Analysis of the treatment planning metrics and their correlation with morphology of intracranial lesions in Gamma Knife stereotactic radiosurgery.

Background: Gamma Knife Radiosurgery (GKRS) has established a role in treating various benign brain pathologies. The radiosurgery planning necessitates a proper understanding of radiation dose distribution in relation to the target lesion and surrounding eloquent area. The quality of a radiosurgery plan is determined by various planning parameters. Here, we have reviewed various GKRS planning parameters and analyzed their correlation with the morphology of treated brain lesions.

Method: A total of 430 treatment plans (71 meningioma, 133 vestibular schwannoma/VS, 150 arteriovenous malformation/AVM, 76 pituitary adenoma/PA treated with GKRS between December 2013 and May 2023) were analyzed for target coverage (TC), conformity index (CI), homogeneity index (HI), and gradient index (GI).

Result: The values of CIPaddick and CILomax for PA were lower and differed significantly from meningioma, VS, and AVM. The value of HI for PA was higher and differed significantly when compared with meningioma, VS, and AVM. The values of HI for AVM were also significantly higher than VS and meningioma. The mean GI was 3.02, 2.92, 3.03, and 2.88 for meningioma, VS, AVM, and PA, respectively. The value of GI for meningioma and AVM was significantly higher when compared with the values for VS and PA. The mean TC was 0.94 for meningioma, 0.96 for VS, 0.95 for AVM, and 0.90 for PA. The value TC of PA was lower and differed significantly when compared with VS, AVM, and meningioma. Lesions with a volume of ≤1 cc had poor planning metrics as the spillage of radiation may be higher.

Conclusion: The GKRS planning parameters depend on the size, shape, nature, and location of intracranial lesions. Therefore, each treatment plan needs to be evaluated thoroughly and a long-term follow-up is needed to establish their relation with clinical outcome.