Researchers from the Arizona State University Physics Department, Proton Calibration Technologies, and the Mayo Clinic Arizona Proton Therapy Center recently conducted experimental tests to characterize the proton energy distribution in the synchrotron beam pulses using scintillation crystal photography.
Arizona State University and Proton Calibration Technologies researchers finalize the optical alignment of components in the experimental testbed beamline.
The YAG crystal emits visible photons in proportion to bombardment with 220 MeV protons. Every proton produces some 50 photons at the camera sensor and there are some 10,000,000 per beam pulse. The high intensity spot, 17mm in diameter, indicates a signal strength more than sufficient to proceed with the next set of measurements – sending protons through materials of varying densities. In the next tests a collimating aperture will create one or more mini-beams. Each mini-beam will let us probe the proton relative stopping power of the different phantom materials.
Pictured is a surface map of the light intensity emitted by the scintillation crystal. Notice how sharply the signal stands out with high resolution and excellent signal-to-noise ratio. The steepness of the peak is a good indication of the resolution of mini-beams during the next experimental tests.
Meetings Held to Plan Preliminary Proton CT Experimentation and Testing
Paul Mulqueen, CEO of Proton Calibration Technologies and Evgeny Galyaev, CEO of Radiation Detection and Imaging Technologies, met with research team members at a prominent proton therapy center to plan preliminary proton computed tomography testing and experimentation.
Researchers at the University of Florida Health Cancer Center concluded in the JCO Oncology Practice article Effect of Proposed Episode-Based Payment Models on Advanced Radiotherapy Procedures that “These data suggest that the RO-APM may have the desired effect of encouraging shorter courses of radiotherapy…”. Due to the high doses involved in hypofractionation, pCT is needed to streamline the clinical processes to ensure that proton Bragg Peaks are delivered safely and effectively.
In a AAPM physicist member survey during an oral presentation at the Annual Meeting, 33% of respondents agree that range uncertainty is a primary barrier to further adoption of proton therapy, and an obstacle to the replacement of X-ray therapy by Proton Therapy. And the AAPM Task Group Report 202 – Physical Uncertainties in the Planning and Delivery of Light Ion Beam Treatments – concluded (p. 53) that “It can be seen that there are quite large differences in the determined RLSTPs between the various facilities, indicating that the uncertainty in converting x-ray CT numbers to RLSTPs is significantly larger than indicated by the single facility experiments.”
According to the article in the Journal of Radiation Oncology – Fast In Situ Image Reconstruction for Proton Radiography, “Recent studies indicate that tomographic imaging using protons has the potential to provide directly more accurate measurement of RSPs with significantly lower radiation dose than X-rays.”
Parodi, K., et. al. state regarding proton CT that “very encouraging simulation studies and experimental campaigns with the available prototypes confirm the promise of this modality” in the journal article.
The American Association of Medical Physicists (AAPM) Task Group 202, studied x-ray CT-number-to-RLSTP conversion functions for the scanners and protocols at a number of facilities and wrote the report “Physical Uncertainties in the Planning and Delivery of Light Ion Beam Treatments”, concluding that (p.53) “It can be seen that there are quite large differences in the determined RLSTPs between the various facilities, indicating that the uncertainty in converting x-ray CT numbers to RLSTPs is significantly larger than indicated by the single facility experiments.” [This means that proton range uncertainties are “all over the place” — Paul M will do some calculations to quantify the import of these discrepancies.]
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