A comparative study of CT-and MRI-based three-dimensional conformal brachytherapy for locally advanced cervical cancer

Abstract

Objective To compare target volume and dosimetry between computed tomography(CT)-and magnetic resonance imaging(MRI)-guided three-dimensional(3D)conformal brachytherapy for locally advanced cervical cancer, and to provide evidence for optimization of the image-guided approach and improvement of treatment regimen. Methods Thirteen patients with locally advanced cervical cancer who were treated with radical radiotherapy in our hospital in 2014 were enrolled as subjects. All patients received MRI-guided 3D conformal intracavitary/interstitial brachytherapy. All patients received MRI and CT scans for each brachytherapy fraction, based on which the target volume delineation, intracavitary/interstitial regimen design, and intracavitary-only treatment regimen design were performed. Comparison of data between MRI and CT scans was performed using paired t test. Results The width and volume of the high-risk clinical target volume(HR-CTV)were significantly smaller in the MRI simulation than in the CT simulation((38.0±9.4)mm vs.(45.1±8.7)mm, P=0. 000; (34.2±15. 3)cm3vs.(42.9±20.4)cm3, P = 0. 002), and the width, thickness, and volume of the intermediate-risk clinical target volume(IR-CTV)were also significantly smaller in the MRI simulation than in the CT simulation((58.8±9. 4)mm vs.(65.4±10. 3)mm, P=0.000;(34.8±6.3)mm vs.(37.5±6.3)mm, P=0. 001;(90.9±28. 5)cm3vs.(109.0±36.4)cm3, P = 0. 000). The D90 values for HR-CTV and IR-CTV were significantly higher in the MRI simulation than in the CT simulation(87. 6 Gy vs. 85. 8 Gy, P=0. 013;67. 7 Gy vs. 66. 3 Gy, P=0. 005), while the average D2 cm3 values for the bladder and rectum were significantly lower in the MRI simulation than in the CT simulation(73. 1 Gy vs. 75. 5 Gy , P= 0.011 ; 61. 0 Gy vs. 65. 7 Gy , P= 0. 000). Conclusions Compared with the MRI simulation, the CT simulation overestimates the width of target volume. MRI has substantial advantages in dosimetry for target volume and normal tissues. The intracavitary/interstitial treatment can make up the reduced dose for the target volume resulting from the CT simulation. Key words: Cervical neoplasms; Image guided brachytherapy; Target volume delineation; Dosimetry