Image-Guided FLASH ProtonTherapy. A dream? Naivety?Arrogance? Or a Necessity?

<b>Objective:</b> The in-vivo therapy guidance by imaging and dosimetry of proton irradiations, generically known as proton range verification, are some of the most underinvested aspects of radiation oncology. They trail behind other advances in radiation therapy due to the scarcity of sensitive instruments compounded by the lack of treatment protocols for precision monitoring of effects of beam radiation. This is despite that such measurements may dramatically enhance the treatment accuracy and lower the postradiation toxicity, thus improving the entire outcome of cancer therapy. <br><b>Methods:</b> In this contribution, we focus on the motivation of designing and building of an in-beam time-of-flight (ToF) positron-emission-tomography (PET) scanner with the depth-of-interaction (DoI) capability for high sensitivity and improved fidelity of imaging. A scanner could be augmented with a tungsten collimator that would enable prompt-gamma imaging (PGI) via single-photon emission computed tomography (SPECT) technique. <br><b>Results:</b> We present selected results of our pre-clinical experiments with a FLASH proton beam and discuss other related ideas towards improving and expanding the use of PET/PGI/SPECT detectors for proton therapy. A scanner provides an access to data during the spill and past the spill permitting to capture the beam interaction and kinetic monitoring of its effect thus allowing a thorough assessment of each irradiation.<br><b>Conclusions:</b> A novel scanner for multiple modalities can substantially improve the treatment precision of proton therapy leading to less toxic outcome of irradiations. Using it in the FLASH modality would additionally expand the patient reach of proton therapy.