She completed her training at the Charité in Berlin and has been a specialist in radiotherapy for 20 years. She worked as a senior physician in all departments of the Charité in Berlin, and from 2007 to 2015 she was a senior physician and deputy director of the Charité clinic in Berlin. In 2015, she was appointed head of the department of radiotherapy at the University Hospital of Cologne and very successfully headed the clinic there until 2022. Since the end of 2022, she has been heading the private radiotherapy clinic "RadioOnkologie Vosspalais". Clinical areas include radioimmunotherapy, high-precision therapy, multimodal therapy of gynecological tumors and prostate carcinoma.
Professor Dr. Marnitz is a member of the German and European Guidelines for the Therapy of Endometrial Carcinoma. She is also an independent external expert of the European Council for the Therapy of Carcinoma of the Cervical, Vulvar and Vaginal Cancer. Professor Dr. Marnitz is a member of the German and European Guidelines for the Therapy of Endometrial Carcinoma. She is also an independent external expert of the European Council for the Therapy of Carcinoma of the Cervical, Vulvar and Vaginal Cancer. Several randomized clinical trials have been conducted under her leadership.
Professor Dr. Marnitz is an honorary member of the Russian Society of Gynecological Oncology, a member of the professional societies DEGRO, ESTRO, ASTRO. In 2024, Professor Dr. Marnitz will be the president of the congress of the annual conference of the German Society of Radiation Oncology.