Dr. Siwillis is a Clinical Radiation Oncologist at the Nakuru Provincial General Hospital. She holds a Masters of Medicine in Clinical Oncology and is extensively trained in radiation therapy and chemotherapy for a variety of cancers. She has particular interest in breast, pediatric, head and neck and neuro-oncology.

She has been key in instituting multidisciplinary meetings within the hospital, problem-oriented research in the department and streamlining patient care within oncology clinics.

Dr. Siwillis has interest in research having attended and presented papers at both local and international conferences and also has a number of publications to her name. She has played a key role in the roll out of National Cancer Screening and Treatment guidelines and has been very instrumental in raising cancer awareness across the country. She is an advocate of quality and affordable cancer care for all patients.