A customized vacuum cushion for immobilization in the radiotherapy of pelvic malignancies / 中华放射医学与防护杂志

ABSTRACT

Objective To evaluate the performance of a customized vacuum-form body immobilization method in the radiotherapy of pelvic malignancies by comparing it with conventional approaches, thus to improve immobilization accuracy in the radiotherapy of pelvic malignancies. Methods A total of 66 patients with pelvic malignancies were enrolled in this study. These patients were divided into three groups according to three immobilization approaches radiotherapy board ( Group N ) , conventional vacuum cushion ( Group V ) , and a customized vacuum cushion specifically for pelvic immobilization ( Group New-V) . Setup deviations of these immobilizations were comparatively evaluated by translational and rotational errors during intra-fractional measurements. Results The average translational setup errors in vertical(x), longitudinal(y), lateral(z) and rotational error r were (0. 35 ± 0. 37), (0. 21 ± 0. 22), (0. 29 ± 0. 28) cm and (0. 70 ± 0. 65)° for Group New-V; (0. 44 ± 0. 43), (0. 31 ± 0. 62), (0. 45 ± 0. 60) cm and (1. 25 ± 1. 00)° for Group N; (0. 38 ± 0. 36), (0. 27 ± 0. 25), (0. 32 ± 0. 29) cm and (1. 09 ± 0. 77)° for Group V, respectively. Significant differences were observed in r direction among these three method (F=7. 859,P <0. 05). Group New-V with customized cushion showed the least standard deviations in four directions and the least setup error in r direction compared with the other two method (F=3. 166,P<0. 05). Reconstructed dose distribution based on the isocenter shift result ed from setup errors revealed that Group New-V showed the least deviations in the minimum and mean dose and of the planning target volume (PTV) before and after isocenter shift(F=8. 018, P<0. 05). Conclusions The customized vacuum cushion provided best immobilization and dosimetric advantage. It helps to optimize the immobilization accuracy and improve the clinic outcome potentially.