Radiation therapy is widely used for the treatment of intraocular and orbital tumors as well as inflammatory ocular diseases.1-3 Both implant brachytherapy and EBRT techniques are widely employed. For example, linear accelerator (LINAC)-based EBRT is widely used to treat metastatic uveal, orbital, and sinus tumors as it involves directing an external radiation beam source to the eye, eyelids, sinuses, and orbit. Should one or both eyes need be irradiated, LINAC-based EBRT can be delivered using an anterior unilateral approach as seen in Figure 1, or as 2 apposing, bilateral confrontational fields.4 In contrast, most patients with uveal melanoma are commonly treated with ophthalmic plaque brachytherapy. Here, disc-shaped radioactive devices are affixed to the sclera beneath the tumor volume within the eye (Fig. 17-2).
Orbital disease is most commonly treated with LINAC-derived EBRT, and less frequently with proton beam, stereotactic radiosurgery (SRS) and Gamma Knife®, and intensity-modulated radiation therapy (IMRT).2 Radiation can be used alone, after surgery, and with chemotherapy. In contrast, orbital brachytherapy involves surgical placement of radiation sources next to a tumor or within a targeted orbital volume. Typically considered the most conformal form of radiotherapy, brachytherapy relatively increases the radiation dose within the targeted volume while decreasing exposure to most normal tissues.
At The New York Eye Cancer Center, orbital high-dose rate brachytherapy is used to treat the resected tumor bed followed by an overlay of lower-dose EBRT to the entire orbit (Fig. 17-3).5-7 Called “brachy-boost”, this technique increases the dose to a targeted portion of the orbit.
This chapter explores the unique challenges associated with irradiation of the eye, lids, and orbit. It includes basic radiobiology, doses, indications, and results of treatment. We discuss the tolerances of normal ocular and orbital tissues. Herein, we review the literature to offer a unique perspective of the world’s experience with ocular and orbital radiation therapy.
Ocular and orbital anatomy, as well as tissue radiosensitivity, provide unique challenges for radiation-based patient care. By definition, the eye globe is bounded by the sclera and cornea, within which there exist tissues that contain melanocytes, retinal, and epithelial cells, amongst others. Each gives rise to unique tumors with different radiosensitivities. Most orbital tumors occur between the eyeball and bony orbital walls, within which there exist even more varieties of progenitor cells and their related tumors. Orbital tumors may also extend either into or from the eye, orbit orbital bone, brain, and sinuses. As a result, radiation delivery systems (teletherapy or brachytherapy)—each with unique characteristics—are carefully selected to deliver tailored dose distributions within the eye and orbit. To better understand the differences between these radiation modalities, this chapter reviews their inherent differences and why each is typically selected.
While any radiation modality can sterilize a cancer, the location and intensity of side effects or normal tissue tolerances typically govern the physician’s choice of method. However, individual tissue tolerances and
thus the incidence of radiation side effects are variable. For example, the sclera, cornea, bones, ocular muscles, optic nerve, and orbital fat can tolerate relatively high doses, whereas the lens, eyelashes, retina, and lacrimal system are more radiosensitive.2 Therefore, side effects of ocular and orbital irradiation commonly include dry eye, eyelash loss, cataracts, neovascular glaucoma, radiation retinopathy (see Chapter 22), and optic neuropathy as opposed to osteonecrosis, strabismus, or enophthalmos.1,2 Depending on the tissue and its function, each ophthalmic side effect results in either cosmetic or functional morbidities. In practice, modality selection and treatment plans are typically created to avoid the retina, lacrimal system, and natural lens.2,8-10 In addition, there exists an oncogenic risk associated with ionizing radiation as most commonly seen in children.11-16
It is important to note that the incidence of side effects is proportional to the volume of irradiated tissue. Therefore, any technique that reduces the irradiated volume, conforms to the tumor, and reduces organ dose will be beneficial. Despite the risks of side effects, radiation therapy has become an essential tool used by eye cancer specialists to provide local control of benign and malignant ocular and orbital diseases. The clinical benefits of improving survival and preserving vision have clearly outweighed the radiation risks. Herein, we review how radiotherapy has played an integral role in the treatment of benign and malignant ocular tumors.