Lymphangiogram-assisted lymph node target delineation for patients with gynecologic malignancies

Abstract

Purpose : Intensity-modulated radiotherapy for gynecologic malignancies requires proper knowledge of the volumes to be irradiated and accurate delineation of these volumes on a three-dimensional projection. In this study, assisted by lymphangiography (LAG), we derived guidelines for delineating nodal target volumes on CT. Methods and Materials : Sixteen patients with cervical cancer who underwent radiotherapy between 1995 and 1999 at the Mallinckrodt Institute of Radiology were enrolled in the study. The initial 6 patients underwent bipedal LAG as part of the staging workup. Cross-sectional CT images were acquired and analyzed, and lymph node locations were described relative to the aorta, vena cava, common iliac, external iliac, and femoral vessels. The greatest distance from lymph node to vessel wall and pelvic sidewall was determined for each nodal group. This served as a guideline from which the clinical target volume (CTV) definitions were developed. This proposed CTV was then applied to CT scans of 10 patients to determine the amounts of normal tissues encompassed. Results : Nodal CTV guidelines were derived to cover 100% of LAG-avid lymph nodes. This CTV definition encompassed an average of 58.1 ± 22.8 cm 3 (6.8% ± 2.8% of total volume) small bowel, 28.4 ± 19.2 cm 3 (4.2% ± 3.2%) large bowel, 8.6 ± 8.6 cm 3 (3.2% ± 2.6%) bladder, and 1.6 ± 3.1 cm 3 (1.0% ± 1.7%) rectum. The absolute volume and fraction of normal tissues encompassed by CTV plus 1- or 2-cm margins were calculated. Conclusion : This study presents the first time that three-dimensional lymph node mapping with the aid of LAG has been used to generate a nodal CTV guideline. This information may assist radiation oncologists in properly determining nodal target volumes and selecting a margin around the CTV for intensity-modulated radiotherapy.