Dosimetric comparison of the helical tomotherapy, intensity-modulated radiotherapy and volumetric-modulated arc therapy in radical radiotherapy for esophageal cancer

Abstract

Objective: To compare the dosimetric parameters of three different modern radiation techniques in radical radiotherapy for esophageal cancer. Methods: A total of 25 patients with pathologically confirmed esophageal squamous cell carcinoma in Zhejiang Cancer Hospital were included from September 2015 to May 2016 and three radiation treatment plans for helical tomotherapy (TOMO), intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) were designed respectively for each patient. Study patients included 24 males and 1 female,aged from 47 to 82 years old, with a median age of 63 years old. All patients received the total prescription dose of 60 Gy in 30 fractions to the planning target volume (PTV). Conformity index (CI), heterogeneity index (HI), D(1), D(2), D(50), D(95), D(98), D(9)9 and V(95), V(100), V(105) of PTV was calculated. The mean dose, V(5), V(10), V(20), V(30), V(40) and V(50) of total lung, heart, and maximum dose (D(max)) to spinal cord were recorded as well. Results: Compared with TOMO and IMRT, VMAT showed higher CI (0.81±0.08) and lower HI (0.10±0.05), and CI was worse in IMRT (0.77±0.05) than TOMO (0.79±0.04) (t=2.604, P=0.016) and VMAT (t=2.817, P=0.010). There was no significant difference in HI among three radiation techniques. The dosimetric parameters of TOMO in normal lung were significantly better than those of VMAT and IMRT, especially in V(20) and V(30). The D(max) of spinal cord (38.24±3.72) Gy in TOMO was significantly lower than that of the VMAT ((39.88±3.27)Gy, t=-3.173, P=0.004) and IMRT plan ((41.09±3.18)Gy, t=-5.559, P=0.000). Subgroup analysis showed that VMAT was superior to TOMO and IMRT in CI and HI, especially HI (0.09±0.01) significantly better than TOMO (0.12±0.03, t=3.024, P=0.029) and IMRT (0.12±0.02, t=-3.800, P=0.013) for patients with cervical and upper thoracic esophageal cancer. TOMO and VMAT were significantly better than IMRT in MLD, lung V(20) and V(30) (all P<0.05). TOMO (38.46±2.15)Gy was significantly superior to VMAT ((41.02±1.28)Gy,t=-2.701, P=0.043) and IMRT ((41.76±1.11)Gy, t=-3.111, P=0.027) at D(max) of the spinal cord. For the patients with middle and lower thoracic esophageal cancer, TOMO, VMAT and IMRT had no statistically significant differences in CI and HI. IMRT was inferior to TOMO and VMAT in MLD, lung V(10), V(20), and V(30) (all P<0.05). TOMO (38.17±4.14) Gy was significantly superior to VMAT ((39.52±3.64)Gy,t=-2.219, P=0.040) and IMRT ((40.87±3.59)Gy,t=-4.528, P=0.000) at D(max) of the spinal cord. Conclusions: The VMAT plan is better than TOMO and IMRT in terms of the conformal degree and dose uniformity of the target volume.TOMO seems significantly better than VMAT and IMRT in protecting normal tissue.