title: Comparison of setup accuracy and intrafraction motion using stereotactic frame versus 3-point thermoplastic mask-based immobilization for fractionated cranial image guided radiation therapy.
abstract: OBJECTIVE
  Prospectively compare patient setup accuracy and intrafraction motion of a standard 3-point thermoplastic mask with the Gill-Thomas-Cosman relocatable stereotactic frame, during fractionated cranial radiation therapy using the ExacTrac system (Brainlab AG Feldkirchen, Germany) for daily online correction.
  
  
  METHODS
  The number of fractions with all postcorrection and post-treatment errors <2 mm was assessed in 21 patients undergoing fractionated stereotactic radiation therapy (13 frame setup, 8 mask setup) using daily online correction. Achievable patient setup accuracy and total intrafraction motion were evaluated. The relative contributions of movement during floor rotation and patient movement to intrafraction motion were calculated.
  
  
  RESULTS
  With daily online correction, patient setup margins can be reduced from 1, 5, and 4 mm in the lateral, longitudinal, and vertical axes for mask setup and from 1-2, 2, and 1 mm, respectively, for frame setup to <1 mm isotropically for either immobilization system. Intrafraction movement was small for frame setup (mean [SD], -0.3 [0.3], -1.1[0.4], and -0.2 [0.6] in lateral, longitudinal and vertical axes, respectively; maximum, -2.7 mm [longitudinal axis]), and mask-setup (mean [SD], -0.4 [0.5], -0.8 [0.7], and 0.0 [0.3], respectively; maximum, -2.0 mm [longitudinal axis]) and is mainly due to floor rotation. Postcorrection and post-treatment errors were all <2 mm in 95% and 99% of fractions in the mask and frame, respectively, meeting the criteria for a 3-mm clinical target volume-planning target volume margin for either immobilization method.
  
  
  CONCLUSIONS
  Daily online correction can compensate for less precise immobilization and permits stereotactic margins to be used for standard thermoplastic masks without the need for specialized mask systems.
authors.affiliation: Department of Clinical Oncology, Royal Marsden NHS Foundation Trust, London, United Kingdom. Electronic address: nrosenfelder@gmail.com.
authors.forename: Nicola Abigail
authors.initials: NA
authors.lastname: Rosenfelder
authors.affiliation: Department of Radiotherapy, Royal Marsden NHS Foundation Trust, London, United Kingdom.
authors.forename: Lee
authors.initials: L
authors.lastname: Corsini
authors.affiliation: Department of Radiotherapy, Royal Marsden NHS Foundation Trust, London, United Kingdom.
authors.forename: Helen
authors.initials: H
authors.lastname: McNair
authors.affiliation: Statistics Unit, Royal Marsden NHS Foundation Trust, London, United Kingdom.
authors.forename: Kjell
authors.initials: K
authors.lastname: Pennert
authors.affiliation: Department of Radiotherapy, Royal Marsden NHS Foundation Trust, London, United Kingdom.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Aitken
authors.affiliation: Department of Physics, Royal Marsden NHS Foundation Trust, London, United Kingdom.
authors.forename: Caroline Mary
authors.initials: CM
authors.lastname: Lamb
authors.affiliation: Department of Physics, Royal Marsden NHS Foundation Trust, London, United Kingdom.
authors.forename: Michelle
authors.initials: M
authors.lastname: Long
authors.affiliation: Department of Clinical Oncology, Royal Marsden NHS Foundation Trust, London, United Kingdom.
authors.forename: Enrico
authors.initials: E
authors.lastname: Clarke
authors.affiliation: Department of Clinical Oncology, Royal Marsden NHS Foundation Trust, London, United Kingdom.
authors.forename: Mauricio
authors.initials: M
authors.lastname: Murcia
authors.affiliation: Department of Clinical Oncology, Royal Marsden NHS Foundation Trust, London, United Kingdom.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Schick
authors.affiliation: Department of Physics, Royal Marsden NHS Foundation Trust, London, United Kingdom.
authors.forename: Kevin
authors.initials: K
authors.lastname: Burke
authors.affiliation: Neuro-oncology Unit, Royal Marsden NHS Foundation Trust, London, United Kingdom.
authors.forename: Sue
authors.initials: S
authors.lastname: Ashley
authors.affiliation: Department of Clinical Oncology, Royal Marsden NHS Foundation Trust, London, United Kingdom.
authors.forename: Vincent
authors.initials: V
authors.lastname: Khoo
authors.affiliation: Neuro-oncology Unit, Royal Marsden NHS Foundation Trust, London, United Kingdom.
authors.forename: Michael
authors.initials: M
authors.lastname: Brada