Effect of the bladder volume difference on radiotherapy for cervical cancer

Objective To investigate the effects of bladder volume difference on dosimetric parameters and positional errors in patients with cervical cancer after radiotherapy.

Methods The clinical data of 71 cervical cancer patients treated with postoperative radiotherapy were retrospectively analyzed.The first positioning and reduction CT images of patients were obtained, respectively, and the two CT images were registered to obtain the positional error.The patients were divided into the group A, group B, and group C according to the change rate of in bladder volume at reduction.The Eclipse planning system was used to study the influence of bladder volume difference of two-time positional on dosimetric parameters and positional error of patients in different groups.

Results In group A, the bladder volume at reduction significantly increased, the difference of PTV HI enlarged(P < 0.05), and the bladder V₃₀, V₃₅, and V₄₀ statistically decreased compared with the first postioning(P < 0.05).In group B, the bladder volume at reduction were essentially the same with the first positioning except the HI of PTV, the differences of the rest dosimetric parameters were not statistically significant(P>0.05).In group C, the bladder volume and CI at reduction significantly decreased, and the D_max, D_mean, and HI of PTV and V₃₀ and V₃₅ of bladder statistically increased compared with the first positioning(P < 0.05).There was no statistical significance in the bladder volume in X direction, Y direction and Z direction among group A, group B and group C(P>0.05).

Conclusions Maintaining appropriate bladder volume at first positioning in intensity-modulated radiation therapy for postoperative cervical cancer is important.When the change rate of bladder volume is -1/3 to 1/3, its effects on dosimetric parameters is less.The bladder volume differences have no effect on positional errors.