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Proton radiation therapy helpful for tumours near optic nerve

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In patients with tumours adjacent to the optic disc (optic nerve head), proton irradiation is associated with preservation of some vision (although sacrificing sharpness) and prevention of eye removal, with low rates of tumour recurrence and no increased risk of metastasis, according to a report in the October issue of Archives of Ophthalmology, one of the JAMA/Archives journals.

“Patients diagnosed with tumours located near the optic nerve experience complications when treated with radiotherapy because irradiation of the nerve is unavoidable,” write the authors as background information in the article. “These complications may lead to vision loss or loss of the eye.” When the tumours touch or surround the optic nerve, using plaque radiotherapy (a radiation treatment for tumours of the eye) can be difficult. The authors investigated whether proton irradiation, a form of radiation therapy which targets cancer cells with a beam of protons, could solve this problem.

Anne Marie Lane, M.P.H., and colleagues from the Massachusetts Eye and Ear Infirmary, Boston, studied 573 patients who had proton irradiation between January 1985 and December 1997. Patients had tumours that were peripapillary (surrounding the optic nerve) or parapapillary (within one disc diameter [DD] of the optic nerve). Researchers followed patients for a median (midpoint) of 96.3 months to determine visual outcomes, cancer-related death rates and tumour recurrence. At diagnosis, the majority of patients had relatively good vision, with a median baseline visual acuity (sharpness) of 20/63.

More than half (53.4 percent) of tumours bordered the optic disc, and the median distance from the tumour to the macula (an area of the eye involved with central vision) was 0.5 DDs. 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 after proton irradiation, 54.9 percent of patients with a baseline visual acuity of at least 20/200 in the treated eye retained vision; at five years posttreatment, this number decreased to 20.3 percent, although the majority of patients were still able to at least count fingers. Local recurrence of the tumour occurred in 3.3 percent of patients at five years and 6 percent of patients at 10 years, respectively. At five years, enucleation (eye removal) rates were 13.3 percent; at 10 years, they were 17.1 percent. Death rates related to melanoma did not differ significantly from those of participants in the Collaborative Ocular Melanoma Study.

“The findings of this study suggest that proton therapy should be considered for patients with tumours encroaching or contiguous to the optic nerve,” write 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.”

(Source: JAMA/Archives: Archives of Ophthalmology)

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Posted On: 26 September, 2011
Modified On: 15 January, 2014


Created by: myVMC