Sorry about the recurrences. Has his tumor morphed into a GBM? That would be a possible explanation for the rapid recurrences.
By the way, why Carboplatin? It is a pretty toxic drug and has shown very little efficacy with GBM. My husband was on it and it made him sick as a dog and did absolutely nothing to arrest the tumor growth. Why not Avastin or Avastin in combination with the carboplatin?
I'm not saying that your husband shouldn't do it, but I would question that treatment choice and see what your NO says. The only reason why my husband was on Carboplatin by itself was that he was in a clinical trial and they were testing it out in combination with an experimental anti-angiogenesis drug ZD6474. He happened to get into the arm of the trial where the drugs were used sequentially and not in combination. We were bummed as we knew that he was in the "control group" so to speak.
God bless, Sally