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Descrizione
Various in vivo studies proved that the FLASH treatment results in a decrease of radiation-induced normal tissue toxicity, compared to conventional treatment, while having the same biological effect on tumoral tissue.
The aim of this study is to verify the possibility of using FLASH electron Radiotherapy as an alternative treatment modality for localized uveal melanoma. This is a highly radioresistant tumor which constitutes the most common type of ocular disease in adults and is generally treated with organ-removal approaches (surgery) or organ-conservative techniques (such as Stereotactic RadioTherapy - SRT), depending on the overall tumor dimensions. This will be possible exploiting ElectronFlash (EF) LINAC situated in Santa Chiara Hospital, Pisa, which can deliver 7MeV-9MeV electrons beams to the target in both FLASH (>40Gy/s) and conventional (2Gy/min) regimes.
The main steps of the project are: i) validation of the EF simulation and optimization on patient CTs, ii) implementation of the FLASH sparing effect in simulations according to in vitro/vivo experimental results, iii) development of a robust method of comparison between FLASH and Stereotactic Radiotherapy (SRT) based on dosiomics and advanced statistics.
A dose deposition code based on EGSnrc MonteCarlo algorithm was developed to simulate EF. Some tests were conducted using flashDiamond detector, to verify the simulated dose distribution in water. Also, a dose distribution calculation on selected clinical cases was performed: patients with different tumor sizes and positions were considered, using different beam sizes and fields geometry to optimize the target coverage.
This analysis demonstrated a good agreement between the simulated and measured dose distributions. However, it soon became evident that these energies were insufficient to cover deep targets (>2cm along the beam axis). To overcome this limitation, virtual energy spectra were generated, starting from the real 9MeV spectrum and extending up to 30MeV. By employing these new energy spectra, it was possible to achieve better target coverage, using at least the 90% of the measured dose at the build-up point (Figure 1).
The simulated EF dose distributions will be further optimized. Simultaneously, radiobiological studies are being performed to quantify the sparing effects generated by FLASH-RT.
The final aim of this study is to evaluate the effectiveness of EF “virtual” treatment on selected patients and to make a direct quantitative comparison with SRT, with the help of dosiomics and advanced statistics.
This work was funded by Piano Nazionale di Ripresa e Resilienza (PNRR), Missione 4, Componente 2, Ecosistemi dell’Innovazione–Tuscany Health Ecosystem (THE), Spoke 1 “Advanced Radiotherapies and Diagnostics in Oncology”—CUP I53C22000780001.
We also thank Fondazione Pisa for funding CPFR with the grant “prog. n. 134/2021”.
