Curie medal lecture 2000. The optimization of delivered dose in radiotherapy: is it related to low dose rate?

From the beginning of the 20th century with Pierre and Marie Curie, it was found that the preparation of radium into needles and tubes results in a continuous low dose rate radiation in which the total time to give an optimal dose of 60 Gy is reduced to 5 or 6 days. Clinical results quickly followed, showing that tumour sterilization was better ensured by low dose rate radiation over several days than by fractionated high dose rate radiation over several weeks. In the light of my experience of very good results with modern 192 Ir endocurietherapy at an optimal dose rate of 0.6 Gy per h for very bulky tumours, I finally became convinced of the need to study low dose rate in teletherapy using telecobalt with low activity sources (1 Gy per h to achieve long duration sessions of 7-8 h per day over a short total duration of 5 or 7 days).I started in January 1970, at the Institut Gustave Roussy and, after my appointment, at the Henri Mondor Hospital in Creteil, a variety of cancer sites were treated but mostly advanced head and neck cancers. Finally I decided to do a trial of classical fractionated high dose rate radiation vs. subcontinuous low dose rate radiation of advanced breast cancers (T3). The results at 3 months were conclusive: 20% of the cancers treated by 45 Gy fractionated irradiation at high dose rate were sterilized while the proportion sterilized at low dose rate was 70% whether the patients received 45 or 35 Gy. This work opened the way to further study but my retirement loomed and I was not able to pursue it.