Impact of Slice Thickness and Grid Size on Dose Calculation in Intensity Modulated and Volumetric-Modulated Arc Radiotherapy in Head and Neck Cancer

Abstract

Background: The grid size in radiotherapy can have an impact on dose values. When calculating the dose, slice width is a crucial component to consider. A thinner slice provides for a more precise mean dose estimate than a thicker slice. Materials and Methods: For this study, 35 patients with Head and Neck (H&N) cancer were chosen. Planning Target Volume (PTV) and Organ At Risks (OARs) were optimized using the same criteria. Intensity Modulated Radiation Therapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans, which were designed with slice thicknesses (3,5,7 mm) and grid sizes (2,3,5, 7 and 8 mm). Homogeneity (HI) and Conformity Index (CI), dose points, such as D2%, D50%, and D98% for each OAR, assessed in relation to slice thickness and grid size. Results: There is a substantial difference (p<0.05) between grid sizes 3mm, 5mm, 7mm, and 8mm in IMRT and VMAT, but no significant difference (p>0.05) in target and OAR dose between grid sizes 2mm and 3mm. Conversely, the target dosage and OAR dose are significantly affected by variations in the Computed Tomography (CT) slice thickness, with a significant difference (p<0.05) seen in the target dose between 3mm, 5mm, and 7mm slice thickness and an insignificant difference (p>0.05) between 5mm and 7mm in OAR dose. Conclusions: According to this study, using the grid size of 2 mm is not recommended because it generates memory issues in the treatment planning system (TPS) and takes a lot of time, neither of which have a practical clinical effect.