What is the general practice for patients that have SpaceOAR placed and then have a delay to treatment start?

I have not encountered this problem yet. Theoretically the SpaceOAR begins to hydrolize after 3 months and completely reabsorbs between 6 and 8 months. The delay would have to be significant due to a major medical event or accident. If the SpaceOAR has completely disappeared it could be reinjected and the patient resimmed and replanned. If partially absorbed a resimmulation (CT with MRI fusion) and replan is in order to get an updated DVH. Fiducials can be monitored for any hints of ongoing reabsorption during treatment since the spaceOAR would be hard to see on CBCT or orthogonal images.