checkbox TV question

I made an TV: keuze-nationaal

Type: checkbox
Option: nationaal==1||internationaal==2

I would like to have a list of titles which i use with ditto.
But when checking them both the titles disapears, when i check one of them its ok.

I use this code for list one: [!Ditto? &startID=`13` &tpl=`ditto_bla` &filter=`keuze-nationaal,1`!]
This code for list two on same page: [!Ditto? &startID=`13` &tpl=`ditto_blabla` &filter=`keuze-nationaal,2`!]

How can i show titles when its checked and hide when not checked?
I think i need to use an other &filter way. Something like &filter=`isBoulean,1,checked` ?!

(im a designer)

Ok, i can either make a new TV, or use &filter=`keuze-nationaal,1,7`


(Thx Dimx)