Effect of bladder volume change on normal tissue doses in 3D conformal brachytherapy for cervical cancer

Objective: To evaluate the effect of bladder volume change on the doses to normal tissues in cervical cancer patients undergoing external three-dimensional conformal radiotherapy (3DRT) plus 3D conformal brachytherapy (3DCBT). Methods: The study included 56 patients with cervical cancer who were admitted to our hospital from 2012 to 2013 and received radical external 3DRT and 3DCBT, During 3DCBT, the doses to 0.1, 1.0, and 2.0 cm³(D_{0.1 cm³}, D_{1.0 cm³}, and D_{2.0 cm³}, respectively) for the rectum, small intestine, sigmoid colon, and bladder under different bladder tilling status (empty, 50, 100, and 150 ml) were compared and analyzed by paired t-lest. Results: The rectum D_{0.1 cm³} with bladder volumes of 50 and 100 ml were significantly reduced compared with that with an empty bladder (P = 0.000, 0.000). The D_{0.1 cm³}, D_{1.0 cm³}, and D_{2.0 cm³} for the small intestine with bladder volumes of 50, 100, and 150 ml were significantly reduced compared with those with an empty bladder (P = 0.008, 0.000, 0.000 and 0.000, 0.000, 0.000 or 0.000, 0.000, 0.000). The D_{0.1 cm³}, D_{1.0 cm³}, and D_{2.0 cm³} for the bladder with bladder volumes of 100 and 150 ml were significantly increased compared with those with an empty bladder (P = 0.000, 0.000 and 0.000, 0.000 or 0.000, 0.000). Conclusions: The doses to the bladder and small intestine are influenced by different bladder Filling status, but the doses to the rectum and sigmoid colon show no significant variation. The increase in bladder volume is helpful in reducing the dose to the small intestine. Without any change in the bladder dose, the bladder volume of 50 ml is more beneficial to reduce the dose to the small intestine than those of 100 and 150 ml. (authors)