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Impact of Grid Size on Dose Calculations for Cranial Tumors
Nayron Medeiros Soares1,2, Maria José Almada1,2, José Alejandro Rojas López3,4
1Department of Medical Physics, Zunino Institute, Córdoba, Argentina.
Purpose:
The purpose of this study was to evaluate the impact of calculation grid size on dose calculations for multiple cranial tumor types using Monte Carlo (MC) calculation, comparing different grid settings.
Methods:
This cross-sectional study optimized 110 treatment plans using Elements Cranial and included arteriovenous malformation (AVM), glioblastoma (GBM), meningioma (MGM), brain metastasis (BM), pituitary adenoma (PA), and vestibular schwannoma (VS). Dose coverage at D98%, D95%, and D2%, along with mean dose, were assessed, and other relevant planning and anatomical parameters were analyzed.
Results:
GBM had the largest gross tumor volume and planning target volume (PTV) volumes, while VS had the smallest volumes and the highest PTV-bone intersection. For MC, grid size variations (1%/1 mm vs. 2%2 mm) did not significantly affect AVM, GBM, or MGM. However, statistically significant dose reductions were observed for BM, PA, and VS. When adjusted for PTV volume and bone intersection, median dose values decreased with the 2%/2 mm grid compared to the 1%/1 mm grid: D98% (25.60 Gy vs. 25.27 Gy, adjusted P = 0.026), D95% (27.05 Gy vs. 26.14 Gy, adjusted P = 0.005), and D2% (30.48 Gy vs. 30.00 Gy, adjusted P < 0.001). Application of the 2%/2 mm grid resulted in increased conformity index (CI) and gradient index (GI) values, with the effect being more pronounced in smaller or anatomically irregular targets, such as VS and PA.
Conclusions:
Grid size impacted dose calculations for small or irregular targets such as BM, PA, and VS. The 2%/2 mm grid led to significant dose reductions and increased CI and GI values.
