Data presented regarding prostatic lymphography(9
) reveals prostatic lymph node drainage to the internal iliac, external iliac, presacral and common iliac nodes with the main drainage to the internal iliac and presacral lymph nodes.(9
Extended lymph node dissection data, which generally involved resection of the external and internal iliac and obturator lymph nodes as well as the common and presacral lymph nodes, showed evidence of nodal drainage in multiple nodal sites.(11
) Often the nodal involvement was not contiguous.(11
) This data also pointed to the need to address nodes beyond the obturator and external iliac lymph nodes if one wishes to address all potentially involved areas with the presacral nodes as a significant area of node positivity.(11
) Finally all the lymph node dissection data presented pointed to the fact that the more lymph nodes removed the more positive nodes found, and therefore, recommendation from this data was that patients with high risk prostate cancer should undergo extended lymph node dissection.(11
) The message here is that the pelvic lymph nodes at risk include obturator, external and internal iliac, and presacral nodes.
Sentinel lymph node concept data shows that the process is not only feasible,(16
) but the more recent data(18
) reported (results on over 1,000 patients where extended lymph node dissection and positive sentinel lymph nodes) defined metastatic disease well beyond the obturator and external iliac regions alone. In this data there was evidence of lymph node metastasis to the presacral regions also.(18
Basic anatomy data revealed three main drainage patterns for the prostate:
- Cranially to the external iliac lymph nodes
- Laterally to the internal iliac lymph nodes
- Posterior to the sub-aortic aspect of the presacral lymph nodes S1–S3 (19,20)
Pelvic MRI imaging with lymphotropic nanoparticles shows evidence of lymph node metastasis for advanced prostate cancer in the drainage areas of the common iliac, external and internal iliac, and presacral regions with an interesting lack of positive lymph nodes below the top of the pubic symphysis.(21
) Similar MRI nanoparticle data from gynecologic malignancies shows evidence of lymph nodes well posterior to the external iliac vessels and well anterior the internal iliac vessels showing a need to include margins beyond the vessels themselves for adequate pelvic iliac lymph node coverage.(22
) In addition this data suggested a minimum 7mm margin around the pelvic blood vessels to cover the involved lymph nodes.
In the interest of consistency in the definition of the pelvic LN regions for IMRT compared to prior techniques ,data from each of the RTOG trials (evaluating the role of hormone therapy and radiation for high risk patients) was reviewed. Previously a four-field box technique was used to address the pelvic lymph nodes.(1
) () The upper border of this technique was at the L4/L5 or L5/S1 interspace and the lower border at the level of the bottom of the ischeal tuberosities. Laterally 2-cm lateral to the true pelvis was recommended. In the lateral fields the anterior border was to include the anterior aspect of the external iliac lymph nodes and the posterior border was to be posterior to the anterior boney sacrum so as to address the presacral lymph nodes superiorly and then to split the rectum inferiorly. These borders were chosen to be sure that the draining pelvic LNs were covered.
Review of all the data above and extensive discussions resulted in a consensus being obtained and contours performed on one of the CT scans used in the contouring project. (8
) Special focus during the discussion had been placed on the importance of treating the presacral lymph nodes. Review of the data presented resulted in a recommendation to treat the presacral lymph nodes (subaortic only S1
). shows representative Clinical Target Volumes (CTV’s) contours drawn on the CT consensus scan. These contours were done by the consensus panel (all co-authors) and a written description was developed as follows:
- Commence contouring the pelvic CTV lymph node volumes at the L5/S1 interspace (the level of the distal common iliac and proximal presacral lymph nodes)
- Place a 7-mm margin around the iliac vessels connecting the external and internal iliac contours on each slice, carving out bowel, bladder, and bone.
- Contour presacral lymph nodes (sub-aortic only) S1 through S3, posterior border being the anterior sacrum and anterior border approximately 10 mm anterior to the anterior sacral bone carving out bowel, bladder, and bone.
- Stop external iliac CTV lymph node contours at the top of the femoral heads (bony landmark for the inguinal ligament)
- Stop contours of the obturator CTV lymph nodes at the top of the pubic symphysis .
Representative pelvic lymph node CTV contours from consensus CT:
Volume definition and dose constraints for organs at risk (OARs) were also discussed and resulted in a consensus for OAR guidelines. () The rectum should be empty at the time of simulation. Consistent with the RTOG definition of the rectum it is to be outlined from the sigmoid flexure to the bottom of the ischial tuberosities. The bladder should be comfortably full at the simulation. Two dose points were selected for both the rectum and bladder. These dose constraints were based on whole (solid) organ contours. No constraints were identified for the penile bulb and the iliac crests. Large bowel dose constraints were to be the same as the rectum. The small bowel dose limit was 52 Gy and the femoral heads <5 % of their volume at 50 Gy. Dose constraints for all OARs were based on the use of conventional fractionation using a dose per fraction of 1.8 to 2.0 Gy per day.
Dose Volume Histogram constraints for Organs At Risk (OARs)