How to use plain radio button, Or, how to add asp radio button

I have a table of thumbnail images with a plain radio button for each. This table is created on page load by reading a file folder into a dataReader and using a string builder to build the html. Radio buttons end up looking like this;
<tr> 
<td><input type='radio' name='group1' value='1_T.jpg'></td><td><img src="path/to/1_T.jpg"/></td>
<td><input type='radio' name='group1'
value='2_T.jpg'></td><td><img src="path/to/2_T.jpg"/></td>
</tr> 
When the selection is made and the submit button clicked, I try to get the selected radio button value with Request.QueryString("group1"), But this doesn't seem to be working. 
What should I be doing to get the selected radio button value? Or, is there a better way to do this with an asp radio button?
Thanks 
extra i ...