How do you approach a solitary pelvic nodal recurrence following definitive radiation therapy to the prostate/SV?
Briefly, I agree with @Dr. First Last and I occassionally offer treatment to solitary nodal disease, most commonly seen in the postprostatectomy, post-salvage RT setting.
I'm generally not offering SBRT to nodal disease, since I think of the nodal basin needing RT (like 45 Gy with SIB to nodal disease). It seems that there is a risk of failure in immediately adjacent nodes if SBRT alone is provided, which distinguishes this clinical scenario (nodal only mets) from other oliogmetastatic scenarios in prostate cancer such as oligometastatic bone disease where one might give met-only SBRT as the sole radiation therapy.
This is a difficult situation, since the approach may vary depending on a number of factors, including the patient's overall health, the duration from treatment to recurrence, the size of the recurrence, rate of rise of the PSA and the original stage and grade of the tumor. If you're contemplating aggressive local therapy, it would be important to rule out distant metastasis. In addressing the prostate and seminal vesicles for residual tumor, I would consider obtaining a multiparametric MRI to see if there is any evidence of local tumor, the presence of which might change your management approach. If the MRI was negative, I would consider a TRUS-guided biopsy if a positive result would change your treatment approach, for example in a young patient, who might be a candidate for a salvage prostatectomy. Assuming that this is a true biopsy-proven solitary pelvic nodal recurrence, the options would be surgery followed by adjuvant therapy or long term ADT plus radiation. If the chance of disease control is high with ADT+RT, I would prefer that approach to spare the patient the morbidity of the node dissection. In patients such as this, I generally will treat the pelvic and presacral nodes, as these patients often are found to have multiple nodes involved if they go to surgery, but I would consider boosting grossly involved lymph nodes to doses as high as 60-70 Gy, usually with an SIB technique, if this can be done safely. If a patient's anatomy is unfavorable for boosting, surgery might be a better option.
I agree with @Dr. First Last's point about making sure there is no distant metastatic disease before pursing any further local therapy. If you have a confirmed isolated nodal recurrence, like @Dr. First Last I favor ADT then treatment to the treatable pelvic nodes electively to 45 Gy with SIB to the involved node, or an SBRT boost. We don't have great data yet on patterns of failure, but one SBRT series over 2/3 failed in untreated nodes.
Anecdotally, we have had good experience with radiosurgery for nodal recurrence, measured as PSA control and also oligomets in general. It's the whack-a-mole approach