การวิเคราะห์คุณภาพแผนรังสีรักษาบริเวณศีรษะและลำคอ ด้วยขนาดปริมาตรการปรับความเข้มรังสีและการคำนวณปริมาณรังสีที่แตกต่างกันด้วยเครื่องวางแผนรังสีรักษาโวโลอัลตร้าของเทคนิคภาพนำแบบเกลียวหมุน

Abstract

The Precision® treatment planning system (TPS) is specifically designed for the helical tomotherapy. This TPS requires the parameters to create the beam geometries for achieving the highest treatment plans quality. The optimization and dose calculation were one of the main impacts, particularly the grid resolution. This TPS allows the independently selection of various grid resolutions between optimization and dose calculation processes. This study then investigated the impact of grid resolution between the selection of the optimization and dose calculation resolution. The study recruited the 41 nasopharyngeal cancer patients who previously treated with helical tomotherapy. Nine treatment planning scenarios were created by the combination between the different resolution of optimization and calculation. This combination was selected among three different resolution level; Low resolution (L), Medium resolution (M), and High resolution (H) where the symbol O/C represented the resolution of optimization/dose calculation (e.g. M/L means medium resolution and low resolution for the optimization and dose calculation, respectively). The plan quality comparison was accessed through the dosimetric parameters both the target and organs at risk (OARs) by the H/H plan scenario benchmark. The results showed the dosimetric parameters of the target were increased when the low grid resolution of the optimization was applied. On the other hand, their dosimetric parameters were decreased when this resolution was used in the dose calculation. However, the study found a M/H, M/M, L/H, and L/M plan scenario had a higher dose when compared to the on the H/H plan scenario (reference plan scenario). The grid resolution affected not only on the CI value but also on the HI value. The results revealed a degraded CI and HI value when the low resolution was applied in the optimization process. On the OARs, the grid resolution influenced some organs, particularly the spinal cord and both parotid glands. The plan scenario of M/H showed low number of dosimetric parameters that were significant different to the reference plan scenario. For the planning time, the study found a highest grid resolution was significantly increased. Finally, this study found a different FOV, had a minimal impact on the dosimetric parameter. The study recommended the plan scenarios of the M/H and M/M were an alternative selection for the treatment planning. These resolutions also provided a high treatment plan quality on the target, low impact on OARs dose and also the calculation time of planning reduction.