Can I get 50 units of botox every 10 weeks?

Botox usually lasts 3-4 months, if the result from your treatment is wearing off too quickly I suggest trying Xeomin or Dysport 

Botox usually lasts 3 and a half to 4 months, so it may be wearing off a little visibly by 10 weeks.  If you wanted complete immobility and could actually see it was wearing off you could supplement it. It probably would not require anything like 50 units to do that. No particular concern from safety standpoint. Anecdotally, some patients who use Botox for several years, regularly, report to me that they need less and need it less often, probably from some atrophy of the muscle. 

The product recommendation is every 3 months. If you have a high metabolism or intense training workouts, your results may not last as long. If movement to the areas is starting to return then additional Botox may be injected. Regarding immunity, it's still unclear if or how its occurs.