title: Different treatment planning protocols can lead to large differences in organ at risk sparing.
abstract: OBJECTIVE
  Different planning protocols may define varying planning target volume (PTV) dose criteria. We investigated the hypothesis that this could result in differences in organ-at-risk (OAR) sparing.
  
  
  METHODS
  Volumetric modulated arc therapy plans were created for ten locally advanced head and neck cancer patients following PTV criteria specified by the RTOG, EORTC and institutional (VUmc) protocols. Resulting plans were evaluated on the basis of the homogeneity index, calculated for the boost/elective PTVs as HIB/HIE=100%*(D2%-D98%)/D50% and mean dose to individual and composite salivary (compsal) and swallowing (compswal) OARs.
  
  
  RESULTS
  RTOG plans were the most homogeneous, with mean HIB of 8.2±0.9%, compared to 9.5±1.0%/11.6±1.5% for the VUmc/EORTC plans. EORTC plans provided most OAR sparing, with compsal/compswal doses of 24.6±7.7/22.9±4.2Gy, compared to 32.2±9.7/29.9±4.2Gy and 28.4±8.1/24.7±5.3Gy for RTOG and VUmc, respectively. EORTC provided 7.2/7.7Gy mean dose reductions to the contra/ipsilateral parotid glands compared to RTOG.
  
  
  CONCLUSIONS
  Different planning protocols resulted in different levels of PTV dose homogeneity. We observed differences of up to ⩾7Gy in composite and individual mean OAR doses. This could influence rates of toxicity and should be taken into account when comparing clinical studies. A consensus should be reached between major trial groups on appropriate PTV parameters.
authors.affiliation: Department of Radiotherapy, VU University Medical Center, Amsterdam, The Netherlands. Electronic address: j.tol@vumc.nl.
authors.forename: Jim P
authors.initials: JP
authors.lastname: Tol
authors.affiliation: Department of Radiotherapy, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Max
authors.initials: M
authors.lastname: Dahele
authors.affiliation: Department of Radiotherapy, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Patricia
authors.initials: P
authors.lastname: Doornaert
authors.affiliation: Department of Radiotherapy, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Slotman
authors.affiliation: Department of Radiotherapy, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Wilko F A R
authors.initials: WF
authors.lastname: Verbakel
mesh_terms: D002985:Clinical Protocols; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D058958:Organs at Risk / Q000528:radiation effects*; D010306:Parotid Gland; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods
keywords: OAR sparing; PTV dose homogeneity; Planning protocols