The cell phone industry topped its global sales at 1.1 billion units in 2007. With more and more people using cell phones and other technological devices, many are wondering if radiation sent to and from these devices is safe.

Thousands of reports over the years conclude there are no links between radiation and health risks; but not all research agrees.

A recent study conducted by doctors from Columbia University Medical Centre suggests excess radiation from CT scans are increasing Americans' risk of someday developing cancer.

The study also pointed out it's possible CT scans cause two per cent of all cancers, simply by exposing people to higher than normal levels of radiation.

A Danish study, meanwhile, looked at more than 400,000 cell phone users and determined there isn't an increased risk between cell phone use and any type of cancer.

Yet when high profile U.S. criminal lawyer Johnnie Cochrane died of brain cancer, even his doctor was convinced the cancer was linked to his heavy cell phone use.

"We know that people that use cell phones a lot also complain of headaches, difficulty of concentration, with memory," said Dr. Keith Black, Cochrane's doctor and chief of neurosurgery at Cedars-Sinai Medical Centre in Los Angeles.

"This is a microwave antenna, so you're essentially cooking the brain," he said.

But Dr. Howard Frumkin, an epidemiologist and cell phone researcher at Emory University in the United States, says the comparison between cell phones and microwaves isn't necessarily accurate.

"The level of energy is so different with a cell phone than it is with a microwave oven or with some of the other big sources of energy that there's really no way to equate the two, they're completely different phenomenon," said Frumkin.

However, research that points away from radiation and potential health risks is an argument a group of people living in Chelsea, Que. have a hard time accepting.

A cell phone tower recently went up in the small community, just outside Ottawa, sparking concern for many residents who've done some research of their own.

Bethany Doyle who lives near the new tower says she's worried about the health risks the tower could bring to area residents.

"The research that we've been looking at is very disturbing and so what we're asking City Hall is to use the precautionary principal which means if you don't know for sure that something is safe, you don't go ahead with it," Doyle told CTV News.

Industry Canada says "social pressures" similar to those expressed by worried residents have led to new rules for cell phone towers.

When a tower is approved, the owner must now allow other companies to put their antennae on it in order to reduce the total number of towers.

With a report from CTV's Paul Brent

For more information on this CTV series visit our Invisible Health Hazards special report