Treatment of hemangiomas with the strontium-90 beta-ray applicator.

Abstract

Beta rays emanating from radium, radon, and radium D and E have been used for therapeutic purposes about the eye for many years. Recently the use of the strontium-90 beta-ray applicator was described in the treatment of superficial tumors of the eyelids and conjunctiva, vernal conjunctivitis, vascularization of the cornea, and corneal ulcers (1). Since beta rays penetrate only a few millimeters of tissue, many hemangiomas of the “strawberry mark” variety, being quite superficial, seemed to be suitable for treatment with this form of radiation. Strontium 90 is especially useful, since it fulfills all the criteria of ideal beta-ray therapy, that is, a long half-life (twenty years, so that frequent replenishment is unnecessary), energetic beta particles which permit sufficient penetration of tissue, absence of gamma rays, affording ease of protection, and ease of manipulation. Since 1952 we have treated several superficial hemangiomas quite successfully with the strontium-90 applicator. Because the applicator has a high output of radiation, the treatment time is extremely short (measured in seconds). This fact alone is a great aid in the management of infants, who rebel at being restrained even for several minutes, which is the usual time for treatment with x-rays. In addition, the treatment is painless. Physical Characteristics of Strontium 90: Strontium 90 is a fission product and is obtained from the Isotopes Branch of the U. S. Atomic Energy Commission. It has a half-life of twenty years and disintegrates through the emission of a beta particle with maximum energy of 0.65 million electron volts to form yttrium 90. Yttrium 90 has a half-life of sixty-two hours and emits beta particles with a maximum energy of 2.16 MEV to form the stable isotope of zirconium, namely zirconium 90. No significant gamma radiation is present. A plaque containing strontium 90 is thus a source of pure beta radiation with two continuous spectra, that of strontium 90 and of yttrium 90. In about twenty years the intensity of radiation which is emitted by the plaque and the radiation intensity resulting therefrom are dependent upon the millicurie strength, area of the radioactive deposit, and the degree of filtration by the metallic protective covering. This protective covering (approximately 100 mg./sq. cm.) is sufficient to reduce the number of beta particles which result from the disintegration of the strontium and yttrium to approximately 3 and 60 per cent of their original values, respectively. The beta particles, therefore, being emitted from this plaque will have essentially the characteristics of a pure yttrium-90 spectrum (with a maximum energy of 2.16 MEV) after it is passed through 100 mg. per square centimeter of filtration (2). The depth dose for the strontium applicator is as follows: Description of Applicator: The strontium applicator is manufactured by Tracerlab, Inc.