javascript function code improvement

I’m looking to improve a function call that returns a file name based on three args that are passed.

arg data examples of category, rptGroup & rptItem:

category    rptGroup    rpItem      
Flash             g1           RptItem1
Flash             g1           RptItem2
Flash             g3           RptItem7
Demand       g5           RptItem6

category   > 1-m rptGroups
rptGroups > 1-m rptItems

variables store the file names (var naming represents the category (f = flash, d = demand, etc.), group (g1 = group1, etc.) and report item # which is sequential within a category/group):

var fg1RptItem1 = '/flashgroup1rpt1.pdf';    
var fg1RptItem2 = '/ flashgroup1rpt2.pdf';
var fg2RptItem1 = '/flashgroup2rpt1.pdf';  
var dg1RptItem1 = '/demandgroup1rpt1.pdf';    
var dg1RptItem2 = '/demandgroup1rpt2.pdf';    
etc.

Call example:

var category = ‘Flash’;
var rptGroup = ‘g1’;
var rptItem   = ‘RptItem1’;

GetFilename(category,rptGroup,rptItem)

returns:  rptItem =  '/flashgroup1rpt1.pdf'

function GetFilename(category,rptGroup,rptItem)
{
   switch(parentCategory+'|'+rptGroup) {

    case 'Flash|g1' :
    //Return appropriate value based on rptItem
    switch(rptItem) {
       case 'RptItem1' : rptItem = fg1RptItem1; break;
       case 'RptItem2' : rptItem = fg1RptItem2; break;  
    } ; break;

    case 'Flash|g2' :
    switch(rptItem) {
       case 'RptItem1' : rptItem = fg2RptItem1; break;
       case 'RptItem2' : rptItem = fg2RptItem2; break;  
       case 'RptItem3' : rptItem = fg2RptItem3; break;  
    } ; break;

    case 'Demand|g1' :
    switch(rptItem) {
       case 'RptItem1' : rptItem = dg1RptItem1; break;
       case 'RptItem2' : rptItem = dg1RptItem2; break;  
    }; break;
   }
   return rptItem;  //returns report file name i.e. '/flashgroup1rpt1.pdf'
}

Suggestions of an improvement (loop, array, ?) along with a code snippet example based on the above example would be greatly appreciated!

Thank you!