I found a work-around solution by using the case statement in SQL and generated figures for Q1 - Q4 and YTD as individual columns. Then in SSRS I used the below expressions:

For Quarters:

=SUM(Switch(Left(Parameters!ReportPeriod.Value,2) = "Q1",Fields!Q1.Value,Left(Parameters!ReportPeriod.Value,2) = "Q2",Fields!Q2.Value,Left(Parameters!ReportPeriod.Value,2) = "Q3",Fields!Q3.Value,Left(Parameters!ReportPeriod.Value,2) = "Q4",Fields!Q4.Value))

For YTD:

=SUM(Fields!YTD.Value)

This works perfectly, the quarterly figures change as I select the relevant parameter (Q1-Q4) and the YTD figures show as of now.

Maybe not the perfect solution but it works, thanks Tee Time for the suggestion.