title: Swallowing sparing intensity modulated radiotherapy (SW-IMRT) in head and neck cancer: Clinical validation according to the model-based approach.
abstract: OBJECTIVE
  The aim of this study was to clinically validate a multivariable normal tissue complication probability (NTCP) model for grade 2-4 swallowing dysfunction at 6months after radiotherapy or chemoradiation (SWALM6) in head and neck cancer patients treated with swallowing sparing intensity modulated radiotherapy (SW-IMRT) and to test if SW-IMRT resulted in a reduction of the prevalence of SWALM6.
  
  
  METHODS
  The primary endpoint was SWALM6. For all 186 patients, a standard IMRT (parotid sparing) and a SW-IMRT plan (additional constraints for swallowing organs at risk) was created. The difference in NTCP for SWALM6 (ΔNTCPSWALM6=NTCPstandard-NTCPSW-IMRT) was calculated. Patients were treated with SW-IMRT. The external validation of the NTCP model was analyzed by comparing performance measures.
  
  
  RESULTS
  The mean ΔNTCPSWALM6 was 4.9% (range 0.01-17.3%), with a significant lower mean predicted NTCPSW-IMRT of 22.6% (95% CI 20.2-24.9%), compared to NTCPstandard of 27.5% (95% CI 24.9-29.9%) (p<0.001). There was a perfect correspondence of NTCPSW-IMRT with the observed prevalence of SWALM6 (22.6%). The overall model performance, discrimination and 'goodness of fit' were good.
  
  
  CONCLUSIONS
  We externally validated the multivariable NTCP model for SWALM6 in SW-IMRT treated patients, showing reduced swallowing dysfunction by reducing the dose parameters included in this NTCP model.
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, The Netherlands.
authors.forename: Miranda E M C
authors.initials: ME
authors.lastname: Christianen
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, The Netherlands.
authors.forename: Arjen
authors.initials: A
authors.lastname: van der Schaaf
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, The Netherlands.
authors.forename: Hans Paul
authors.initials: HP
authors.lastname: van der Laan
authors.affiliation: Department of Otorhinolaryngology-Head and Neck Surgery, VU University Medical Center Amsterdam, The Netherlands.
authors.forename: Irma M
authors.initials: IM
authors.lastname: Verdonck-de Leeuw
authors.affiliation: Department of Radiation Oncology, VU University Medical Center Amsterdam, The Netherlands.
authors.forename: Patricia
authors.initials: P
authors.lastname: Doornaert
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, The Netherlands.
authors.forename: Olga
authors.initials: O
authors.lastname: Chouvalova
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, The Netherlands.
authors.forename: Roel J H M
authors.initials: RJ
authors.lastname: Steenbakkers
authors.affiliation: Department of Otorhinolaryngology-Head and Neck Surgery, VU University Medical Center Amsterdam, The Netherlands.
authors.forename: Charles René
authors.initials: CR
authors.lastname: Leemans
authors.affiliation: Department of Medical Oncology, University of Groningen, University Medical Center Groningen, The Netherlands.
authors.forename: Sjoukje F
authors.initials: SF
authors.lastname: Oosting
authors.affiliation: Department of Otorhinolaryngology-Head and Neck Surgery, University of Groningen, University Medical Center Groningen, The Netherlands.
authors.forename: Bernard F A M
authors.initials: BF
authors.lastname: van der Laan
authors.affiliation: Department of Oral and Maxillofacial Surgery, University of Groningen, University Medical Center Groningen, The Netherlands.
authors.forename: Jan L N
authors.initials: JL
authors.lastname: Roodenburg
authors.affiliation: Department of Radiation Oncology, VU University Medical Center Amsterdam, The Netherlands.
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Slotman
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, The Netherlands.
authors.forename: Hendrik P
authors.initials: HP
authors.lastname: Bijl
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, The Netherlands. Electronic address: j.a.langendijk@umcg.nl.
authors.forename: Johannes A
authors.initials: JA
authors.lastname: Langendijk
mesh_terms: D000293:Adolescent; D000368:Aged; D015331:Cohort Studies; D003679:Deglutition / Q000528:radiation effects*; D003680:Deglutition Disorders / Q000517:prevention & control*; D005260:Female; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D011336:Probability; D011446:Prospective Studies; D011832:Radiation Injuries / Q000517:prevention & control*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D015203:Reproducibility of Results; D055815:Young Adult
keywords: Head and neck cancer; Model based approach; Radiotherapy; Swallowing sparing IMRT