"For" VS "in" usage

"Resource" can take a complement with "for", specifying the purpose or target of the resource. So A resource for the medical field means a resource applied to the medical field, which doesn't make a lot of sense, and would probably be interpreted as A resource for certain unspecified activities in the medical field.

"Resource" does not take a complement with "in", so if you use an "in" phrase with it, it is an adjunct, with no special meaning attached to "in". If you say a resource in the medical field it means A resource for something unspecified in the medical field.

So in this case, there is no difference in meaning that I can find. But if the complement were something that the resource could be directly applied to (eg a resource for calculating the best graph) I think "in" would be strange, and imply that there was some (unspecified) part of the calculating that the resource helped with.