title: Comparison of two different IMRT planning techniques in the treatment of nasopharyngeal carcinoma. Effect on parotid gland radiation doses.
abstract: OBJECTIVE
  To compare the effect of two different intensity-modulated radiation therapy (IMRT) planning techniques on parotid gland doses in patients with nasopharyngeal carcinoma (NPC).
  
  
  METHODS
  Radiotherapy for 10 NPC patients referred to the University of Istanbul Cerrahpasa Medical School was planned with arc- and static seven-field IMRT. The simultaneous integrated boost (SIB) technique was used to deliver 70 Gy (2.12 Gy per fraction) to the primary tumor and involved nodes; 60 Gy (1.81 Gy per fraction) to the entire nasopharynx and 54 Gy (1.63 Gy per fraction) to elective lymph nodes in 33 fractions. Plans also aimed to keep the mean parotid dose below 26 Gy and limit the maximum doses to the spinal cord and brain stem to 45 and 54 Gy, respectively. Mean parotid gland doses for the two planning techniques were compared using a paired t-test. Target coverage and dose inhomogeneity were evaluated by calculating conformity- (CI) and homogeneity index (HI) values.
  
  
  RESULTS
  Target coverage and dose homogeneity were identical and good for both planning techniques: CI = 1.05 ± 0.08 and 1.05 ± 0.08; HI = 1.08 ± 0.02 and 1.07 ± 0.01 for arc- and static field IMRT, respectively. Mean doses to contralateral parotid glands were 25.73 ± 4.27 and 27.73 ± 3.5 Gy(p = 0.008) for arc- and static field IMRT plans, respectively, whereas mean ipsilateral parotid doses were 30.65 ± 6.25 and 32.55 ± 5.93 Gy (non-significant p-value), respectively. Mean monitor units (MU) per fraction for the 10 patients were considerably lower for arc- than for static field treatments-540.5 ± 130.39 versus 1288.4 ± 197.28 (p < 0.001).
  
  
  CONCLUSIONS
  Normal tissues--particularly the parotid glands--are better spared with the arc technique in patients with NPC. MU and treatment times are considerably reduced in arc IMRT plans.
authors.affiliation: Department of Radiation Oncology, Şişli Etfal Teaching and Research Hospital, 34303, Istanbul, Turkey. dresengulkocak@gmail.com
authors.forename: E K
authors.initials: EK
authors.lastname: Uzel
authors.forename: S
authors.initials: S
authors.lastname: Karaçam
authors.forename: O
authors.initials: O
authors.lastname: Eliçin
authors.forename: O
authors.initials: O
authors.lastname: Uzel
mesh_terms: D001933:Brain Stem / Q000528:radiation effects; D003198:Computer Simulation; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D019583:Dose Fractionation, Radiation; D006801:Humans; D008198:Lymph Nodes / Q000528:radiation effects; D008207:Lymphatic Metastasis / Q000532:radiotherapy; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D010306:Parotid Gland / Q000528:radiation effects*; D011446:Prospective Studies; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000175:diagnosis* / Q000209:etiology* / Q000517:prevention & control; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013116:Spinal Cord / Q000528:radiation effects; D014987:Xerostomia / Q000175:diagnosis / Q000209:etiology