Proton irradiation can preserve some vision and prevent eye removal in patients with tumors adjacent to the optic disc, according to a study published online Sept. 13 in Archives of Ophthalmology.
The study, conducted by Anne Marie Lane, MPH, and colleagues from the Massachusetts Eye and Ear Infirmary in Boston, also demonstrated low rates of tumor recurrence and no increased risk of metastasis when using proton irradiation, making it a possible alternative to other treatments, such as internal radiotherapy.
Internal radiotherapy, which requires the radiation source to be placed inside or next to the area to be treated, can be difficult to use when the tumors touch or surround the optic nerve.
“Patients diagnosed with tumors located near the optic nerve experience complications when treated with radiotherapy because irradiation of the nerve is unavoidable,” wrote the authors. “These complications may lead to vision loss or loss of the eye.”
To circumvent these problems, Lane et al used proton irradiation, a form of radiation therapy which targets cancer cells with a beam of protons.
The study reviewed data from 573 patients with tumors that were peripapillary or parapapillary who had proton irradiation between 1985 and 1997. At diagnosis, the majority of patients had relatively good vision, with a median baseline visual acuity of 20/63.
Within five years of treatment, damage to the optic nerve and to the macula occurred in 56.8 percent and 60.4 percent of patients, respectively. At two years post-treatment, 54.9 percent of patients still had a baseline visual acuity of at least 20/200, but this number decreased to 20.3 percent by five years post-treatment. The majority of patients, however, were still able to at least count fingers.
Local recurrence of the tumor occurred in 3.3 percent of patients at five years and 6 percent of patients at 10 years, respectively. At five years, eye removal rates were 13.3 percent; at 10 years, they were 17.1 percent. Melanoma-related mortality rates were similar to those receiving other treatments, according to the study.
The authors stressed the challenge of preserving eye function after treating peripapillary or parapapillary tumors. While the sharper focus of proton therapy is often able to save the eye, vision loss is common, though not guaranteed.
“The findings of this study suggest that proton therapy should be considered for patients with tumors encroaching or contiguous to the optic nerve,” wrote the authors. “Eye conservation is possible in the vast majority of cases, with low rates of recurrence and metastasis. However, vision loss is still significant in this group of patients.”