Radiation fields in gynecologic oncology: correlation of soft tissue (surgical) to radiologic landmarks

Abstract

Objectives. (1) To determine if radiation fields defined by bony structure landmarks correlate to anatomic boundaries of lymph node dissection marked intraoperatively; and (2) to determine if a patient's body mass index (BMI) correlates with these anatomic or radiographic boundaries. Methods. One hundred patients undergoing exploratory laparotomy with pelvic and paraaortic lymph node dissection had three medium hemoclips placed at vascular junctions considered of clinical significance to lymph node dissection: insertion of the left ovarian vein into the renal vein, insertion of the right ovarian vein into the vena cava, inferior mesenteric artery (IMA), bifurcation of the aorta, bifurcation of the common iliacs (bilateral), and the insertion of the deep circumflex vein (DCV) in to the external iliac vein (bilateral). Postoperatively, an abdominal X-ray was obtained. Comparisons were made between these eight major vascular landmarks and radiographic bony landmarks that are used to define radiation field boundaries. The percentage of vascular landmarks that were encompassed or fell outside of traditional radiation fields was determined with a 1-cm margin considered an adequate boundary for radiation. These measurements were also compared to patient BMIs. Results. Radiation fields defined by traditional bony landmarks would adequately encompass the paraaortic lymph nodes in the majority of patients (91%). For pelvic radiation fields, there was a significant “miss” (39%) of common iliac lymph nodes. Approximately one quarter (26%) of patients would receive inadequate coverage of one or both of the lateral boundaries of pelvic radiation. There was no apparent correlation of BMI to vascular or bony landmarks. Conclusions. Radiation fields determined by traditional bony landmarks do not adequately reflect the anatomic (surgical) landmarks associated with the lymphatic drainage of the female reproductive organs. Although the majority of tertiary care centers now use advanced imaging techniques (e.g. computed tomography) to plan their radiation treatments, the historical guidelines of radiographic landmarks are still used in smaller institutions and continue to be referenced in Gynecologic Oncology Group protocols. For centers still using radiographic landmarks, the application of hemoclips with X-ray identification is a low-cost modality that is easily reproducible and may be clinically useful in guiding treatment.