Impact of Different Grid Sizes and Different Dose Calculation Algorithms on Dosimetric Parameters forHead and Neck IMRT.

Purpose: study the dosimetric impact of grid size and dose calculation algorithm on the intensity modulated radiotherapy (IMRT) plans for head and neck (H&N) cancer cases. Method: IMRT plans were generated in the MONACO® treatment planning system (TPS). That supports calculations to different algorithms (Monte Carlo (MC) and pencil beam (PB)) for patients already treated for H&N cancer. Retrieve patients and recalculate the plans by changing between grid size (2, 3, 4, 5 mm) and algorithm (MC and PB) for each plan. Dosimetric parameters for planning target volume (PTV) are minimum, maximum, and mean doses, D5%, V95%, homogeneity index (HI), conformity index (CI), and gradient index (GI). For organs at risk (OARs) maximum dose (Dmax), mean dose (Dmean). For the volume of the whole body (WB) receiving 2 Gy (V2Gy) and 5 Gy (V5Gy).Results: 11 patients were enrolled in this study for analysis. Regarding HI and CI, MC plans show better results than PB plans. Comparing algorithms at the same grid size shows significance (P-value < 0.05) in all PTV parameters (except Dmin and mGI). Comparing grid sizes shows significance in only Dmax, Dmean, D5%, V95%, and CI2.

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