Retinal changes induced by heavy particles: a new therapy modality?

The nature of the lesions produced by the oxygen particles appears similar to the experimental and clinical radiation retinopathies which have been reported previously. These reports, as well as our own findings, indicate that the lesion is primarily a circulatory one, with other retinal changes being secondary. Retinal changes of the magnitude produced with the oxygen ions have been reported with the use of cobalt plaques sewn to the sclera in the treatment of intraocular tumors. Doses that led to such clinical changes, however, were 8 times that required with the accelerated particles and required months to develop rather than 1 day or 1 week. Thus, retinal lesions produced with accelerated oxygen particles exhibit a significant compression of time and dose over those reported in the clinical literature. This study demonstrated that the tissue effectiveness of the accelerated particle is far greater than that of any previously utilized irradiation source. The oxygen atom is only the beginning; with the introduction of the Bevalac at the Lawrence Radiation Laboratory, multiple ion sources of various atomic weights will be available in future years. The radiation levels reported in this paper represent an ''overkill'' in the amount of radiation required for destruction ofmore » ocular tissue. With the development of a suitable particle source, and a collimated beam, these particles could become a clinically important therapeutic modality. By using B-scan ultrasonography and taking advantage of the relative energy absorption in tissue following heavy ion irradiation, one may have an effective radiation tool for treatment of choroidal melanomas and retinal blastomas.« less