Speaker
Description
The main challenge in radiotherapy (RT) is to deliver a sufficiently high curative dose to the tumour while keeping doses to nearby organs at risk tolerable. New treatment modalities are emerging rapidly. In this context, novel dosimetry systems for hadrontherapy and FLASH radiotherapy have been designed and manufactured at the Centro Nacional de Microelectrónica (IMB-CNM, CSIC) in Barcelona, Spain in recent years.
First, silicon based microdosimeter arrays with dimensions comparable to those of human cell nuclei (a few micrometres) and 3D cylindrical detectors were designed and manufactured with a spatial resolution of 200 µm. These arrays are integrated with custom electronic readout systems based on multichannel ASICs, which provide beam triggering and analogue readout for 128 microdetectors per chip. An array covering 12 cm² of radiation-sensitive area has been successfully tested at the Danish Centre for Particle Therapy in Aarhus, Denmark. It has been obtained the first 2D-LET distribution so far. It was used which could contribute to a possible optimisation of proton therapy treatments.
Secondly, silicon carbide (SiC) diodes have been developed for use in dosimetry during ultra-high dose rate (UHDR) FLASH radiotherapy. The diodes were characterised using electron and proton UHDR beams at various centres. Regarding electron UHDR tests, measurements at the National Metrology Institute (PTB, Germany) and the Institut Curie (France) demonstrated linearity independent of dose per pulse and pulse dose rate up to 25 Gy per pulse and 6 MGy/s respectively, with relative dosimetry deviations below 5%. Following an accumulated dose of 100 kGy with 20 MeV electrons, sensitivity loss remained below 2%. Regarding proton UHDR tests, the performance of the SiC diodes was tested with 7 MeV protons at the CMAM, where good signal linearity with dose rate and a reproducible response were demonstrated up to a dose per pulse of at least 20 Gy. All these measurements were made without the need for an applied external voltage. Additionally, pixelated SiC detector arrays have been developed for spatially resolved dosimetry. A 12-pixel array was fabricated and tested using 7 MeV electron beams at Inst. Curie. The system successfully generated accurate two-dimensional dose maps at dose-per-pulse values of 10 Gy, demonstrating the feasibility of SiC arrays for real-time quality assurance under FLASH conditions. Ongoing efforts are focused on scaling the pixelated system to a larger 400-channel array, coupled with custom readout electronics, to support a wider range of clinical and preclinical applications. In conclusion, SiC diodes fabricated at IMB-CNM are a viable alternative to silicon and diamond dosimeters for radiation-hard clinical applications requiring accurate real-time relative dosimetry, a fast response and long-term stability.