Is surgery needed for indentation of the ventral thecal sac and spinal cord at t8-t9? bcos dorsal central degenerative intervertebral disc protrusion

Back surgery : It depends if you are having symptoms of weakness in legs or other related clinical issues. If its just pain and no other symptoms then it can be managed conservatively.

Likely no: Protrusion may not be symptomatic.

Generally No: Typically surgoens do not perform surgery in this area of the spine as the risk to vital organs is too great.