Linear Accelerator Based Stereotactic Ablative Radiation of Orbital Malignancies

Orbit has a complex anatomy with multiple structures embedded in it. Primary malignant tumors of the orbit are rare. Orbital neoplasms are usually multifaceted and require an interdisciplinary approach. They occur in adults over the age of 60 years. But benign orbital conditions can occur at young age [1]. After confirming the diagnosis of orbital tumors; various treatment methods performed are either surgery, chemotherapy, hormone therapy or radiation therapy (external beam, plaque brachytherapy, proton beam therapy). Treating the tumors located in the orbital apex region with radiation therapy is always challenging with dose limits to the optic nerve, optic chiasm and retina. Each treatment modality can have different tumor responses depending on the size, type and location of the tumor. Advanced radiation treatment techniques have achieved high tumor control rate of approximately 90% with globe preservation [1,2]. Stereotactic body radiotherapy (SBRT) or stereotactic radiosurgery (SRS) is an advanced radiation delivery method in the treatment of orbital and periorbital tumors. SBRT using either Gamma knife (frame based SRS), Cyber Knife (CK; frameless fractionated image-guided radiosurgery) or linear accelerator (e.g. True Beam) delivers high dose radiation precisely to the local orbital tumors thereby avoiding damage to the neighboring structures [3]. The orbital tumors that can treated by SBRT are orbital lymphoma, orbital apex tumors (optic nerve sheath meningioma, neurofibroma, schwannoma, optic nerve glioma), cavernous hemangioma, orbital melanoma, orbital metastasis, basal cell carcinoma, orbital pseudotumor, and few benign orbital conditions such as Graves’ disease and chronic orbital inflammation [4-10]. Indications for using the SBRT are non-resectable or surgically complicated tumors, recurrent or previously irradiated tumors [3,4]. This procedure spares the patient of extensive orbital surgeries like orbitotomy and exenteration.