Abstract
Purpose: Residual uncertainties on the order of 1-2 mm are frequently observed when delivering stereotactic radiosurgery via on-line imaging guidance with a relocatable frame. In this study, a predictive model was developed to evalute potentiral late radiation effects associated with such uncertainties. Methods: A mathematical model was first developed to correlate the peripherial isodose volume with the internal and/or setup margins for a radiosurgical target. Such a model was then integrated with a previoulsy published logistic regression normal tissue complication model for determining the symptomatic radiation necrosis rate at various target sizes and prescription dose levels. The model was tested on a cohort of 15 brain tumor and tumor resection cavity patient cases and model predicted results were compared with the clinical results reported in the literature. Results: A normalized target diameter (D{sub 0}) in term of D{sub 0} = 6V/S, where V is the volume of a radiosurgical target and S is the surface of the target, was found to correlate excellently with the peripheral isodose volume for a radiosurgical delivery (logarithmic regression R{sup 2} > 0.99). The peripheral isodose volumes were found increase rapidly with increasing uncertainties levels. In general, a 1-mm residual uncertainties as calculated to resultmore » in approximately 0.5%, 1%, and 3% increases in the symptomatic radiation necrosis rate for D{sub 0} = 1 cm, 2 cm, and 3 cm based on the prescription guideline of RTOG 9005, i.e., 21 Gy to a lesion of 1 cm in diameter, 18 Gy to a lesion 2 cm in diameter, and 15 Gy to a lesion 3 cm in diameter respectively. Conclusion: The results of study suggest more stringent criteria on residual uncertainties are needed when treating a large target such as D{sub 0}≤ 3 cm with stereotactic radiosurgery. Dr. Ma and Dr. Sahgal are currently serving on the board of international society of stereotactic radiosurgery (ISRS)« less
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