A radiologist is a physician (i.e. a doctor) with an MD and median salary in the US of over $300,000. A radiology tech is not a physician. Median salary for techs is probably around $50,000 or so,...
Gross pay is almost always greater than net pay, as net pay is after taxes, benefits, etc. Gross pay is what the company tells you that they will pay you. Net pay is what you actually take home.