During the 1970s, Mohan developed computer-aided systems for automated dosimetry and record-and-verify systems. Subsequently, in the 1980s and 1990s, he was a leader in researching newer methods of radiation treatments such as 3-D conformal radiation therapy, intensity modulation radiation therapy, and in the 2000s, proton therapy. His research activities include intensity-modulated radiotherapy, Monte Carlo techniques and image-guided radiotherapy. Dr. Mohan is the author or co-author of over 600 papers, book chapters and publications in proceedings of conferences. He has been the principal investigator, co-PI or co-investigator on numerous grants from the National Cancer Institute and research projects sponsored by industry.