Yttrium-90 (90Y) Brachytherapy for Small Iridociliary Melanomas

Abstract

<h3>Purpose/Objective(s)</h3> Beta irradiation has been useful in treating numerous ocular tumors and benign growths. However, strontium-90 applicators are no longer supported and ruthenium-106 is not available for high dose rate (HDR) brachytherapy. Herein we present the first clinical use of a new HDR ⁹⁰Y brachytherapy source that is FDA 510(k) cleared for the treatment of ocular tumors and benign growths. <h3>Materials/Methods</h3> The iWand A® is a new single-use ophthalmic hand-held brachytherapy applicator, with a surface contact diameter of 10 mm. In addition, the applicator's translucent polymer backing both attenuates radiation exposure towards the surgeon and ancillary staff and allows visualization of the disc-shaped ⁹⁰Y source during treatment. A well-shaped recess on the anterior surface of the applicator accommodates a 6-mm disc-shaped source, where it is flush-mounted and affixed by biocompatible adhesive. The titanium shell of the source provides rigid encapsulation of the radioactive ⁹⁰Y source. Though the LV Y-90 Disc is FDA cleared to be utilized at up to 20 millicuries (mCi); the activity used for these 2 treatments was mean 12.4 mCi. For example, a 20 mCi LV ⁹⁰Y Disc which decays by β-emission with an end point energy of 2.28 MeV (0.98 MeV average), yields 30.0, 21.6, 16.2, and 4.8 Gy/minute at depths of 0.0, 0.6, 1.0, and 2.6 mm, respectively. While planning tool simulations were used to demonstrate the treatment volume and penumbra characteristics of the ⁹⁰Y disc, NIST-traceable preoperative calibrations were performed by an independent authorized medical physicist. <h3>Results</h3> Two patients (mean age=74 years) were diagnosed with AJCC 8^th edition T1-sized, biopsy-proven iridociliary melanoma. High-frequency ultrasound was used to measure tumor size, basal dimensions and distance from the overlying sclera. Measurements revealed a mean maximum tumor thickness of 0.7 mm (0.6-0.8) and a mean maximum largest tumor basal diameter of 3.0 mm (2.9-3.1). Surgery required a minor conjunctival recession to expose the episcleral target zone. The 10 mm application site was marked with tissue dye on the cornea and sclera. Then the ⁹⁰Y source, affixed within the iWand A® applicator, was applied to deliver HDR episcleral brachytherapy to doses of 25 - 30 Gy to a 2.5-mm depth. Treatment durations ranged from 5 to 13 minutes. During treatment, the acrylic of the iWand A® applicator was found capable of shielding the patient, surgeon and operating-room personnel. No acute or post-operative ⁹⁰Y-radiation-related complications were noted. The ⁹⁰Y source's 64-hour half-life allowed for single-use, decay in storage, and return for disposal. <h3>Conclusion</h3> A novel, FDA-cleared, HDR ⁹⁰Y beta source was used to treat 2 patients with uveal melanoma. It was affixed within a hand-held, single-use applicator that aids guidance, targeting and facilitates radiation safety (as measured during both surgeries). Future research is needed to explore additional applications for this novel ⁹⁰Y HDR brachytherapy source.