Use of high-frequency ultrasound imaging to improve delineation of anterior uveal melanoma for proton irradiation

The aim of this study was to evaluate high-frequency ultrasound imaging (HF UI) as, an aid in localizing anterior margins of tumours of the eye for pro ton therapy. Proton irradiation of ocular melanoma requires an accurate ass essment of all tumour margins. The tumour is marked surgically by suturing to the sclera four or five tantalum rings on the borders of the tumour defi ned by transillumination. In order to evaluate the clinical usefulness of h igh-frequency ultrasound imaging, four and five rings were surgically place d in a patient with an iris/ciliary body melanoma and in a patient with cil iochoroidal melanoma using transillumination to localize the tumour margins . Subsequently margins were verified by HFUI. In the first patient, the dis tances between the rings and the limbus were measured using calipers during surgery and were compared with HFUI measurements and measurements from pla nning software. The distances were comparable within 0.5 mm. In the second patient the treatment was planned in two different ways using EYEPLAN softw are. In the first scenario the shape of the tumour and its relation to the rings were obtained from the surgeon's mapping, the fundus drawing using a transilluminating point light source, and the HFUI. In the second scenario, the shape of the tumour was deduced from the ring positions only. It was o bserved that the maximum difference between the tumour edge as seen on high -frequency ultrasound images and the rings was 2.6 mm. The tumour volume wa s underestimated by 39% when tumour shape was obtained from ring positions only. During the past year we have utilized HFUI in 18 patients having tumo urs involving the anterior segment of the eye, among which four were treate d with proton therapy. In conclusion, we believe that high-frequency ultras ound imaging provides additional information with respect to the location o f tumour margins in ciliary body and anterior uveal melanoma. Occult extens ion of the tumour within the ciliary body or posterior iris may not be appr eciated by transillumination alone.