Repositioning accuracy of a noninvasive head fixation system for stereotactic radiotherapy

Abstract

We report on the repositioning accuracy of patient setup achieved with a noninvasive head fixation device for stereotactic radiotherapy. A custom head mask which attaches to our stereotactic radiosurgery head ring assembly is fabricated for each patient. The position and orientation of a patient in the stereotatic space at the time of treatment are determined from analyzing portal films containing images of radio-opaque spheres embedded in a custom mouthpiece. From analysis of 104 setups of 12 patients, we find that the average distance between the treated isocenter and its mean position is 1.8 mm, and that the standard deviations of the position of the treated isocenter in stereotactic coordinate space about its mean position are less than 1.4 mm in translation in any direction and less than 1 degree of rotation about any axis.

Patient Position Reproducibility in Fractionated Stereotactically Guided Conformal Radiotherapy Using the BrainLab® Mask System

“…Current data from the literature indicate a reproducibility of patient position in the order of 1-2 mm by use of dedicated mask systems [3,6,9,10,12,13,16]. However, the values vary between the different institutions making it desirable to know the accuracy achievable at the own institution.…”

“…The planning target volume was generated by allowing a safety margin around the gross tumor volume of 3-5 mm to account for set-up inaccuracies. Several publications have shown a reproducibility of the patients head within the stereotactic frame in the order of 1-2 mm [3,9,10,12,13,16] for various systems. Therefore safety margins of 2-4 mm should provide coverage of the target in 95.5% of all set-ups.…”

Algorithms for modeling anatomic and target volumes in image‐guided neurosurgery and radiotherapy

“…A megavoltage portal image is typically first matched with a simulator or a DRR image for the best accuracy (McGee et al 1995, van Herk et al 1995, Fraas & McSchan 1995, Gilhuijs 1997. Non-invasive head immobilization systems without CCD-based imaging are reported with a 1.8 mm average error (Hamilton et al 1996) and a 1.35 mm average repositioning error (Westerman & Hauser 1997).…”

Relocatable fixation systems in intracranial stereotactic radiotherapy

“…The main indications for stereotactic radiotherapy are benign tumours which do not infiltrate into surrounding tissue and, thus, do not need an added margin in the form of a clinical target volume (CTV) [3,12], whereas for malignant tumours in case of reirradiation or dose escalation, the dose is given to the tumour with a small restricted CTV margin only [4,11]. Thus, the addition of margins takes into account only daily treatment inaccuracy and delineation accuracy.…”

“…Patient set-up and daily repositioning for SCRT is usually checked by an electronic portal-imaging device (EPID) [1,12,24] which is also performed for radiosurgery [29]. Another way of assessing isocentre repositioning accuracy is serial computer tomography (CT) at regular intervals [17,21,22,25,30,31].…”