A simulation study on the impact of two different radiotherapy plans on radiation situation of the brain of patients with nasopharyngeal carcinoma with magnetic resonance imaging and computed tomography image difference in cranial base

Objective To study the impact of the treating dose of target volume in different radiotherapy plans on radiation situation of the brain of patients who suffer from nasopharyngeal carcinoma (NPC) with magnetic resonance imaging (MRI) and computed tomography(CT) image difference in cranial base.Methods According to the MRI and CT image difference in cranial base, we applied ARTP-TOP3D-TPS system to delineate target volume and develop the three-dimensional conformal radiotherapy (3-DCRT) plans. Tewenty-six NPC patients were treated by the 3-DCRT plans. The mean dose and D5 mean dose of the target volume in the two group(CT based plan and MRI based plan) were compared.Results Compared with CT based plan(34.66±4.99)Gy,(52.11±7.15)Gy,(5.66±3.95)Gy,(6.36±4.11)Gy,(29.94±5.69)Gy,(30.23±6.54)Gy, the mean dose of brainstem, pituitary, temporal lobe and both eyes in MRI based plan(47.01±4.61)Gy,(59.59±8.80)Gy,(5.92±3.72)Gy,(6.55±3.80)Gy,(38.27±6.15)Gy,(38.78±7.52)Gy were larger (P0.05). There was no statistic difference in the mean dose of spinal cord between two plans[MRI (29.51±5.80)Gy,CT(30.30±4.04)Gy]. Compared with CT based plan(56.49±2.52)Gy,(41.51±4.65)Gy,(54.04±7.31)Gy,(20.17±10.47)Gy,(19.37±11.44)Gy,(60.69±3.62)Gy,(60.04±6.84)Gy, the D5 mean dose of brainstem, spinal cord, pituitary, temporal lobe and both eyes in MRI based plan(66.15±3.43)Gy,(44.26±4.35)Gy,(61.59±8.89)Gy,(20.65±10.66)Gy,(20.09±11.65)Gy,(67.60±2.39)Gy,(67.31±6.88)Gy were larger (P0.05).Conclusion The dose of target volume in 3D-CRT plan based MRI is superior to CT. The dose of important organ of the brain in 3D-CRT plan based MRI is higher.