You don't say what type of tumor you have but some types have a hard effect on the body. Acromegaly, Cushing's can be truly nasty on the body... changing the bones and the muscles so the doc may prescribe it.
After my Cushing's, my body was nasty - weak and fat. My shoulders seized up and I had two frozen shoulders (that was idiopathic, it does not usually happen). I went for 6 months. I learned a lot of basic exercises.
You need to be far enough past surgery that you can bend over and all - all restrictions are off, before you can start the PT. But yes, it is a good idea.
Hiya-
I did a few rounds of PT after my original pituitary through the nose surgery. This was to help me to get me up and moving again. Also I had gained a lot of weight from the tumor and my hormones being off that I just wanted some structure to help to jump start me.
The first time, I just did basic strengthening type exercises for my legs and abdomen/ lower back. I began the PT about two months after my surgery and I found it very helpful. By that point I was healed up and my hormones were being adjusted. So be sure to get clearance form the doctor that it is ok. Mine are always supportive of things that will help me to move around more :) About a year after my surgery I was almost 30 pounds lighter, Two years after I was ~60 pounds lighter.
The weight loss was hard but I've kept it off. The PT helped me as It was like having my own personal trainer...hee hee