A prospective study of supine versus prone positioning and whole-body thermoplastic mask fixation for craniospinal radiotherapy in adult patients.

Abstract

To evaluate neuroaxis irradiation for adults in the supine position using head body thermoplastic mask fixation, from the aspects of dose distribution, patient comfort and set-up accuracy. Nine of the 12 adult patients were positioned for craniospinal axis irradiation in both prone and supine positions. After mask fixation and planning CTs in both positions, a questionnaire relating to the comfort was completed. The doses to the target and to the organs at risk of the 3D conformal plans in the supine and prone positions were compared. Portal images of all 12 patients irradiated in the supine position were evaluated, the van Herk formulas being used to calculate the systemic and random errors. No significant difference was found between the prone and supine positions target coverage, the dose homogeneity and the dose to the organs at risk. The supine position was considered more comfortable by the patients (scores of 2.8 versus 4.29), with a vector random error of 3.27 mm, and a systematic error of 0.32 mm. The largest random set-up error was observed in the lateral direction: 4.83 mm. The more comfortable supine position is recommended for craniospinal irradiation in adult patients. Whole-body thermoplastic mask immobilization provides excellent repositioning accuracy.