Background and Aims

One of the challenges in investigating FLASH radiation therapy is the reliable measurement of the absorbed dose at ultra-high dose per pulse (DPP). This work aims to evaluate a probe-type graphite calorimeter (Aerrow) at ultra-high DPP.

Methods

The DPP was varied between 0.5 to 5.5 Gy. The signal was compared to the pulse charge measured by a non-destructive Integrating Current Transformer (ICT). In addition, a depth dose curve was measured and compared to an ionization chamber measurement and a Monte-Carlo simulation.

Results

The response of the calorimeter was proportional to the ICT signal. On average, the standard deviation of the calorimeter response was 0.2 % in high dose rate and reached 1% at the lower rate. In figure 1, the depth dose measurement with calorimeter and ionization chamber is compared to Monte-Carlo simulation. The half-value depths in water R50 obtained from measurement and simulation agree within 1 mm.

Figure 1: Depth dose in water measured and simulated.

Conclusions

Calorimetry is showing promising results for absorbed dose measurements. Calorimetry gets simpler at FLASH dose rates as the dose delivery is in a few seconds or less. The preliminary results show that advanced thermal insulation of the calorimeter is not required, nor the use of a heat lost correction factor.

Acknowledgement: This project 18HLT04 UHDpulse has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.