Median and group by

[Doc94]

I am trying to expand upon and already useful median query in SQL. I need to figure out where to put a GROUP BY statement so I can get the median "length of stay" grouped by a field in the table called "TSheetTitleDescription". The folowing is the median query that works flawlessly:
SELECT Avg([R1]) AS Median
FROM [

SELECT Max(Q1.R2) AS R1

FROM

(SELECT TOP 50 PERCENT LOS_min_amb_work.los AS R2

FROM LOS_min_amb_work

ORDER BY LOS_min_amb_work.los ASC) AS Q1

UNION

SELECT Min(Q2.R2) AS R1

FROM

(SELECT TOP 50 PERCENT LOS_min_amb_work.los AS R2

FROM los_min_amb_work

ORDER BY LOS_min_amb_work.los DESC) AS Q2

]. AS Q3;

Question is where to put the group by in this query. And I suspect I need to define in the query structure that I want the filed in the query.
Any help would be greatly appreciated.