Simple invasive fixation device for fractionated stereotactic LINAC based radiotherapy

Summary.

 Background: The aim of this study was to develop a relocatable fixation device for linear accelerator (LINAC) based fractionated stereotactic radiotherapy.

 Method: The device consists of a CT- and MRI-compatible stereotactic frame, monocortical titan bone screws, four frame-posts with a lock for the fixation pins and a modified head clamp with additional arms that allows the exact and rigid placement of the frame in the desired final position prior to the final placement of the bone screws. By simply disconnecting the lock from the posts, the frame can be dismounted after treatment planning and after each treatment session. The accuracy of reposition was assessed prospectively, using phantom studies and also by comparison of isocenter movements during fractionated radiotherapy in 10 patients with an intracranial lesion.

 Findings: No adverse events were seen after the surgical procedure and the screws were well tolerated throughout the course of treatment. The mean isocenter shifts observed during phantom reposition studies were x=0.05 mm, y=−0.32 mm, z=0.18 mm and the mean isocenter shifts during fractionated treatment were x=0.67 mm, y=0.65 mm, z=0.44 mm.

 Interpretation: This new fixation device provides excellent accuracy of reposition during stereotactic radiotherapy. It appears superior to non-invasive, mask fixation techniques. Safety margins as small as 1–1.5 mm may therefore be sufficient for this method of stereotactic radiotherapy.