Bony landmarks are not an adequate substitute for lymphangiography in defining pelvic lymph node location for the treatment of cervical cancer with radiotherapy

Purpose: Curative radiotherapy (RT) for carcinoma of the cervix requires adequate irradiation of regional lymph node groups. The best nonsurgical method of defining lymph node anatomy in the pelvis remains the lymphangiogram (LAG). This study was designed to determine if bony landmarks could accurately substitute for LAG as a means of determining lymph node position for the purpose of pelvic RT treatment planning. Methods and Materials: The post-LAG simulation films of 22 patients treated at the Fox Chase Cancer Center for cervical cancer were examined. On anterior/posterior (A/P) simulation films, the distance of lymph nodes was determined from the top, middle, and bottom of the sacroiliac joint, and at the pelvic rim, 1 and 2 cm above the acetabulum. On lateral (LAT) simulation films, lymph node position was measured at points 0, 4, and 8 cm along a line from the bottom of L5 to the anterior aspect of the pubic symphysis. Positive values represent lateral and anterior distances relative to the reference point on A/P and LAT films, respectively. Negative values represent distances in the opposite direction. The adequacy of standard pelvic fields as defined by the Gynecologic Oncology Group (GOG) (A/P: 1.5 cm margin on the pelvic rim; LAT field edge is a vertical line anterior to the pubic symphysis) was also examined. Data are expressed as the mean +/- two standard deviations, (i.e. 95% confidence level). Results: On A/P simulation films, the distance of visualized lymph nodes had mean values of -1.6 +/- 1.7 cm (range -4.1 to -0.4 cm), -1.3 +/- 1.5 cm (range -3.4 to 0.0 cm), and 1.2 +/- 1.8 cm (range -1.0 to 2.6 cm) from the sacro-iliac (SI) joint at the superior, middle, and inferior points, respectively. The mean distance of the nodes from the pelvic rim at points 1 and 2 cm above the acetabulum was 0.3 +/- 1.2 cm (range -0.6 to 1.8 cm) and 0.2 +/- 1.8 cm (range -1.6 to 2.1 cm), respectively. On LAT simulation films, the distance of lymph nodes from points 0, 4, and 8 cm from the previously described reference line had mean values of 2.0 +/- 1.0 cm (range 1.3 to 3.0 cm), 0.9 +/- 3.9 cm (range -1.9 to 5.1 cm), and 1.8 +/- 2.1 cm (range -0.8 to 3.5 cm), respectively. Ten of 22 (45%) patients would have had inadequate nodal irradiation if their fields had been designed according to standard GOG parameters. In all cases, these incompletely irradiated lymph nodes were from the lowest of the lateral external iliac group. Conclusion: Great variability in pelvic lymph node location is demonstrated when LAG is used to directly visualize their location. Bony structures are inaccurate landmarks for pelvic lymph node position. The GOG standard pelvic fields are not consistently adequate to cover all lateral external iliac lymph nodes, although the clinical significance of this subgroup of lymph nodes is not known. At this time, LAG remains the ideal radiographic modality to define anatomic location of regional lymph nodes for pelvic RT treatment planning. The clinical importance of the most lateral group of external iliac lymph nodes in various stages of cervical cancer represents a potential area of future research.