Following the advice of the manufacturer is your best bet. Personally, if they told me that being exposed to high RF fields was going to be a problem, I'd have to think a long time about having it done, ham radio or no ham radio. In modern life, we're all exposed to high levels of RF. Do you ever drive by a 50,000 watt broadcast station? There are high powered paging radios all over the place. If medical implant devices caused problems in such environments, I think there'd be bodies stacked up like cord wood on the road in front of the local FM station.
In any case, having the antennas as far from the house as possible is a good idea, anyway. regardless of implants.
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