Conventional modalities of external-beam radiation therapy (EBRT) are associated with high incidences of severe vision-threatening ocular and orbital toxicities when used to treat orbital malignancies. We investigate toxicities associated with high-dose volumetric modulated arc therapy (VMAT), a commonly used contemporary treatment modality for these tumors.
Retrospective analysis of malignant orbital tumors managed with adjuvant high-dose VMAT preceded by globe-salvaging surgical therapy (GST) or exenteration. Dosimetric quantitation of target volumes and critical structures was performed. Incidence and severity of ocular, orbital, and adnexal toxicities were evaluated and assessed with regard to conventional EBRT toxicities for orbital malignancies described in the literature.
Eighty-four subjects (mean age = 65.9 ± 9.7 years) were included (N = 48 and N = 36 in GST and exenteration subgroups, respectively). Mean dose was 64.8 ± 2.1 Gy to the planning target volume. Dosing to critical structures typically did not surpass known tissue tolerance limits. Median follow up was 18.3 months. Visual acuity in the GST subgroup was not significantly different after VMAT (0.25 ± 0.06) compared with baseline (0.23 ± 0.02; P = 0.302). Whereas severe toxicities reported by major systematic analyses in the literature with older EBRT modalities were relatively common-for example, retinopathy (16-40%), optic neuropathy (16%), and corneal perforation (13%)-toxicities with VMAT were typically mild and less common. The most common toxicities with VMAT were mild dry eye (81.3%; 39/48), cataract (21.1%; 8/38 phakic eyes), and periocular dermatitis (15.5%; 13/84). Vision-threatening toxicities, including severe corneal pathologies, retinopathy, or optic neuropathy, were rare. There were no contralateral ocular or adnexal toxicities.
High-dose VMAT for orbital malignancies demonstrated low incidence and severity of eye-related toxicity, in contradistinction to adverse events reported from conventional forms of radiotherapy.

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