Evaluation of pelvic lymph node coverage of conventional radiotherapy fields based on bony landmarks in Chinese cervical cancer patients using CT simulation

Objective: To evaluate the pelvic lymph node coverage of conventional pelvic fields based on bony landmarks in Chinese patients with cervical cancer by using computed tomography (CT) simulation images to contour pelvic vessels as substitutes for lymph nodes location. Methods: A retrospective review of CT simulation images and conventional pelvic radiation planning data sets was performed in 100 patients with cervical cancer at the International Federation of Gynecology and Obstetrics (FIGO) Stage IIB to IIIB in our hospital. Pelvic arteries were contoured on CT simulation images, and the outlines of conventional pelvic fields were drawn as defined by the gynecologic oncology group (GOG) after hiding the contours. The distances between the following vessel contours and field borders were measured: D1, the superior border of the anterior/posterior (AP) field and the bifurcation of abdominal aorta; D2, the ipsilateral border of the AP field and the distal end of external iliac artery; and D3, the anterior border of the lateral (LAT) field and the distal end of the external iliac artery. The distances were recorded as positive values if the measuring point was within the conventional pelvic fields, or they were recorded as negative values. Lymph nodes coverage was considered adequate when D1≥0 mm, D2≥17 mm or D3≥7 mm. Results: All patients had at least 1 inadequate margin, 97 patients (97.0%) had 2, and 22 patients (22.0%) had all the 3. On the AP field, 95 patients (95%) had the measuring point, the bifurcation of the abdominal aorta, out of the field (D1<0 mm), and all the patients had a distance less than 17.0 mm between the distal end of the external iliac artery and ipsilateral border (D2<17.0 mm). On the LAT field, 24 patients (24%) had a distance less than 7.0 mm between the distal end of the external iliac artery and anterior border (D3<7.0 mm). Conclusion: We observed that conventional pelvic fields based on bony landmarks provided inadequate coverage of pelvic lymph nodes in our patients with cervical cancer. CT simulation may be a feasible technique for planning pelvic fields optimally and individually.