Create YTD and Prior YTD and slice the cube

[Rosanero4Ever]

Hi all,

I have a simple question for MDX guru (in my experience, I prefer, if possible, relational packages)
I need to create a slicer in order to filter a crosstab using a startDate and an endDate parameters.
In particular the endDate should be the current date, while startDate is on 1st Jan of each year.
So, I must create  YTD and  Prior YTD and I must slice for these periods.
How can I perform this in my report?
Thanks in advance for your time

EDIT:
I'm trying with this statement but it doesn't work:
set (periodstodate([Cube].[Time].[Time].[Day];[Cube].[Time].[Time].[Day]->:[PC].[@MEMBER].[20160228]);periodstodate([Cube].[Time].[Time].[Giorno];[Cube].[Time].[Time].[Day]->:[PC].[@MEMBER].[20150228]))