title: Dosimetric evaluation of an ipsilateral intensity modulated radiotherapy beam arrangement for parotid malignancies.
abstract: BACKGROUND
  We conducted a dosimetric comparison of an ipsilateral beam arrangement for intensity modulated radiotherapy (IMRT) with off-axis beams.
  
  
  METHODS
  Six patients who received post-operative radiotherapy (RT) for parotid malignancies were used in this dosimetric study. Four treatment plans were created for each CT data set (24 plans): 1) ipsilateral 4-field off-axis IMRT (4fld-OA), 2) conventional wedge pair (WP), 3) 7 field co-planar IMRT (7fld), and 4) ipsilateral co-planar 4-field quartet IMRT (4fld-CP). Dose, volume statistics for the planning target volumes (PTVs) and planning risk volumes (PRVs) were compared for the four treatment techniques.
  
  
  RESULTS
  Wedge pair plans inadequately covered the deep aspect of the PTV. The 7-field IMRT plans delivered the largest low dose volumes to normal tissues. Mean dose to the contralateral parotid was highest for 7 field IMRT. Mean dose to the contralateral submandibular gland was highest for 7 field IMRT and WP. 7 field IMRT plans had the highest dose to the oral cavity. The mean doses to the brainstem, spinal cord, ipsilateral temporal lobe, cerrebellum and ipsilateral cochlea were similar among the four techniques.
  
  
  CONCLUSIONS
  For postoperative treatment of the parotid bed, 4-field ipsilateral IMRT techniques provided excellent coverage while maximally sparing the contralateral parotid gland and submandibular gland.
authors.affiliation: Department of Radiation Oncology, Kocaeli University Faculty of Medicine, Kocaeli, Turkey ; Department of Radiation Oncology, University of North Carolina Hospitals, Chapel Hill, NC, USA.
authors.forename: Eda
authors.initials: E
authors.lastname: Yirmibesoglu
authors.forename: David V
authors.initials: DV
authors.lastname: Fried
authors.forename: Mark
authors.initials: M
authors.lastname: Kostich
authors.forename: Julian
authors.initials: J
authors.lastname: Rosenman
authors.forename: William
authors.initials: W
authors.lastname: Shockley
authors.forename: Mark
authors.initials: M
authors.lastname: Weissler
authors.forename: Adam
authors.initials: A
authors.lastname: Zanation
authors.forename: Bhishamjit
authors.initials: B
authors.lastname: Chera
keywords: dosimetry; intensity modulated radiotherapy; parotid