The radiation an angiogram has in spine angiogram can be comparable to what?3yo daughter had one-worried about cancer.how likely future cancer?

Not measurable: If your daughter needed a spine angiogram, she is likely to be seriously sick and you have my sympathy. An angiogram delivers perhaps 4 mSv. Mother Nature delivers about 3 mSv yearly in normal background radiation; living in Denver rather than Washington is an extra 1.5 mSv for altitude, an hour plane flight 0.005 or so and nobody's shown any cancer risk in pilots or Denver-dwellers.

Unlikely: the dose of radiation for a one time angiogram is very low as is the risk of future cancer from this isolated one time doseage of radiation.