You cannot pursue 2 full time courses as a regular student from 2 different or same institutions at the same time. But if you are already practising as a surgeon, you must have completed MBBS/MS. This means you are academically free to study another course. It might be in research or any other relevant field. There is no objection to it. To join such course on research, you might have to select the Institution which offers this course. If you want to pursue this cpurse as full time, you might not be able to continue practising as a surgeon full timw because then you will be a research fellow and you might not have time. But if you want to pursue this course part time, you can still practise your profession.