Small dose monitor based on silicon-carbide diodes for FLASH radiotherapy

The FLASH biological effect in radiotherapy has been observed to appear at ultra-high dose rates UHDR ( $>$ 40 Gy/s), where the accurate dosimetry at such high rates is still a challenge.

A new 4 $\times$ 4 array of SiC-based detectors (1 mm diameter, 2.2 mm pitch) is proposed for dosimetry in UHDR, as well as the feasibility of a position sensitive technology demonstrator covering 7 $\times$ 7  ${\mathrm{mm}}^2$ placed on a movable micro-stage to cover larger surfaces.

In the ElectronFlash LINAC at the Institute Curie, two silicon carbide prototypes (a 2.2 mm diameter single diode and a 4 $\times$ 4-array of 1 mm diameter with a pitch of 2.2 mm), biased at 0 V, are exposed to a 0.5-5  $\mu s$ pulsed electron beam of 7 MeV alongside a flashDiamond PTW as reference dosimeter to characterize their response, time structure and position response.

A linearity better than 3.5% is observed up to 10 Gy per pulse of the single diode device only limited by the reference dosimetry. The pulse structure measured is consistent with the reference beam current transformer installed in the LINAC, allowing for instantaneous pulse discrimination at UHDR and its verification in the measurement point. Moreover, results demonstrate the viability of using SiC arrays to quantify the dose per pulse in a 70 $\times$ 50  ${\mathrm{mm}}^2$ area with a granularity of 1 $\times$ 2.2  ${\mathrm{mm}}^2$ , paving the way to larger arrays and thus toward potential 2D dose monitoring.

The possibility of a position sensitive SiC dose monitor for UHDR is demonstrated, as the technology demonstrator has been proven to maintain good linearity up to at least 10 Gy per pulse, with a time resolution enough to observe microsecond pulses and position sensitive readout.