Listbox Depending On The Value Of 2 Fields.

I have a table "residents" with a field "doctor" which is selected with a listbox.
The value of this field "doctor" depends on two other fields:

• "residence" smallint
  
• "datereport" date
  In the definition of the listbox I can set the value depends on another field: I chose "residence".
  But I need to know the value that has been written in the field "datereport" for use in the where clause of the listbox.
  I've seen that you can access the value of the field with a javascript function, but then, how and where I can store it to use it in the listbox where?
  Thank you very much.