Jornal de cirurgia ocular e de catarata Acesso livre

Abstrato

Predictive models for radio-induced effects after stereotactic radiosurgery (SRS) for uveal melanoma

Antonella Del Vecchio

Uveal melanoma (UM) is the most common primary intraocular malignant tumour in adults. The mortality is 40-50% in 15years, mainly due to liver metastasis. In the recent decades,conservative techniques able to control the disease while preserving the eye have replaced, when possible, the enucleation.Gamma Knife stereotactic radiosurgery (GKRS) is one of the techniques to perform a conservative treatment of UM, as it can deliver very high doses to the target sparing in the same time to the surrounding tissue, creating a high dose gradient. Several studies have shown that GKRS allows the survival, local control and preservation of the eye. The therapeutic dose for this disease is very high (35 Gy to 50%) and it is necessary that the reference isodose is much larger than the tumour volume identified by the diagnostic exams. Several side effects are obviously associated to an important treatment from dosimetric point of view. Despite the deterioration of vision or complete blindness are often reported in the literature as important side effects and several authors argued that with the optimization of the treatment plan in terms of the prescription dose to the target and absorbed doses to critical structures, the visual function loss may be limited. Now-a-days, in the literature there are still no studies designed to investigate the dose-effect relationship of critical structures of interest with reference to adverse events. The aim of our study was to develop a predictive model for the radio-induced side effects in patients affected by uveal melanoma, treated with GKSR. The adverse effect which focuses the attention of the project is the partial or complete loss of the visual function. The aim is to find predictive dosimetric and/or clinical factors to obtain dose constraints to critical structures. With any external beam radiation therapy, the highest dose of radiation develops where multiple beams intersect. Thus, the fewer beams there are, the greater the dose reaching other areas traversed by the beams. For example, if only 2 beams are used, the highest dose would develop at the site where the beams intersect, but a significant portion of the dose would be distributed to fields anterior and posterior to the intersection. Stereotactic radiosurgery (SRS) uses the above principle to deliver a highly focused ionizing beam so that the desired target is obliterated, leaving adjacent structures nearly unaffected.