Reduction of recombination effects in large plane parallel beam monitors for FLASH radiotherapy with scanned ion beams.

PURPOSE: Radiotherapy escalating dose rates above 50Gys-1, might offer a great potential in treating tumours while further sparing healthy tissue. However, these ultra-high intensities of FLASH-RT lead to new challenges with regard to dosimetry and beam monitoring. FLASH experiments at HIT (Heidelberg Ion Beam Therapy Center) and at GSI (GSI Helmholtz Centre for Heavy Ion Research) have shown a significant loss of signal in the beam monitoring system due to recombination effects. To enable accurate beam monitoring, this work investigates the recombination loss of different fill gases in the plane parallel ionisation chambers (ICs). METHODS: Therefore, saturation curves at high intensities were measured for the currently used fill gases Ar/CO2 (80/20) and pure He and also for He/CO2 mixtures as alternative fill gases. Furthermore, breakdown voltages and ion mobilities were measured in ICs filled with He/CO2 mixtures. A numerical model for volume recombination in plane parallel ionisation chambers was developed and implemented in Python. This includes a novel simulation method of the space charge effect from the charge carriers in the detector volume and predicts a significant effect on the electric field for high intensity beams. RESULTS: Even at high intensities the He/CO2 mixtures allow operation of the ICs at an electric field strength of 2 kVcm-1 or more which reduces recombination to negligible levels at intensities larger than 3 × 101012C-ions per second. Our measurements show that added fractions of CO2 to He decrease the ion mobility in the fill gas but significantly increase the breakdown voltage in the ICs compared to pure He.

Ultra-High Dose Rate (FLASH) Carbon Ion Irradiation: Dosimetry and First Cell Experiments.

PURPOSE: To establish a beam monitoring and dosimetry system to enable the FLASH dose rate carbon ion irradiation and investigate, at different oxygen concentrations, the in vitro biological response in comparison to the conventional dose rate. METHODS AND MATERIALS: CHO-K1 cell response to irradiation at different dose rates and at different levels of oxygenation was studied using clonogenic assay. The Heidelberg Ion-Beam Therapy Center (HIT) synchrotron, after technical improvements, was adjusted to extract ≥5 × 108 12C ions within approximately 150 milliseconds. The beam monitors were filled with helium. RESULTS: The FLASH irradiation with beam scanning yields a dose of 7.5 Gy (homogeneity of ±5%) for a 280 MeV/u beam in a volume of at least 8 mm in diameter and a corresponding dose rate of 70 Gy/s (±20%). The dose repetition accuracy is better than 2%, the systematic uncertainty is better than 2%. Clonogenic assay demonstrates a significant FLASH sparing effect which is strongly oxygenation-dependent and mostly pronounced at 0.5% O2 but absent at 0% and 21% O2. CONCLUSION: The FLASH dose rates >40 Gy/s were achieved with carbon beams. Cell survival analysis revealed FLASH dose rate sparing in hypoxia (0.5%-4% O2).

Radioactive Beams for Image-Guided Particle Therapy: The BARB Experiment at GSI.

Several techniques are under development for image-guidance in particle therapy. Positron (ß+) emission tomography (PET) is in use since many years, because accelerated ions generate positron-emitting isotopes by nuclear fragmentation in the human body. In heavy ion therapy, a major part of the PET signals is produced by ß+-emitters generated via projectile fragmentation. A much higher intensity for the PET signal can be obtained using ß+-radioactive beams directly for treatment. This idea has always been hampered by the low intensity of the secondary beams, produced by fragmentation of the primary, stable beams. With the intensity upgrade of the SIS-18 synchrotron and the isotopic separation with the fragment separator FRS in the FAIR-phase-0 in Darmstadt, it is now possible to reach radioactive ion beams with sufficient intensity to treat a tumor in small animals. This was the motivation of the BARB (Biomedical Applications of Radioactive ion Beams) experiment that is ongoing at GSI in Darmstadt. This paper will present the plans and instruments developed by the BARB collaboration for testing the use of radioactive beams in cancer therapy.

Adherence to the National Guidelines for Follow-Up Protocol in Subjects with Type 2 Diabetes Mellitus in Greece: The GLANCE Study.

INTRODUCTION: Physician adherence, or lack therefore, to diabetes care and follow-up guidelines may be linked to the rates of achieving suboptimal glycaemic, blood pressure and lipid targets in people with type 2 diabetes mellitus (T2DM). In this cross-sectional study we evaluated physician adherence to the patient follow-up protocol (PFP) of the 2017 Hellenic Diabetes Association (HDA) guidelines and also assessed glycated haemoglobin (HbA1c), blood pressure and lipid control achievement rates in the routine care setting in Greece. METHODS: Eligible subjects were adults with T2DM receiving oral hypoglycaemic agents (OHAs) for ≥ 1 year who had ≥ 2 HbA1c measurements in the previous year and an HbA1c target < 7%. Overall adherence at the subject level was defined as the percentage of the 62 HDA PFP items that had been met during the past year. RESULTS: Between June and December 2018, 601 eligible subjects (54.6% men; mean age 65.2 years; median T2DM duration 5.9 years, of whom 96.5% had ≥ 1 medical condition/comorbidity), were enrolled into the study by 53 hospital- and office-based endocrinologists, internists and general practitioners. The main OHAs prescribed at enrolment were metformin (91.0%), dipeptidyl peptidase-4 inhibitors (60.7%), sodium-glucose co-transporter-2 inhibitors (23.5%) and sulphonylureas (16.3%). Mean overall physician adherence to the PFP was 43.6%. Predictors of greater higher physicans' adherence were female sex (p = 0.026), > 3 medical conditions/comorbidities (p = 0.043) and diabetic complications (p < 0.001). HbA1c, low-density lipoprotein-cholesterol, systolic/diastolic blood pressure and composite metabolic targets were achieved by 82.1, 57.0, 42.6 and 21.6% of subjects, respectively. CONCLUSIONS: In Greek routine care, physician adherence to the PFP of the 2017 HDA guidelines is suboptimal. Future efforts should focus on identifying the barriers to an adequate adherence by physicians to the full PFP, with the aim to provide optimal patient care.

Experimental comparison of clinically used ion beams for imaging applications using a range telescope.

In particle therapy, the x-ray based treatment planning converting photon attenuation values to relative stopping power ratio (RSP) introduces clinically relevant range uncertainties. Recently, novel imaging technologies using transmission ion beams have been investigated to directly assess the water equivalent thickness (WET) of tissue, showing improved accuracy in RSP reconstruction, while potentially reducing the imaging dose. Due to their greater availability, protons have been mostly used for ion imaging. To this end, in this work, the influence of three ion species (protons, helium and carbon ions) on the image quality of radiographic WET retrieval has been explored with a dedicated experimental setup and compared to Monte Carlo (MC) simulations. Three phantom setups with different tissue interfaces and features have been irradiated with clinically validated proton, helium and carbon ion pencil beams under comparable imaging dose and beam settings at the Heidelberg Ion-Beam Therapy Center. Ion radiographies (iRADs) were acquired with an integration mode detector, that functions as a range telescope with 61 parallel plate ionization chambers. For comparison, experiments were reproduced in-silico with FLUKA MC simulations. Carbon ions provide iRADs with highest image quality in terms of normalized root mean square error, followed by helium ions and protons. All ions show similar capabilities of resolving WET for the considered phantoms, as shown by the similar average relative error < 3%. Besides for the slab phantom, MC simulations yielded better results than the experiment, indicating potential improvement of the experimental setup. Our results showed that the ability to resolve the WET is similar for all particles, intrinsically limited by the granularity of the detector system. While carbon ions are best suited for acquiring iRADs with the investigated integration mode detector, helium ions are put forward as a less technical challenging alternative.

Real-World Adequacy of Glycaemic Control in Treatment-Naïve Greek Patients with Type 2 Diabetes Mellitus Initiating Treatment with Metformin Monotherapy at the Maximum Tolerated Dose: The Reload Study.

BACKGROUND: Metformin, in the absence of contraindications or intolerance, is recommended as first-line treatment for patients with type 2 diabetes mellitus (T2DM). This observational, retrospective study assessed the real-world adequacy of glycaemic control in Greek patients with T2DM initiating metformin monotherapy at maximum tolerated dose. METHODS: Included patients received metformin monotherapy for ≥24 months; relevant patient data were collected immediately prior to metformin initiation (baseline) and at other prespecified time points. The primary objective was to report, after 9 months of metformin treatment, the percentage of patients with baseline glycated haemoglobin (HbA1c) levels ≥6.5% (≥48 mmol/mol) achieving HbA1c<6.5%. Secondary objectives included the assessment of time spent with poor glycaemic control and time to treatment intensification. A sensitivity analysis assessed the percentage of patients with baseline HbA1c≥7% (≥53 mmol/mol) achieving HbA1c<7% (<53 mmol/mol). RESULTS: Of the enrolled patients (N=316), 247 had baseline HbA1c ≥6.5%; following 9 months on metformin, 90 (36.4%) patients achieved HbA1c<6.5% (mean HbA1c change-1.3% [-14 mmol/mol]). Median time of exposure to HbA1c ≥6.5% was 23.4 months and time to treatment intensification was 28.0 months. The sensitivity analysis revealed that the proportion of patients achieving HbA1c<7.0% was 50% (mean HbA1cpy for up to 24 months. Addressing clinical inertia could improve disease outcomes and, possibly, economic burden.

Influence of Supervised Disease Understanding and Diabetes Self-Management on Adherence to Oral Glucose-Lowering Treatment in Patients with Type 2 Diabetes.

INTRODUCTION: Systematic patient education has been reported to improve adherence to treatment, leading to better clinical outcomes. This cluster randomized real-world study investigated the effect of a systematic education program and telephone support on self-reported adherence to oral glucose-lowering treatment in patients with type 2 diabetes mellitus (T2DM). METHODS: Centers were randomized (1:1) to provide either standard-of-care (control group) or standard-of-care along with the education program and telephone support (empowerment group). Adherence to treatment and satisfaction with treatment were assessed using the four-item Morisky Medication Adherence Scale (MMAS-4) and the Diabetes Treatment Satisfaction Questionnaire (DTSQ). The study population included 457 patients (258/199 male/female) with T2DM and non-optimal glycemic control, on oral antidiabetic treatment (age 62.7 [11.4]; disease duration 8.5 [6.5] years). RESULTS: MMAS-4 high adherence rates for the control and empowerment groups were increased by 3.8% and 16.8% at 4 months (Breslow-Day test p = 0.04) and by 8.5% and 18.8% at 8 months of follow-up, respectively (Breslow-Day test p = 0.09), compared to baseline. Intense physical activity was increased in both control and empowerment groups by 2.3% and 13.9% at 4 months (Breslow-Day test p = 0.082) and by 4.0% and 22.5% at 8 months of follow-up (Breslow-Day test p < 0.001). Baseline mean (SD) HbA1c was significantly lower in the control group compared with the empowerment group [7.7% versus 8.0%, p = 0.001] and decreased in both groups at 4 months by 0.7% and 0.9%, respectively. The change from baseline in the mean DTSQ status score at 4 months was greater in the empowerment group, and the effect was sustained at 8 months (control group: 29.1, 30.5, and 30.9; empowerment group: 25.0, 28.7, and 29.4 at baseline, 4 and 8 months, respectively, p < 0.001). CONCLUSION: Systematic education combined with telephone support delivered by physicians might be associated with improvement in treatment adherence and treatment satisfaction in patients with T2DM. FUNDING: MSD, Greece.

Impact of differing glucose-lowering regimens on the pattern of association between glucose control and survival.

AIMS: To characterize survival in relation to achieved glycated haemoglobin (HbA1c) level within alternative glucose-lowering regimens with differing risks of hypoglycaemia. METHODS: Data were extracted from the UK Clinical Practice Research Datalink and the corresponding Hospital Episode Statistics. Patients with type 2 diabetes prescribed glucose-lowering therapy in monotherapy or dual therapy with metformin between 2004 and 2013 were identified. Risk of all-cause mortality within treatment cohorts was evaluated using the Cox proportional hazards model, introducing mean HbA1c as a quarterly updated, time-dependent covariable. RESULTS: There were 6646 deaths in a total follow-up period of 374 591 years. Survival for lower (<7%) vs moderate HbA1c levels (≥7%, <8.5%) differed by cohort: metformin, adjusted hazard ratio (aHR) 1.03 (95% confidence interval [CI] 0.95-1.12); sulphonylurea, aHR 1.11 (95% CI 0.99-1.25); insulin, aHR 1.47 (95% CI 1.25-1.72); combined regimens with low hypoglycaemia risk, aHR 1.02 (95% CI 0.94-1.10); and combined regimens with higher hypoglycaemia risk excluding insulin, aHR 1.24 (95% CI 1.13-1.35) and including insulin, aHR 1.28 (95% CI 1.18-1.37). Higher HbA1c levels were associated with increased mortality in regimens with low hypoglycaemia risk. Post hoc analysis by HbA1c deciles revealed an elevated risk of all-cause mortality for the lowest deciles across all cohorts, but particularly in those regimens associated with hypoglycaemia. High HbA1c was associated with no difference, or a small increase in mortality risk in regimens with increased risk of hypoglycaemia. CONCLUSIONS: The pattern of mortality risk across the range of HbA1c differed by glucose-lowering regimen. Lower HbA1c was associated with increased mortality risk compared with moderate control, especially in those regimens associated with hypoglycaemia. High levels of HbA1c were associated with the expected elevated mortality risk in regimens with low hypoglycaemia risk.

Comparative Monte Carlo study on the performance of integration- and list-mode detector configurations for carbon ion computed tomography.

Ion beam therapy offers the possibility of a highly conformal tumor-dose distribution; however, this technique is extremely sensitive to inaccuracies in the treatment procedures. Ambiguities in the conversion of Hounsfield units of the treatment planning x-ray CT to relative stopping power (RSP) can cause uncertainties in the estimated ion range of up to several millimeters. Ion CT (iCT) represents a favorable solution allowing to directly assess the RSP. In this simulation study we investigate the performance of the integration-mode configuration for carbon iCT, in comparison with a single-particle approach under the same set-up. The experimental detector consists of a stack of 61 air-filled parallel-plate ionization chambers, interleaved with 3 mm thick PMMA absorbers. By means of Monte Carlo simulations, this design was applied to acquire iCTs of phantoms of tissue-equivalent materials. An optimization of the acquisition parameters was performed to reduce the dose exposure, and the implications of a reduced absorber thickness were assessed. In order to overcome limitations of integration-mode detection in the presence of lateral tissue heterogeneities a dedicated post-processing method using a linear decomposition of the detector signal was developed and its performance was compared to the list-mode acquisition. For the current set-up, the phantom dose could be reduced to below 30 mGy with only minor image quality degradation. By using the decomposition method a correct identification of the components and a RSP accuracy improvement of around 2.0% was obtained. The comparison of integration- and list-mode indicated a slightly better image quality of the latter, with an average median RSP error below 1.8% and 1.0%, respectively. With a decreased absorber thickness a reduced RSP error was observed. Overall, these findings support the potential of iCT for low dose RSP estimation, showing that integration-mode detectors with dedicated post-processing strategies can provide a RSP accuracy comparable to list-mode configurations.

A spectrometer on chemical vapour deposition-diamond basis for the measurement of the charge-state distribution of heavy ions in a laser-generated plasma.

This article reports on the development and the first applications of a new spectrometer which enables the precise and time-resolved measurement of both the energy loss and the charge-state distribution of ion beams with 10 < Z < 30 at energies of 4-8 MeV/u after their interaction with a laser-generated plasma. The spectrometer is based on five 20 × 7 mm(2) large and 20 µm thick polycrystalline diamond samples produced via the Chemical Vapour Deposition (CVD) process and was designed with the help of ion-optical simulations. First experiments with the spectrometer were successfully carried out at GSI using (48)Ca ions at an energy of 4.8 MeV/u interacting with a carbon plasma generated by the laser irradiation of a thin foil target. Owing to the high rate capability and the short response time of the spectrometer, pulsed ion beams with 10(3)-10(4) ions per bunch at a bunch frequency of 108 MHz could be detected. The temporal evolution of the five main charge states of the calcium ion beams as well as the corresponding energy loss values could be measured simultaneously. Due to the outstanding properties of diamond as a particle detector, a beam energy resolution ΔEE ≈ 0.1% could be reached using the presented experimental method, while a precision of 10% in the energy loss and charge-state distribution data was obtained.