title: Which is the most optimal technique to spare hippocampus?-Dosimetric comparisons of SCRT, IMRT, and tomotherapy.
abstract: OBJECTIVE
  To evaluate current focal high precision radiotherapy (RT) techniques to spare hippocampi most optimally, in view of mounting clinical evidence to preserve neurocognition.
  
  
  METHODS
  Computed tomography/magnetic resonance imaging (CT/MRI) datasets of 10 patients with benign/low-grade brain tumors, treated with focal conformal RT were replanned with helical tomotherapy (Tomo), intensity-modulated radiotherapy (IMRT) with high definition multileaf collimator (HD-MLC), and forward planning stereotactic conformal radiotherapy (SCRT). The primary planning objective was to encompass 99% of planning target volume (PTV) by 95% of prescribed dose (54 Gy/30#). Assessments included target coverage (TC), homogeneity index (HI), and maximum (max) and minimum (min) dose. Hippocampal dose was assessed with mean, maximum, minimum, median dosem and various dose levels.
  
  
  RESULTS
  Mean V 95 for PTV coverage in Tomo, IMRT, and SCRT were 99.7, 99.4, and 98.3%, respectively. PTV coverage was significantly better in Tomo and IMRT compared to SCRT (P = 0.03). Tomotherapy (HI ≤ 0.06) and IMRT (HI ≤ 0.06) plans were more homogenous than SCRT (HI > 0.7) (P = 0.00). Right hippocampus mean dose with Tomo (20Gy) was 18.5% less than SCRT (30 Gy); but for left hippocampus, difference decreased to 3.3% (Tomo-32.2Gy and SCRT-34Gy). At 30% dose level, 9% more volume of right hippocampus was treated in IMRT and 20% in SCRT when compared to Tomo plan. At 80% dose, 6 and 12% more volumes were treated with IMRT and SCRT, respectively, in comparison to Tomo plan. For left hippocampus all three techniques were comparable.
  
  
  CONCLUSIONS
  Tomotherapy and Linear accelerator (LINAC)-based IMRT achieved significantly better PTV coverage than forward planned SCRT. Tomo as compared to SCRT and IMRT plans showed trend towards significant sparing of the contralateral hippocampus, in eccentrically located tumors.
authors.forename: Vikas
authors.initials: V
authors.lastname: Kothavade
authors.forename: S V
authors.initials: SV
authors.lastname: Jamema
authors.forename: Tejpal
authors.initials: T
authors.lastname: Gupta
authors.forename: Sona
authors.initials: S
authors.lastname: Pungavkar
authors.forename: Mahesh
authors.initials: M
authors.lastname: Upasani
authors.forename: Shashikant
authors.initials: S
authors.lastname: Juvekar
authors.affiliation: Department of Radiation Oncology, Global Hospital, Mumbai, Maharashtra, India.
authors.forename: Rakesh
authors.initials: R
authors.lastname: Jalali
mesh_terms: D000293:Adolescent; D000328:Adult; D001932:Brain Neoplasms / Q000473:pathology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006624:Hippocampus / Q000473:pathology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult