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Brain Dose From Gamma Knife Depends Primarily On the Treated Volume and Not On the Number, Shape Or Location of the Lesions

G Narayanasamy

G Narayanasamy*, A Smith, E Van Meter, R McGarry, J Molloy, University of Kentucky, Lexington, KY

SU-E-T-703 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To assess the hypothesis that the volume of brain parenchyma that receives a certain dose level in Gamma-Knife is dependent on the treated volume and not on the number, shape or location of the lesions. This would help a physician validate the suitability of GammaKnife based stereotactic radiosurgery (GKSR) prior to treatment.

Methods:Simulation studies were performed to establish the hypothesis for an oblong, a spherical lesion of various sizes and multiple spherical lesions. A similar study was performed on forty patients who underwent GKSR with mean age 54 (range 7-80), mean number of lesions 2.5 (range 1-6) and mean lesion volume at presentation 4.4cc (range 0.02cc-22.2cc). Following recommendations of QUANTEC, V12 of brain (VB12) was measured and a power-law based relation is proposed here for estimating VB12 from the volume of target treated to 50% of maximum dose (VT50%).

Results:In the simulation study, the volume of brain irradiated by 50% (VB50%), 10% (VB10%) and 1% (VB1%) of maximum dose was found to have linear, linear and exponentially increasing dependence on VT50%, respectively. In the retrospective study on forty GKSR patients, a similar relationship was found to predict the brain dose with a Spearman correlation coefficient >0.9 and the corresponding p-value from Students T-test <1*10-4 for all the above 3 dependences. The relationships between clinical VT50% and the number and aspect ratio of lesions were statistically insignificant. The measured VB12 of brain agrees with the calculated value of VB12 to within 1.7%.

Conclusion:The simulation and the retrospective clinical studies indicate that the volume of brain irradiated by a percentage of maximum dose is dependent on the treated volume and not on the number, shape or location of the lesions.

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