title: Dosimetric consequences of rotational errors in radiation therapy of pediatric brain tumor patients.
abstract: OBJECTIVE
  To quantify the rotational offsets and estimate the dose effect of rotation on the target volume and normal tissues in children with brain tumor.
  
  
  METHODS
  Twenty-one pediatric patients with brain tumors were included in this study. Cone-beam CT was performed before each treatment and at the end of every other treatment. Translational offsets were corrected before the treatment. An offline analysis was performed to quantify rotational errors. The treatment plans were altered and recalculated to simulate a rotation of 2° and 4°, and the dose changes were quantified.
  
  
  RESULTS
  1016 CBCT datasets were analyzed for this report. The mean of the rotations were not meaningfully different from zero. 18.1% of the fractions had rotations with a magnitude ≥2°, 5.0% had rotations ≥3° and 0.9% had rotations ≥4°. For the 2° rotational simulation, the gEUD values of the PTV and critical structures changed by less than 2%. For the 4° simulation, parallel type normal structures had minor changes (<2%), but serial type normal structures and the PTV had changes of 10% and 5%, respectively.
  
  
  CONCLUSIONS
  The majority of rotational errors observed were less than 1°. A rotational error of 2° produced negligible changes in the gEUD to critical structures or target volumes. Rotational errors ≥4° produced undesirable results, therefore, at a minimum, errors >2° should be corrected.
authors: Department of Radiological Sciences, St. Jude Children's Research Hospital, Memphis, TN 38120, USA. chris.beltran@stjude.org
authors: Chris
authors: C
authors: Beltran
authors: Alexander
authors: A
authors: Pegram
authors: Thomas E
authors: TE
authors: Merchant
mesh_terms: D000293:Adolescent; D001932:Brain Neoplasms / Q000532:radiotherapy*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D011879:Radiotherapy Dosage; D061106:Radiotherapy Setup Errors; D016683:Supine Position; D055815:Young Adult