title: Functional avoidance of lung in plan optimization with an aperture-based inverse planning system.
abstract: OBJECTIVE
  To implement SPECT-based optimization in an anatomy-based aperture inverse planning system for the functional avoidance of lung in thoracic irradiation.
  
  
  METHODS
  SPECT information has been introduced as a voxel-by-voxel modulation of lung importance factors proportionally to the local perfusion count. Fifteen cases of lung cancer have been retrospectively analyzed by generating angle-optimized non-coplanar plans, comparing a purely anatomical approach and our functional approach. Planning target volume coverage and lung sparing have been compared. Statistical significance was assessed by a Wilcoxon matched pairs test.
  
  
  RESULTS
  For similar target coverage, perfusion-weighted volume receiving 10 Gy was reduced by a median of 2.2% (p=0.022) and mean perfusion-weighted lung dose, by a median of 0.9 Gy (p=0.001). A separate analysis of patients with localized or non-uniform hypoperfusion could not show which would benefit more from SPECT-based treatment planning. Redirection of dose sometimes created overdosage regions in the target volume. Plans consisted of a similar number of segments and monitor units.
  
  
  CONCLUSIONS
  Angle optimization and SPECT-based modulation of importance factors allowed for functional avoidance of the lung while preserving target coverage. The technique could be also applied to implement PET-based modulation inside the target volume, leading to a safer dose escalation.
authors.affiliation: Département de Physique, de Génie Physique et d'Optique, Université Laval, Québec, Que., Canada.
authors.forename: Jason
authors.initials: J
authors.lastname: St-Hilaire
authors.forename: Caroline
authors.initials: C
authors.lastname: Lavoie
authors.forename: Anne
authors.initials: A
authors.lastname: Dagnault
authors.forename: Frédéric
authors.initials: F
authors.lastname: Beaulieu
authors.forename: Francis
authors.initials: F
authors.lastname: Morin
authors.forename: Luc
authors.initials: L
authors.lastname: Beaulieu
authors.forename: Daniel
authors.initials: D
authors.lastname: Tremblay
mesh_terms: D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008168:Lung / Q000528:radiation effects*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D008297:Male; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D018709:Statistics, Nonparametric; D015899:Tomography, Emission-Computed, Single-Photon; D016896:Treatment Outcome