Dr Callaghan qualified as a Radiation Oncologist in 1993. He served his period as a registrar at Addington Hospital in Durban and entered private practice in 1994. During this time he continued to work as a part-time consultant in the public sector. He also acted as Part-time lecturer and examiner/moderator for the Department of Radiography, Technikon, Natal. He moved to establish an independent practice in 1995. Dr Callaghan has been active in SASCRO (South African Society of Clinical and Radiation Oncologists) for many years. He has presented several papers at congresses and meetings. He is recognised as an expert in cranial stereotactic radiotherapy (the treatment of small lesions within the brain). He also performs the highly specialised prostate brachytherapy treatments in conjunction with a urologist and a physicist. Here, a minute radioactive pellet is inserted directly into the prostate to treat small, localised lesions.