title: Development and evaluation of multiple isocentric volumetric modulated arc therapy technique for craniospinal axis radiotherapy planning.
abstract: OBJECTIVE
  To develop and compare a volumetric modulated arc therapy (VMAT) technique with conventional radiotherapy for craniospinal irradiation with respect to improved dose conformity and homogeneity in the planning target volume (PTV) and to reduced dose to organs at risk (OAR).
  
  
  METHODS
  Conventional craniospinal axis radiotherapy plans of 5 patients were acquired. The median (range) length of the PTV was 58.9 (48.1-83.7) cm. The 6-MV VMAT plans were inversely planned with one isocenter near the base of the brain and the minimum number of isocenters required for the specified lengths of spine. The plans were optimized with high weighting for PTV coverage and low weighting for OAR sparing. Conformity and heterogeneity indices, dose-volume histograms, mean doses, and non-PTV integral doses from the two plans (prescription dose 23.4 Gy in 13 fractions) were compared.
  
  
  RESULTS
  The median (range) conformity index of VMAT was 1.22 (1.09-1.45), compared with 1.69 (1.44-2.67) for conventional plans (p = 0.04). The median (range) heterogeneity index was also lower for VMAT compared with conventional plans: 1.04 (1.03-1.07) vs. 1.12 (1.09-1.19), respectively (p = 0.04). A significant reduction of mean and maximum doses was observed in the heart, thyroid, esophagus, optic nerves, and eyes with VMAT when compared with conventional plans. A decrease in body V(10Gy) was observed, but for 4 of 5 patients non-PTV integral dose was increased with VMAT when compared with the conventional plans.
  
  
  CONCLUSIONS
  A VMAT technique to treat the craniospinal axis significantly reduces OAR dose, potentially leading to lower late organ toxicity. However, this is achieved at the expense of increased low-dose volumes, which is inherent to the technique, carrying a potentially increased risk of secondary malignancies.
authors.affiliation: Joint Department of Physics, Royal Marsden National Health Service Foundation Trust, Sutton, Surrey, United Kingdom. Young.Lee@rmh.nhs.uk
authors.forename: Young K
authors.initials: YK
authors.lastname: Lee
authors.forename: Corrinne J
authors.initials: CJ
authors.lastname: Brooks
authors.forename: James L
authors.initials: JL
authors.lastname: Bedford
authors.forename: Alan P
authors.initials: AP
authors.lastname: Warrington
authors.forename: Frank H
authors.initials: FH
authors.lastname: Saran
mesh_terms: D002528:Cerebellar Neoplasms / Q000532:radiotherapy*; D002648:Child; D002675:Child, Preschool; D004947:Esophagus / Q000528:radiation effects; D005123:Eye / Q000528:radiation effects; D006321:Heart / Q000528:radiation effects; D006801:Humans; D008297:Male; D008527:Medulloblastoma / Q000532:radiotherapy*; D009900:Optic Nerve / Q000528:radiation effects; D058958:Organs at Risk / Q000528:radiation effects*; D056888:Patient Positioning / Q000379:methods; D011832:Radiation Injuries / Q000517:prevention & control*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects / Q000379:methods*; D012189:Retrospective Studies; D013961:Thyroid Gland / Q000528:radiation effects; D047368:Tumor Burden; D055815:Young Adult