treatment planning study, conventional treatment plans and various types of IMRT plans were constructed for four clinical cases (cancer of the bladder, pancreas, chordoma of the sacrum, and breast). The conventional plans were used for the actual treatment of the patients. The IMRT plans were optimized using the Orbit optimization code (Löf et al., 2000) with a radiobiologic objective function. The IMRT plans were either photon or combined electron and photon beam plans, with or without dose homogeneity constraints assuming standard or increased radiosensitivities of organs at risk.
  
  
  RESULTS
  Large improvements in expected treatment outcome are found using IMRT plans compared to conventional plans, but differences in tumor control probability (TCP) and normal tissue complication probabilities (NTCP) values between IMRT plans with and without electrons are small. However, the use of electrons improves the dose-volume histograms for organs at risk, especially at lower dose levels (e.g., 0-40 Gy).
  
  
  CONCLUSIONS
  This preliminary study indicates that addition of higher energy electrons to IMRT can only marginally improve treatment outcome for the selected cases. The dose-volume histograms of organs at risk show improvements for IMRT with higher energy electrons, which may reduce tumor induction but does not substantially reduce NTCP.
authors.affiliation: Daniel den Hoed Cancer Center, University Hospital Rotterdam, Rotterdam, The Netherlands. erik.korevaar@dmr.usz.ch
authors.forename: Erik W
authors.initials: EW
authors.lastname: Korevaar
authors.forename: Henk
authors.initials: H
authors.lastname: Huizenga
authors.forename: Johan
authors.initials: J
authors.lastname: Löf
authors.forename: Joep C
authors.initials: JC
authors.lastname: Stroom
authors.forename: Jan Willem H
authors.initials: JW
authors.lastname: Leer
authors.forename: Anders
authors.initials: A
authors.lastname: Brahme
mesh_terms: D000368:Aged; D001859:Bone Neoplasms / Q000532:radiotherapy*; D001943:Breast Neoplasms / Q000532:radiotherapy*; D002817:Chordoma / Q000532:radiotherapy*; D004583:Electrons / Q000627:therapeutic use; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010190:Pancreatic Neoplasms / Q000532:radiotherapy*; D017785:Photons / Q000627:therapeutic use; D055585:Physical Phenomena; D010825:Physics; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy; D012447:Sacrum; D001749:Urinary Bladder Neoplasms / Q000532:radiotherapy*