How many patients on average receive combined chemotherapy and radiation therapy procedures each year?
average = DIVIDE(COUNT(procedures.PATIENT), COUNT(substr(procedures.DATE, 1, 4))); combined chemotherapy and radiation therapy refers to procedures.DESCRIPTION = 'Combined chemotherapy and radiation therapy (procedure)';
SELECT CAST(COUNT(PATIENT) AS REAL) / COUNT(DISTINCT strftime('%Y', DATE)) FROM procedures WHERE DESCRIPTION = 'Combined chemotherapy and radiation therapy (procedure)'