In addition to the above...
It looks like you are just receiving PR yourself now and are outside of Canada. If so, you'll need to move to Canada and work here for three full tax years before you'll meet the income requirements to sponsor your parents. So best case scenario, your parents will be early eighties and mid seventies before you'll be in a position to sponsor them. If their health conditions are relatively serious, that will likely prevent them from being approved for PR.
As PMM said, the super visa may be a more realistic option.