Study on the Ooptimization of Dose Gradients at the Overlapping Fields in Craniospinal Radiotherapy

• Main Authors: YANG, YA-YUN, 楊雅雲
• Other Authors: YU, CHENG-CHING
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/cfjm2d

碩士 === 元培醫事科技大學 === 醫學影像暨放射技術系碩士班 === 106 === The traditional overlapping fields in craniospinal radiotherapy uses the moving junction technique to make the dose delivered uniformly, and requires a longer time to verify the position of the treatment field. This longer time action may cause patient discomfort. Due to advances in the treatment planning software, this study designs an overlapping method that the doses are designed to have complementary gradients at the overlapping area. One designed dose group presents a gradient increase, and the other dose group presents a gradient decrease. Influence in dose uniformly due to displacement is designed to be reduced. The patient presented in a comfortable position with his hands on both sides, using a mask and a vacuum cushion from the entire skull to the pelvis, and then performing tomographic simulation imaging. The thickness of the image slice was 5 mm. The image was transmitted to the treatment planning system. Four gradients were designed to overlap 5, 8, 10 and 16 cm with the field in the treatment planning. Dose influences caused by the clinical radiological technician setup error (±5 mm) and the patient's movement were considered. Simulated clinical displacements, field overlap of 5 cm, dose differences of 112.2 %, conformity index of 94.87 %, homogeneity index of 7.89 %; field overlap of 8 cm, dose differences of 109.2 %, conformity index of 94.4 %, homogeneity index of 9.86 %; field overlap 10 cm, dose differences of 107.73 %, conformity index of 97.86 %, homogeneity index of 6.33 %; field overlap of 16 cm, dose differences of 104.82 %, conformity index of 78.92 %, homogeneity index of 12.22 %. The gentlest gradient of the treatment plan is the most difficult and time-consuming to plan. Considering the economic effect, it is recommended that the optimal field over 10 cm is divided into 9 segments. The simulated clinical displacement results in a dose difference of ± 7.73 %.