title: Sparing the contralateral submandibular gland without compromising PTV coverage by using volumetric modulated arc therapy.
abstract: BACKGROUND
  Salivary gland function decreases after radiation doses of 39 Gy or higher. Currently, submandibular glands are not routinely spared. We implemented a technique for sparing contralateral submandibular glands (CLSM) during contralateral elective neck irradiation without compromising PTV coverage.
  
  
  METHODS
  Volumetric modulated arc therapy (RapidArc™) plans were applied in 31 patients with stage II-IV HNC without contralateral neck metastases, all of whom received elective treatment to contralateral nodal levels II-IV. Group 1 consisted of 21 patients undergoing concurrent chemo-radiotherapy, with elective nodal doses of 57.75 Gy (PTVelect) and 70 Gy to tumor and pathological nodes (PTVboost) in 7 weeks. Group 2 consisted of 10 patients treated with radiotherapy to 54.45 Gy to PTVelect and 70 Gy to PTVboost in 6 weeks. All clinical plans spared the CLSM using individually adapted constraints. For each patient, a second plan was retrospectively generated without CLSM constraints ('non-sparing plan').
  
  
  RESULTS
  PTV coverage was similar for both plans, with 98.7% of PTVelect and 99.2% of PTVboost receiving ≥95% of the prescription dose. The mean CLSM dose in group 1 was 33.2 Gy for clinical plans, versus 50.6 Gy in 'non-sparing plans' (p < 0.001). In group 2, mean CLSM dose was 34.4 Gy for clinical plans, and 46.8 Gy for non-sparing plans (p = 0.002).
  
  
  CONCLUSIONS
  Elective radiotherapy to contralateral nodal levels II-IV using RapidArc consistently limited CLSM doses well below 39 Gy, without compromising PTV-coverage. Future studies will reveal if this extent of dose reduction can reduce patient symptoms.
authors.affiliation: Department of Radiation Oncology, VU University Medical Center, PB 7057, 1007 MB Amsterdam, The Netherlands. p.doornaert@vumc.nl
authors.forename: Patricia
authors.initials: P
authors.lastname: Doornaert
authors.forename: Wilko F A R
authors.initials: WF
authors.lastname: Verbakel
authors.forename: Derek H F
authors.initials: DH
authors.lastname: Rietveld
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Slotman
authors.forename: Suresh
authors.initials: S
authors.lastname: Senan
mesh_terms: D003131:Combined Modality Therapy / Q000379:methods; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000517:prevention & control*; D011874:Radiometry / Q000379:methods; D011878:Radiotherapy / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012469:Salivary Glands / Q000528:radiation effects*; D013363:Submandibular Gland / Q000473:pathology* / Q000528:radiation effects*; D014987:Xerostomia / Q000517:prevention & control