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2 Bio-Algorithms and Med-Systems

2 2024

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First PET Studies of a FLASH Proton Beam: Summary and Future Prospects

100%

Cesar J. P. , Abouzahr F. , Crespo P. , Gajda M. , Kuo A. , Mawlawi O. , Morozov A. , Ojha A. , Poenisch F. , Proga M. , Sahoo N. , Seco J. , Takaoka T. , Tavienier S. , Titt U. , Wang X. , Zhu X. , Lang K.

tom Vol. 20, Special issue

49--54

Objectives: Proton therapy, while highly effective and successful, still lacks a key feature: the ability to assess, in-vivo, the dose and end-point location of irradiations. Known as proton range verification, this capability can be realized by incorporating positron emission tomography (PET) systems in both conventional and emerging modalities, such as FLASH proton therapy. FLASH itself may revolutionize radiation oncology with its purported ability to better spare healthy tissues, but only if the underlying mechanisms can be understood. We summarize our work towards establishing in-beam PET modalities and elucidating the mystery of the FLASH effect. Materials: We've developed a PET scanner designed for live, in-beam imaging during therapeutic proton irradiations that can use short-lived positron emitting species (PES) activated by the beam to validate the range and dose of proton depositions. This scanner is made up of PET modules consisting of arrays of LYSO (lutetium-yttrium oxyorthosilicate) scintillating crystals coupled one-to-one to silicon photomultiplier (SiPM) arrays. These modules are readout by electronics based on the TOFPET2 ASIC platform from PETsys Electronics. Methods: Our collaboration with MD Anderson Cancer Center has given us opportunities to take real in-beam data using a non-clinical beamline capable of delivering FLASH proton irradiations into target phantoms made of polymethyl methacrylate (PMMA), high density polyethylene (HDPE), and water. Data collected both during and afterirradiations were used to perform novel analyses and to reconstruct images of PES activity due to the beam. Results: Exploratory studies, using a subset of our PET scanner, have demonstrated successful data acquisition during and after FLASH beam spills including quantitative imaging and dosimetry of activated phantoms. The full results, explored in this work, are highly promising and prove that in-beam PET can deliver on its goals. Upcoming experiments conducted using both FLASH and conventional beams will employ the full PET scanner and involve a rich experimental program with novel ideas for irradiation targets, beam characterization, and in-depth comparisons of the two irradiation modalities. Conclusions: This work demonstrates the unprecedented proof-of-principle for the capabilities of an in-beam PET scanner for imaging and dosimetry of both conventional and FLASH proton beams. These results open a new PET modality with proton beams which is particularly attractive for FLASH therapy but can serve effectively all proton irradiations, leading to improved treatment monitoring and image-guided therapy.

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

58%

Lang K.

tom Vol. 20, Special issue

17--26

Objective: 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. Methods: 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. Results: 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. Conclusions: 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.