Abstract
Purpose: The aim of this study was to compare the plan results that were obtained by using different calculation grid sizes ranging from 3 mm to 10 mm, and the same dose calculation algorithm Pencil Beam (PB), in Intensity Modulated Radiotherapy (IMRT) for different treatment sites Head-And –Neck, Pelvis (Carcinoma Cervix) And Brain Cancers. Introduction: Ever since the advent and development of treatment planning systems, the uncertainty associated with calculation grid size has been an issue. Even to this day, with highly sophisticated 3D conformal and intensity-modulated radiation therapy (IMRT) treatment planning systems (TPS), dose uncertainty due to grid size is still a concern. Materials and methods: Twelve patients in which four patients of Head-And –Neck, Pelvis And Brain tumors respectively were considered for the study. IMRT Plans were generated for a 6,600cGy, 5,000cGy & 5,400cGy prescribed doses for Head-And –Neck, Pelvis and Brain tumors respectively using Oncentra v 4.3 TPS. For each patient, dose calculation with Pencil Beam (PB) algorithms using dose grid sizes of 3.0 mm, 5.0 mm, and 10.0 mm were performed. Results: The plans were evaluated as per the ICRU guidelines and dose constraints were maintained as per the Quantec guidelines. The dose differences for the varying grid sizes in Tumor Volumes and Organs at Risk were analyzed and tabulated. Conclusion: Overall, the effect of varying grid size on dose variation appears to be insignificant. However, 3 mm is recommended to ensure acceptable dose calculations, especially in high gradient regions.
Highlights
Ever since the advent and development of treatment planning systems, the uncertainty associated with calculation grid size has been an issue
Clinical studies have shown that intensity-modulated radiation therapy (IMRT) reduces grade-3 xerostomia comparison to threedimensional conformal radiotherapy (3D CRT) [4,5], for that reason IMRT has become the standard treatment in many centers
IMRT places a higher requirement on dose grid resolution than conventional radiation therapy
Summary
Ever since the advent and development of treatment planning systems, the uncertainty associated with calculation grid size has been an issue. Even to this day, with highly sophisticated 3D conformal and intensity-modulated radiation therapy (IMRT) treatment planning systems (TPS), dose uncertainty due to grid size is still a concern. One way of improving the treatment accuracy is to reduce geometrical errors. Margins are added to clinical volumes in order to take into account geometrical uncertainties. These planning margins are commonly calculated from measured systematic and random geometrical errors [7]
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