I have had Botox by Dr. Donahue multiple times and he usually does anterior scalene and pec minor of the affected side, unless like me where there is no longer a anterior scalene related to a 1st rib resection and scalenectomy.
The last set of injections that I had were for both sides as my left side (operative side) and now my right (initially no symptom side), have Been increasingly flared and unbearable and I had an awful time with these injections.
I am scheduled for a cervical fusion for a non-union at C6-7, with an iliac crest graft, this is all related to a work related injury in 2009 and it just keeps getting more and more involved.
Good luck and I hope these injections give thou some additional relief.

Warm regard,
NMC