A linac-based stereotactic irradiation technique of uveal melanoma.
OBJECTIVE
To describe a stereotactic irradiation technique for uveal melanomas performed at a linac, based on a non-invasive eye fixation and eye monitoring system.


METHODS
For eye immobilization a light source system is integrated in a standard stereotactic mask system in front of the healthy eye: During treatment preparation (computed tomography/magnetic resonance imaging) as well as for treatment delivery, patients are instructed to gaze at the fixation light source. A mini-video camera monitors the pupil center position of the diseased eye. For treatment planning and beam delivery standard stereotactic radiotherapy equipment is used. If the pupil center deviation from a predefined 'zero-position' exceeds 1 mm (for more than 2 s), treatment delivery is interrupted. Between 1996 and 1999 60 patients with uveal melanomas, where (i) tumor height exceeded 7 mm, or (ii) tumor height was more than 3 mm, and the central tumor distance to the optic disc and/or the macula was less than 3 mm, have been treated. A total dose of 60 or 70 Gy has been given in 5 fractions within 10 days.


RESULTS
The repositioning accuracy in the mask system is 0.47+/-0.36 mm in rostral-occipital direction, 0.75+/-0.52 mm laterally, and 1.12+/-0.96 mm in vertical direction. An eye movement analysis performed for 23 patients shows a pupil center deviation from the 'zero' position<1 mm in 91% of all cases investigated. In a theoretical analysis, pupil center deviations are correlated with GTV 'movements'. For a pupil center deviation of 1 mm (rotation of the globe of 5 degrees ) the GTV is still encompassed by the 80% isodose in 94%.


CONCLUSIONS
For treatments of uveal melanomas, linac-based stereotactic radiotherapy combined with a non-invasive eye immobilization and monitoring system represents a feasible, accurate and reproducible method. Besides considerable technical requirements, the complexity of the treatment technique demands an interdisciplinary team continuously dedicated to this task.
Dieckmann
K
K
Department of Radiotherapy and Radiobiology, University of Vienna, General Hospital Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria.
Bogner
J
J
Georg
D
D
Zehetmayer
M
M
Kren
G
G
Pötter
R
R
D005133:Eye Movements; D005240:Feasibility Studies; D006801:Humans; D007103:Immobilization; D008545:Melanoma / Q000532:radiotherapy*; D008991:Monitoring, Physiologic; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D013238:Stereotaxic Techniques; D014604:Uveal Neoplasms / Q000532:radiotherapy*