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Patients with tremor, trigeminal neuralgia, and refractory obsessive disorder are now being treated with OBJECTIVE Functional Gamma Knife radiosurgery techniques. And with a standardized prescription dose, rates of functional GKRS toxicity increase after replacing an old cobalt-60 source with a new one, according to Anecdotal reports. Changes in the chemically safe dose delivered to neural tissue may be significant in the clinically effective dose delivered to neural tissue, and no change in the duration of the useful life of cobalt-60 is reported in the study of patients treated with functional GKRS. From published scientific results, biologically plausible estimates for the ratio for radiosensitivity to fraction size and double-strand break DNA repair halftimes were found. In obtaining an accurate 1 halftime and 2 halftime, the biphasic characteristics of DSB repair in normal tissue were accounted for. RESULTS Following the conversion of the cobalt-60 source, the useful GKRS dose rate increased from 1. 48 to 2. 99 Gy/min, treatment time decreased, and estimated BED increased. With 85 Gy, 15. 6% for thalamotomy with 130 Gy, and 18. 6% for capsulotomy with 180 Gy, based on the most biologically plausible assumptions, source replacement resulted in an immediate relative BED increase of 11. 7% for GKRS-based TN management with 85 Gy, 15. 6% for thalamotomy with 130 Gy, and 18. 6% for capsulotomy with 180 Gy. CONCLUSIONS based on the same physical dose prescription, use of a new cobalt-60 source after the replacement of an old source significantly raises the predicted BED for functional GKRS treatments. In the study of results after high-dose functional GKRS treatments, source age, dosage rise, and treatment time should be considered.
Source link: https://doi.org/10.3171/2016.6.gks161497
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