Carbon fiducials for large choroidal melanoma treated with gamma knife radiosurgery.

Abstract

Uveal melanoma (UM) is the most common primary intra-ocular malignancy in adults (Singh et al. 2011). Gamma Knife radiosurgery (GKR) has been demonstrated to have similar outcomes as enucleation with less morbidity and is, therefore, utilized for the treatment of UMs (Koutsandrea et al. 2008; Lund 2013). Because some tumour margins are difficult to visualize with magnetic resonance imaging (MRI), this study utilized carbon fiducials for assistance with GKR treatment planning. To our knowledge, this is the first report of utilizing carbon fiducials to mark eye tumours for targeted radiotherapy. Two patients underwent this procedure. Case 1 is a 79-year-old man who was otherwise asymptomatic and noted to have a ciliochoroidal mass, T4bN0M0 (Fig. 1A–C) in the right eye during a Neodymium-doped yttrium aluminum garnet (Nd:YAG) laser capsulotomy in the left eye. His visual acuity was 20/25 on the right (OD), 20/20 on the left (OS); intra-ocular pressure (IOP) was 17 OD, 15 OS. The tumour measured 8.5 × 17.9 × 20.5 mm on ultrasound. Case 2 is a 69-year-old woman who presented with 6 weeks of decreased vision in the left eye (20/20 OD, 20/400 OS) with pressures of 19 OD, 16 OS. She was noted to have a large UM (T4cN0M0), (Fig. 1D–F) measuring 3.5 × 16.3 × 20.5 mm by ultrasound. Treatment options were discussed. Because of basal dimensions, plaque brachytherapy was not considered an option. Both patients had tumours incompletely visualized on MRI. Particularly, Case 2 (Fig. 1D) had infiltrative, thin edges and a retinal detachment that could not be well distinguished by MRI without fiducials. Both patients elected to undergo fiducial placement and GKR. Fiducials were placed in the operating room. A 360-degree conjunctival peritomy preceded tagging of rectus muscles with silk sutures. Sclera was inspected for evidence of extrascleral tumour extension. Transillumination and indirect ophthalmoscopy were utilized to mark the gross tumour volume (GTV). Three BioMARC fiducials 1 mm × 5 mm (Carbon Medical Technologies, Saint Paul, MN, USA), composed of carbon-coated zirconium for biocompatibility, with preplaced double-armed 5-0 nylon sutures (Fig. 1G), were secured 2 mm beyond the border of the GTV. Conjunctiva was closed. Patients were treated with subconjunctival Ancef, Decadron, and discharged with atropine and Blephamide. Five days after fiducial placement, patients underwent GKR. Retrobulbar block was performed with 2% lidocaine, bupivacaine and hyaluronidase. Leksell stereotactic head frame was applied. Magnetic resonance imaging (MRI) orbits with contrast were repeated and imported into the treatment planning system Leksell GammaPlan, Elekta AB, Stockholm, Sweden. The clinical target volume (CTV), determined by the GTV plus 2 mm delineated by the fiducials, was treated. Patients were discharged the same day. Case 1 was treated with 11 isocenters to a CTV of 3010 mm3, 25 Gy to the 50% isodose line, maximum dose of 50 Gy. Case 2 was treated with 11 isocenters to a CTV of 2680 mm3, 27 Gy to the 50% isodose line, maximum dose of 54 Gy. At 4.8 months postradiosurgery, Case 1 had decreased visual acuity (20/60) and tumour thickness (8.1–8.2 mm) by ultrasound (Fig. 1H). After 3.4 months, Case 2 had improved visual acuity (20/125) and tumour volume (2.9 × 15.1 × 16.6 mm) by ultrasound (Fig. 1I). Notably, one of three fiducials (the most anterior fiducial) for Case 1 demonstrated extrusion at 4.8 months and was surgically removed. In summary, we present two patients with large UMs who were managed with GKR after fiducial placement. This approach may be beneficial for patients whose tumours are difficult to visualize on MRI. It may also be worthwhile to compare the tantalum fiducials currently used for proton beam radiotherapy (PBT) to mark UMs (Gragoudas et al. 1977) with carbon fiducials.