Denby started the successful prostate brachytherapy seed implantation programs for prostate cancer at Calvary North Adelaide Hospital and the Royal Adelaide Hospital in 2004. He has attended overseas brachytherapy training courses, presented research papers, helped run training courses, conference and lectured overseas. He has performed nearly 500 LDR prostate brachytherapy seed implants at Calvary North Adelaide Hospital and the Royal Adelaide Hospital for low to intermediate risk prostate cancer and HDR brachytherapy at the Royal Adelaide Hospital for high risk prostate cancer.
Denby was the inaugural chairman of the Urological Society of Australasia's Endourology special advisory group for several years and has a particular interest in laser stone surgery. Since 1999 he has been performing percutaneous stone surgery in the supine position. This previously neglected position is a safer and more efficient approach to the kidney and is gaining increasing popularity around the world. Denby has lectured and run training courses around Australia and overseas on this technique and he has the second largest published series of stones treated this way in the world. He is a reviewer for the American Journal of Endourology and British Journal of Urology International on stone surgery.