Postoperative irradiation for pterygium: guidelines for optimal treatment.
OBJECTIVE
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
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.
Brenner
D J
DJ
College of Physicians and Surgeons of Columbia University, New York, NY 10032.
Merriam
G R
GR
D003131:Combined Modality Therapy; D006801:Humans; D011625:Pterygium / Q000532:radiotherapy* / Q000601:surgery; D011879:Radiotherapy Dosage; D012008:Recurrence; D013326:Strontium Radioisotopes
D013326:Strontium Radioisotopes