What nodal volumes would you cover for a melanoma of the posterior scalp with poor response to immunotherapy, s/p wide excision and occipital nodal dissection with multiple positive nodes and ENE?

With multiple involved nodes and no pathologic response to neoadjuvant immunotherapy, I would suggest adjuvant radiotherapy. I would target the suboccipital, postauricular, and posterior cervical lymphatics (2B, 5B). If the tumor was midline, I would cover bilaterally, and if it was well lateralized, then ipsilateral.

I suggest looking at the nodal bed and covering it. Coverage of the nodal bed, as shown by clips and abnormal nodes on pre-operative imaging, is wise. Likely, the primary site will need consideration. Melanoma can behave unpredictably. Ensure that pre-radiotherapy imaging is recent, as this patient is prone to distant metastases.

Dating back just over a decade now, a consensus guideline from Gregoire et al., PMID 24183870, for delineating neck nodes exists. Data stretching back to the pre-immunotherapy era might help you understand what to expect; a neat summary from MD Anderson can help; adjuvant radiotherapy was noted to be helpful in a randomized trial by Burmeister et al., PMID 22575589. With further follow-up reported by Henderson et al...

Let us review some issues: what constitutes risk; where does this disease spread; what benefits and risks exist.

1. "High-risk features include extranodal spread of melanoma, more than two positive lymph nodes, large nodal size, or recurrent disease in previously dissected nodal basin." This statement from 2009 is still valid, and a non-responder to immune therapy would also qualify as high risk. Mitra et al., PMID 32544573 published an excellent review in 2020 of adjuvant nodal irradiation in the era of immune therapy. Thank you!
2. Melanoma is unpredictable, so as @Dr. First Last pointed out chasing nodal basins may not lead to an overall survival benefit, so consider treating only the involved areas. Ensure your imaging is recent, e.g. within ...