How do you contour the pre-sacral elective nodes for prostate cancer?

This is an interesting question. There is some heterogeneity between cooperative groups in their recommendations for pre-sacral nodal coverage. For example, while the RTOG and the UK guidelines recommend coverage of the pre-sacral lymph node basins. The recent Indian POP-RT trial also included an 8-10mm presacral strip from S1-3 in their lymph node volume. The 2015 GETUG guidelines, however, do not recommend that the presacral lymph nodes be covered within the treatment volume citing lower incidence of involvement < 5-10% and the fact that the pre-sacral space is not routinely part of the lymph node dissection during a prostatectomy.

As Dr. @Dr. First Last mentions, there is official guidance from the NRG recently which contains guidance on ...

I follow the recent NRG Pelvic Lymph Node Consensus Atlas update:

1. Contour the pre-sacral/prevertebral nodes down to the inferior border of S3, with anterior limit generally around 1.5 cm anterior to bone (although there is significant discrepancy for this ranging from 1 cm to 3 cm).

2. Contour the posterior edge of the internal iliac CTV expansion to the anterior edge of the piriformis muscle.