Background and Purpose: The aim of this study was to determine set-up accuracy when comparing an Orfit® thermoplastic shell to a traditional acetate shell for the treatment of patients with age related macular degeneration.

Method and Materials: 20 patients with age related macular degeneration were sequentially allocated to be positioned in either an Orfit® shell or a traditional acetate shell (ten patients in each group). On each day of treatment, radiographic portal imaging was used to ascertain accuracy by comparison with the CT image and verification radiograph.

Results: 140 portal images were assessed by three independent readers. Pearson Correlation and ANOVA statistics were performed on the data to assess differences between the two types of shell. Inter- and intraobserver variations were also analysed. Results, for both Orfit® and Acetate, revealed that over 95% of error movements were 2 mm or less.

Conclusions: The study indicates that both devices are of comparable accuracy and that the Orfit® shell is an acceptable method of immobilisation for the treatment of age related macular degeneration.