Effects of Kinematic Hardening of Mucus Polymers in an Airway Closure Model.

The formation of a liquid plug inside a human airway, known as airway closure, is computationally studied by considering the elastoviscoplastic (EVP) properties of the pulmonary mucus covering the airway walls for a range of liquid film thicknesses and Laplace numbers. The airway is modeled as a rigid tube lined with a single layer of an EVP liquid. The Saramito-Herschel-Bulkley (Saramito-HB) model is coupled with an Isotropic Kinematic Hardening model (Saramito-HB-IKH) to allow energy dissipation at low strain rates. The rheological model is fitted to the experimental data under healthy and cystic fibrosis (CF) conditions. Yielded/unyielded regions and stresses on the airway wall are examined throughout the closure process. Yielding is found to begin near the closure in the Saramito-HB model, whereas it occurs noticeably earlier in the Saramito-HB-IKH model. The kinematic hardening is seen to have a notable effect on the closure time, especially for the CF case, with the effect being more pronounced at low Laplace numbers and initial film thicknesses. Finally, standalone effects of rheological properties on wall stresses are examined considering their physiological values as baseline.

Comprehensive dosimetric characterization of novel silicon carbide detectors with UHDR electron beams for FLASH radiotherapy.

BACKGROUND: The extremely fast delivery of doses with ultra high dose rate (UHDR) beams necessitates the investigation of novel approaches for real-time dosimetry and beam monitoring. This aspect is fundamental in the perspective of the clinical application of FLASH radiotherapy (FLASH-RT), as conventional dosimeters tend to saturate at such extreme dose rates. PURPOSE: This study aims to experimentally characterize newly developed silicon carbide (SiC) detectors of various active volumes at UHDRs and systematically assesses their response to establish their suitability for dosimetry in FLASH-RT. METHODS: SiC PiN junction detectors, recently realized and provided by STLab company, with different active areas (ranging from 4.5 to 10 mm2) and thicknesses (10-20 µm), were irradiated using 9 MeV UHDR pulsed electron beams accelerated by the ElectronFLASH linac at the Centro Pisano for FLASH Radiotherapy (CPFR). The linearity of the SiC response as a function of the delivered dose per pulse (DPP), which in turn corresponds to a specific instantaneous dose rate, was studied under various experimental conditions by measuring the produced charge within the SiC active layer with an electrometer. Due to the extremely high peak currents, an external customized electronic RC circuit was built and used in conjunction with the electrometer to avoid saturation. RESULTS: The study revealed a linear response for the different SiC detectors employed up to 21 Gy/pulse for SiC detectors with 4.5 mm2/10 µm active area and thickness. These values correspond to a maximum instantaneous dose rate of 5.5 MGy/s and are indicative of the maximum achievable monitored DPP and instantaneous dose rate of the linac used during the measurements. CONCLUSIONS: The results clearly demonstrate that the developed devices exhibit a dose-rate independent response even under extreme instantaneous dose rates and dose per pulse values. A systematic study of the SiC response was also performed as a function of the applied voltage bias, demonstrating the reliability of these dosimeters with UHDR also without any applied voltage. This demonstrates the great potential of SiC detectors for accurate dosimetry in the context of FLASH-RT.

Quantitative Contrast Sensitivity Function and the Effect of Aging in Healthy Adult Eyes: A Normative Database.

BACKGROUND AND OBJECTIVE: We sought to establish normative quantitative contrast sensitivity function (qCSF) values in healthy adult eyes and investigate the effect of age on qCSF. PATIENTS AND METHODS: Healthy eyes underwent qCSF testing (adaptive sensory technology) and Snellen's visual acuity (VA). Descriptive statistics and mixed-effects multivariable linear regressions were evaluated. RESULTS: A total of 334 eyes (290 patients) with median age 61 years (range 21 to 88) had qCSF values as follows: area under the log contrast sensitivity function curve: 1.18; contrast acuity: 1.32; contrast sensitivity (CS) at 1 cycle per degree (cpd): 1.32; CS at 1.5 cpd: 1.37; CS at 3 cpd: 1.38; CS at 6 cpd: 1.20; CS at 12 cpd: 0.69; CS at 18 cpd: 0.22. Linear reductions in qCSF values per decade of age ranged from -0.02 to -0.07 vs 0.01 for visual acuity (VA). Age had a greater effect on the majority of qCSF values than VA (beta standardized regression coefficient ranged from -0.309 to -0.141 for qCSF values vs 0.177 for VA). CONCLUSIONS: We herein establish a normative database for qCSF and quantify the effect of age on qCSF values, adding evidence towards the validation of qCSF as a clinical endpoint. [Ophthalmic Surg Lasers Imaging Retina 2024;55:212-219.].

The Epidemiology of Anal Human Papillomavirus (HPV) in HIV-Positive and HIV-Negative Women and Men: A Ten-Year Retrospective Observational Study in Rome (Italy).

Human papillomaviruses (HPVs) commonly infect the anogenital mucosa; most infections are transient, but a fraction of those caused by high-risk (HR) types persist and may lead to anogenital cancer. The epidemiology of HPV genotypes in anal infections in groups at different risk for anal cancer has not been well described in Italy. This retrospective study reports the results of HPV DNA testing and complete genotyping performed on anal swabs from 691 female and male patients attending proctology clinics in Rome during 2012-2021; one-third had repeated testing. Cumulative HPV positivity in 1212 anal swabs was approximately 60%, was not age related, and showed an increasing trend over the study period. HPV rates differed significantly by sex and HIV status: HIV-negative women had the lowest (43.6%) and HIV-positive men the highest (83.5%) HPV prevalence. HIV-positive men had more oncogenic HPV genotypes detected, more multiple infections, and the highest frequency of persistent infections. Two-thirds of all infections were vaccine-preventable. This study found that anal HPV infection rates are still elevated and even increasing in groups at low and high risk of developing anal cancer. Prevention programs need to be improved to reduce rates of anal infection in young women and men.

Lesion area progression in eyes with neovascular age-related macular degeneration treated using a proactive or a reactive regimen.

BACKGROUND: To compare the change in lesion area over 4 years of follow-up in eyes with neovascular age-related macular degeneration (nAMD) treated with anti-vascular endothelial growth factor (VEGF) agents using either a proactive or a reactive regimen in routine clinical practice. METHODS: This was a multicentre, retrospective comparative study. Totally, 202 treatment-naïve nAMD eyes (183 patients) received anti-VEGF therapy according to a proactive (n = 105) or reactive (n = 97) regimen. Eyes were included if they had received anti-VEGF injections for a period of at least 4 years and had baseline fluorescein angiography and annual optical coherence tomography (OCT) imaging. Two masked graders independently delineated the lesion's margins from serial OCT images and growth rates were calculated. RESULTS: At baseline, the mean [SD] lesion area was 7.24 [5.6] mm2 in the proactive group and 6.33 [4.8] mm2 in the reactive group respectively (p = 0.22). After four years of treatment, the mean [SD] lesion area in the proactive group was 5.16 [4.5] mm2 showing a significant reduction compared to the baseline (p < 0.001). By contrast, the mean [SD] lesion area kept expanding in the reactive group during the follow-up and was 9.24 [6.0] mm2 at four years (p < 0.001). The lesion area at 4 years was significantly influenced by treatment regimen, baseline lesion area, and proportion of visits with active lesions. CONCLUSIONS: Eyes treated using a reactive strategy had an increased lesion area and worse visual outcomes at 4 years. By contrast, the proactive regimen was associated with fewer recurrences of active disease, shrinkage of the lesion area, and better vision at four years.

Assessment and tailored physical rehabilitation approaches in persons with cerebellar impairments targeting mobility and walking according to the International Classification of Functioning: a systematic review of case-reports and case-series.

PURPOSE: Cerebellar impairment (CI) manifests from different etiologies resulting in a heterogenic clinical presentation affecting walking and mobility. Case-reports were reviewed to provide an analytical clinical picture of persons with CI (PwCI) to differentiate cerebellar and non-cerebellar impairments and to identify interventions and assessments used to quantify impact on walking and mobility according to the International Classification of Functioning, Disability and Health (ICF). MATERIALS AND METHODS: Literature was searched in PubMed, Web Of Science and Scopus. Case-reports conducting physical rehabilitation and reporting at least one outcome measure of ataxia, gait pattern, walking or mobility were included. RESULTS: 28 articles with a total of 38 different patients were included. Etiologies were clustered to: spinocerebellar degenerations, traumatic brain injuries, cerebellar tumors, stroke and miscellaneous. The interventions applied were activity-based, including gait and balance training. Participation based activities such as tai chi, climbing and dance-based therapy had positive outcomes on mobility. Outcomes on body function such as ataxia and gait pattern were only reported in 22% of the patients. CONCLUSIONS: A comprehensive test battery to encompass the key features of a PwCI on different levels of the ICF is needed to manage heterogeneity. Measures on body function level should be included in interventions.

This review reports on 38 cerebellar cases from 14 different aetiologies.Distinguishing cerebellar and non-cerebellar symptoms and categorising patients within the three cerebellar syndromes can assist with heterogeneity.Reporting of assessment on the body function level of ICF in terms of ataxia and gait pattern was only present in a minority of reports and thus increased reporting is encouraged.Multimodal and patient-tailored strategies are promising for targeting walking and mobility in persons with cerebellar impairment.

Salvage Surgery After First-Line Alectinib for Locally-Advanced/Metastatic ALK-Rearranged NSCLC: Pathological Response and Perioperative Results.

BACKGROUND: The role of salvage surgery after tyrosine kinase inhibitors in advanced oncogene-addicted non-small cell lung cancer is largely unexplored. PATIENTS: We aimed to describe the pathological features and surgical early-outcomes of Anaplastic Lymphome Kinase anaplastic lymphome kinase positive non-small cell lung cancer patients undergoing surgery after first-line alectinib treatment. We retrospectively collected and analyzed multicentric data of 10 patients treated with alectinib for advanced-stage anaplastic lymphome kinase positive lung adenocarcinoma who underwent anatomical surgical resection from January 2020 to Decemeber 2021. All patients were treatment naive and received alectinib (600 mg twice daily). Surgery was always proposed after multidisciplinary discussion. The primary endpoints were pathological response and surgical feasibility (technical intraoperative complications, postoperative outcomes). RESULTS: Alectinib was received for a mean of 212 days before surgery (42-415 days) and was generally interrupted about one week before surgery (range: 0-32 days) with no patient experienced grade 4 toxicity. All patients received an R0 resection with surgery consisting of lobectomy in 8 cases with bilobectomy and (left) pneumonectomy in 1 case each. Intra-operative difficulties were described in 7 cases (70%), mostly due to perivascular fibrosis or thickening of mediastinal lymph nodal tissues. Major and minor complications occurred in 0 and 3 cases (30%), respectively. A pathological complete response and major pathological response (defined as 0% and < 10% viable tumor cells, respectively) were observed in 50% and 90% of cases, respectively. Despite short follow-up, only one tumor recurrence was observed (in the only patient who did not resume alectinib after surgery). INTERPRETATION: Despite some technical intraoperative difficulties, salvage surgery was safe and feasible after Alectinib for advanced lung adenocarcinoma.

Ten-Year Incidence of Fibrosis and Risk Factors for Its Development in Neovascular Age-Related Macular Degeneration.

PURPOSE: To report the incidence and risk factors for fibrosis at 10 years in a large cohort of persons with neovascular age-related macular degeneration (nAMD). DESIGN: Retrospective, multicenter, cohort study. METHODS: We included 225 naive nAMD eyes that underwent intravitreal anti-vascular endothelial growth factor treatment over 10 years of follow-up at two Italian referral centers. Demographic and clinical data were reviewed at baseline and on an annual basis. Onset of fibrosis was defined by clinically assessing photographs, fundus descriptions, or fluorescein angiograms. Optical coherence tomography (OCT) scans of fibrosis were inspected by an external reading center and graded as subretinal pigment epithelium (RPE), mixed, or subretinal. RESULTS: The mean age at baseline was of 72.1 ± 6.9 years. The incidence rate of fibrosis was estimated to be 8.9 per 100 person-years, with a cumulative incidence of 62.7% at 10 years. Fibrotic lesions were sub-RPE in 46.1%, mixed in 29.8%, and subretinal in 22.7%. Independent factors associated with fibrosis included the following: larger central subfield thickness variation (P < .001), submacular hemorrhages (P = .008), higher number of injections (P = .01), and worse baseline visual acuity (VA) (P = .03). Type 2 macular neovascularization was significantly associated with mixed and subretinal fibrosis. VA significantly declined over 10 years (-16.4 Early Treatment Diabetic Retinopathy Study [ETDRS] letters), particularly in eyes with mixed and subretinal fibrosis (P < .001). CONCLUSIONS: We identified a 62.7% cumulative incidence of fibrosis in a large nAMD cohort at 10 years. Fibrosis was more common with frequent reactivations and lower baseline VA; its onset had a significant impact on final VA. This supports the hypothesis that nAMD patients should be promptly treated with proactive regimens.

Recent developments in absolute dosimetry for FLASH radiotherapy.

Ultra-high dose-rate (UHDR) irradiations, known as FLASH radiotherapy (RT), rely on delivery of therapeutic doses at instantaneous dose-rates several orders of magnitude higher than those currently used in conventional radiotherapy. It has been shown that such an extremely short delivery of radiation leads to remarkable reduction of normal tissue toxicity with respect to conventional dose-rate RT. However, dosimetry at UHDRs is complicated and it is essential to understand the effects that will influence detector response. To date, FLASH RT research has been focused on finding pragmatic solutions that allow the use of UHDR beams in the research setting, but there has been limited focus on absolute dosimetry utilizing primary and secondary standard devices. However, very recently, the data on existing standard dosimeters and novel solutions which could serve as secondary standard devices in UHDR dosimetry started emerging. This review provides an overview of the studies that have been conducted employing calorimeters and innovative solutions utilizing ionization chambers.

Update on Retinal Vein Occlusion.

Retinal vein occlusion represents the second leading cause of retinal vascular disorders, with a uniform sex distribution worldwide. A thorough evaluation of cardiovascular risk factors is required to correct possible comorbidities. The diagnosis and management of retinal vein occlusion have changed tremendously in the last 30 years, but the assessment of retinal ischemia at baseline and during follow-up examinations remains crucial. New imaging techniques have shed light on the pathophysiology of the disease and laser treatment, once the only therapeutic option, is now only one of the possible approaches with antivascular endothelial growth factors and steroid injections being preferred in most cases. Nowadays long-term outcomes are better than those achievable 20 years ago and yet, many new therapeutic options are under development, including new intravitreal drugs and gene therapy. Despite this, some cases still develop sight-threatening complications deserving a more aggressive (sometimes surgical) approach. The purpose of this comprehensive review is to reappraise some old but still valid concepts and to integrate them with new research and clinical data. The work will provide an overview of the disease's pathophysiology, natural history, and clinical features along with a detailed discussion on the advantages of multimodal imaging and of the different treatment strategies with the aim of providing retina specialists with the most updated knowledge in the field.

Absolute dosimetry for FLASH proton pencil beam scanning radiotherapy.

A paradigm shift is occurring in clinical oncology exploiting the recent discovery that short pulses of ultra-high dose rate (UHDR) radiation-FLASH radiotherapy-can significantly spare healthy tissues whilst still being at least as effective in curing cancer as radiotherapy at conventional dose rates. These properties promise reduced post-treatment complications, whilst improving patient access to proton beam radiotherapy and reducing costs. However, accurate dosimetry at UHDR is extremely complicated. This work presents measurements performed with a primary-standard proton calorimeter and derivation of the required correction factors needed to determine absolute dose for FLASH proton beam radiotherapy with an uncertainty of 0.9% (1[Formula: see text]), in line with that of conventional treatments. The establishment of a primary standard for FLASH proton radiotherapy improves accuracy and consistency of the dose delivered and is crucial for the safe implementation of clinical trials, and beyond, for this new treatment modality.

Radiation Hardness Study of Silicon Carbide Sensors under High-Temperature Proton Beam Irradiations.

Silicon carbide (SiC), thanks to its material properties similar to diamond and its industrial maturity close to silicon, represents an ideal candidate for several harsh-environment sensing applications, where sensors must withstand high particle irradiation and/or high operational temperatures. In this study, to explore the radiation tolerance of SiC sensors to multiple damaging processes, both at room and high temperature, we used the Ion Microprobe Chamber installed at the Ruder Boskovic Institute (Zagreb, Croatia), which made it possible to expose small areas within the same device to different ion beams, thus evaluating and comparing effects within a single device. The sensors tested, developed jointly by STLab and SenSiC, are PIN diodes with ultrathin free-standing membranes, realized by means of a recently developed doping-selective electrochemical etching. In this work, we report on the changes of the charge transport properties, specifically in terms of the charge collection efficiency (CCE), with respect to multiple localized proton irradiations, performed at both room temperature (RT) and 500 °C.

Neutrophil-to-Lymphocyte Ratio Is a Major Prognostic Factor in Non-small Cell Lung Carcinoma Patients Undergoing First Line Immunotherapy With Pembrolizumab.

BACKGROUND/AIM: Lung cancer is one of the most common malignant neoplastic diseases and by far the leading cause of cancer death worldwide. Recently, immune checkpoint inhibitors (ICIs) have received increasing attention for playing a crucial role in non-small cell lung cancer (NSCLC). Biomarkers, such as programmed cell death-ligand 1 (PD-L1) and tumor mutational burden (TMB), seemed to be helpful in selecting patients who are more likely to benefit from ICI treatment: however, their role has not yet been fully clarified. PATIENTS AND METHODS: In this retrospective study, we evaluated the relationship between pre-treatment peripheral blood neutrophil-to-lymphocyte ratio (NLR) and survival in 252 patients suffering from advanced NSCLC who had received pembrolizumab as their first-line immunotherapy. RESULTS: Compared to their NLR low counterparts who had a median overall survival (OS) of 34.8 months, patients with NLRs above 4.8 had a median OS of 7.6 months (HR=3.26, 95%Cl=2.3-4.6, p-value<0.0000001). In multivariate Cox regression analysis, alongside other variables, such as metastatic sites, age, and sex, NLR and PD-L1 predicted progression-free survival and OS; furthermore, a very high NLR - over 10 - seemed to forecast a very dismal prognosis in patients undergoing immunotherapy, with sudden deaths in the days immediately following therapy (median OS=3.8 months). CONCLUSION: NLR acts as a valuable and reliable prognostic factor in non-small cell lung carcinoma patients undergoing first line immunotherapy with pembrolizumab. Additional investigation is necessary to fully elucidate the underlying biological rationale, which can be found in myeloid derived suppressor cells, a heterogeneous population of cells with neutrophil-like immunophenotypic features.

Ileoanal pouch-related fistulae: A systematic review with meta-analysis on incidence, treatment options and outcomes.

BACKGROUND: Ileoanal pouch related fistulae (PRF) are a complication of restorative proctocolectomy often requiring repeated surgical interventions and with a high risk of long-term recurrence and pouch failure. AIMS: To assess the incidence of PRF and to report on the outcomes of available surgical treatments. METHODS: A PRISMA-compliant systematic literature search for articles reporting on PRF in patients with inflammatory bowel diseases (IBD) or familial adenomatous polyposis (FAP) from 1985 to 2020. RESULTS: 34 studies comprising 770 patients with PRF after ileal-pouch anal anastomosis (IPAA) were included. Incidence of PRF was 1.5-12%. In IBD patients Crohn's Disease (CD) was responsible for one every four pouch-vaginal fistulae (PVF) (OR 24.7; p=0.001). The overall fistula recurrence was 49.4%; procedure-specific recurrence was: repeat IPAA (OR 42.1; GRADE +); transvaginal repair (OR 52.3; GRADE ++) and transanal ileal pouch advancement flap (OR 56.9; GRADE ++). The overall failure rate was 19%: pouch excision (OR 0.20; GRADE ++); persistence of diverting stoma (OR 0.13; GRADE +) and persistent fistula (OR 0.18; GRADE +). CONCLUSION: PVFs are more frequent compared to other types of PRF and are often associated to CD; surgical treatment has a risk of 50% recurrence. Repeat IPAA is the best surgical approach with a 42.1% recurrence rate.

A new calculation method for the free electron fraction of an ionization chamber in the ultra-high-dose-per-pulse regimen.

The free electron fraction is the fraction of electrons, produced inside the cavity of an ionization chamber after irradiation, which does not bind to gas molecules and thereby reaches the electrode as free electrons. It is a fundamental quantity to describe the recombination processes of an ionization chamber, as it generates a gap of positive charges compared to negative ones, which certainly will not undergo recombination. The free electron fraction depends on the specific chamber geometry, the polarizing applied voltage and the gas thermodynamic properties. Therefore, it is necessary to evaluate such fraction in an accurate and easy way for any measurement condition. In this paper, a simple and direct method for evaluating the free electron fraction of ionization chambers is proposed. We first model the capture process of the electrons produced inside an ionization chamber after the beam pulse; then we present a method to evaluate the free electron fraction based on simple measurements of collected charge, by varying the applied voltage. Finally, the results obtained using an Advanced Markus chamber irradiated with a Flash Radiotherapy dedicated research Linac (ElectronFlash) to estimate the free electron fraction are presented. The proposed method allows the use of a conventional ionization chamber for measurements in ultra-high-dose-per-pulse (UHDP) conditions, up to values of dose-per-pulse at which the perturbation of the electric field due to the generated charge can be considered negligible.

Ultrahigh dose rate pencil beam scanning proton dosimetry using ion chambers and a calorimeter in support of first in-human FLASH clinical trial.

PURPOSE: To provide ultrahigh dose rate (UHDR) pencil beam scanning (PBS) proton dosimetry comparison of clinically used plane-parallel ion chambers, PTW (Physikalisch-Technische Werkstaetten) Advanced Markus and IBA (Ion Beam Application) PPC05, with a proton graphite calorimeter in a support of first in-human proton FLASH clinical trial. METHODS: Absolute dose measurement intercomparison of the plane-parallel plate ion chambers and the proton graphite calorimeter was performed at 5-cm water-equivalent depth using rectangular 250-MeV single-layer treatment plans designed for the first in-human FLASH clinical trial. The dose rate for each field was designed to remain above 60 Gy/s. The ion recombination effects of the plane-parallel plate ion chambers at various bias voltages were also investigated in the range of dose rates between 5 and 60 Gy/s. Two independent model-based extrapolation methods were used to calculate the ion recombination correction factors ks to compare with the two-voltage technique from most widely used clinical protocols. RESULTS: The mean measured dose to water with the proton graphite calorimeter across all the predefined fields is 7.702 ± 0.037 Gy. The average ratio over the predefined fields of the PTW Advanced Markus chamber dose to the calorimeter reference dose is 1.002 ± 0.007, whereas the IBA PPC05 chamber shows ∼3% higher reading of 1.033 ± 0.007. The relative differences in the ks values determined from between the linear and quadratic extrapolation methods and the two-voltage technique for the PTW Advanced Markus chamber are not statistically significant, and the trends of dose rate dependence are similar. The IBA PPC05 shows a flat response in terms of ion recombination effects based on the ks values calculated using the two-voltage technique. Differences in ks values for the PPC05 between the two-voltage technique and other model-based extrapolation methods are not statistically significant at FLASH dose rates. Some of the ks values for the PPC05 that were extrapolated from the three-voltage linear method and the semiempirical model were reported less than unity possibly due to the charge multiplication effect, which was negligible compared to the volume recombination effect in FLASH dose rates. CONCLUSIONS: The absolute dose measurements of both PTW Advanced Markus and IBA PPC05 chambers are in a good agreement with the National Physical Laboratory graphite calorimeter reference dose considering overall uncertainties. Both ion chambers also demonstrate good reproducibility as well as stability as reference dosimeters in UHDR PBS proton radiotherapy. The dose rate dependency of the ion recombination effects of both ion chambers in cyclotron generated PBS proton beams is acceptable and therefore, both chambers are suitable to use in clinical practice for the range of dose rates between 5 and 60 Gy/s.

A systematic study of the contribution of counting statistics to the final lineal energy uncertainty in microdosimetry.

Objectives.Microdosimetry is proving to be a reliable and powerful tool to be applied in different fields such as radiobiology, radiation protection and hadron therapy. However, accepted standard protocols and codes of practice are still missing. With this regard, a systematic and methodical uncertainty analysis is fundamental to build an accredited uncertainty budget of practical use. This work studied the contribution of counting statistics (i.e. number of events collected) to the final frequency-mean and dose-mean lineal energy uncertainties, aiming at providing guidelines for good experimental and simulation practice. The practical limitation of current technologies and the non-negligible probability of nuclear reactions require careful considerations and nonlinear approaches.Approach.Microdosimetric data were obtained by means of the particle tracking Monte Carlo code Geant4. The uncertainty analysis was carried out relying on a Monte Carlo based numerical analysis, as suggested by the BIPM's 'Guide to the expression of uncertainty in measurement'. Final uncertainties were systematically investigated for proton, helium and carbon ions at an increasing number of detected events, for a range of different clinical-relevant beam energies.Main results.Rare events generated by nuclear interactions in the detector sensitive volume were found to massively degrade microdosimetric uncertainties unless a very high statistics is collected. The study showed an increasing impact of such events for increasing beam energy and lighter ions. For instance, in the entrance region of a 250 MeV proton beam, about 5 ∗ 107events need to be collected to obtain a dose-mean lineal energy uncertainty below 10%.Significance.The results of this study help define the necessary conditions to achieve appropriate statistics in computational microdosimetry, pointing out the importance of properly taking into account nuclear interaction events. Their impact on microdosimetric quantities and on their uncertainty is significant and cannot be overlooked, particularly when characterising clinical beams and radiobiological response. This work prepared the ground for deeper investigations involving dedicated experiments and for the development of a method to properly evaluate the counting statistics uncertainty contribution in the uncertainty budget, whose accuracy is fundamental for the clinical transition of microdosimetry.

Ultra-high dose rate dosimetry: Challenges and opportunities for FLASH radiation therapy.

The clinical translation of FLASH radiotherapy (RT) requires challenges related to dosimetry and beam monitoring of ultra-high dose rate (UHDR) beams to be addressed. Detectors currently in use suffer from saturation effects under UHDR regimes, requiring the introduction of correction factors. There is significant interest from the scientific community to identify the most reliable solutions and suitable experimental approaches for UHDR dosimetry. This interest is manifested through the increasing number of national and international projects recently proposed concerning UHDR dosimetry. Attaining the desired solutions and approaches requires further optimization of already established technologies as well as the investigation of novel radiation detection and dosimetry methods. New knowledge will also emerge to fill the gap in terms of validated protocols, assessing new dosimetric procedures and standardized methods. In this paper, we discuss the main challenges coming from the peculiar beam parameters characterizing UHDR beams for FLASH RT. These challenges vary considerably depending on the accelerator type and technique used to produce the relevant UHDR radiation environment. We also introduce some general considerations on how the different time structure in the production of the radiation beams, as well as the dose and dose-rate per pulse, can affect the detector response. Finally, we discuss the requirements that must characterize any proposed dosimeters for use in UDHR radiation environments. A detailed status of the current technology is provided, with the aim of discussing the detector features and their performance characteristics and/or limitations in UHDR regimes. We report on further developments for established detectors and novel approaches currently under investigation with a view to predict future directions in terms of dosimetry approaches, practical procedures, and protocols. Due to several on-going detector and dosimetry developments associated with UHDR radiation environment for FLASH RT it is not possible to provide a simple list of recommendations for the most suitable detectors for FLASH RT dosimetry. However, this article does provide the reader with a detailed description of the most up-to-date dosimetric approaches, and describes the behavior of the detectors operated under UHDR irradiation conditions and offers expert discussion on the current challenges which we believe are important and still need to be addressed in the clinical translation of FLASH RT.