Proton neutron gamma-x detection (PNGXD) is a novel imaging concept being investigated for tumor localization during proton therapy that uses secondary neutron interactions with a gadolinium contrast agent (GDCA) to produce characteristic photons within the 40–200 keV energy region. The purpose of this study is to experimentally investigate the feasibility of implementing this procedure by performing experimental measurements on a passive double scattering proton treatment unit. Five experimental measurements were performed with varying concentrations and irradiation conditions. Photon spectra were measured with a 25 mm2, 1 mm thick uncollimated X-123 CdTe spectrometer. For a 10.4 Gy administration on a 100 ml volume phantom with 10 mg g−1 Gd solution placed in a water phantom, 1129  ±  184 K-shell Gd counts were detected. For an administered dose of 21 Gy and the same Gd solution measured in air, resulted in 3296  ±  256 counts. A total of 1094  ±  171, 421  ±  150 and 23  ±  141 K-shell Gd counts were measured for Gd concentrations of 10 mg g−1, 1 mg g−1 and 0 mg g−1 for 7 Gy dose in air. The signal to noise ratio for these five measurements were: 7, 15, 6, 3, and 0.2, respectively. The spectrum contained 43 keV Kα and 49 keV Kβ peaks, however a small amount of 79.5 and 181.9 keV prompt gamma rays were detected from gadolinium neutron capture. This discrepancy is due to a drop in the intrinsic detection efficiency of the CdTe spectrometer over this energy range. The measurements were compared with Monte-Carlo simulation to determine the contributions of Gd neutron capture from internal and external neutrons on a passive scattering proton therapy unit and to investigate the discrepancy in detected characteristic x-rays versus prompt gamma rays.

this study investigates the photon production from thermal neutron capture in a gadolinium (Gd) infused tumor as a result of secondary neutrons from particle therapy. Gadolinium contrast agents used in MRi are distributed within the tumor volume and can act as neutron capture agents. As a result of particle therapy, secondary neutrons are produced and absorbed by Gd in the tumor providing potential enhanced localized dose in addition to a signature photon spectrum that can be used to produce an image of the Gd enriched tumor. to investigate this imaging application, Monte carlo (Mc) simulations were performed for 10 different particles using a 5-10 cm spread out-Bragg peak (SOBP) centered on an 8 cm 3 , 3 mg/g Gd infused tumor. For a proton beam, 1.9 × 10 6 neutron captures per RBE weighted Gray equivalent dose (Gye) occurred within the Gd tumor region. Antiprotons (P), negative pions (− π), and helium (He) ion beams resulted in 10, 17 and 1.3 times larger Gd neutron captures per Gye than protons, respectively. therefore, the characteristic photon based spectroscopic imaging and secondary Gd dose enhancement could be viable and likely beneficial for these three particles.

In this article, we elucidate the protein activity from the perspective of protein softness and flexibility by studying the collective phonon-like excitations in a globular protein, human serum albumin (HSA), and taking advantage of the state-of-the-art inelastic X-ray scattering (IXS) technique. Such excitations demonstrate that the protein becomes softer upon thermal denaturation due to disruption of weak noncovalent bonds. On the other hand, no significant change in the local excitations is detected in ligand- (drugs) bound HSA compared to the ligand-free HSA. Our results clearly suggest that the protein conformational flexibility and rigidity are balanced by the native protein structure for biological activity.

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challenge to structural biology. The folded domain structures for the scaffold protein PSD-95 were long known but such fragmentary knowledge lacks methods to assemble these pieces. We used single-molecule FRET studies with multi-parameter fluorescence detection [1] and filtered fluorescence correlation spectroscopy [2, 3] to describe the native state ensemble of this canonical scaffold protein. Our approach represents a solution to describing the flexibility in any multi-domain protein from nanoseconds to seconds. The five domains in PSD-95 partitioned into two independent supramodules. Intramolecular interactions were limited to neighboring domains, which did not interact without being tethered. Although MAGUK proteins are flexible, there are conformational preferences encoded in the primary sequence. [1.] McCann, J. J., Zheng, L. Rohrbeck, D., Felekyan, S., Kühnemuth, R., Sutton, R. B., Seidel, C. A. M., Bowen, M. E.; The supertertiary structure of the synaptic MAGuK scaffold proteins is conserved. Proc. Natl. Acad. Sci. USA. 109, 15775-15780 (2012). [2.] Felekyan, S., Kalinin, S., Sanabria, H., Valeri, A., Seidel, C. A. M.; Filtered FCS: Species auto and cross correlation functions highlight binding and dynamics in biomolecules.