Proton Beam Radiotherapy for Uveal Melanoma: The Relationship of Tantalum Marker Number and Clinical Outcomes

Purpose:: Proton Beam Radiotherapy (PBRT) is the most common form of accelerated particle irradiation treatment for uveal melanoma. For PBRT to maximize tumor destruction while sparing adjacent ocular tissues, the ophthalmologist sutures tantalum markers to the outer scleral surface of the globe to delineate the tumor margins. The radiation oncologist is then able to use these markers, along with other ocular landmarks, to plan PBRT. Treatment failures can often be attributed to improper marker placement and modeling, but little data is available to inform methods of marker placement. This study examines the relationship of the number of tantalum markers used for planning to the safety and efficacy of PBRT for the treatment of uveal melanoma. Methods:: A retrospective cohort of all 78 patients treated with PBRT for uveal melanoma at a single center between April 1995 and August 2001 was identified. Demographic, clinical, and tumor data were compiled. Data were analyzed according to whether three tantalum markers or more than three tantalum markers were used for treatment planning. Outcome measures included visual acuity loss to below 20/200, development of radiation retinopathy, local treatment failure, enucleation, metastases, and all-cause mortality. Results:: Of all tumors treated with PBRT, 60% were small or medium sized.Use of more than three markers was more common for large tumors. For all tumors, average treatment margins were significantly smaller when more than three markers were used ( 2.69mm vs. 2.92, p<0.001). No difference in clinical outcomes was noted for three versus more than three markers, although analysis of small and medium tumors revealed a trend toward more frequent loss of vision below 20/200 (RR= 2.6, 95% CI=0.71-9.1) and more common development of radiation retinopathy (RR=2.3, 95% CI=0.46-11.2) with the use of only three markers. No complications were associated with the placement of increasing numbers of tantalum markers. Conclusions:: This study provides evidence that using more than three tantalum markers for PBRT of uveal melanoma provides more accurate tumor demarcation. The data also suggest that this improved demarcation translates to decreased treatment morbidity without sacrificing tumor control.