Objective To introduce the method and results of modeling validation of the treatment planning system used in the first Mevion proton therapy system in China.Methods The SOBP(Spread-Out Bragg Peak)beams in water were designed according to the TG-185 report.The treatment plans in water were designed according to the TG-350 report.The treatment plans of patients were designed on the CT images.The plane dose of each beam was measured by using the MatriXX ONE ioni-zation chambers at different depths in the water,and the measurment results were compared with the TPS calculated results to verify the accuracy of the output doses,the error requirements were 2％/2 mm.Results Except for the distal fall-off position,the doses deviation at the SOBP beams center were less than 3％,and the γ analysis pass rates of plane doses were more than 90％.The measured results of the treatment plan beams were within the tolerance of deviation,and the output doses of the beams without or with static adaptive aperture were more accurate in general.With the decrease of beam energy,the error of dose calculation will increase.Conclusion According to the accuracy requirements of the planning system calculation and treat-ment system implementation,the proton therapy system supporting the treatment planning system has been modeled.Some basic performance such as IDD and beam spot is consistent with the actual measurement,and the TPS modeling conforms to the actual performance of the machine executing when calculating the same proton radiotherapy plan.

Objective To introduce the method and results of modeling validation of the treatment planning system used in the first Mevion proton therapy system in China.Methods The SOBP(Spread-Out Bragg Peak)beams in water were designed according to the TG-185 report.The treatment plans in water were designed according to the TG-350 report.The treatment plans of patients were designed on the CT images.The plane dose of each beam was measured by using the MatriXX ONE ioni-zation chambers at different depths in the water,and the measurment results were compared with the TPS calculated results to verify the accuracy of the output doses,the error requirements were 2％/2 mm.Results Except for the distal fall-off position,the doses deviation at the SOBP beams center were less than 3％,and the γ analysis pass rates of plane doses were more than 90％.The measured results of the treatment plan beams were within the tolerance of deviation,and the output doses of the beams without or with static adaptive aperture were more accurate in general.With the decrease of beam energy,the error of dose calculation will increase.Conclusion According to the accuracy requirements of the planning system calculation and treat-ment system implementation,the proton therapy system supporting the treatment planning system has been modeled.Some basic performance such as IDD and beam spot is consistent with the actual measurement,and the TPS modeling conforms to the actual performance of the machine executing when calculating the same proton radiotherapy plan.

As important biocatalysts, nitrilases can efficiently convert nitrile groups into acids and ammonia in a mild and eco-friendly manner, being widely used in the synthesis of important pharmaceutical intermediates. Early studies reported that nitrilases only had the hydrolysis activity of catalyzing the formation of corresponding carboxylic acid products from nitriles, showing catalytic specificity. However, recent studies have shown that some nitrilases exhibit the hydration activity for catalyzing the formation of amides from nitriles, showing catalytic promiscuity. The catalytic promiscuity of nitrilases has dual effects. On the one hand, the presence of amide by-products increases the difficulties and costs of subsequent separation and purification of carboxylic acid products. On the other hand, however, if the catalytic reaction pathways of nitrilases can be precisely regulated to reshape enzyme functions, the reactions catalyzed by nitrilases can be broadened to provide new ideas for the biosynthesis of high-value amides, which is crucial for the development of artificial enzymes and biocatalysis. This review summarized the research progress in the catalytic promiscuity of nitrilases and discussed the key regulatory factors that may affect the catalytic promiscuity of nitrilases from the evolutionary origin, catalytic domains, and catalytic mechanisms, hoping to provide reference and inspiration for the application of nitrilases in biocatalysis.
Aminohydrolases/chemistry* ; Biocatalysis ; Nitriles/chemistry* ; Substrate Specificity ; Catalytic Domain ; Catalysis

Transaminases are a class of enzymes that catalyze the transfer of amino between amino acids and keto acids, playing an important role in the biosynthesis of organic amines and the corresponding derivatives. However, natural enzymes often have low catalytic efficiency against non-natural substrates, which limits their widespread applications. Enzyme engineering serves as an effective approach to improve the catalytic properties and thereby expand the application scope of transaminases. In this study, a high-throughput screening method for transaminases was established based on the fluorescent color reaction between methoxy-2-aminobenzoxime (PMA) and ketones. According to the changes in fluorescence intensity, the concentration changes of ketones could be easily monitored. The efficiency, sensitivity, and accuracy of the screening method were improved by optimization of the system. With 4-hydroxy-2-butanone as the substrate, the mutant library of the transaminase from Actinobacteria sp. was established and a mutant with increased activity was successfully obtained, which improved the production efficiency of (R)-3-aminobutanol by enzyme-catalyzed synthesis. This study laid an important foundation for efficient screening, modification, and application of transaminase.
Transaminases/metabolism* ; Fluorescent Dyes/chemistry* ; High-Throughput Screening Assays/methods* ; Ketones/metabolism* ; Actinobacteria/enzymology*

Objective To evaluate the dose distribution of hippocampal sparing whole-brain proton therapy based on the treatment planning system of Mevion S250i proton therapy system.Methods Twenty patients undergoing hippocampal sparing whole-brain radiotherapy were selected.Under the same optimal conditions,plans using VMAT,fixed-angle IMPT without a-daptive aperture,IMPT with static adaptive aperture and IMPT with dynamic adaptive aperture were designed for each pa-tient.HI,CI,GI and the dose of hippocampus,lens,optic nerve,cochlea in different groups were compared.Results Compared with the VMAT plans,the IMPT plans without the adaptive aperture improved the target homogeneity index from(0.45±0.15)to(0.60±0.08),and the high-dose D2 in the targets decreased from(3368.22±65.94)cGy to(3270.67±104.78)cGy,and the irradiation doses of the hippocampus,lens and cochlea were significantly reduced(P＜0.05).The target gradient of IM-PT plans could be improved using static adaptive aperture,and the dose of lens could be further reduced(P＜0.05).The target gradient and conformal degree of the IMPT plans were significantly improved using dynamic adaptive aperture,and the dose of the optic nerves,lens and cochleae were further reduced(P＜0.05).Conclusion IMPT has a dosimetric advantage over VMAT in hippocampal sparing whole-brain radiotherapy.The use of Mevion adaptive aperture can not only further optimize the dose to the target area,but also minimize the radiation doses to the normal tissue around the target area,which has a good clinical appli-cation prospect.

Objective To present and discuss beam characteristics of the first Mevion S250i gantry-mounted accelerator pencil beam scanning proton therapy system in China.Methods The output dose was measured using a parallel-plate ionization chamber.The integrated depth dose was measured with a large-radius Bragg peak ionization chamber,covering 19 energy levels ranging from 227 MeV to 28 MeV,to analyze the proton beam characteristics.The spots in the air were measured with Phoenix flat panel detector on the beam central axis,and the precision of the delivery position was verified by measuring the multi-spot beam map.The interleaf leakage and penumbra reduction of adaptive aperture were measured to characterize its performance.Results The proton system was calibrated for a maximum energy of 227 MeV,with a(10×10)cm2uniform field delivering 1 Gy dose at a depth of 5 cm underwater.The system effectively modulated the proton beam range to the patient's surface,maintaining a constant 80%-80%Bragg peak width of 8.6 mm at all energy levels.The spot size of the highest energy beam at the isocenter was about 4 mm in the air,and the spot delivery position error was less than 1 mm.The interleaf leakage rate of the adaptive aperture for the highest energy beam was below 1.5%,and the penumbra was significantly reduced.Conclusion Mevion S250i proton therapy system demonstrates unique design and beam characteristics,which is reflected in the Bragg peak shape,spot size variation with energy,and penumbra sharpening of adaptive aperture;and these differences should be considered in treatment planning system modeling and planning for precision treatment.

Objective:To evaluate the clinical application value of the adaptive aperture by comparing intensity-modulated proton radiotherapy(IMPT) plans using and not using the aperture for brain tumors.Methods:A total of twenty patients treated with postoperative radiotherapy for brain tumors were enrolled in this study. IMPT plans were developed for each patient using and not using the adaptive aperture under the same optimization conditions. The target conformal index (CI) value, target homogeneity index (HI) value, and the dose to normal tissues of the two sets of plans were compared.Results:The IMPT plans designed using the adaptive aperture significantly increased the mean CI value from 0.58 to 0.66, while decreasing the mean 50% prescription dose volume from 797.70 cm 3 to 638.15 cm 3. These plans also reduced the irradiation doses to the cochlea, brainstem, optic chiasm, optic nerve, and lens ( t = 2.06, 3.02, 2.11, 2.58, 2.67, P < 0.05). Additionally, there was no significant difference in the HI value of the target volumes and the machine jumps (MU) between the two sets of plans ( P > 0.05). Conclusions:The adaptive aperture can significantly reduce the irradiation dose to normal tissues outside the target volumes, positively impacting the protection of organs at risk (OARs) around the target values. This demonstrates its great potential for clinical application.

Objective:To discuss the acceptance test of beam performance and mechanical precision of the first Mevion type S250i proton therapy system in China,and verify the stability and reliability of that in clinical treatment.Methods:According to the requirements of acceptance report of manufacturer,the output and range of machine unit(MU),the accuracy and stability of size and position of beam spot,the penumbra and position accuracy of adaptive aperture(AA)of Mevion type S250i proton therapy system,as well as the tests of mechanical properties and functions of the requirement of clinical use,were checked and tested for acceptance.Results:The maximum deviation of MU output was 1.3%,and the maximum deviation of the range was 0.037 g/cm2,and the maximum distal fall-off was 0.465 cm,and the minimum range of energy modulation was 0.21 g/cm2.The maximum deviations of the size of beam spot and the maximum deviation of the position were respectively 0.07 cm and 0.05 cm.The maximum AA penumbra was 0.007 cm,and the AA position accuracy was less than 0.1 cm.Conclusion:The acceptance test of the Mevion type S250i proton therapy system indicates that the parameters of the beam performance and mechanical precision can meet the requirements of the acceptance contract and AAPM-TG224 report of manufacturer,which has verified the machine has better favorable stability and reliability.

Objective:To measure and assess relevant radiation doses at the radiotherapy site of the first domestic single-vault proton therapy system.Methods:The radiation levels of the therapy system during and after beam irradiation were measured, and annual effective doses were assessed for personnel at the site.Results:During beam irradiation, the highest radiation dose was detected at the shielded door of the equipment floor, with a gamma radiation level of 2.140 μSv/h and a neutron radiation level of 0.850 μSv/h. Neutron radiation disappeared immediately once the beams stopped. In contrast, the radiation activated originated mostly from gamma rays. A longer time after beams stopped was associated with lower induced radiation intensity at the same location. Furthermore, a farther distance from the irradiated object corresponded to lower induced radiation intensity at the same time. The assessment result reveal that the annual effective doses to the personnel were at the safe level, with physicists exposed to the highest dose of 2.138 mSv.Conclusions:The radiation level at the studied proton therapy site meets the safety requirement, and the treatment can be performed safely at this site.

Objective:To verify and calibrate the CT modeling curves of three CT devices in RayStation proton treatment planning system (TPS).Methods:CT-mass density (CT-MD) curves were established by CT Hounsfield units of different tissue substitute materials obtained by scanning the model with CT equipment. CT-stopping power (CT-SP) curves were established by calculation based on the chemical composition of various human tissues. The equivalent water thickness of tissue substitute modules was calculated with different CT modeling curves in TPS. The actual equivalent water thickness of various modules was measured by a Bragg peak detector, and compared with the calculated values of TPS to verify the accuracy of different CT models.Results:The differences of CT modeling curves were significantly different under different tube voltage scanning protocols. Compared with CT-MD curves, CT-SP curves based on the stoichiometric calibration were more suitable for proton dose calculation. However, the values of stopping power corresponding to high CT values still needed to be optimized, and the calculation error after calibration was less than 3%.Conclusion:The method of verifying and calibrating CT unit curves of proton TPS is described, proving that the CT-SP curves after stoichiometric calculation are more suitable for proton dose calculation.