Development of a hydrated electron dosimeter for radiotherapy applications: A proof of concept.

BACKGROUND: Hydrated electrons, which are short-lived products of radiolysis in water, increase the optical absorption of water, providing a pathway toward near-tissue-equivalent clinical radiation dosimeters. This has been demonstrated in high-dose-per-pulse radiochemistry research, but, owing to the weak absorption signal, its application in existing low-dose-per-pulse radiotherapy provided by clinical linear accelerators (linacs) has yet to be investigated. PURPOSE: The aims of this study were to measure the optical absorption associated with hydrated electrons produced by clinical linacs and to assess the suitability of the technique for radiotherapy (⩽ 1 cGy per pulse) applications. METHODS: 40 mW of 660-nm laser light was sent five passes through deionized water contained in a 10 × 4 × $\times 4\times$ 2 cm3 glass-walled cavity by using four broadband dielectric mirrors, two on each side of the cavity. The light was collected with a biased silicon photodetector. The water cavity was then irradiated by a Varian TrueBeam linac with both photon (10 MV FFF, 6 MV FFF, 6 MV) and electron beams (6 MeV) while monitoring the transmitted laser power for absorption transients. Radiochromic EBT3 film measurements were also performed for comparison. RESULTS: Examination of the absorbance profiles showed clear absorption changes in the water when radiation pulses were delivered. Both the amplitude and the decay time of the signal appeared consistent with the absorbed dose and the characteristics of the hydrated electrons. By using literature value for the hydrated electron radiation chemical yield (3.0±0.3), we inferred doses of 2.1±0.2 mGy (10 MV FFF), 1.3±0.1 mGy (6 MV FFF), 0.45±0.06 mGy (6 MV) for photons, and 0.47±0.05 mGy (6 MeV) for electrons, which differed from EBT3 film measurements by 0.6%, 0.8%, 10%, and 15.7%, respectively. The half-life of the hydrated electrons in the solution was ∼ 24 µ $\umu$ s. CONCLUSIONS: By measuring 660-nm laser light transmitted through a cm-scale, multi-pass water cavity, we observed absorption transients consistent with hydrated electrons generated by clinical linac radiation. The agreement between our inferred dose and EBT3 film measurements suggests this proof-of-concept system represents a viable pathway toward tissue-equivalent dosimeters for clinical radiotherapy applications.

GEANT4-DNA simulation of temperature-dependent and pH-dependent yields of chemical radiolytic species.

Objective.GEANT4-DNA can simulate radiation chemical yield (G-value) for radiolytic species such as the hydrated electron (eaq-) with the independent reaction times (IRT) method, however, only at room temperature and neutral pH. This work aims to modify the GEANT4-DNA source code to enable the calculation ofG-values for radiolytic species at different temperatures and pH values.Approach.In the GEANT4-DNA source code, values of chemical parameters such as reaction rate constant, diffusion coefficient, Onsager radius, and water density were replaced by corresponding temperature-dependent polynomials. The initial concentration of hydrogen ion (H+)/hydronium ion (H3O+) was scaled for a desired pH using the relationship pH = -log10[H+]. To validate our modifications, two sets of simulations were performed. (A) A water cube with 1.0 km sides and a pH of 7 was irradiated with an isotropic electron source of 1 MeV. The end time was 1µs. The temperatures varied from 25 °C to 150 °C. (B) The same setup as (A) was used, however, the temperature was set to 25 °C while the pH varied from 5 to 9. The results were compared with published experimental and simulated work.Main results.The IRT method in GEANT4-DNA was successfully modified to simulateG-values for radiolytic species at different temperatures and pH values. Our temperature-dependent results agreed with experimental data within 0.64%-9.79%, and with simulated data within 3.52%-12.47%. The pH-dependent results agreed well with experimental data within 0.52% to 3.19% except at a pH of 5 (15.99%) and with simulated data within 4.40%-5.53%. The uncertainties were below ±0.20%. Overall our results agreed better with experimental than simulation data.Significance.Modifications in the GEANT4-DNA code enabled the calculation ofG-values for radiolytic species at different temperatures and pH values.

A dual-function fluorescent probe for Hg (II) and Cu (II) ions with two mutually independent sensing pathways and its logic gate behavior.

A dual-function fluorescent Probe 1 has been synthesized conveniently by coupling rhodamine hydrazone with O-vinyl protected hydroxyl benzaldehyde. Probe 1 was a highly selective and sensitive chemodosimeter for Hg2+ through specific hydrolysis reaction of vinyl ethers with significant fluorescence quenching in CH3CN-PBS buffer (3:7, v/v) solution. Meanwhile, Probe 1 showed a ratiometric fluorescent detection of Cu2+ with a remarkable large Stokes shift (150 nm) by the opening of the spirolactam ring in CH3CN-PBS buffer (3:7, v/v) solution. Hence, the two recognition mechanisms realized well by using a single fluorescent probe. Moreover, Probe 1 could be efficiently applied to the combinatorial logic circuit of NOR and INHIBIT gates through the procured spectral results, respectively.

Nutrient stoichiometry and concentrations influence silver toxicity in the aquatic macrophyte Lemna gibba.

Though nutrients and silver often co-occur in aquatic ecosystems, the combined effects of these environmental stressors on aquatic plants are poorly understood. Such coexposures are important because nanosilver is increasingly released to the environment, and recent studies in aquatic systems indicate that nanosilver represents an environmental source of ionic silver (Ag(+)), which exerts relatively high acute toxicity to aquatic life. The primary objective of this study was to understand the effects of nitrogen (N) and phosphorus (P) concentrations and N:P ratios on the toxicity of ionic silver to the model aquatic macrophyte Lemna gibba over 7-d study periods. L. gibba were more sensitive to silver (e.g., lower EC50 values) when N and P concentrations were higher. In addition, greater ionic silver toxicity occurred under higher P-availability (e.g., lower N:P ratios). L. gibba frond number and fresh weight were also differentially affected across nutrient×silver treatment combinations. Such observations highlight the importance of considering site-specific nutrient conditions during the prospective and retrospective risk assessments and management of silver impacts to primary producers.