title: Improved VMAT planning for head and neck tumors with an advanced optimization algorithm.
abstract: OBJECTIVE
  In this study, the "Progressive Resolution Optimizer PRO3" (Varian Medical Systems) is compared to the previous version "PRO2" with respect to its potential to improve dose sparing to the organs at risk (OAR) and dose coverage of the PTV for head and neck cancer patients.
  
  
  METHODS
  For eight head and neck cancer patients, volumetric modulated arc therapy (VMAT) treatment plans were generated in this study. All cases have 2-3 phases and the total prescribed dose (PD) was 60-72 Gy in the PTV. The study is mainly focused on the phase 1 plans, which all have an identical PD of 54 Gy, and complex PTV structures with an overlap to the parotids. Optimization was performed based on planning objectives for the PTV according to ICRU83, and with minimal dose to spinal cord, and parotids outside PTV. In order to assess the quality of the optimization algorithms, an identical set of constraints was used for both, PRO2 and PRO3. The resulting treatment plans were investigated with respect to dose distribution based on the analysis of the dose volume histograms.
  
  
  RESULTS
  For the phase 1 plans (PD = 54 Gy) the near maximum dose D2% of the spinal cord, could be minimized to 22 ± 5 Gy with PRO3, as compared to 32 ± 12 Gy with PRO2, averaged for all patients. The mean dose to the parotids was also lower in PRO3 plans compared to PRO2, but the differences were less pronounced. A PTV coverage of V95% = 97 ± 1% could be reached with PRO3, as compared to 86 ± 5% with PRO2. In clinical routine, these PRO2 plans would require modifications to obtain better PTV coverage at the cost of higher OAR doses.
  
  
  CONCLUSIONS
  A comparison between PRO3 and PRO2 optimization algorithms was performed for eight head and neck cancer patients. In general, the quality of VMAT plans for head and neck patients are improved with PRO3 as compared to PRO2. The dose to OARs can be reduced significantly, especially for the spinal cord. These reductions are achieved with better PTV coverage as compared to PRO2. The improved spinal cord sparing offers new opportunities for all types of paraspinal tumors and for re-irradiation of recurrent tumors or second malignancies.
authors.affiliation: Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, Switzerland. Electronic address: norbert.klippel@insel.ch.
authors.forename: Norbert
authors.initials: N
authors.lastname: Klippel
authors.affiliation: Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Schmücking
authors.affiliation: Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, Switzerland.
authors.forename: Dario
authors.initials: D
authors.lastname: Terribilini
authors.affiliation: Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, Switzerland.
authors.forename: Andreas
authors.initials: A
authors.lastname: Geretschläger
authors.affiliation: Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, Switzerland.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Aebersold
authors.affiliation: Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, Switzerland.
authors.forename: Peter
authors.initials: P
authors.lastname: Manser
mesh_terms: D065638:Absorption, Radiation; D000465:Algorithms; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D059351:Organ Sparing Treatments / Q000379:methods*; D058958:Organs at Risk / Q000528:radiation effects; D011835:Radiation Protection / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity
keywords: Head and neck tumors; Kopf- und Hals-Tumore; Radiation oncology; Radio-Onkologie; Therapieplanung; Therapy planning; VMAT