PURPOSE:FLASH radiation therapy using high-energy x rays combines ultrahigh dose rate irradiation with the physical characteristics of high-energy x-ray beams, achieving a significant reduction in normal tissue biological damage while maintaining sufficient tissue penetration, thereby presenting great potential for clinical translation. However, the absence of a traceable absolute dosimetry method for FLASH x-ray beams remains a substantial limitation to its clinical implementation. This study aims to establish a quasi-adiabatic water-controlled probe-type graphite calorimeter for the absolute measurement of absorbed dose to water in the 10 MV FLASH x-ray beam, to address the current lack of a traceable dosimetry standard for x-ray FLASH radiation therapy. METHODS AND MATERIALS:A probe-type graphite calorimeter was developed, employing thermally stabilized water as the thermal control medium to precisely regulate the thermal equilibrium of the graphite core. This quasi-adiabatic system is designed to facilitate accurate absolute dose measurements under ultrahigh dose rate conditions. RESULTS:The results indicate that for a single irradiation with a total dose exceeding 2 Gy, the mean type A relative uncertainty, determined from 5 repeated measurements using the sample standard deviation, is less than 0.2%. By deriving the necessary correction factors for determining the absolute dose (ie, in Gy) of FLASH photon radiation therapy, the uncertainty in water absorbed dose measurement is determined to be 1.0% (k = 1). CONCLUSIONS:This study develops a probe-type graphite calorimeter for the absolute measurement of absorbed dose to water in 10 MV FLASH x-ray beams. The system is designed to address the current lack of a traceable dosimetric standard for x-ray FLASH radiation therapy, thereby supporting its clinical translation and application.

Purpose FLASH radiotherapy using high-energy X-rays combines ultra-high dose-rate irradiation with the physical characteristics of high-energy X-ray beams, achieving a significant reduction in normal tissue biological damage while maintaining sufficient tissue penetration, thereby presenting great potential for clinical translation. However, the absence of a traceable absolute dosimetry method for FLASH X-ray beams remains a substantial limitation to its clinical implementation. This study aims to establish a quasi-adiabatic water-controlled probe-type graphite calorimeter for the absolute measurement of absorbed dose to water in the 10 MV FLASH X-ray beam, to address the current lack of a traceable dosimetry standard for X-ray FLASH radiotherapy. Methods and Materials A probe-type graphite calorimeter was developed, employing thermally stabilised water as the thermal control medium to precisely regulate the thermal equilibrium of the graphite core. This quasi-adiabatic system is designed to facilitate accurate absolute dose measurements under ultra-high dose rate conditions. Results The results indicate that for a single irradiation with a total dose exceeding 2 Gy, the mean Type A relative uncertainty, determined from five repeated measurements using the sample standard deviation, is less than 0.2%. By deriving the necessary correction factors for determining the absolute dose (i.e., in Gy) of FLASH photon radiotherapy, the uncertainty in water-absorbed dose measurement is determined to be 1.0% (1σ). Conclusions This study develops a probe-type graphite calorimeter for the absolute measurement of absorbed dose to water in 10 MV FLASH X-ray beams. The system is designed to address the current lack of a traceable dosimetric standard for X-ray FLASH radiotherapy, thereby supporting its clinical translation and application.

Ionization chambers used for air kerma measurements in photon beams typically utilize a wall and cavity design primarily either of cylindrical or spherical shape. The corrections and conversions of such chambers have been widely studied using Monte Carlo (MC) codes. In this work, we look at two ionization chambers with a shape that is a combination of spherical and cylindrical, which we will refer to as a compound geometry. The chambers share similar structures but possess varied volumes. They were separately investigated under specific 60Co gamma radiation fields, where the corrections and conversions for air kerma reproductions including the wall effect were studied via comprehensive MC simulations using EGSnrc. The reproduced air kerma values were disseminated to three thimble chambers, the calibration factors of which demonstrated consistency between experiments and simulations. A similar to 0.1% discrepancy was observed from both of the different types of thimble chambers. Aside from providing specific results for these chambers, the investigation of the differences aims to highlight the importance of MC simulations in the calculation of chamber correction factors, especially for those cannot be readily deduced by experiment.

大部分用于辐射剂量学研究的辐照器都安装比活度较高的放射源，这类放射源只能采用合规的容器运输以完成现场装源。为了使国产辐照器能够更好地符合国内外放射源的运输及安装要求，研制了一种新型三重屏蔽辐照器，用于进行现场装源及开展后续工作。首先基于对辐照器的精确构建，开展了系统的模拟计算，分析了辐照器对射束的控制特性。然后结合模拟计算和分析，研究了开展辐射剂量学相关研究所关心的辐射场性能。本工作研制的新型三重屏蔽辐照器适用于现场装源，散射腔能够将射束中的散射成分减少25%。辐照器的三重屏蔽结构能够将常规工作区域的射线强度衰减约7个数量级，据此为辐照器的关键部件安装方案的优化提出了建议。准直器组对辐射野平面内能谱的影响约为0.2%。利用辐照器构建的辐射场计算了三种典型电离室的 60 Co γ空气比释动能绝对测量相关的壁修正因子，与早期发表的结果偏差小于0.2%。在现行要求下，该辐照器可作为支撑辐射剂量学相关工作的一个备选方案，其紧凑的结构可以扩展剂量率的动态范围，从而在相对较长周期提供服务。

Objective.To experimentally determine beam quality correction factors (kQ) for six cylindrical and four parallel-plate ionization chambers (ICs) in both spread-out Bragg peak (SOBP) and single-layer proton beam configurations.Approach.Water calorimetry was implemented to establish absorbed dose to water (Dw) at 10 g cm-2depth for SOBP and single-layer proton beams. IC measurements were performed under identical geometrical conditions as calorimetric measurements, with the exception of water temperature control in the phantom. Systematic evaluation of ion recombination and polarity effects was achieved through sequential measurements at operational voltages of -400 V, -300 V, -200 V, -150 V, and +400 V in scanned proton beams. All chambers were calibrated against the60CoDwstandard at the National Institute of Metrology to obtainDwcalibration coefficients (ND,w). ThekQvalues were determined through integrated water calorimetry and IC measurements.Main results.The relative standard uncertainties inDwdetermination were quantified as 0.43% for SOBP beams and 0.51% for single-layer beams. The experimentally determinedkQvalues demonstrated agreement with both TRS-398 reference data and published literature within declared measurement uncertainties.Significance.This work presents the first comprehensive determination ofkQfactors for SOBP and single-layer proton beams using water calorimetry. The obtainedkQvalues with reduced uncertainties (0.56%-0.63%) establish metrological traceability for ten clinical IC models, directly enhancing the accuracy of scanned proton beam dosimetry in radiotherapy practice.

Ionization chambers were calibrated regarding absorbed dose to water in MeV X-ray fields of a medical linear accelerator, with nominal maximum energies of 6 MeV and 15 MeV. Whereas, absorbed doses to water at a depth of 10 cm below the water surface were measured using the same ionization chamber (referred to as IC-1) in two different manners (i.e., applying the old beam quality correction factor kQ0 from the old IAEA/TRS-398 protocol, referred to as D1-old10 and using the new one, kQ from the updated protocol, referred to as D1-new10. The calibration factors of IC-1, ND1,D,w, Q were deduced (for beam qualities Q of MeV X-ray fields with maximum energies of 6 MeV and 15 MeV). The identical procedure was applied to two other ionization chambers (IC-i, i=2,3) to obtain absorbed doses to water at a depth of 10 cm (referred to as Di-new10) using the new beam quality correction factor. A comparison between D1-new10 and Di-new10 was conducted to derive the calibration factors of the IC-i, NiD,w,Q. The combined standard uncertainties of NiD,w,Q (i =1,2,3) were estimated within 1.22% and 2.30%, respectively.

External radiotherapy ion chambers were calibrated (in term of absorbed dose to water) in Megavoltage (MV) X-ray reference fields of a Varian Truebeam STx medical linear accelerator (LINAC) with two nominal maximum energies of 6 and 15 MeV. Following results have been obtained:(i) the MV X-ray fluence spectra of the LINAC (in air at the source-to-chamber distance of 100 cm) were simulated using the GATE code. Their averaged energies were consistent with published data;(ii) the absorbed doses to water at the depth of 10 cm under water surface, $D_{10}$ (for different investigated geometries) were measured using a same ion chamber (IC-1) in 02 different manners: (i) applying the old beam quality correction factor (BQCF), $k_{Q,Q_0}$ following the current IAEA/TRS-398 protocol, $D^{1-old}_{10}$ and (ii) applying the new BQCF (soon available in the updated IAEA/TRS-398 protocol), $D^{1-new}_{10}$. The calibration factor of the IC-1, $N^1_{D,w,Q}$ was deduced (in term of $D_{10}$, in the MV X-ray reference field with the beam quality $Q$ with the nominal maximum energy of MV X-ray as 6 and 15 MeV);(iii) the values of $D_{10}$ (for different investigated geometries) were measured using 02 other ion chambers (IC-$i$, $i$ = 2, 3), applying the new BQCF, referred to $D^{i-new}_{10}$. Comparison between the corresponding pair values of $D^{1-new}_{10}$ and $D^{i-new}_{10}$ was conducted to derive the calibration factors of the IC-$i$, $N^i_{D,w,Q}$ (in term of $D_{10}$, in the MV X-ray reference field with the beam quality of $Q$). The combined standard uncertainties of $N^i_{D,w,Q}$ ($i$=1, 2, 3) were estimated within 1.22 and 2.30\%, respectively.

BACKGROUND:The clinical use of flattening filter free (FFF) radiotherapy has significantly increased in recent years due to its effective enhancement of dose rates and reduction of scatter dose. A proposal has been made to adjust the incident electron angle of the accelerator to expand the application of FFF beams in areas such as large planning target volumes (PTVs). However, the inherent softening characteristics and non-uniformity of lateral dose distribution in FFF beams inevitably lead to increased dosimetry errors, especially for ionization chambers widely used in clinical practice, which may result in serious accidents during FFF radiotherapy. PURPOSE:This study constructs a comprehensive Monte Carlo model that encompasses not only conventional FFF beams but also incorporates FFF beams with varying incident electron angles, to investigate dosimetry errors and correction methods in FFF radiotherapy. METHODS:We have innovatively introduced a FFF output correction factor ( k Q F F F , Q W F F ${k}_{{Q}_{FFF},{Q}_{WFF}}$ ) to address dosimetry errors in various ionization chambers under different incident electron angle conditions in FFF beams. The primary variations in k Q F F F , Q W F F ${k}_{{Q}_{FFF},{Q}_{WFF}}$ were analytically determined to result from changes in s w , a i r ${s}_{w,air}$ and the perturbation correction terms of the ionization chamber. RESULTS:Ionization chambers with smaller sensitive volumes typically exhibit reduced dosimetry errors. Our findings indicate that for ionization chambers with sensitive volumes ranging from 0.016  to 0.125 cm3, the dosimetry error under various FFF beam conditions consistently remains below 1.15%. This study provides crucial guidance for selecting appropriate ionization chambers in FFF radiotherapy. CONCLUSION:A correlation was established between the absorbed dose to water in beams with a flattening filter (WFF) and those without (FFF), defined by the FFF output factor ( O F Q F F F , Q W F F $O{F}_{{Q}_{FFF},{Q}_{WFF}}$ ). Using the proposed Monte Carlo model, the O F Q F F F , Q W F F $O{F}_{{Q}_{FFF},{Q}_{WFF}}$ can be derived and applied to theoretically calculate the absorbed dose to water in FFF beams at varying incident electron angles, with a relative standard uncertainty of 0.2. This study provides a valuable reference for clinical dose measurements and crucial support for establishing dose calibration standards in FFF radiotherapy.

为测量小野输出因子,采用国际原子能机构(IAEA)出版的TRS483报告方法,测量了 Elekta Synergy直线加速器标称6 MV、10 MV辐射场的组织模体比(TPR20,10(10)),6 MV、10 MV能量TPR20,10(10)分别为0.683和0.735.通过计算电离室适用的最小半高宽验证了多种电离室可测射野范围,选用的电离室可测最小半高宽在3～4 cm之间.对探测器灵敏体积、测量剂量和剂量率线性、漏电流、重复性和稳定性进行比较,选择了 18种不同型号共21支探测器,在加速器TPR20,10(10)为0.683和0.735的辐射场,源皮距(SSD)分别为90 cm和100 cm的条件下计算1 cm×1 cm,2 cm×2cm,3 cm×3cm,4cm×4cm,5 cm×5cm 和8cm×8cm方野与 10cm×10cm 方野的探测器电荷比值得到未修正的射野输出因子,乘以TRS-483报告的修正系数后得到修正射野输出因子,修正后的射野输出因子与平均值最大差异小于2.5％.结果表明:使用TRS-483报告的修正因子可提高不同探测器测量小野剂量的一致性.

Objective:To study the influence of intensive magnet fields on radiation dose measurement, and to demonstrate the feasibility of measuring magnet field correction factor by a combination of medical linac with variable magnet fields in view of needing for accurate measurement of the doses from reference beam arising in MR image-guided radiotherapy.Methods:A photon radiation field and a variable field with 6 MV nominal high voltage were produced by using conventional medical electron linear accelerator equipped with a pair of electromagnets with magnetic field strength up to 1.5 T. Both PTW30013 and PTW31010 ionization chambers were used to test the responses of ionization chambers under different magnetic field strengths at four orientations in which the angles between ionization chamber axis and magnetic field direction were 0°, 180°, 90° and 270°, respectively. The magnetic factors, kB, M was calculated and compared with the reported values in literature. Results:The response of ionization chamber was proportional to the magnetic field strength before it reached to a peak around 1 T, and then fell down as the magnetic field continued to rise. When the magnetic field was 0.35 T, the magnetic factors of PTW31010 were 0.988 2±0.000 3 and 0.997 4±0.000 4 corresponding to 90° and 0° directions, the discrepancy between 0° scenario and literature was 0.05% ± 0.04%. When the magnetic field reached 1.5 T, the magnetic factor of PTW30013 was 0.958 9±0.000 5 at the situation of 90°, which was 0.60% ± 0.05% different from the literature value.Conclusions:Conventional 6 MV medical accelerator equipped with electromagnet can be used to measure the magnetic field factor of reference dosimetry for MRIgRT.

Several new glass vessels, thermistor probes, and water phantoms have been designed and built at the National Institute of Metrology (China) to upgrade and develop the existing water calorimeter. The increased plane-parallel vessels have shorter thermal stability times and shallower positioning depths (∼1.3 cm) than the previous cylindrical vessels, which makes them suitable for electron beams. The sensitivity of the new probes is 10% greater than the previous ones. In this study, detailed experimental and theoretical investigations of various factors affecting the new water calorimeter are performed. The system uncertainty of the water calorimeter is reduced and the robustness of the determination of the absorbed-dose-to-water D w is improved using a variety of geometric detector vessels and two kinds of high-purity water systems saturated with high-purity gases. This new calorimeter is employed as a primary standard for determining the D w , has achieved a combined standard uncertainty of 0.24% for a 60 Co beam, 0.27% for 6 MV and 10 MV photon beams and 0.30% for a 25 MV photon beam. The beam quality conversion factors k Q of ten cylindrical and three plane-parallel ionization chambers are measured using the new calorimeter to improve the reference dosimetry accuracy of high-energy clinical photon beams.

Laser-induced periodic surface structures (LIPSSs) are a universal phenomenon that can be observed on a variety of materials, including metals, semiconductors, and dielectrics, upon irradiation with ultrafast laser pulses. It has found various potential applications in the fields of optics, biologics, and mechatronics due to its efficient and flexible fabrication process and subwavelength quasi-periodic property. However, LIPSSs face the challenge of uniformity control because the formation of micro-/nanostructures induced by ultrafast laser is a complex process involving multiple interacting factors, including laser energy deposition, phase change, light scattering, and instantaneous local changes of material properties and their feedback mechanisms. Recently, there has been some significant progress regarding the control of LIPSS uniformity. In this work, we review recent experimental and methodological advances on this topic from three aspects: 1) laser-induced modified-LIPSS, 2) feedback mechanism of LIPSS formation, and 3) ultrafast laser pulse shaping. This review can stimulate further investigations into the uniformity control of LIPSSs to support and accelerate the industrial applications of uniform LIPSSs.

Proton radiotherapy has gradually become a precision radiotherapy technique owing to the characteristic of Bragg Peak on the depth-dose distribution. This paper introduces the details of three proton beam reference dosimetry methods as well as the corresponding limitations in clinical proton modalities. Further discussions on the correction terms and improvement methods of measurements combined with Monte Carlo techniques have been proposed. Finally, the state-of-the-art determination on microdosimetry of proton beams has been summarized, which provides a reference for research on proton beam water absorption dose measurement.

Linear energy transfer (LET), a key parameter of relative biological effectiveness (RBE) in proton therapy, is not easy to measure or simulate in a standardized protocol. A multi-centric analysis of dose-averaged LET (LETd) and track-averaged LET (LETt) including individual particle contributions, scoring slab thickness, inhomogeneous medium and clinical beam configurations are investigated using the Monte Carlo code TOPAS. Primary and secondary protons are scored separately within the simulation. It is found that the primary protons are the major contribution to LET at the dose plateau and Bragg Peak (BP) regions, whilst the secondary protons have complete contribution to the tail-LET beyond the BP. The calculated LETt is always lower than LETd, nearly a factor of two lower in the region distal to the BP. Varying the scoring slab thickness shows a negligible influence on LETt, whereas, there is up to 26% discrepancy in LETd at 5-cm depth with thicknesses varying from 0.1 mm to 2 mm for 153.3 MeV proton beam. Moreover, smaller scoring thickness of 0.1 mm results in large fluctuations for tail LETd. LETd distributions with 3-cm thick bone-and lung-slab at the entrance of water phantom against primary and secondary protons' contribution are derived. A small trough appears at the position of inserted inhomogeneous material and large spikes which could account for the changes of cross section in nuclear interactions by secondary protons display on the tail of LETd curve. Regarding the modulated beams, substantial-high LET values are obtained at both-sides along the beam path which should gain more attention when calculating LET in clinical applications. In conclusion, the selection of Monte Carlo simulation schemes indeed affects the calculated LET values, more procedures should be considered when building bridges between LET and radiological effectiveness.

68 Ge- 68 Ga模体主要用于PET/CT图像均匀性的调节以及SUV值的校正。为了实现该模体的国产化,本文采用改性后的环氧树脂为填充基质,通过载体溶液模拟 68 Ge- 68 Ga放射性溶液。将载体溶液、树脂以及固化剂混匀后的物料浇注在高密度聚乙烯（HDPE）外壳中,然后在物料完全固化后制成质地坚硬、色泽通透、无气泡的非放模体。使用电感耦合等离子体发射光谱仪（ICP-OES）检测该模体中Ge、Ga元素浓度,均匀性分析结果显示该模体中Ge、Ga浓度分布差异性不显著,相对标准偏差分别为2.20%、3.65%,与国外同类产品水平相当。表明文中所述工艺可用于 68 Ge- 68 Ga模体的制备。

针对高能电子束剂量学的研究,中国计量科学研究院研制了三维水模体系统并提出精确测量方案.该三维水模体采用全闭环位置反馈系统以确保探测器精准定位,采用人造金刚石和半导体等探测器以确保信号的稳定性和高灵敏度,并具有完善的辐射场监测方案以修正辐射场扰动,环境信息采集系统以实时修正测量信号.完成了9档电子束中心轴百分深度剂量曲线(PDD)的测量和剖面剂量分布(Profile)的扫描,结果表明采用该方案测量电子束射线质时不同探测器一致性好于1mm,该三维水模体达到了设计目标.

重离子束水吸收剂量是开展重离子束治疗最基本的物理量.在开展重离子束水吸收剂量的量值复现研究前,需用间接测量的方法开展相关工作以熟悉实验条件.本文用传统电离法开展了能量400 M eV/u、具有6 cm展宽Bragg峰的碳离子束的水吸收剂量测量研究,并评价了重离子束条件下的相关电离室的极化、离子复合修正因子.在电离室的极化和离子复合修正项方面,重离子束水吸收剂量测量的相关不确定度分量显著大于60 Coγ辐射水吸收剂量的相关值.用不同电离室测量重离子束水吸收剂量的结果在不确定度允许的范围内符合.以电离室测量为基础,开展更深入的包括量热法绝对测量在内的辐射剂量学研究,对进一步优化重离子束水吸收剂量测量的不确定度至关重要.

针对水等效材料校准医用加速器中存在的问题,通过对比法测量水体模和3种水等效材料校准医用加速器的剂量学差异,分别给出PTW 30013和IBA FC65-G两种类型探测器在校准深度为5cm和10cm的修正因子.针对加速器日稳定性校准的必要性,通过近7个月的日稳定性测量结果,给出加速器漂移量和引起漂移的可能原因;针对水等效材料在相对测量中对水的等效性,通过测量12个辐射野的输出因子,得出水等效材料在相对测量中与水一致.最后给出水等效材料在高能X射线下水吸收剂量校准时的建议和注意事项.