Early changes of volume and spatial location in target and normal tissues caused by IMRT for cervical cancer

Aims: To investigate the early changes of volume and spatial location in target and normal tissues caused by intensity-modulated radiotherapy (IMRT) for cervical cancer. Methods: Forty patients with cervical cancer were included in this study and treated by IMRT. Computed tomography (CT) was performed before radiotherapy and when the patient had received 27 Gy in 15 fractions. After image registration, the volume of interest (VOI) for the targets and organs at risk was delineated by clinicians on the CT images. Changes of volume, spatial location and Dice similarity were calculated for all VOIs. Results: There were significant changes in gross tumor volume (GTV) in the primary tumor (GTV-T) with t = 8.304 (p<0.01) and visible pelvic lymph nodes (GTV-N) with t = 4.996 (p<0.01) caused by IMRT. The mean volume differences for GTV-T and GTV-N were 38.64% +/- 19.50% (range 3.16%-86.49%) and 42.49% +/- 25.68% (range 2.79%-87.42%), respectively. Among the organs at risk, the bladder had the greatest volume change with 55.13% +/- 33.40% (range 3.25%-116.01%). The Dice similarity for GTV-T and GTV-N was 0.50 +/- 0.18 (range 0.10-0.85) and 0.31 +/- 0.20 (range 0.00-0.71), respectively. The rectum had the least Dice similarity among the normal tissues, with a mean value of 0.57 +/- 0.14 (range 0.18-0.76). Conclusions: There were significant changes in volume and spatial location of the target and normal tissues after 27 Gy IMRT. In order to maintain the radiation dose to the targets and minimize the radiation to normal tissues, it is necessary to modify the radiotherapy planning.