I don't know your circumstances pertaining to your access to fresh cilantro, but most grocery stores have home delivery. I also learned how to keep it fresh for at least 6 days in the frig and if I bought excess I would wash, dry and place in indiviual portions in the freezer, the fresh frozen worked just as well for me. Sometimes cilantro can look tired even in the best of grocery stores, but even with home delivery I image you could get a refund if you find it unacceptable.
If you are concerned about heavy metals in your blood based on your chemo, perhaps your insurance will justify medical blood chelation to remove heavy metals by filtering your blood.
The theory is that cilantro and other herbs can remove heavy metals, but perhaps there is also something else in these herbs helping some of us go into remission.