Establishing Dosimetry standards for underpinning FLASH Radiotherapy

In the last three decades, survival of radiotherapy (RT) patients has greatly improved due to technological advances in delivery of radiation to tumour volumes. However, in spite of improvements in delivery of RT, a significant number of patients still experience severe toxicity from radiation treatment, particularly when the treatment volume overlaps with organs at risk.
It was recently established that ultra-high dose rate (UHDR), known as FLASH RT, leads to remarkable reduction of normal tissue toxicity while maintaining tumour control with respect to conventional dose-rate RT. This so called "FLASH effect" was demonstrated in vivo on different animal models and different organs by delivering the total amount of radiation dose in a very short time (usually <200 ms). FLASH RT could represent a paradigm shift in modern radiotherapy with significant benefits for cancer patients and healthcare providers.
However, the complexity of this new technology and the limited understanding of the underpinning radiobiological mechanisms hamper clinical exploitation. Even though the literature demonstration of the FLASH effect is growing very rapidly, the published studies may lead to flawed interpretation of data due to lack of established dosimetry methods for this new radiotherapy modality. Dosimetry at UHDR is complicated and it is essential to understand the effects that impact detector response in this radiotherapy modality. Without a clear understanding of the fundamental dosimetry issues, there is potential for significant errors and misinterpretation of research results and trials. Accurate dosimetry is crucial for the safe implementation of any radiotherapy technique and ensures best practice and consistency of treatments across different radiotherapy centres. The full clinical exploitation and optimization of FLASH RT requires a multidisciplinary approach to best solve the multiple complex challenges this field faces. The major part of solving these challenges will be through the development of metrology in measurement of dose and dose-rate for FLASH radiotherapy. This will enable validation of treatment planning for FLASH RT, commissioning of the new UHDR delivery systems, demonstration of compliance with safety requirements and support accurate radiobiological investigations.