Movement inaccuracies of up to two centimeters may occur in prostate radiation. "During the radiation treatment, patients have to lie on a table for some 20 minutes without moving. Over time, the muscles relax and the pelvis drops. As a consequence, the radiation may focus on the bladder or other organs. In our calculations, we concentrated on the precision of localizing the prostate and on improvement potentials in treatment", explained Karin Poljanc, Assistant Professor at the Atomic Institute of Austrian Universities.
In a study conducted in co-operation with SMZ Ost - East-Vienna Center of Social Medicine, Danube Hospital, Karin Poljanc and her research associates, Tanja Futschek and Leila Teymournia, used a number of ultrasound examinations that allowed for a precise localization of the patients' organs from the outside.
In a next step, the scientists analysed the positioning of 60 patients, and evaluated the deviation of radiation in various spatial directions, such as to the right or left, and upward or downward - using 420 radiation plans for thirty patients. While it takes more time, an ultrasound system makes the shifts in position visible and traceable.
If the deviation exceeds 0,8 cm, the radiology technicians are responsible for returning the patient to the correct position to ensure that the radiation only targets the specified area. In the subsequent study phase, Karin Poljanc and her group calculated normal tissue compensation rates and the probability of tumour control.
"This provides us with an overview of the probability that the tumour is targeted directly and the probability of side effects for individual patients", noted Karin Poljanc. These approaches serve as forecasts and provide clues for the likelihood of healing. After a study period of some 2,5 years, with generous sponsorship of the Anniversary Fund of the Austrian National Bank, the scientists were able to implement the calculated average positioning inaccuracies in a radiation planning system.
Summed up Leila Teymournia: "Depending on the calculation model used, the normal tissue compensation rate can vary widely in the results. While the use of Model A may yield a negligible complication rate, the same process calculated with Model B shows a deviation of up to 40 percent." Due to the absence of biological parameters, major discrepancies may result with different models. Nevertheless, the results of calculations can provide physicians with data for improving patient positioning accuracy and therefore, and improvement of treatment success.
As part of their study of different radiation sources, Karin Poljanc, Tanja Futschek, and Leila Teymournia found that localization aids, such as ultrasound systems, are indispensable for accurate proton therapy of prostate carcinomas. In most cases, this combination leads to therapy results with a high level of tissue preservation.
The future establishment of the cancer research and therapy centre "Med-AUSTRON" in Wiener Neustadt will implement such a treatment method in Austria.