Evaluating Critical Brain Radiation Doses in the Treatment of Multiple Brain Lesions with Gamma Knife Radiosurgery

Background: Treatment of patients with multiple brain metastases has shifted to stereotactic radiosurgery, withholding whole-brain (WB) radiation therapy. However, radiation toxicity to the brain is a concern when treating multiple brain lesions with single-fraction stereotactic radiosurgery. Objective: The purpose of this study was to determine the changes in brain radiation doses when treating various numbers of targets and lesion volumes. Methods: We simulated different treatment plans with different combinations of varying tumor volumes including 0.1, 0.5, 1, 2, and 5 cm³, and tumor numbers including 1, 3, 5, 10, 15, 20, and 25. Treatment planning was performed for all combinations in a computerized tomography of the head of a patient, using Leksell GammaPlan version 10.1.1 (Elekta AB, Stockholm, Sweden). Two different dosing strategies were used. In the lower-prescription dosing schedule, a marginal dose was given to the 50% isodose line, and 20 Gy were used when the number of lesions was less than 15 and 18 Gy were applied when the number of lesions was equal to or more than 15. In the higher-prescription dosing schedule, a marginal dose of 24 Gy was used for lesions of less than 5 cm³ and 20 Gy were applied for lesions equal to 5cm³. The mean WB dose, the WB integral dose, and the volume of brain receiving 12 Gy (V12 Gy) were calculated for each scenario. Also, the beam-on time of the Gamma Knife 4C unit was reported for all treatment scenarios. Results: Regression analysis showed that the total tumor volume was a more significant predictor of V12 Gy than the number of lesions, and a linear correlation between the total tumor volume and V12 Gy was found. We also found that the total tumor volume was a more significant predictor of the mean WB dose and the WB integral dose compared to the number of lesions. Conclusion: Our results suggest that multiple small to mid-sized lesions could be safely treated with a single-fraction gamma knife.
Stereotact Funct Neurosurg 2017;95:268-278

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