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Here, we highlight the potential translational benefits of delivering FLASH radiotherapy using ultra-high dose rates (>100 Gy·s−1). Compared with conventional dose-rate (CONV; 0.07–0.1 Gy·s−1) modalities, we showed that FLASH did not cause radiation-induced deficits in learning and memory in mice. Moreover, 6 months after exposure, CONV caused permanent alterations in neurocognitive end points, whereas FLASH did not induce behaviors characteristic of anxiety and depression and did not impair extinction memory. Mechanistic investigations showed that increasing the oxygen tension in the brain through carbogen breathing reversed the neuroprotective effects of FLASH, while radiochemical studies confirmed that FLASH produced lower levels of the toxic reactive oxygen species hydrogen peroxide. In addition, FLASH did not induce neuroinflammation, a process described as oxidative stress-dependent, and was also associated with a marked preservation of neuronal morphology and dendritic spine density. The remarkable normal tissue sparing afforded by FLASH may someday provide heretofore unrealized opportunities for dose escalation to the tumor bed, capabilities that promise to hasten the translation of this groundbreaking irradiation modality into clinical practice.

Background Deep learning (DL)‐based auto‐planning has emerged as a powerful tool for optimizing radiotherapy treatment plans, reducing variability, and improving efficiency. However, current approaches often rely on predefined beam angles and arc spans, which may not be optimal for individual patients. Automated beam angle optimization can further enhance plan quality, particularly in early‐stage breast cancer radiotherapy, where precise beam configurations are crucial for balancing target coverage and organ‐at‐risk (OAR) sparing. Purpose This study presents an automated segment reduction‐based beam angle optimization technique to improve DL‐based auto‐planning for radiotherapy in early‐stage breast cancer. The method optimizes arc spans for volumetric‐modulated‐arc‐therapy (VMAT) and beam configurations for intensity‐modulated‐radiation‐therapy (IMRT) to improve dose distribution while reducing OAR exposure. Methods Plans using three different irradiation strategies—partial arc VMAT (PA‐VMAT), complex IMRT (C‐IMRT), and simple IMRT (S‐IMRT)—were generated using two full arcs for dose mimicking of the predicted dose, followed by the segment reduction performed using a stepwise PAMU (Product of segment Area and Monitor Units) thresholding approach to determine optimal arc spans and beam angles. These strategies were compared against the standard continuous partial arc VMAT (CPA‐VMAT) technique currently used in our clinical practice. Twenty left‐sided breast cancer patients treated under deep inspiration breath‐hold (DIBH) conditions were included for evaluation. Plan quality was assessed using dosimetric criteria, conformity indices, dose mimicking index (DMI), and statistical comparisons. Results PA‐VMAT exhibited superior OAR sparing and the best overall dose mimicking performance, reducing the heart, left lung, and right lung mean doses by 27%, 11%, and 50%, respectively, compared to CPA‐VMAT. C‐IMRT provided the best target coverage but required higher monitor units, while S‐IMRT showed suboptimal dose homogeneity. The automated segment reduction method significantly improved plan efficiency, optimizing beam angles without requiring manual intervention. Conclusion This study demonstrates the feasibility of an automated segment reduction‐based optimization technique for DL auto‐planning in early‐stage breast cancer. PA‐VMAT emerged as the preferred strategy, balancing plan quality, delivery efficiency, and OAR sparing. The proposed approach enhances treatment planning flexibility and will be incorporated into future clinical practice.

Background Treatment delivery safety and accuracy are essential to control the disease and protect healthy tissues in radiation therapy. For usual treatment, a phantom‐based patient specific quality assurance (PSQA) is performed to verify the delivery prior to the treatment. The emergence of adaptive radiation therapy (ART) adds new complexities to PSQA. In fact, organ at risks and target volume re‐contouring as well as plan re‐optimization and treatment delivery are performed with the patient immobilized on the treatment couch, making phantom‐based pretreatment PSQA impractical. In this case, phantomless PSQA tools based on multileaf collimator (MLC) leaf open times (LOTs) verifications provide alternative approaches for the Radixact® treatment units. However, their validity is compromised by the lack of independent and reliable methods for calculating the LOT performed by the MLC during deliveries. Purpose To provide independent and reliable methods of LOT calculation for the Radixact® treatment units. Methods Two methods for calculating the LOTs performed by the MLC during deliveries have been implemented. The first method uses the signal recorded by the build‐in detector and the second method uses the signal recorded by optical sensors mounted on the MLC. To calibrate the methods to the ground truth, in‐phantom ionization chamber LOT measurements have been conducted on a Radixact® treatment unit. The methods were validated by comparing LOT calculations with in‐phantom ionization chamber LOT measurements performed on two Radixact® treatment units. Results The study shows a good agreement between the two LOT calculation methods and the in‐phantom ionization chamber measurements. There are no notable differences between the two methods and the same results were observed on the different treatment units. Conclusions The two implemented methods have the potential to be part of a PSQA solution for ART in tomotherapy.

Purpose To commission and evaluate the Monte Carlo (MC) dose calculation algorithm for the CyberKnife equipped with a multileaf collimator (MLC). Methods We created a MC model for the MLC using an integrated module of the CyberKnife treatment planning software (TPS). Two parameters could be optimized: the maximum energy and the source full width at half‐maximum (FWHM). The optimization was performed by minimizing the differences between the measured and the MC calculated tissue phantom ratios and profiles. MLC plans were calculated in the TPS with the MC algorithm and irradiated on different phantoms. The dose was measured using an A1SL ionization chamber and EBT3 Gafchromic films, and then compared to the TPS dose to obtain dose differences (ΔD). Finally, patient‐specific quality assurances (QA) were performed with global gamma index criteria of 3%/1 mm. Results The maximum energy and source FWHM showing the best agreement with measurements were 6.4 MeV and 1.8 mm. The output factors calculated with these parameters gave an agreement within ±1% with measurements. The ΔD showed that MC model systematically underestimated the dose with an average of −1.5% over all configurations tested. For depths deeper than 12 cm, the ΔD increased, up to −3.0% (maximum at 15.5 cm depth). Conclusions The MC model for MLC of CyberKnife is clinically acceptable but underestimates the delivered dose by an average of −1.5%. Therefore, we recommend using the MC algorithm with the MLC only in heterogeneous regions and for shallow‐seated tumors.

Background RaySearch (AB, Stockholm) has released a module for CyberKnife (CK) planning within its RayStation (RS) treatment planning system (TPS). Purpose To create and validate beam models of fixed, Iris, and multileaf collimators (MLC) of the CK M6 for Monte Carlo (MC) and collapsed cone (CC) algorithms in the RS TPS. Methods Measurements needed for the creation of the beam models were performed in a water tank with a stereotactic PTW 60018 diode. Both CC and MC models were optimized in RS by minimizing the differences between the measured and computed profiles and percentage depth doses. The models were then validated by comparing dose from the plans created in RS with both single and multiple beams in different phantom conditions with the corresponding measured dose. Irregular field shapes and off‐axis beams were also tested for the MLC. Validation measurements were performed using an A1SL ionization chamber, EBT3 Gafchromic films, and a PTW 1000 SRS detector. Finally, patient‐specific QAs with gamma criteria of 3%/1 mm were performed for each model. Results The models were created in a straightforward manner with efficient tools available in RS. The differences between computed and measured doses were within ±1% for most of the configurations tested and reached a maximum of 3.2% for measurements at a depth of 19.5‐cm. With respect to all collimators and algorithms, the maximum averaged dose difference was 0.8% when considering absolute dose measurements on the central axis. The patient‐specific QAs led to a mean result of 98% of points fulfilling gamma criteria. Conclusions We created both CC and MC models for fixed, Iris, and MLC collimators in RS. The dose differences for all collimators and algorithms were within ±1%, except for depths larger than 9 cm. This allowed us to validate both models for clinical use.

IntroductionStereotactic radiosurgery (SRS) is increasingly used as a minimally invasive alternative in many neurosurgical conditions, including benign and malignant tumors, vascular malformations, and functional procedures. As for any surgical procedure, strict safety guidelines and checklists are necessary to avoid errors and the inherent unnecessary complications. With regard to the former, other groups have already reported human and/or technical errors. We describe our safety checklist for Gamma Knife radiosurgical procedures.MethodsWe describe our checklist protocol after an experience gained over 1500 radiosurgical procedures, using Gamma Knife radiosurgery, performed over a period of 8 years, while employing the same list of items. Minor implementation has been performed over time to address some safety issues that could be improved.ResultsTwo types of checklist are displayed. One is related to the indications when a specific tissue volume is irradiated, including tumors or vascular disorders. The second corresponds to functional disorders, such as when the dose is prescribed to one specific point. Using these checklists, no human error had been reported during the past 8 years of practice in our institution.ConclusionThe use of a safety checklist for SRS procedures promotes a zero-tolerance attitude for errors. This can lower the complications and is of major help in promoting multidisciplinary cooperation. We highly recommend the use of such tool, especially in the context of the increased use of SRS in the neurosurgical field.

Ventricular tachycardia (VT) caused by myocardial scaring bears a significant risk of mortality and morbidity. Antiarrhythmic drug therapy (AAD) and catheter ablation remain the cornerstone of VT management, but both treatments have limited efficacy and potential adverse effects. Stereotactic body radiotherapy (SBRT) is routinely used in oncology to treat non-invasively solid tumors with high precision and efficacy. Recently, this technology has been evaluated for the treatment of VT. This review presents the basic underlying principles, proof of concept, and main results of trials and case series that used SBRT for the treatment of VT refractory to AAD and catheter ablation.

Laser-plasma accelerators can produce ultra-short electron bunches in the femtosecond to picosecond duration range, resulting in very high peak dose rates in comparison with clinical accelerators. This unique characteristic motivates their possible application to radiation biology studies to elucidate the effect of high peak dose rates and peculiar temporal structures on the biological response of living cells, which might improve the differential response between tumour and healthy tissues. Electron beams driven by kHz laser systems are an attractive option among laser-plasma accelerators since the high repetition rate can boost the mean dose rate and improve the stability of the delivered dose in comparison with J-class laser accelerators running at few Hz. In this work, we present the dosimetric characterisation of a kHz, low energy laser-driven electron source and preliminary results on in-vitro irradiation of cancer cells. A shot-to-shot dosimetry protocol enabled monitoring of the beam stability and the irradiation conditions for each cell sample. Results of survival assays on HCT116 colorectal cancer cells are in good agreement with previous findings reported in the literature and validate the robustness of the dosimetry and irradiation protocol.

Background and purpose Intensity-modulated radiotherapy (IMRT) credentialing for a EORTC study was performed using an anthropomorphic head phantom from the Radiological Physics Center (RPC; RPC PH ). Institutions were retrospectively requested to irradiate their institutional phantom (INST PH ) using the same treatment plan in the framework of a Virtual Phantom Project (VPP) for IMRT credentialing. Materials and methods CT data set of the institutional phantom and measured 2D dose matrices were requested from centers and sent to a dedicated secure EORTC uploader. Data from the RPC PH and INST PH were thereafter centrally analyzed and inter-compared by the QA team using commercially available software (RIT; ver.5.2; Colorado Springs, USA). Results Eighteen institutions participated to the VPP. The measurements of 6 (33%) institutions could not be analyzed centrally. All other centers passed both the VPP and the RPC ±7%/4 mm credentialing criteria. At the 5%/5 mm gamma criteria (90% of pixels passing), 11(92%) as compared to 12 (100%) centers pass the credentialing process with RPC PH and INST PH (p = 0.29), respectively. The corresponding pass rate for the 3%/3 mm gamma criteria (90% of pixels passing) was 2 (17%) and 9 (75%; p = 0.01), respectively. Conclusions IMRT dosimetry gamma evaluations in a single plane for a H&N prospective trial using the INST PH measurements showed agreement at the gamma index criteria of ±5%/5 mm (90% of pixels passing) for a small number of VPP measurements. Using more stringent, criteria, the RPC PH and INST PH comparison showed disagreement. More data is warranted and urgently required within the framework of prospective studies.

Purpose To implement and validate a beam current transformer as a passive monitoring device on a pulsed electron beam medical linear accelerator (LINAC) for ultra‐high dose rate (UHDR) irradiations in the operational range of at least 3 Gy to improve dosimetric procedures currently in use for FLASH radiotherapy (FLASH‐RT) studies. Methods Two beam current transformers (BCTs) were placed at the exit of a medical LINAC capable of UHDR irradiations. The BCTs were validated as monitoring devices by verifying beam parameters consistency between nominal values and measured values, determining the relationship between the charge measured and the absorbed dose, and checking the short‐ and long‐term stability of the charge‐absorbed dose ratio. Results The beam parameters measured by the BCTs coincide with the nominal values. The charge‐dose relationship was found to be linear and independent of pulse width and frequency. Short‐ and long‐term stabilities were measured to be within acceptable limits. Conclusions The BCTs were implemented and validated on a pulsed electron beam medical LINAC, thus improving current dosimetric procedures and allowing for a more complete analysis of beam characteristics. BCTs were shown to be a valid method for beam monitoring for UHDR (and therefore FLASH) experiments.