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Background: The use of electron beams has been rekindled by the advent of ultra‐high‐dose rate radiotherapy (FLASH) and very high energy electrons (VHEE). The need for development of novel technology for beam monitoring and dosimetry of such beams is of paramount importance prior to their clinical translation. Purpose: In this work we explore the potential of a multi‐layer nanoporous aerogel High‐Energy‐Current (HEC) detector as a dosimeter for electron beam. The detector does not suffer from radiation damage or signal saturation, making it suitable for very‐high‐dose‐rate applications. Standard dose rates and energies are used to establish reference for FLASH and VHEE. We explore detector response to electron energy and residual range both experimentally and computationally. Methods: Multilayer HEC detectors were constructed using 1×–10× basic modules of Aluminum(Al)_aerogel(A)_Tantalum(Ta) with 10–70 µm layer thicknesses. Signals are collected from all electrodes (3–21, depending on module multiplicity) with zero external voltage bias. Measurements are acquired as a function of depth(z) in water equivalent plastic using Varian TrueBeam for energies E = 6,9,12,15 MeV (SAD = 105 cm, 6 × 6 cone, 1000 MU/min). Computational simulations of identical detector geometries are performed using the 1D deterministic code CEPXS/ONEDANT. Additionally, percent‐depth‐doses PDD(z), measured with diode in water, are used to explore the response of HEC for various energies and residual ranges. Results: The current measured from Ta electrodes resembles the shape of deposited charges in water and it is proportional to the derivative of the clinical PDD corrected for contribution from photon contamination. The signal is positive on the surface, and it decreases with depth reaching a negative local minimum at z = R50, before increasing again, reaching zero at about the practical range z = Rp. In contrast, the signal from Al electrodes is shaped like the electron PDD(z) shape but with lower signal at the surface and higher bremsstrahlung tail. By subtracting the signal from Ta and Al electrodes we obtained a curve resembling PDD(z,E) after Bremsstrahlung contamination correction. Conclusions: Multi‐layer HEC sensors exhibit characteristic responses to electron beams that are unlike responses of ion chambers or diodes. Since the sensor structures are sensitive to electronic disequilibrium, high‐Z electrodes give a signal proportional to the charge deposition pattern and can be modeled using the derivative of PDD(z). [ABSTRACT FROM AUTHOR]

Purpose: We investigated the characteristics of radiation-induced current in nano-porous pellet and thin-film anodized tantalum exposed to kVp X-ray beams. We aim at developing a large area (≫cm2) thin-film radiation sensor for medical, national security and space applications. Methods: Large area (few cm2) micro-thin Ta foils were anodized and coated with a counter electrode made of conductive polymer. In addition, several types of commercial electrolytic porous tantalum capacitors were assembled and prepared for irradiation with kVp X-rays. We measured dark current (leakage) as well as transient radiation-induced currents as a function of external voltage bias. Results: Large transient currents (up to 50 nA) under X-ray irradiation (dose rate of about 3 cGy/s) were measured in Ta2O5 capacitors. Small nano-porous Ta and large-area flat Ta foil capacitors show similar current–voltage characteristic curve after accounting for different X-ray attenuation in capacitor geometry. The signal is larger for thicker capacitor oxide. A non-negligible signal for null external voltage bias is observed, which is explained by fast electron production in Ta foils. Conclusions: Anodized tantalum is a promising material for use in large-area, self-powered radiation sensors for X-ray detection and for energy harvesting. [ABSTRACT FROM AUTHOR]

Recent studies have highlighted the potential of smart radiotherapy biomaterials (SRBs) for combining radiotherapy and immunotherapy. These SRBs include smart fiducial markers and smart nanoparticles made with high atomic number materials that can provide requisite image contrast during radiotherapy, increase tumor immunogenicity, and provide sustained local delivery of immunotherapy. Here, we review the state-of-the-art in this area of research, the challenges and opportunities, with a focus on in situ vaccination to expand the role of radiotherapy in the treatment of both local and metastatic disease. A roadmap for clinical translation is outlined with a focus on specific cancers where such an approach is readily translatable or will have the highest impact. The potential of FLASH radiotherapy to synergize with SRBs is discussed including prospects for using SRBs in place of currently used inert radiotherapy biomaterials such as fiducial markers, or spacers. While the bulk of this review focuses on the last decade, in some cases, relevant foundational work extends as far back as the last two and half decades. [ABSTRACT FROM AUTHOR]

Purpose: Determine the dosimetric quality and the planning time reduction when utilizing a template-based automated planning application. Methods: A software application integrated through the treatment planning system application programing interface, QuickPlan, was developed to facilitate automated planning using configurable templates for contouring, knowledge-based planning structure matching, field design, and algorithm settings. Validations are performed at various levels of the planning procedure and assist in the evaluation of readiness of the CT image, structure set, and plan layout for automated planning. QuickPlan is evaluated dosimetrically against 22 hippocampal-avoidance whole brain radiotherapy patients. The required times to treatment plan generation are compared for the validations set as well as 10 prospective patients whose plans have been automated by QuickPlan. Results: The generations of 22 automated treatment plans are compared against a manual replanning using an identical process, resulting in dosimetric differences of minor clinical significance. The target dose to 2% volume and homogeneity index result in significantly decreased values for automated plans, whereas other dose metric evaluations are nonsignificant. The time to generate the treatment plans is reduced for all automated plans with a median difference of 9′ 50″ ± 4′ 33″. Conclusions: Template-based automated planning allows for reduced treatment planning time with consistent optimization structure creation, treatment field creation, plan optimization, and dose calculation with similar dosimetric quality. This process has potential expansion to numerous disease sites. [ABSTRACT FROM AUTHOR]

Background: Paramagnetic species such as O2 and free radicals can enhance T1 and T2 relaxation times. If the change in relaxation time is sufficiently large, the contrast will be generated in magnetic resonance images. Since radiation is known to be capable of altering the concentration of O2 and free radicals during water radiolysis, it may be possible for radiation to induce MR signal change. Purpose: We present the first reported instance of x‐ray‐induced MR signal changes in water phantoms and investigate potential paramagnetic relaxation enhancement mechanisms associated with radiation chemistry changes in oxygen and free radical concentrations. Methods: Images of water and 10 mM coumarin phantoms were acquired on a 0.35 T MR‐linac before, during, and after a dose delivery of 80 Gy using an inversion‐recovery dual‐echo sequence with water nullified. Radiation chemistry simulations of these conditions were performed to calculate changes in oxygen and free radical concentrations. Published relaxivity values were then applied to calculate the resulting T1 change, and analytical MR signal equations were used to calculate the associated signal change. Results: Compared to pre‐irradiation reference images, water phantom images taken during and after irradiation showed little to no change, while coumarin phantom images showed a small signal loss in the irradiated region with a contrast‐to‐noise ratio (CNR) of 1.0–2.5. Radiation chemistry simulations found oxygen depletion of −11 µM in water and −31 µM in coumarin, resulting in a T1 lengthening of 24 ms and 68 ms respectively, and a simulated CNR of 1.0 and 2.8 respectively. This change was consistent with observations in both direction and magnitude. Steady‐state superoxide, hydroxyl, hydroperoxyl, and hydrogen radical concentrations were found to contribute less than 1 ms of T1 change. Conclusion: Observed radiation‐induced MR signal changes were dominated by an oxygen depletion mechanism. Free radicals were concluded to play a minor secondary role under steady‐state conditions. Future applications may include in vivo FLASH treatment verification but would require an MR sequence with a better signal‐to‐noise ratio and higher temporal resolution than the one used in this study. [ABSTRACT FROM AUTHOR]