Iniciar o primeiro dia da semana como domingo no SQL

SELECT
  UID,  
  DATEADD(d, -1, DATEDIFF(d, -1, t.DT)/7 * 7) [WeekBeginDate] ,
  SUM(HOURS) AS TOTAL_HOURS 
FROM myTable t 
WHERE DT >= DATEADD(WEEK, -6, GetDate()) 
GROUP BY UID, DATEDIFF(d, -1, t.DT)/7