Assessment of the radiobiological implications for treatment outcome of the variability in target delineation in stereotactic radiosurgeryIuliana Toma-Dasu1, Håkan Nordström2, Jonas Johansson, PhD3, Iuliana Toma-Dasu41 2Elekta Instrument AB, Stockholm, Sweden 3Stockholm, Sweden 4Solna, Sweden Keywords: radiobiology, dose planning, gamma knife, radiosurgery, technique
Radiosurgical treatment planning and target identification can vary.
The aim of the study was to assess the influence of the inaccuracy in delineating the target on the treatment outcome predicted with radiobiological models for four brain disorders of a general complex nature.
Four brain disorders, anaplastic astrocytoma, AVM, meningioma and vestibular schwannoma, were delineated by twenty centres chosen for their high experience with Leksell Gamma Knife®. For each investigated brain disorder an average target which was assumed to resemble the accurate target was calculated. For the three tumours included in the study several scenarios regarding the infiltrations of the tumour cells in the neighbouring tissue were assumed according to the specific pathology. The outcome of the treatment expressed as probability of controlling the tumours or the probability of AVM obliteration was modelled in each case for the constructed plan coupled with the average target for each disorder.
Target delineation resulted in considerable differences in the planned target volume and hence the average target resulted to be rather small. The currently available parameters regarding the radiation sensitivity of the cells and the assumption that the average target gives an indication of the actual size of the tumour to be eradicated, lead to the prediction of a very high probability of controlling the tumour. In contrast, for AVM the calculated probability of obliteration was much lower than the clinically observed probabilities.
This was a survey using a limited number of tests.
The implications on treatment outcome of the variability in target delineation are difficult to accurately assess in individual cases due to the fact that they depend on both the choice of the radiobiological models with reliable parameters and the difference in size and position between the actual and the delineated target.
Therefore the theoretical simulation of the treatment outcome should be further analysed in relation to the clinical follow-up of the patients for the fine adjustment of the modelling parameters. Project Roles:
I. Toma-Dasu (), H. Nordström (), J. Johansson (), I. Toma-Dasu ()