Stereotactic Radiotherapy for Ocular Melanoma: Initial Experience Using Closed Eyes for Ocular Target Immobilization

Abstract

To assess the reliability and target positioning reproducibility with eyes closed in uveal melanoma patients treated with a micromultileaf-based linear accelerator dedicated for stereotactic radiotherapy. Five consecutive patients treated with curative radiotherapy for uveal melanoma were monitored for positioning reproducibility with resimulation CT scans performed every two days while on treatment (23 resimulation CTs available). All patients underwent MRIs of the orbits before simulation to help to define the target and organs at risk (e.g., lenses, optic nerves, ciliary bodies, and lacrimal glands) in the simulation CT (MRI-to-CT bone registration). Patients were simulated, resimulated, and treated with eyes closed. Patient #1 was treated with 5 daily fractions while patients #2 to #5, were treated with 10 daily fractions. We chose the lens of the tumor-bearing eye as the structure to be controlled, assuming that correct repositioning of the lens should be a valid surrogate for correctness of target repositioning. Displacements (mean and standard deviations, SD) of the lens in the three axes were measured for each patient. Systematic and standard errors were calculated. Planning target volume (PTV) margins were estimated according to McKenzie et al. [Phys Med Biol 45, 3331-3342 (2000)]. For both AP-PA and left-right shifts calculated SD were always below 1 mm, except for patient #4, who was treated with a non-customized bolus that pushed the globe backwards in a random fashion. In ideal set-up conditions PTV margins around the target were estimated to be 3 mm. Asking patients to close their eyes is a simple and reliable immobilization procedure when treating ocular tumors with stereotactic radiotherapy. Margins of 3 mm around the target may be necessary to safely treat these tumors under ideal set-up conditions.

A mechanical eyeball phantom for uveal melanoma radiosurgery by cyberknife

“…A metal bead that was used to simulate a tumor can be clearly identified in the bottom right image secondary glaucoma. Other options are available along with the development of radiotherapy, including plaque brachytherapy [16,28], proton radiotherapy [23], transpupillary thermotherapy [24], and the promising stereotactic radiotherapy [2,18,21]. Taking the advantages of non-invasive treatment, Cyberknife radiosurgery has become an effective alternative for uveal melanoma.…”

Novel 3D conformal technique for treatment of choroidal melanoma with external beam photon radiotherapy

“…Second daily ‘resimulation CTs’ are performed during treatment to check eye position. Only five patients are described in an early report with no tumour outcomes reported …”

Magnetic Resonance Imaging in the Clinical Care for Uveal Melanoma Patients—A Systematic Review from an Ophthalmic Perspective

“…Conventionally, MRI has had a limited role in ocular radiotherapy [139,140]. A notable exception has been stereotactic radiosurgery, where MRI is reportedly being used to complement CT imaging [141][142][143][144][145][146][147] and has shown to contribute to an increase in local control [148]. However, for other forms of ocular radiotherapy, such as brachytherapy and proton beam therapy, the therapy is planned using a dome-shaped model to approximate the tumour geometry.…”