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

Abstract

Purpose: (1) To describe the technique of postoperative 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.

Design: Retrospective review.

Subjects: Three hundred seventy-two consecutive patients with uveal melanoma (small, medium, and large) treated with plaque brachytherapy at the University of Iowa from August 2008 to February 2019.

Methods: Patient demographics and tumor characteristics were recorded for each patient. Patients with posterior tumors treated with plaque brachytherapy (n = 355) underwent intraoperative ultrasound to confirm plaque placement, and additional postoperative ultrasound on day 1 to 3 postplaque insertion. In cases where intratumor/episcleral plaque edema or hemorrhage shifted the dose to the prescription point to < 85 Gray (Gy), the duration of plaque brachytherapy was increased to compensate. Statistical analysis was performed to compare variables associated with the need for plaque adjustment.

Main outcomes measures: Variables associated with plaque dose needing to be recalculated, local tumor control, and visual acuity outcomes.

Results: In 31 (8.3%) cases, postoperative echography showed that the tumor apex had shifted outside 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 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 with those that were not adjusted (median 4.9 mm vs. 3.0 mm, P < 0.01). Local tumor control was 99% (95% confidence interval, 97%-100%) at 5 years and 99% (95% confidence interval, 97%-100%) at 10 years. The percentage of patients who had experienced a visual acuity decline of ≥ 3 lines of vision or had < 20/200 acuity was 14.9% at 1 year after brachytherapy, 35.3% at 3 years, and 51.6% at 5 years.

Conclusions: Postoperative ultrasound performed on postoperative day 1 to 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.

Financial disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Keywords: Echography; Plaque brachytherapy; Uveal melanoma.