Today (Tuesday, 23 April) marks the beginning of a new era in treatment planning at the University Proton Therapy Dresden of the University Hospital Carl Gustav Carus, Dresden (Germany): For the worldwide first time, a new approach, increases the accuracy, safety and probably also the tolerability of proton therapy. The range prediction procedure was developed and extensively validated by medical physicists from the Dresden OncoRay Center, the Helmholtz-Zentrum Dresden-Rossendorf and the German Cancer Research Center in Heidelberg. Together with radiation oncologists, its clinical advantages were investigated. With the “DirectSPR” method, the proton range in human tissue can be predicted more accurately and on an individual patient basis. The Dresden researchers were able to demonstrate that the volume of irradiated healthy tissue surrounding the target volume can be reduced by 35 to 40 percent. The range accuracy, which has remained practically unchanged for more than 30 years, is thus for the first time significantly improved. The patients in Dresden will be the first benefitting from this.

Protons have particularly favorable properties for cancer therapy, as they release a large part of their energy exactly at the moment when they stop in the body. Thus, healthy tissue beyond the target can be better spared. However, medical physicists are faced with the challenge to determine the stopping behavior of the different tissue types, which the protons pass on their way to the tumor. So far, mostly conventional computed tomography (CT) images have been used for this purpose. However, in human tissue the interaction processes of X-rays used for CT differ from those of protons used for therapy. Hence, the stopping behavior of protons and thus their total range can only be predicted with limited accuracy. For this reason, a safety margin of healthy tissue surrounding the tumor needs to be irradiated with the same dose as the tumor to ensure that the tumor is completely irradiated. For prostate cancer, for example, this safety margin can be up to 12 millimeter. The range uncertainty concept in proton therapy has been standardly used since the 1980s. Also, the safety margins employed have been practically unchanged since then.

Dual-energy computed tomography (DECT), which was originally developed for the field of Radiology, provides medical physicists with more meaningful information for proton treatment planning. "So far, it was not possible to predict the range of the protons with high accuracy in patients," explains Dr. Christian Richter, head of the research group “High Precision Radiotherapy” at the HZDR, which is one of the three founding partners of the hospital-based OncoRay Center, together with the University Hospital Dresden and the Technische Universität Dresden. "Until now, we were lacking a technology for determining the individual parameters that define the stopping behavior of protons in different tissue types. With the DirectSPR approach, which is based on DECT, we are now able to do this. We can much better resolve differences in tissue composition between different patients, as well as in different tissues in the same patient, and take them into account during treatment planning. With this innovation, proton therapy becomes better tolerable, more accurate and also more tailor-made.”

Rad Oncology Homepage