Postoperative irradiation for pterygium: guidelines for optimal treatment.
PURPOSE: Postoperative adjuvant strontium-90 beta-ray therapy is a proven technique for reducing the recurrence rate of pterygium. A wide variety of doses and fractionation schemes have been used in the application of the radiation. There have been recent reports of significant rates of late-occurring complications after single-fractioned treatment. Compared with a single-dose application, fractionation would only offer a therapeutic benefit if recurrence prevention were an early-responding tissue phenomenon, in contrast to late-responding sequellae. We investigate this point with a view to elucidating better treatment protocols for postoperative beta-ray therapy for pterygium. METHODS AND MATERIALS: We use the linear-quadratic formalism to analyze published nonrecurrence rates, as a function of dose and fraction number, to obtain a value for the parameter alpha/beta, which is an indicator of whether nonrecurrence is an early or late-responding phenomenon. RESULTS: The estimated value of the linear-quadratic parameter, alpha/beta, is 25 Gy, with 90% confidence limits of +/- 9 Gy. This large value unequivocally suggests that nonrecurrence is an early responding phenomenon, implying that fractionation should give an increased therapeutic ratio between nonrecurrence and late sequellae. CONCLUSIONS: Compared with a single-fractioned treatment, an improved therapeutic ratio (nonrecurrence vs. complications) would be expected from fractionated application of the beta-ray therapy. Given the parameters obtained from fitting literature data, we calculate guidelines for the dose/fraction schemes that should give equivalent disease control to different single-fraction applications, but should reduce the incidence of late-occurring sequellae.[1]References
- Postoperative irradiation for pterygium: guidelines for optimal treatment. Brenner, D.J., Merriam, G.R. Int. J. Radiat. Oncol. Biol. Phys. (1994) [Pubmed]
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