BONY LANDMARKS ARE NOT AN ADEQUATE SUBSTITUTE FOR LYMPHANGIOGRAPHY INDEFINING PELVIC LYMPH-NODE LOCATION FOR THE TREATMENT OF CERVICAL-CANCER WITH RADIOTHERAPY

Purpose: Curative radiotherapy (RT) for carcinoma of the cervix requir es adequate irradiation of regional lymph node groups. The best nonsur gical method of defining lymph node anatomy in the pelvis remains the lymphangiogram (LAG). This study was designed to determine if bony lan dmarks could accurately substitute for LAG as a means of determining l ymph node position for the purpose of pelvic RT treatment planning. Me thods and Materials: The post-LAG simulation films of 22 patients trea ted at the Fox Chase Cancer Center for cervical cancer were examined. On anterior/posterior (A/P) simulation films, the distance of lymph no des 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 late ral (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 asp ect of the pubic symphysis. Positive values represent lateral and ante rior distances relative to the reference point on A/P and LAT films, r espectively. Negative values represent distances in the opposite direc tion. The adequacy of standard pelvic fields as defined by the Gynecol ogic Oncology Group (GOG) (A/P: 1.5 cm margin on the pelvic rim; LAT f ield 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 di stance of visualized lymph nodes had mean values of -1.6 +/- 1.7 cm (r ange -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 dist ance of the nodes from the pelvic rim at points 1 and 2 cm above the a cetabulum 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 di stance of lymph nodes from points 0, 4, and 8 cm from the previously d escribed reference line had mean values of 2.0 +/- 1.0 cm (range 1.3 t o 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 ha ve 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 i liac group. Conclusion: Great variability in pelvic lymph node locatio n is demonstrated when LAG is used to directly visualize their locatio n. Bony structures are inaccurate landmarks for pelvic lymph node posi tion. The GOG standard pelvic fields are not consistently adequate to cover all lateral external iliac lymph nodes, although the clinical si gnificance of this subgroup of lymph nodes is not known. At this time, LAG remains the ideal radiographic modality to define anatomic locati on of regional lymph nodes for pelvic RT treatment planning. The clini cal importance of the most lateral group of external iliac lymph nodes in various stages of cervical cancer represents a potential area of f uture research.