Do antioxidants interfere with chemotherapy?
Since it's a very broad argument I'll try to summarize in a few sentences.

First of all the sentence:


  Since most of the chemotherapy drugs kill cancer cells by damaging their DNAs by means of free radicals. So antioxidants, which will detoxify free radicals, should theoretically decrease the efficacy of the chemotherapy.


is a bit inaccurate as of today. The chemotherapy today uses the "classical" chemotherapy drugs which IN PART use the mechanism of free radical but there are a lot of mechanism such as microtubule damage and so on which do not depend on free radical toxicity. Today there are also a lot of biological drugs and inhibitors of tyrosine kinase inhibitor which use a completely different pathway.

You cite a paper from 2007, a bit dated, I cannot access full text because it's an abstract. It seems it's not performed in a systematic manner (it's a not a systematic review or meta-analysis) and is published in a journal of alternative medicine. Maybe there are more recent paper but unfortunately at the moment I cannot have the time to check.

Finally you are comparing the effects of a chemotherapy drug administered usually in high dosage to the use of antioxidant which I cannot recall are sold as drugs used regularly, so it's a potential interesting biological question but practically it's a bit difficult to compare the oxidative effect of a cancer drug with the effect of an antioxidant one in real patients since I don't think there are randomized controlled clinical trials comparing chemotherapy to antioxidant alone.