BACKGROUND:Many preclinical studies involving novel particle radiotherapy techniques have been conducted without precise image guidance due to the lack of an image-guided small animal radiotherapy research platform for them, such as ultra-high dose rate radiation (UHDR), mini-beam, and grid therapy. This limitation restricts the complexity of research questions that can be effectively addressed. PURPOSE:We developed a workflow to utilize 3D imaging on a Small Animal Radiation Research Platform (SARRP) for precise targeting of internal regions in small animals with a separated treatment beam. METHODS:Our approach mimics the workflow of patient treatment to decouple the imaging process from the radiation system. The SARRP cone-beam CT system was used to image and center the target. Alignment markers were then added to the top surface of the animal platform using the SARRP's well-calibrated laser system, which was consequently transferred and aligned to a collimator in a clinical treatment room. Validation of the method was performed using BB targets within both a mouse phantom and a euthanized rat. The distance between the center of the radiation field and the BB was measured to determine the setup error for the entire procedure. The use of a collimator reduces the impact of setup uncertainty in the treatment room. RESULTS:Our approach achieved a setup accuracy of approximately 0.5 mm, ensuring the target was consistently positioned at the center of the collimated radiation field center after transferring from the SARRP system. This is comparable to the isocentricity of the SARRP itself (∼±0.5 mm). CONCLUSIONS:By decoupling the imaging and radiation systems while maintaining sub-millimeter setup accuracy, this workflow introduces flexibility for conducting high-precision, image-guided preclinical studies across different radiation modalities and techniques, for example, protons, electrons, neutrons, UHDR (FLASH), Small-Field-RT, etc. The workflow uses simple equipment and can be easily implemented by other centers.

BACKGROUND:HyperArc is an effective technique for treating multiple small brain metastases using high-definition, precise radiation. However, the small size of individual lesions makes treatment vulnerable to inherent inaccuracies from beam-limiting devices such as multi-leaf collimators (MLCs), as well as patient setup errors. These uncertainties must be thoroughly evaluated prior to administering a single-fraction, high-dose HyperArc treatment to ensure optimal clinical outcomes. PURPOSE:To comprehensively evaluate the robustness of HyperArc VMAT plans for multiple brain metastases (MBT) against (i) high-definition MLC leaf positional errors and (ii) patient rotational and translational setup variations. METHODS AND MATERIALS:A retrospective analysis of 34 MBT plans from 30 patients with 123 lesions treated using HyperArc VMAT plans was performed. Prescription doses (21-24 Gy) targeted PTVs (GTV + 1 mm), with each plan addressing 2-7 brain metastases (< 2 cm). D100% for GTV and V12Gy for normal brain were re-evaluated under simulated (i) 20 MLC positional errors (0.2-1 mm) and (ii) 26 patient rotational (Yaw/Pitch/Roll by 1°) and 26 translational errors (SI/LR/AP by 1 mm). The impact of target distance to isocenter (DTI), target volume, and plan modulation factor on plan robustness was assessed. Replans with larger PTV margins, 1.5 and 2 mm, were investigated for a proper PTV margin for the worst-case scenarios. RESULTS:Per our cohort, D100% of GTV is highly sensitive to both MLC and patient errors. Their dosimetric effects follow linear regressions: 1 mm shift reduces GTV D100% by 8%; 1 mm symmetric MLC openings increase GTV D100% by > 22%, while 1 mm symmetric closings decrease it by > 25.8% per 1 mm; Patient rotation/translation impacts GTV D100% by 0.04-1.28% per 1° or ∼7% per 1 mm. Normal brain V12Gy is only sensitive to MLC errors, increasing slightly with shifts and significantly with symmetric openings (+5cc/1 mm), but decreasing with closings (-2.77cc/1 mm). DTI shows minimal correlation with MLC shifts but is affected by patient setup uncertainties. Large targets amplify dose sensitivity to symmetric MLC errors, whereas plan modulation factor shows no significant impact. A minimum 1 mm margin is required to absorb these uncertainties, with 2 mm margins recommended in the worst cases to ensure treatment accuracy. CONCLUSIONS:Overall, the target dose and V12Gy for HyperArc VMAT plans are more significantly affected by symmetric MLC opening and closing errors than by patient rotational setup errors. The pronounced effects of these errors highlight the importance of rigorous plan robustness verification, accounting for target size, margins, and DTI.

BACKGROUND:The recent rediscovery of the FLASH effect, a normal tissue sparing phenomenon observed in ultra-high dose rate (UHDR) irradiations, has instigated a surge of research endeavors aiming to close the gap between experimental observation and clinical treatment. However, the dependences of the FLASH effect and its underpinning mechanisms on beam parameters are not well known, and large-scale in vivo studies using murine models of human cancer are needed for these investigations. PURPOSE:To commission a high-throughput, variable dose rate platform providing uniform electron fields (≥15 cm diameter) at conventional (CONV) and UHDRs for in vivo investigations of the FLASH effect and its dependences on pulsed electron beam parameters. METHODS:A murine whole-thoracic lung irradiation (WTLI) platform was constructed using a 1.3 cm thick Cerrobend collimator forming a 15 × 1.6 cm2 slit. Control of dose and dose rate were realized by adjusting the number of monitor units and couch vertical position, respectively. Achievable doses and dose rates were investigated using Gafchromic EBT-XD film at 1 cm depth in solid water and lung-density phantoms. Percent depth dose (PDD) and dose profiles at CONV and various UHDRs were also measured at depths from 0 to 2 cm. A radiation survey was performed to assess radioactivation of the Cerrobend collimator by the UHDR electron beam in comparison to a precision-machined copper alternative. RESULTS:This platform allows for the simultaneous thoracic irradiation of at least three mice. A linear relationship between dose and number of monitor units at a given UHDR was established to guide the selection of dose, and an inverse-square relationship between dose rate and source distance was established to guide the selection of dose rate between 20 and 120 Gy·s-1 . At depths of 0.5 to 1.5 cm, the depth range relevant to murine lung irradiation, measured PDDs varied within ±1.5%. Similar lateral dose profiles were observed at CONV and UHDRs with the dose penumbrae widening from 0.3 mm at 0 cm depth to 5.1 mm at 2.0 cm. The presence of lung-density plastic slabs had minimal effect on dose distributions as compared to measurements made with only solid water slabs. Instantaneous dose rate measurements of the activated copper collimator were up to two orders of magnitude higher than that of the Cerrobend collimator. CONCLUSIONS:A high-throughput, variable dose rate platform has been developed and commissioned for murine WTLI electron FLASH radiotherapy. The wide field of our UHDR-enabled linac allows for the simultaneous WTLI of at least three mice, and for the average dose rate to be modified by changing the source distance, without affecting dose distribution. The platform exhibits uniform, and comparable dose distributions at CONV and UHDRs up to 120 Gy·s-1 , owing to matched and flattened 16 MeV CONV and UHDR electron beams. Considering radioactivation and exposure to staff, Cerrobend collimators are recommended above copper alternatives for electron FLASH research. This platform enables high-throughput animal irradiation, which is preferred for experiments using a large number of animals, which are required to effectively determine UHDR treatment efficacies.

PURPOSE:This study aims to illustrate how a script-based automated tool can efficiently verify documentation for LDR prostate brachytherapy. METHODS AND MATERIALS:An in-house Python-scripts-based tool was developed to automatically verify the specific checklists, aligned with our institutional practice guidelines for prostate seed implants (PSI). The scripts, compatible with our radiation oncology information system, could be executed with an optional web-based middleware to access and evaluate Aria documents. Optimized based on data from the previous 400 patients, the automated tool was applied to a random cohort of 50 LDR patients. It evaluated the adequacy of specific EMR documents by performing checks for data completeness, consistency, and allowable value range. We analyzed the efficiency of using this tool against conventional manual checks in two LDR processes: seed ordering and monthly audits for our PSI programs. RESULTS:The automated tool effectively performed chart checks on the involved PSI documents. Human errors, such as typos and inconsistent information, were identified in 7 out of 50 patients during the seed ordering process and in 2 out of 50 patients during the monthly audit. Meanwhile, this automation reduced the majority of manual chart-checking time by an average of 5 and 10 min per patient for these processes, respectively. The anticipated efficiency gains will continue to accrue as more check items are digitalized and assessable to the scripts. CONCLUSIONS:The implementation of an automated tool tailored for LDR prostate brachytherapy has demonstrated its efficiency benefits. Such an approach can help other clinics substantially enhance routine chart checks, periodic audits, and other applications in similar clinical settings.

Medical physicists play an important role in the delivery of radiotherapy. Compared with China′s mainland, Hong Kong has established a more mature training mode and a more complete management system for medical physics talents. In this article, the authors introduced the current state of medical physics talent training, as well as the recruitment, certification and promotion of medical physicist in Hong Kong by querying the official websites of medical physics organizations, reviewing related literature and interviewing senior medical physicists in Hong Kong. The authors also analyzed the shortcomings in the construction of medical physics talent system in China′s mainland and made valuable suggestions.

PURPOSE While FLASH-RT is a promising novel technique which has the potential to achieve a better therapeutic ratio between tumor control and normal tissue complications, the ultra high pulsed dose rates (UHPDR) mean that experimental dosimetry is very challenging. There is a need for real-time dosimeters in the development and implementation of FLASH-RT. In this work, we characterize a novel plastic scintillator capable of temporal resolution short enough (2.5 ms) to resolve individual pulses. METHODS We characterized a novel plastic dosimeter for use in a linac converted to deliver 16 MeV electrons at 100 Gy/s UHPDR average dose rates. The linearity and reproducibility was established by comparing relative measurements with a pinpoint ionization chamber placed at 10 cm water-equivalent depth where the electrometer is not saturated by the high dose per pulse. The accuracy was established by comparing the plastic scintillator dose measurements with EBT-XD Gafchromic radiochromic films, the current reference dosimeter for UHPDR. Finally, the plastic scintillator was compared against EBT-XD films for on-line dosimetry of two in-vitro experiments performed at UHPDR. RESULTS Relative ion chamber measurements were linear with plastic scintillator response within ≤1% over 4-20 Gy and pulse frequencies (18-180 Hz). When characterized under reference conditions with NIST-traceability, the plastic scintillator maintained its dose response under UHPDR conditions and agreed with EBT-XD film dose measurements within 4% under reference conditions and 6% for experimental on-line dosimetry. CONCLUSION The plastic scintillator shows a linear and reproducible response, and is able to accurately measure the radiation absorbed dose delivered by 16 MeV electrons at UHPDR. The dose is measured accurately in real-time with a greater level of precision than that achieved with radiochromic film. This article is protected by copyright. All rights reserved.

美国放射治疗师培训项目成立较早，培养模式、资格认证和继续教育较为完善。查阅美国劳工部、放射技师注册资格认证协会、放射技师协会、放射技术教育联合审查委员会网站以及中国内地外相关文献资料，分析了美国放射治疗师的培养模式、资格认证、工作内容、继续教育、就业情况，为建立适合中国内地国情的放射治疗师专业人才培养的新模式提供一些借鉴和启示。

Theoretical studies indicated that C_{60} exposed to linearly polarized intense infrared pulses undergoes periodic cage structural distortions with typical periods around 100 fs (1  fs=10^{-15}  s). Here, we use the laser-driven self-imaging electron diffraction technique, previously developed for atoms and small molecules, to measure laser-induced deformation of C_{60} in an intense 3.6  μm laser field. A prolate molecular elongation along the laser polarization axis is determined to be (6.1±1.4)% via both angular- and energy-resolved measurements of electrons that are released, driven back, and diffracted from the molecule within the same laser field. The observed deformation is confirmed by density functional theory simulations of nuclear dynamics on time-dependent adiabatic states and indicates a nonadiabatic excitation of the h_{g}(1) prolate-oblate mode. The results demonstrate the applicability of laser-driven electron diffraction methods for studying macromolecular structural dynamics in four dimensions with atomic time and spatial resolutions.

The low-energy photoelectron spectra from strong-field ionization of C-60 fullerenes and noble gases (xenon and krypton) with 3 mu m laser pulses are measured and compared. It is found that the low-energy structure (LES), a universal spikelike feature in the strong-field limit of atoms and small molecules, is significantly suppressed in the C-60 photoelectron distribution. We propose that the large polarizability of the C-60 core disrupts the corresponding electron trajectories. In particular, the induced dipole force repels the electron, which opposes the focusing and bunching due to the Coulomb potential that is responsible for the LES, thus leading to its reduction.

Ionization of atoms in intense laser fields is experimentally studied to evaluate the validity of the widely used ionization rate formulas from the ADK and PPT models at different laser wavelengths, intensities, polarizations and types of targets. It is found that the PPT model including the Coulomb correction agrees well with all the experimental data in the study, whereas the ADK formula can only be applied in some limited regimes.

High-harmonic generation from gases produces attosecond bursts and enables high-harmonic spectroscopy to explore electron dynamics in atoms and molecules. Recently, high-harmonic generation from solids has been reported, resulting in novel phenomena and unique control of the emission, absent in gas-phase media. Here we investigate high harmonics from semiconductors with controllable induced photo-carrier densities, as well as the driving wavelengths. We demonstrate that the dominant generation mechanism can be identified by monitoring the variation of the harmonic spectra with the carrier density. Moreover, the harmonic spectral dependence on the driving wavelength is reported and a different dependence from the well-known one in gas-phase media is observed. Our study provides distinct control of the harmonic process from semiconductors, sheds light on the underlying mechanism and helps optimize the harmonic properties for future solid-state attosecond light sources.