Not 100% sure I know what you are after but you might try this (I have CS but it should work if you have a circle drawing object). Draw a coloured circle on a new layer big enough so that half of it is what you would like the left side to fit into. I would use guides or grids to centre the circle. Then I would use the selection tool to select the right hand side of the circle up to the middle (doesn't matter if you use a rectangular selection--you are going to delete it). With guides or grids, the selection marquee will go right up the middle. Then delete. That will leave you with half a circle. Then I would use magic wand to select the semi-circle. Inverse selection so that everything outside of the semi-circle is picked. Then select layer that you wanted to be a semi-circle and hit delete. That should delete everything but the semi-circle. If you have another layer you also want cropped to the semi-circle, select it next and delete again.

Because I am not totally sure what you want, please do this on a dup if you are going to try it so nothing is permanently mucked up! If PSE has masks, I would mask out the layers to be cropped in case I changed my mind rather than deleting but not sure if PSE supports masks.

If this doesn't help, maybe you could point me to an example of what you want and I might be able to come up with something.