Inter- and intrafraction patient positioning uncertainties for intracranial radiotherapy: A study of four frameless, thermoplastic mask-based immobilization strategies using daily cone-beam CT

Erik Tryggestad, Matthew Christian, Eric Ford, Carmen Kut, Yi Le, Giuseppe Sanguineti, Danny Y. Song, Lawrence Kleinberg

Research output: Contribution to journalArticlepeer-review

Abstract

Purpose: To determine whether frameless thermoplastic mask-based immobilization is adequate for image-guided cranial radiosurgery. Methods and Materials: Cone-beam CT localization data from patients with intracranial tumors were studied using daily pre- and posttreatment scans. The systems studied were (1) Type-S IMRT (head only) mask (Civco) with head cushion; (2) Uni-Frame mask (Civco) with head cushion, coupled with a BlueBag body immobilizer (Medical Intelligence); (3) Type-S head and shoulder mask with head and shoulder cushion (Civco); (4) same as previous, coupled with a mouthpiece. The comparative metrics were translational shift magnitude and average rotation angle; systematic inter-, random inter-, and random intrafraction positioning error was computed. For strategies 1-4, respectively, the analysis for interfraction variability included data from 20, 9, 81, and 11 patients, whereas that for intrafraction variability included a subset of 7, 9, 16, and 8 patients. The results were compared for statistical significance using an analysis of variance test. Results: Immobilization system 4 provided the best overall accuracy and stability. The mean interfraction translational shifts (± SD) were 2.3 (± 1.4), 2.2 (± 1.1), 2.7 (± 1.5), and 2.1 (± 1.0) mm whereas intrafraction motion was 1.1 (± 1.2), 1.1 (± 1.1), 0.7 (± 0.9), and 0.7 (± 0.8) mm for devices 1-4, respectively. No significant correlation between intrafraction motion and treatment time was evident, although intrafraction motion was not purely random. Conclusions: We find that all frameless thermoplastic mask systems studied are viable solutions for image-guided intracranial radiosurgery. With daily pretreatment corrections, symmetric PTV margins of 1 mm would likely be adequate if ideal radiation planning and targeting systems were available.

Original languageEnglish
Pages (from-to)281-290
Number of pages10
JournalInternational Journal of Radiation Oncology Biology Physics
Volume80
Issue number1
DOIs
Publication statusPublished - May 1 2011

Keywords

  • Frameless thermoplastic mask immobilization
  • Image-guided cranial radiosurgery
  • Interfraction positioning uncertainties
  • Intrafraction positioning uncertainties
  • Patient positioning accuracy

ASJC Scopus subject areas

  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Radiation
  • Cancer Research

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