Abstract: Objective To evaluate changes in small intestine position during whole pelvic intensity-modulated radiation therapy for patients with gynecologic malignancies using computed tomographic (CT) images during treatment and to investigate whether the small intestine should be avoided for delineation of pelvic lymph node drainage area in patients with gynecologic malignancies. 
Methods Thirty-one patients with gynecologic malignancies were included for pelvic radiotherapy and divided into surgical group (n=15) and non-surgical group (n=16). The 10th, 15th, and 20th fractions of the CT images during treatment were reviewed and changes in the avoidance area formed by the intersection of the observation area with the small intestine compared with the initially planned CT scan images were recorded. We defined the scope of CTV radiation therapy in the drainage area of the pelvic lymph nodes formed by pelvic vascular expansion in the initially planned scan images as the observation area and its intersecting volume with the small bowel as avoidance area of the small intestine. 
Results During radiotherapy, the volume ratio of small intestine staying in its avoidance area of planned target area in the observation area, which included the left common iliac region, right common iliac region, left internal iliac region, right internal iliac region, left external iliac region, right external iliac region, left obturator region, right obturator region, and presacral region, was 16.52%, 28.05%, 18.65%, 37.16%, 39.18%, 49.67%, 23.74%, 50.07%, and 42.65%, respectively, for the non-surgical group, and 39.57%, 34.41%, 18.45%, 31.21%, 44.21%, 43.39%, 31.32%, 49.67%, and 27.59%, respectively, for the surgical group. 
Conclusion The volume ratio of small intestine staying in its avoidance area of planned target area accounted for 50% or less in patients during radiotherapy, regardless of whether they had received surgery for gynecological malignancies. Combined with the mobility of the intestine itself and the percentage of overlapping volume, it is recommended that the small intestines do not need to be avoided for delineation of drainage area of pelvic lymph nodes for gynecological malignancies.

Key words: genital neoplasms, female, radiotherapy, high-energy, lymph nodes