Loading Selet fields values dynamically

Hello my friends,
I am a new to Kirby, and I came across a problem in using Select field in the panel.
How can I load the options dynamically either from a file or dynamically generated in a php template.
I tried the ‘query’ keyword but I think it loads on pages and files of the current page.

Here is an example from Kirby docs (I do not want the options to be hard-coded like the following example but can be updated by the admin, then loaded here)

fields:

category:
label: Category
type: select
options:
design: Design
architecture: Architecture
photography: Photography
3d: 3D
web: Web

Well, unfortunately, you cannot select a field on a specific page in the query options, all available options are described here:
http://getkirby.com/docs/cheatsheet/panel-fields/select

And in the changelog:
http://getkirby.com/changelog/kirby-2-1-0#core

As you can see, you can use an URL to fetch a json encoded file, but I guess, that might be too complicated.

Another option would be to create a custom field that fetches the values e.g. from a field in the site variables. Address pages in custom fields

Thanks a lot. I think a custom field would solve my problem. I will try to create one.