Evaluation of Silverman® and Posifix® headrests for head and neck immobilisation

Purpose : The accurate delivery of intensity modulated radiotherapy (IMRT), volumetric‐modulated arc therapy (VMAT) and conformal head and neck (H&N) radiotherapy (RT) relies on patient stabilisation. With the multitude of products and variations available, it is imperative to investigate which product or combination of products offer the most optimal immobilisation. This quality improvement paper investigates the feasibility of using Posifix® (Civco Medical Solutions, Iowa, USA) headrests compared with Silverman® (Civco Medical Solutions, Iowa, USA) headrests in H&N RT stabilisation. This investigation is based on the hypothesis that foam Posifix® headrests may improve stabilisation and reproducibility as compared with the rigid plastic cast moulds of Silverman® headrests. Methods : A retrospective group of 12 consecutive patients (six Silverman® and six Posifix®) were used to evaluate the accuracy of positioning from planning to treatment. In the assessment, 204 treatment portal images were matched to planning digitally reconstructed radiographs (DRR). The resultant shifts were documented for anterior/posterior and lateral films. For all three directions; left/right, anterior/posterior and superior/inferior (x, y and z) set‐up deviations from the planning DRR were measured and averaged. A change in patient position by removal or addition of plastic spacers (shims) was collated from the treatment set‐up sheet. Results : A total of 33 shifts of ≥ 3 mm were required for Silverman® headrests compared with 11 for Posifix® headrests. Total shim adjustments made were 10 and 0 for Silverman® and Posifix® headrests respectively. Conclusion : Using Posifix® headrests reduced shifts of ≥ 3 mm and patient set‐up adjustments. As a result, Posifix® headrests have been implemented as part of the department's protocol for head and neck patient positioning.