Pediatric Synovial Cell Sarcoma

My son was diagnosed with Synovial Cell Sarcoma at 9, and after a very rough year of surgery, chemo, and radiation, he is now done with treatment and his last scans were clean. (Yay!)

However, I've read so much about this particular cancer coming back, or leading to other types of cancer, so I'm not at all feeling like we're out of the water.
His tumor was in the chest wall near the shoulder. He's supposed to go in for chest xrays every 6 weeks now, but I'm not convinced that's good enough.
Is there any maintenance drug available for synovial sarcoma patients who are done with treatment? A parent of an osteosarcoma patient mentioned that there was a breathing treatment available to keep it from metastasizing to the lungs, but I can't find any info on that.
What kind of post-treatment scan regimen do most synovial sarcoma patients have?