A Designed Tomotherapy Planning Technique for Esophageal Cancer： the Relationship between Fan-shaped Complete Block and Lung Dose

• Main Authors: Pei-Yi Tsai, 蔡沛宜
• Other Authors: Tung-Hsin Wu
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/76401709797814666783

碩士 === 國立陽明大學 === 生物醫學影像暨放射科學系 === 105 === Introduction: Radiation therapy is an important component in the multimodality treatment for esophageal cancer. Radiation pneumonitis (RP) is an acute complication for radiotherapy of esophageal cancer and is associated with the cumulative low dose in lung tissue. This study aims to evaluate the relationship between the fan-shaped complete block (FSCB) and lung dose, and to predict the proportion of the lung volume receiving 5 Gy (V5) utilizing various designs of the FSCB in helical tomotherapy. In addition, we analyze the dosimetric parameters for organs at risk (OARs) and evaluate the appropriate FSCB angles. Material and Methods: We simulated virtual esophageal tumor treated by Tomotherapy on an anthropomorphic body phantom. The FSCB was defined as the fan-shaped radiation restricted area located in both lungs and the volume of FSCB formed the non-irradiated volume (VNR). The proportion of the VNR in lung (VNR ratio) was used to predict the V5. Our study included two parts.In the first part, sixteen treatment plans were performed with non-block design and FSCB with different fan angles (from 10ﾟto 150ﾟ, with increment of 10ﾟ). The association between FSCB angle, VNR ratio and lung dose were evaluated using Pearson correlation analysis. The actual value and predictive value of V5 were compared. In the second part, the homogeneous index (HI) and conformal number (CN) of PTV and the dosimetric quality for lung, heart, and spinal cord were determined for each treatment scheme with FSCB 70ﾟto 150ﾟ to evaluate the FSCB angles suitable for use. Result: First, in the right lung, FSCB angle was highly correlated to reduced mean dose (r＝-0.988, P < 0.05) and V5 (r＝-0.994, P < 0.05), and moderately correlated to reduced V20 (r = -0.616, P < 0.05).VNR ratio was also highly correlated to reduced mean dose (r＝-0.997, P < 0.05) and V5 (r＝-0.999, P < 0.05), and moderately correlated to reduced V20 (r = -0.660, P < 0.05). In the left lung, FSCB angle was highly correlated to reduced mean dose (r = -0.989, P < 0.05), V20 (r = -0.979, P < 0.05) and V5 (r = -0.991, P < 0.05). VNR ratio was also highly correlated to reduced mean dose (r = -0.997, P < 0.05), V20 (r = -0.982, P < 0.05) and V5 (r = -0.998, P < 0.05).The difference between the actual value and predictive value of V5 was within 3.7%. Second, we found the V5, V10, V15, V20 and mean dose for the lungs were lower when the FSCB angle increased, with simultaneous increase of the maximum dose of spinal cord, mean dose, and V30 of the heart. Treatment plans with FSCB 80ﾟto 140ﾟdesigns could reach the dose constraints of OARs. Discussion and conclusion: Helical tomotherapy using FSCB plans provided reduction of the mean dose, V5 and V20 to lungs for esophageal cancer. The FSCB angle and VNR ratio were highly associated with reduction of mean dose and V5. In addition, treatment plans with FSCB 80ﾟto 140ﾟ in helical tomotherapy were a feasible protective method for reducing complications from radiotherapy of esophageal cancer.