Program Information
Assessment of Skull Measurement for Deformed Skull Contours in Gamma Knife Radiosurgery
N GOPISHANKAR*, RK BISHT , D AGRAWAL , SS KALE , AK MAHAPATRA , ALL INDIA INSTITUTE OF MEDICAL SCIENCES, NEW DELHI, INDIA
Presentations
SU-I-GPD-T-605 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To investigate the effect of skull measurement in treatment planning calculation for deformed skull contours in Gamma Knife Radiosurgery.
Methods: Three deformed skull contours were chosen for this study. Existing CT images of deformed skull in the Leksell Gamma Plan (LGP) TPS (Version 10.1) were selected for contouring. Two modes of skull measurements, Bubble Helmet based (BH) and CT based contour (CBC) were chosen. MRI images of the same contours were co-registered and fused with CT for CBC definition. The targets were delineated in the MRI images. The treatment planning was performed using TMR10 and Convolution algorithm in three planning modes such as TMR10-BH, TMR10-CBC and Convolution-CBC (CCBC). The dose grids with 1mm resolution were extracted from TPS for all three calculation situations and were analysed using in-house Matlab programme for comparison.
Results: The skull definition based on CBC accurately reconstructed the skull surface, whereas BH based definition generated skull-underdefined (SUD) and skull-overdefined (SOD) regions due to limited skull measurement points for interpolation. Dose-Volume Histogram analysis done at SUD regions showed that in TMR10-BH, TMR10-CBC, CBCC 50% volume received minimum 0.5Gy, 1.8Gy and 3.3 Gy respectively. The TMR10-BH severely underestimates the doses for organs at tumor vicinity. At SOD regions the lower isodoses shifted outward from true skull surface. Line profile measurements of three volumetric skull dose grids showed dose difference ranging between 6-10% for TMR10-BH versus CCBC and within 3% for TMR10-CBC versus CCBC. A close examination of Skull Contour2 demonstrated that from skull surface the lower isodoses shifted inward distance of 13mm in TMR10-BH and shifted outwardly 24mm in CCBC. The mean treatment time in CCBC was 1.25 times more than TMR10-BH.
Conclusion: In deformed skull, CBC performs realistic calculation and removes several uncertainties in treatment planning in comparison with BH based skull contouring approach.
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