Unfortunately, the Vitamin C that is taken orally is much worse then intravenous vitamin C. Because the problem with oral Vitamin C is that not all of it is absorbed, especially with high dosages. The Vitamin C that is used for cancer treatment is intravenous Vitamin C, because the Vitamin C directly enters the bloodstream there is no absorption problem.
I have a scietific article here I can send you. The title is:
Vitamin C Pharmacokinetics: Implications for Oral and
Intravenous Use
It contains graphs that show you that with oral dosage, the maximum Vitamin C concentration in blood is only 225 micromol, while the maximum Vitamin C concentration in blood is 15 millimol (15.000 micromol), which is about 67 times more.