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 con¬trast, 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 LIN¬AC-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 chemother¬apy. 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 radiosen¬sitivity, 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 char¬acteristics—are carefully selected to deliver tailored dose distributions within the eye and orbit. To better under¬stand 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 tis¬sue 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, radia¬tion retinopathy (see Chapter 22), and optic neuropathy as opposed to osteonecrosis, strabismus, or enophthal¬mos.1,2 Depending on the tissue and its function, each ophthalmic side effect results in either cosmetic or func¬tional 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 radia¬tion 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. There¬fore, 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 malig¬nant 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.
Chapter Keyword: charged particles
Ocular Proton Beam Therapy: Experience Maximizing Outcomes
Primary malignant tumors of the eye and orbit are rare., Their treatment requires special knowledge of the anatomical, conditions, individualized, usually very complex, irradiation techniques, and cooperation between the, clinical disciplines involved. The risks are blindness-related, extreme loss of quality of life, cosmetic changes, to patient appearance, and economic effects. With few, able to pay for complex radiation techniques, only select, patients, willing insurance companies, and high-resource, national health systems allow complex radiation therapy, techniques that preserve eye, function, and life., The rarity of eye tumors and the complex technical, requirements needed to develop conservative treatments, led to the formation of highly specialized regional, referral centers. Unfortunately, each center typically has, only one radiation technology for ocular malignancies., These radiation alternatives include plaque brachytherapy, (e.g., iodine-125 [125I], palladium-103 [103Pd], and/, or ruthenium-106 [106Ru]) or proton beam irradiation.1, Since there is usually only one approach available at each, center, there is little possibility of choosing the optimal, radiation technique for each clinical situation., This chapter reflects our initiative to pair two clinical, centers—one in Essen, Germany and one in Nice,, France—such that each offered a different treatment, modality to maximize clinical outcomes based on select, physical tumor characteristics. We considered the following, hypothetical treatment recommendations. For, example, in Essen we used 106Ru beta-applicators for relatively, flat tumors, as to utilize its most favorable ratio, of tumor dose/dose to normal tissues, as well as 125I (or, mixed 106Ru with 125I), whose dose distribution allows, treatment of larger target tumor volumes.2 Other nonparticipating, centers have reportedly used low-dose rate, (LDR) 90Sr and 103Pd as well as high-dose rate (HDR) 90Y, (see Chapters 17–19, 21, and 22).3-5 However, it is important, to note that along with deeper plaque radiation, penetration, existing LDR plaque therapy is associated, with a wider side-scatter penumbra, leading to less, favorable irradiation of surrounding healthy tissues.6-8 In, our experience, plaque brachytherapy for tumors at the, posterior pole (in the immediate vicinity of the radiation-, sensitive structures of the macula, optic disc, and, optic nerve) rarely results in functional vision. In contrast,, proton treatment of tumors of the posterior pole, offers at least theoretical advantages, provided that the, beam energy, treatment planning, and technical implementation, offer the highest quality to obtain precision., In our experience, compared to LDR plaque brachytherapy,, proton therapy can produce better results in large, tumor volumes where there exists more dose homogeneity., Thus, we have seen less subsequent necrosis, local, accumulation of toxic degradation products, and secondary, glaucoma. However, in general practice, the potential, of proton therapies has not yet been realized in that the, currently used high single-dose fractions have had an, opposite effect., In 1991, a collaboration between the Cancer Center, Antoine Lacassagne in Nice (France) and the University, Hospital in Essen (Germany) provided availability, to a dedicated proton facility for German patients. Cases, were selected for proton therapy when brachytherapy, was not technically feasible (Mind map 20-1). Examples, include diffuse conjunctival melanoma and intraocular, tumor locations that would certainly lead to short-term, blindness (e.g., choroidal melanomas near or touching, the optic disc and/or fovea). This chapter reports on our, subjective experience over 3 decades of proton therapy, and teaches on pragmatic aspects we have used to optimize, our proton beam therapy.