How to return latest results without a polygon intersect?

If I have a table of the following form:

id (integer) event_time (timestamp) lat_lon (polygon)
3497 1977-01-01 00:00:00
((-64.997,45.975),(,(-64.9981,45.975),(-64.8981,45.875),(-64.9978,45.9751))
3431 2007-06-06 01:00:00
((-64.971,45.982),(-64.921,45.982),(-64.972,45.982),(-64.973,45.98209),(-64.97,45.98237))
3498 1977-01-01 00:00:00
((-64.97838,45.9778),(-64.9783,45.97767),(-64.978,45.977),(-64.9781,45.97728),(-64.9781,45.97714),(-64.977,45.976))
...

How would I return a list of the latest events for a particular
lat/lon region? More precisely, how would a return a result set with
the greatest event times with polygons that don't intersect any other
polygon in the result set?

Any help would be greatly appreciated,
Dave