Technique for Robotic Stereotactic Irradiation of Choroidal Melanoma

Feasibility, Method and Early Outcome of Image-Guided Volumetric Modulated Arc Radiosurgery Followed by Resection for AJCC Stage IIA–IIIB High-Risk Large Intraocular Melanoma

Simple Summary

The aim of this trial was to define one optimal contemporary treatment procedure for large intraocular melanoma. Radiosurgery is a highly effective treatment in cancer. In this trial, all consecutive patients with large intraocular melanoma treated with multimodality treatment, comprising 4D image-guided volumetric modulated arc radiosurgery procedure followed by resection, were evaluated. In the short-term follow-up there was no clinical toxicity due to external beam radiation therapy, and no local tumor recurrence. In 98% of the cases, the eye bulb could be maintained with partial residual visual acuity in the mean follow-up of 18 months. The outcome estimates one optimal treatment procedure for high-risk, large intraocular melanoma, with excellent results in the first follow-up.

Abstract

The main objective of this prospective observational study was the characterization of the feasibility and early outcome of image-guided (IG) volumetric modulated arc (VMAT) radiosurgery (SRS) followed by resection for patients with large intraocular melanoma. Our study included consecutive patients with unfavorable-risk melanoma, enrolled in an ophthalmic oncology center. IG-VMAT-SRS was applied by high-resolution 4D image guidance and monitoring. Current stereotactic technique parameters were evaluated for comparison. Side effects and eye function, based on a 5-point CTC assessment score, were quantified. In patients with tumors located more than 0.7–1 mm apart from the optic nerve, partial to complete volume-sparing of the optic nerve head could be achieved. In 95.5% of this subgroup, the vitality of the optic nerve and vision could be preserved by the multimodality-treatment approach (mean follow-up: 18 months (7.5–36 months)). The advanced technology of stereotactic radiotherapy demonstrated the achievability of steep dose gradients around the high-dose volume, with 4D-IG-VMAT dose application. These results enforce IG-VMAT-SRS followed by resection as one of the major therapeutic options for patients with large intraocular melanoma. The combination of 4D-IG high-precision SRS and resection provides an effective treatment for large intraocular melanoma, with few side effects, and enables an eye bulb and even vision preserving modus operandi.

Stereotactic radiotherapy for choroidal melanomas by means of HybridArc™ : Physics and technique of linac-based photon beam therapy

PURPOSE

Stereotactic radiotherapy (SRT) is suitable to treat ocular tumours. The optimal beam geometry for SRT, however, has not been defined. Here we evaluate a combination technique with dynamic conformal arcs (DCAs) and intensity-modulated static fields (IMRT), known as HybridArc™ (HA).

METHODS

For the first consecutive 25 cases with choroidal melanomas with volumes of 0.02 to 1.18 cm³ treated with 50 Gy in five fractions, the results with respect to dose conformity, homogeneity, and dose distributions were summarised. To describe the dose distribution at the planning target volume (PTV) boundary, we defined a spatially averaged dose gradient (SADG) and compared it with Paddick's gradient index (GI). We made dosimetric comparisons between HA and other irradiation techniques.

RESULTS

The PTVs ranged from 0.42 to 3.37 cm³. The conformity index (CI) was 1.25 ± 0.15, and the homogeneity index (HI) 0.08 ± 0.02. The SADG was (-3.5 ± 0.5) Gy/mm or (-7.0 ± 1.0) %/mm between the isodose levels 95 and 20%; local minima reached -11.5 Gy/mm or -22.9%/mm. The coefficient of determination for a nonlinear regression of GI on SADG was 0.072. After a median follow-up time of 19.6 months, local tumour control was 100% without any case of post-therapeutic enucleation. Two patients (8%) developed liver metastases.

CONCLUSION

SRT of ocular tumours by HA is highly appropriate, and HA is superior to intensity-modulated arc therapy (IMAT) concerning dose reduction in organs at risk (OARs). The novel gradient measure SADG is more informative than Paddick's GI.

Reproducibility of a Noninvasive System for Eye Positioning and Monitoring in Stereotactic Radiotherapy of Ocular Melanoma

Purpose:

Our preferred treatment for juxtapapillary choroidal melanoma is stereotactic radiotherapy. We aim to describe our immobilization system and quantify its reproducibility.

Materials and Methods:

Patients were identified in our radiosurgery database. Patients were imaged at computed tomography simulator with an in-house system which allows visual monitoring of the eye as the patient fixates a small target. All patients were reimaged at least once prior to and/or during radiotherapy. The patients were treated on the CyberKnife system, 60 Gy in 10 daily fractions, using skull tracking in conjunction with our visual monitoring system. In order to quantify the reproducibility of the eye immobilization system, computed tomography scans were coregistered using rigid 6-dimensional skull registration. Using the coregistered scans, x, y, and z displacements of the lens/optic nerve insertion were measured. From these displacements, 3-dimensional vectors were calculated.

Results:

Thirty-four patients were treated from October 2010 to September 2015. Thirty-nine coregistrations were performed using 73 scans (2-3 scans per patient). The mean displacements of lens and optic nerve insertion were 0.1 and 0.0 mm. The median 3-dimensional displacements (absolute value) of lens and nerve insertion were 0.8 and 0.7 mm (standard deviation: 0.5 and 0.6 mm). Ninety-eight percent of 3-dimensional displacements were below 2 mm (maximum 2.4 mm). The calculated planning target volume (PTV) margins were 0.8, 1.4, and 1.5 mm in the anterior–posterior, craniocaudal, and right–left axes, respectively. Following this analysis, no further changes have been applied to our planning margin of 2 to 2.5 mm as it is also meant to account for uncertainties in magnetic resonance imaging to computed tomography registration, skull tracking, and also contouring variability.

Conclusion:

We have found our stereotactic eye immobilization system to be highly reproducible (<1 mm) and free of systematic error.