Intra-operative ocular ultrasonography of iodine-125 brachytherapy plaques in patients with uveal melanoma

Abstract

Purpose: Brachytherapy with iodine-125 (¹²⁵I) has been extensively used as a conservative treatment for uveal melanoma (UM). Surgical technique for correct placement of episcleral radioactive plaques (ERP) in UM cases with posterior choroidal location and/or small size can be difficult and inaccurate. In this study, the correct positioning of plaques was assessed by intra-operative ultrasound control.

Material and methods: This was a longitudinal, retrospective study of consecutive 20 patients with UM (small-medium size and/or posterior location) who received ¹²⁵I brachytherapy. Location of plaques was adjusted by intra-operative ocular ultrasonography control. To perform ocular intra-operative ultrasonography, a 10 MHz probe was used to longitudinal and transverse bases in corresponding dummy plaques.

Results: The study included 8 males and 12 females, with a mean age of 66.3 years (SD = 14.53), 5 right eyes (RE) and 15 left eyes (LE). In ultrasound examination, 4 UMs were of mushroom morphology and the rest nodular. Means of the size of UM by ultrasound were (mm): Lb: 10.60 (SD = 2.24) × Tb: 9.88 (SD = 1.54) × H: 4.02 (SD = 1.44) (3 cases corresponding to small size of collaborative ocular melanoma study (COMS), and 17 cases to medium). The plaques used were between 14 and 20 mm in diameter, with an average distance between the edge of greater base of the tumor and the edge of plate of 2.44 mm (SD = 0.34). It was necessary to surgically reposition the plaque in 4 cases (20%).

Conclusions: Intra-operative ultrasound control improves the accuracy of radioactive plaque placement for the treatment of medium-small UMs in posterior location. Probably, this technique should be applied in all cases of brachytherapy, regardless of the isotope chosen and the location of tumor mass, in order to perfectly adjust therapeutic position.

Keywords: brachytherapy; iodine-125; ocular ultrasound; tilting; uveal melanoma.

Fig. 1

The main clinical characteristics of three cases are shown. Case 7: Case with correctly centered plaque. The signs of a radioactive plaque placed at the time of the ultrasound study can be detected (blue arrow). Case 12: Case with previously had a partially off-centered in the longitudinal base. This case required relocation in the longitudinal meridian (blue arrows). Finally, the plaque was not perfectly centered but that cover all the base from the UM. Case 16: Case with previously had a complete off-centered in longitudinal and transverse base. The evolution of the error in the longitudinal projection can be seen in these sections, as corrected with the repositioning from red arrow to blue arrow. RE – right eye, LE – left eye, L – longitudinal base and number of equator, T – transversal base and number equator centered