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ESTRO 2020

Session Item

Physics track: Dose measurement and dose calculation
9319
Poster
Physics
00:00 - 00:00
Dose calculation algorithm for a compact x-ray source in Microbeam Radiation Therapy
Mabroor Ahmed, Germany
PO-1416

Abstract

Dose calculation algorithm for a compact x-ray source in Microbeam Radiation Therapy
Authors: Mabroor AHMED.(Helmholtz Zentrum München, Institute of Radiation Medicine, Neuherberg, Germany), Stefan Bartzsch.(Helmholtz Zentrum München, Institute of Radiation Medicine, Neuherberg, Germany), Stephanie E. Combs.(Technical University of Munich, Department of Radiation Oncology, Munich, Germany), Jan J. Wilkens.(Technical University of Munich, Department of Radiation Oncology, Munich, Germany)
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Purpose or Objective

Microbeam Radiotherapy (MRT) is a novel approach of treating cancer with ionizing radiation, where dose is applied spatially fractionated, leading to high dose peak- and low dose valley-regions. This principle has proven to have higher normal tissue tolerance while remaining the same tumor control compared to broad beam irradiation. For its clinical use, sources of high brilliance such as synchrotrons seem to provide the most promising properties. However due to their size and cost alternative compact photon sources are being investigated for their usability in MRT.
Therefore, a special collimator with divergent slits has been manufactured, that is able to shape photons from a conventional X-ray source to microbeams.
The purpose of this work is to develop an algorithm for the dose calculation of MRT at the Xenx x-ray irradiator (Xstrahl Ltd, UK), which is a preclinical radiation device for small animal research. 

Material and Methods

The dose calculation is based on a hybrid approach that combines Monte Carlo simulation and convolution based dose calculation [1].The method, which was originally developed for synchrotron radiation, was adjusted for dose calculation in the divergent field of an x-ray tube. Calculations were benchmarked against full Monte Carlo (MC) simulations in Geant4 and film dosimetry at the XenX. In all calculations the x-ray source was modelled as an anode surface emitting photons isotopically in all directions from an Gaussian shaped focal spot according to the x-ray tube specifications. The energy spectrum of the Xenx x-ray tube was simulated with Monte Carlo. The dose distribution was scored and measured in a PMMA phantom.  

Results

Figures 1 and 2 show the results of both calculation techniques for the peaks and valleys. The dose curves were normalized to the maximum value of the peaks. It can be seen that Hybrid and full MC show agreement in the valley dose for all depth. In the peak region the deviation from the maximum is less than 5% for doses in up to 60 mm depth, while it increases to over 10% for lower doses deeper in the phantom.

Conclusion

In the peak region the hybrid algorithm shows excellent agreement with Monte Carlo for high doses. The discrepancy for lower doses will be further investigated, although it is of minor importance for small animal treatment. More importantly, this data will be verified by experiments before using this algorithm for treatment planning.





References

[1] Donzelli, Mattia, et al. "Hybrid dose calculation: a dose calculation algorithm for microbeam radiation therapy." Physics in Medicine & Biology 63.4 (2018): 045013.