There are no really good studies to help with your decision, and what we have is equivocal. You are quite right that adjuvant radiation carries the risk of significant side effects.
Adjuvant or salvage RT to the pelvic LNs when cancerous nodes have been identified was the subject of a retrospective studies published last year by Abdollah et al. that showed a benefit to salvage RT, and two by and Rusthoven et al. and by Kaplan et al. that showed no
In the Abdollah study, they found that men with two or fewer positive nodes, identified by extended
lymph node dissection (ePLND), had better prostate cancer survival. This study was retrospective and subject to selection bias (the ones who received aRT got it because
they had better chance of survival with it). Also, the LNs were identified by ePLND, a procedure more popular in Europe and at Mayo, whereas you only had 4 LNs removed.Impact of Adjuvant Radiotherapy on Survival of Patients With Node-Positive Prostate Cancer
The Rusthoven study was a data analysis. They saw no difference in 10-year PC survival between those LN-positive men who had RP and those who had RP+salvage RT.The Impact of Definitive Local Therapy for Lymph Node-Positive Prostate Cancer: A Population-Based Study
The Kaplan study study was also a data analysis. They also found no benefit to adjuvant RT in LN positive men:Patterns of care and outcomes of radiotherapy for lymph node positivity after radical prostatectomy
What is needed is a randomized clinical trial to sort this out. There's one in the works (RTOG 0534) but it won't have results until 2021.
FWIW, what I would do is wait to get a PSA in January (they usually like to wait 3 months before giving adjuvant radiation anyway.) Then:
(1) If it's undetectable or under 0.03 ng/ml on an ultrasensitive test, continue to wait.
(2) If it's between 0.03-0.2 ng/ml consider adjuvant RT
(3) If it's ≥0.2 ng/ml but < 2.0 ng/ml, try to get in on one of these clinical trials that may be able to detect distant mets that bone scans, NaF18 or C11 Choline or Acetate PET scans can't detect:/clinicaltrials.gov/ct2/show/NCT02190279/clinicaltrials.gov/ct2/show/NCT02523924/clinicaltrials.gov/ct2/show/NCT01666808/clinicaltrials.gov/ct2/show/NCT02624518