Postoperative Echography for Optimization of Radiation Dosimetry in Patients with Uveal Melanoma Treated with Plaque Brachytherapy

Abstract

1) To describe the technique of post-operative echography to confirm the intended treatment dose to the tumor apex in patients with uveal melanoma treated with plaque brachytherapy, 2) To describe the local tumor control rate and visual outcomes with the brachytherapy strategies used at our institution. Retrospective review SUBJECTS: 372 consecutive patients with uveal melanoma (small, medium, and large) treated with plaque brachytherapy at the University of Iowa from 8/2008-2/2019. Patient demographics and tumor characteristics were recorded for each patient. Patients with posterior tumors treated with plaque brachytherapy (n=355) underwent intra-operative ultrasound to confirm plaque placement, and additional post-operative ultrasound on day 1-3 post plaque insertion. In cases where intra-tumor/episcleral plaque edema or hemorrhage shifted the dose to the prescription point to less than 85 Gray (Gy), the duration of plaque brachytherapy was increased to compensate. Statistical analysis was performed to compare variables associated with need for plaque adjustment. Variables associated with plaque dose needing to be re-calculated, local tumor control, and visual acuity outcomes. In 31 cases (8.3%), post-operative echography showed the tumor apex had shifted outside of the 85 Gy isodose curve, requiring adjustment of the duration of brachytherapy (28 cases) or repositioning of the plaque (3 cases). Collaborative Ocular Melanoma Study (COMS) tumor size was significantly associated with need to adjust the plaque prescription dose (p=0.03), with large tumors having the highest rate of adjustment. Tumor thickness was larger in cases requiring plaque adjustment compared to those that were not adjusted (median 4.9 mm versus 3.0 mm, p<0.01). Local tumor control was 99% (95% CI: 97-100%) at 5 years and 99% (95% CI: 97-100%) at 10 years. The percentage of patients who had experienced a visual acuity decline of ≥3 lines of vision or had less than 20/200 acuity was 14.9% at one year post brachytherapy, 35.3% at three years, and 51.6% at five years. Post-operative ultrasound performed on post-operative day 1-3 after plaque insertion for patients undergoing brachytherapy for uveal melanoma may result in improved local tumor control, particularly in the setting of thicker or larger tumors.