While I don't have an answer to your question I do recommend that you consult with a highly experienced neurologist before proceeding with ECT treatments. If you are near a university medical center or a Mayo Clinic that would be your best place to get a second opinion.
Just wondering if the ECT is being recommended for long term depression. If so, what other depression treatments have you tried?
Also, have you had surgery for this brain tumor?
Please remember that "an informed decision is the best decision", so get plenty of information and opinions from highly reliable sources.