[Standard versus individually planned irradiation field in radiotherapy of infradiaphragmatic lymph node sites]

In prophylactic irradiation of infradiaphragmatic lymphatic nodes, the width of the paraaortic and pelvic field is given by a line joining the tips of the transverse processes of the 11th thoracic to the 4th lumbar vertebra from where the field boundary follows a straight line to the most lateral point of the acetabulum as seen in simulation film. Another way to build the field border is to project the lateral contours of the large abdominal vessels from T1-weighted coronal MR images of the abdomen on the simulator radiographs and add a 2-cm margin along the vessels delineated. In our study, we compared both methods as to full enclosure of paraaortic and pelvic lymphatics or nodal miss.

Abdominal CT scans of 81 patients with involvement of paraaortic lymph node regions were examined with maximum lymph node sizes of 2.5 cm. The distance from the center of the appropriate vertebra to the lateral lymph node contour referring to the transverse process as well as to the outside contour of the aorta on the left and the vena cava on the right side, respectively, the iliac vessels were measured from T12 through S1. At the level of the hip joint the measurement point was given by the caput femoris.

Our measurement prove that 10% of the lymph nodes were found lateral from the transverse processes of the thoracic and lumbar vertebras and 12% outside the 2-cm safety margin from the lateral contour of the large abdominal vessels.

Our data show, that the customary fields for infradiaphragmatic lymphatic nodes have so far not been able to enclose all retroperitoneal and pelvic lymph nodes with certainty.