List of reports from users personal folders??

Hi,

We are on BI 4.0 SP4 P6.

We have 300+ users and each user have personal folder where they saved all webi reports.

For example, if one user have 15 reports in his personal folder. Out of 15 reports few are not in use and also not refreshed for past few months.

So my question: as an admin how can I identify what are the reports are not refreshed by user past few months and how to make sure that user delete it .

I am not talking about instance of any report.

Thanks