Experimental and Monte Carlo based dosimetric investigation of a novel 3 mm radiosurgery 3 MV beam using the microSilicon detector

BACKGROUND

The ZAP-X system is a novel gyroscopic radiosurgical system based on a 3 MV linear accelerator and collimator cones with a diameter between 4 and 25 mm. Advances in imaging modalities to detect small and early-stage pathologies allow for an early and less invasive treatment, where a smaller collimator matching the anatomical target could provide better sparing of surrounding healthy tissue.

PURPOSE

A novel 3 mm collimator cone for the ZAP-X was developed. This study aims to investigate the usability of a commercial diode detector (microSilicon) for the dosimetric characterization of this small collimator cone; and to investigate the underlying small field perturbation effects.

METHODS

Profile measurements in five depths as well as PDD and output ratio measurements were performed with a microSilicon detector and radiochromic EBT3 films. In addition, comprehensive Monte Carlo simulations were performed to validate the measurement observations and to quantify the perturbation effects of the microSilicon detector in these extremely small field conditions.

RESULTS

It is shown that the microSilicon detector enables an accurate dosimetric characterization of the 3 mm beam. The profile parameters, such as the FWHM and 20%-80% penumbra width, agree within 0.1 to 0.2 mm between film and detector measurements. The output ratios agree within the measurement uncertainty between microSilicon detector and films, whereas the comparisons of the PDD results show good agreement with the Monte Carlo simulations. The analysis of the perturbation factors of the microSilicon detector reveals a small field correction factor of approximately 3% for the 3 mm circular beam and a correction factor smaller than 1.5% for field diameters above 3 mm.

CONCLUSIONS

It could be shown that the microSilicon detector is well-suitable for the characterization of the new 3 mm circular beam of the ZAP-X system.

A Self-Powered Biochemical Sensor for Intelligent Agriculture Enabled by Signal Enhanced Triboelectric Nanogenerator

Precise agriculture based on intelligent agriculture plays a significant role in sustainable development. The agricultural Internet of Things (IoTs) is a crucial foundation for intelligent agriculture. However, the development of agricultural IoTs has led to exponential growth in various sensors, posing a major challenge in achieving long-term stable power supply for these distributed sensors. Introducing a self-powered active biochemical sensor can help, but current sensors have poor sensitivity and specificity making this application challenging. To overcome this limitation, a triboelectric nanogenerator (TENG)-based self-powered active urea sensor which demonstrates high sensitivity and specificity is developed. This device achieves signal enhancement by introducing a volume effect to enhance the utilization of charges through a novel dual-electrode structure, and improves the specificity of urea detection by utilizing an enzyme-catalyzed reaction. The device is successfully used to monitor the variation of urea concentration during crop growth with concentrations as low as 4 µm, without being significantly affected by common fertilizers such as potassium chloride or ammonium dihydrogen phosphate. This is the first self-powered active biochemical sensor capable of highly specific and highly sensitive fertilizer detection, pointing toward a new direction for developing self-powered active biochemical sensor systems within sustainable development-oriented agricultural IoTs.

Adapting a practical EPR dosimetry protocol to measure output factors in small fields with alanine

PURPOSE

Modern radiotherapy techniques often deliver small radiation fields. In this work, a practical Electron Paramagnetic Resonance (EPR) dosimetry protocol is adapted and applied to measure output factors (OF) in small fields of a 6 MV radiotherapy system. Correction factors and uncertainties are presented and OFs are compared to the values obtained by following TRS-483 using an ionization chamber (IC).

METHODS

Irradiations were performed at 10 cm depth inside a water phantom positioned at 90 cm source to surface distance with a 6 MV flattening filter free photon beam of a Halcyon radiotherapy system. OFs for different nominal field sizes (1 × 1, 2 × 2, 3 × 3, 4 × 4, normalized to 10 × 10 cm2 ) were determined with a PinPoint 3D (PTW 31022) IC following TRS-483 as well as with alanine pellets with a diameter of 4 mm and a height of 2.4 mm. EPR readout was performed with a benchtop X-band spectrometer. Correction factors due to volume averaging and due to positional uncertainties were derived from 2D film measurements.

RESULTS

OFs obtained from both dosimeter types agreed within 0.7% after applying corrections for the volume averaging effect. For the used alanine pellets, volume averaging correction factors of 1.030(2) for the 1 × 1 cm2 field and <1.002 for the larger field sizes were determined. The correction factor for positional uncertainties of 1 mm was in the order of 1.018 for the 1 × 1 cm2 field. Combined relative standard uncertainties uc for the OFs resulting from alanine measurements were estimated to be below 1.5% for all field sizes. For IC measurements, uc was estimated to be below 1.0%.

CONCLUSIONS

A practical EPR dosimetry protocol is adaptable for precisely measuring OFs in small fields down to 1 × 1 cm2 . It is recommended to consider the effect of positional uncertainties for field sizes <2 × 2 cm2 .

Biomedical advances and future prospects of high-precision three-dimensional radiotherapy and four-dimensional radiotherapy

Biomedical advances of external-beam radiotherapy (EBRT) with improvements in physical accuracy are reviewed. High-precision (±1 mm) three-dimensional radiotherapy (3DRT) can utilize respective therapeutic open doors in the tumor control probability curve and in the normal tissue complication probability curve instead of the one single therapeutic window in two-dimensional EBRT. High-precision 3DRT achieved higher tumor control and probable survival rates for patients with small peripheral lung and liver cancers. Four-dimensional radiotherapy (4DRT), which can reduce uncertainties in 3DRT due to organ motion by real-time (every 0.1-1 s) tumor-tracking and immediate (0.1-1 s) irradiation, have achieved reduced adverse effects for prostate and pancreatic tumors near the digestive tract and with similar or better tumor control. Particle beam therapy improved tumor control and probable survival for patients with large liver tumors. The clinical outcomes of locally advanced or multiple tumors located near serial-type organs can theoretically be improved further by integrating the 4DRT concept with particle beams.

Successful treatment of facet joint synovial cyst through percutaneous rupture: a case report

Facet joint synovial cysts can cause significant back pain and radiculopathy. Treatment options for symptomatic facet joint synovial cysts include surgical excision, facet joint steroid injections, and cyst aspiration. Herein, we report our experience of successfully rupturing a lumbar facet joint synovial cyst through a percutaneous approach with two needles using forceful pressure under C-arm fluoroscopic guidance. The patient experienced immediate symptom improvement that persisted throughout the 24-month follow-up. Our experience highlights that the volume effect technique is a valuable treatment option for symptomatic facet joint synovial cysts under fluoroscopic guidance.

Conversion of Dielectric Surface Effect into Volume Effect for High Output Energy

Improving the output energy and durability of triboelectric nanogenerators (TENGs) remains a considerable challenge for their practical applications. Owing to the interface effect of triboelectrification and electrostatic induction, thinner films with higher dielectric constants yield a higher output; however, they are not durable for practical applications. Herein, the dielectric surface effect is changed into a volume effect by adopting a millimeter-thick dielectric film with an inner porous network structure so that charges can hop in the surface state of the network. Charge migration inside the dielectric film is the key factor affecting the output of the triboelectric nanogenerator (TENG) with a thick film, based on which each working stage follows the energy-maximization principle in the voltage-charge plot. The maximum peak and average power densities of the TENG with polyurethane foam film in 1 mm thickness reach 40.9 and 20.7 W m-2  Hz-1 , respectively, under environmental conditions, and the output charge density is 5.14 times that of TENGs with a poly(tetrafluoroethylene) film of the same thickness. Superdurability is achieved in the rotary-mode TENG after 200 000 operation cycles. This study identifies the physical mechanism of the thick dielectric film used in TENGs and provides a new approach to promote the output and durability of TENGs.

Comprehensive investigation of lateral dose profile and output factor measurements in small proton fields from different delivery techniques

BACKGROUND AND PURPOSE

As part of the commissioning and quality assurance in proton beam therapy, lateral dose profiles and output factors have to be acquired. Such measurements can be performed with point detectors and are especially challenging in small fields or steep lateral penumbra regions as the detector's volume effect may lead to perturbations. To address this issue, this work aims to quantify and correct for such perturbations of six point detectors in small proton fields created via three different delivery techniques.

METHODS

Lateral dose profile and output measurements of three proton beam delivery techniques (pencil beam scanning, pencil beam scanning combined with collimators, passive scattering with collimators) were performed using high-resolution EBT3 films, a PinPoint 3D 31022 ionization chamber, a microSilicon diode 60023 and a microDiamond detector 60019 (all PTW Freiburg, Germany). Detector specific lateral dose response functions K(x,y) acting as the convolution kernel transforming the undisturbed dose distribution D(x,y) into the measured signal profiles M(x,y) were applied to quantify perturbations of the six investigated detectors in the proton fields and correct the measurements. A signal theoretical analysis in Fourier space of the dose distributions and detector's K(x,y) was performed to aid the understanding of the measurement process with regard to the combination of detector choice and delivery technique.

RESULTS

Quantification of the lateral penumbra broadening and signal reduction at the fields center revealed that measurements in the pencil beam scanning fields are only compromised slightly even by large volume ionization chambers with maximum differences in the lateral penumbra of 0.25 mm and 4% signal reduction at the field center. In contrast, radiation techniques with collimation are not accurately represented by the investigated detectors as indicated by a penumbra broadening up to 1.6 mm for passive scattering with collimators and 2.2 mm for pencil beam scanning with collimators. For a 3 mm diameter collimator field, a signal reduction at field center between 7.6% and 60.7% was asserted. Lateral dose profile measurements have been corrected via deconvolution with the corresponding K(x,y) to obtain the undisturbed D(x,y). Corrected output ratios of the passively scattered collimated fields obtained for the microDiamond, microSilicon and PinPoint 3D show agreement better than 0.9% (one standard deviation) for the smallest field size of 3 mm.

CONCLUSIONS

Point detector perturbations in small proton fields created with three delivery techniques were quantified and found to be especially pronounced for collimated small proton fields with steep dose gradients. Among all investigated detectors, the microSilicon diode showed the smallest perturbations. The correction strategies based on detector's K(x,y) were found suitable for obtaining unperturbed lateral dose profiles and output factors. Approximation of K(x,y) by considering only the geometrical averaging effect has been shown to provide reasonable prediction of the detector's volume effect. The findings of this work may be used to guide the choice of point detectors in various proton fields and to contribute towards the development of a code of practice for small field proton dosimetry. This article is protected by copyright. All rights reserved.

Container volume may affect growth rates of ciliates and clearance rates of their microcrustacean predators in microcosm experiments

We studied the effect of volume in small containers (microcosms) on five common planktonic freshwater ciliates and three zooplankton species, namely Daphnia sp., the calanoid copepod Eudiaptomus sp., and the cyclopoid copepod Cyclops sp. We measured ciliate specific growth rates and their loss rates due to microcrustacean predation in short-term experiments. We hypothesized that container volume ranging from 10 to 200 mL would not affect the activity of our prey and predator species. We found that the response to volume was species-specific; growth rates of three ciliate species were sensitive to volume. However, the volume effect was not unequivocal because different timing of the microcosm experiments (block effects) may have caused random bias due to varying morphological and/or physiological conditions of the ciliates and their predators. For predator clearance rate, the volume effect was insignificant in the filter-feeding Daphnia and Eudiaptomus but was significant for the predatory copepod Cyclops, which was hampered in the smallest experimental containers. Total crustacean clearance rates averaged over all treatments appeared unaffected by predator species, while ciliate species significantly affected the results. Our growth and clearance rates are close to previous findings with the same or similar planktonic prey and predator species.

Surgical Trend and Volume Effect on the Choice of Hysterectomy Benign Gynecologic Conditions

With the advance of minimally invasive surgery (MIS), the surgical trends of hysterectomy changed significantly during past 2 decades. Total number (age-standardized) of all types of hysterectomy decreased, which may be due to the availability of some other alternatives, e.g. hysteroscopy, laparoscopic myomectomy. However, laparoscopic hysterectomy (LH) still remains the mainstream of surgical treatment. LH significantly increases for benign gynecologic conditions in Taiwan and worldwide. The increase of LH was accompanied with decrease of TAH; VH kept stationary, and SAH increased slightly. The increase in popularity of LH and SAH; provides evidence of surgical trends and a paradigm shift for hysterectomy. This time-frame shift suggests LH has reached a u during the later years. Older patients tend to receive AH, while middle-aged women tend to receive LH. Oder surgeons tend to perform AH, while younger surgeons tend to perform LH. However, all type hysterectomy and LH were more commonly performed by older surgeons aged over 50 years. It means both patients and surgeons became older during the time-frames. The above phenomena may also happen due to less young surgeons entered in the gynecologic practice. Most of the LHs were performed by high-volume surgeons, however, there is a shift from high-volume, to medium- and low-volume surgeons. The above scenario may be due to the wide spread of LH techniques. Surgical volume has important impacts on both complications and costs. The high-volume surgeons have lower complications, which result in lower costs. In the future, how to increase the use of LH, to improve the training and monitoring system deserves more attentions.

Analysis of the applicability of two-dimensional detector arrays in terms of sampling rate and detector size to verify scanned intensity-modulated proton therapy plans

PURPOSE

The introduction of advanced treatment techniques in proton therapy, such as intensity-modulated proton therapy, leads to an increased need for patient-specific quality assurance, especially an accurate treatment plan verification becomes inevitable. In this study, signal theoretical analysis of dose distributions in scanned proton therapy is performed to investigate the feasibility and limits of two-dimensional (2D) detector arrays for treatment plan verification.

METHODS

2D detector arrays are characterized by two main aspects: the distance between the single detectors on the array or the sampling frequency; and the lateral response functions of a single detector. The analysis is based on single spots, reference fields and on measured and calculated dose distributions of typical intensity-modulated proton therapy treatment plans with and without range shifter. Measurements were performed with Gafchromic EBT3 films (Ashland Speciality Ingredients G.P., Bridgewater, NJ, USA), the MatriXX PT detector array (IBA Dosimetry, Schwarzenbruck, Germany) and the OCTAVIUS detector array 1500XDR (PTW-Freiburg, Germany) at an IBA Proteus PLUS proton therapy system (Ion Beam Applications, Louvain-la-Neuve, Belgium). Dose calculations were performed with the treatment planning system RayStation 6 or 8 (RaySearch Laboratories, Sweden).

RESULTS

The Fourier analysis of the data of the treatment planning system and film measurements show maximum frequencies of 0.06/mm for the plan with range shifter and 0.083/mm for the plan without range shifter. According to the Nyquist theorem, this corresponds to minimum required sampling distances of 8.3 and 6 mm, respectively. By comparison, the sampling distances of the arrays of 7.6 mm (MatriXX PT) and 7.1 mm (OD1500XDR) are sufficient to reconstruct the dose distributions adequately from measurements if range shifters are used, whereas some fields of the plans without range shifter violated the Nyquist requirement. The lateral dose response functions of the single detectors within the arrays have clearly higher frequencies than the treatment plans and thus the volume effect only slightly influences the measurements. Consequently, the array measurements show high gamma passing rates with at least 96 % and a good agreement between the investigated line profiles.

CONCLUSION

The results indicate that the detector dimensions and sampling distances of the arrays are in most studied cases adequate not to substantially influence the measurement process when they are used for analyzing typical intensity-modulated proton therapy treatment plans. Nevertheless, clinical conditions have been identified, for instance treatment plans without range shifter, under which the Nyquist theorem is violated such that a full representation of the dose distributions with the measurements is not feasible. In these cases, analysis of measurements is limited to pointwise comparisons.

High/low-volume center experience predicts outcome of AMS 800 in male stress incontinence: Results of a large middle European multicenter case series

AIM

To analyze the influence of implantation volume of artificial sphincters (AMS 800) on outcome in a large central European multicenter cohort study.

METHODS

As part of the DOMINO (Debates on Male Incontinence) project, the surgical procedures and outcomes were retrospectively analyzed in a total of 473 patients who received an artificial sphincter (AMS 800) between 2010 and 2012. Clinics that implanted at least 10 AMS 800 per year were defined as high-volume centers.

RESULTS

Sixteen centers had a mean rate of 9.54 AMS 800/y of which five clinics were identified as high-volume centers. They implanted significantly more double cuffs (55% vs 12.1%; P < .001), used the perineal approach significantly more often (78% vs 67.7%; P = .003) and chose larger mean cuff sizes (4.63 cm vs 4.42 cm; P = .002). With a mean follow-up of 18 months, the revision rate was significantly higher at low-volume centers (38.5% vs 26.7%; P = .037), urethral erosion being the main reason for revision. Social continence (0-1 pads/24 h) was achieved significantly more often in high-volume centers (45.5% vs 24.2%; P = .002).

CONCLUSIONS

Our study showed significantly better continence results and lower revision rates at high-volume centers, confirming earlier results that are still true in this decade. We, therefore, recommend surgery for male incontinence at qualified centers.

Technical Note: Characterization of the new microSilicon diode detector

Purpose

Dosimetric properties of the new microSilicon diode detector (60023) have been studied with focus on application in small‐field dosimetry. The influences of the dimensions of the sensitive volume and the density of the epoxy layer surrounding the silicon chip of microSilicon have been quantified and compared to its predecessor (Diode E 60017) and the microDiamond (60019, all PTW‐Freiburg, Germany).

Methods

Dose linearity has been studied in the range from 0.01 to 8.55 Gy and dose‐per‐pulse dependence from 0.13 to 0.86 mGy/pulse. The effective point of measurement (EPOM) was determined by comparing measured percentage depth dose curves with a reference curve (Roos chamber). Output ratios were measured for nominal field sizes from 0.5 × 0.5  cm² to 4 × 4 cm². The corresponding small‐field output correction factors, k, were derived with a plastic scintillation detector as reference. The lateral dose–response function, K(x), was determined using a slit beam geometry.

Results

MicroSilicon shows linear dose response (R² = 1.000) in both low and high dose range up to 8.55 Gy with deviations of only up to 1% within the dose‐per‐pulse values investigated. The EPOM was found to lie (0.7 ± 0.2) mm below the front detector’s surface. The derived k for microSilicon (0.960 at s_eff = 0.55 cm) is similar to that of microDiamond (0.956), while Diode E requires larger corrections (0.929). This improved behavior of microSilicon in small‐fields is reflected in the slightly wider K(x) compared to Diode E. Furthermore, the amplitude of the negative values in K(x) at the borders of the sensitive volume has been reduced.

Conclusions

Compared to its predecessor, microSilicon shows improved dosimetric behavior with higher sensitivity and smaller dose‐per‐pulse dependence. Profile measurements demonstrated that microSilicon causes less perturbation in off‐axis measurements. It is especially suitable for the applications in small‐field output factors and profile measurements.

The role of radiation-induced charge imbalance on the dose-response of a commercial synthetic diamond detector in small field dosimetry

Purpose

Discrepancy between experimental and Monte Carlo simulated dose–response of the microDiamond (mD) detector (type 60019, PTW Freiburg, Germany) at small field sizes has been reported. In this work, the radiation‐induced charge imbalance in the structural components of the detector has been investigated as the possible cause of this discrepancy.

Materials and methods

Output ratio (OR) measurements have been performed using standard and modified versions of the mD detector at nominal field sizes from 6 mm × 6 mm to 40 mm × 40 mm. In the first modified mD detector (mD_reversed), the type of charge carriers collected is reversed by connecting the opposite contact to the electrometer. In the second modified mD detector (mD_shortened), the detector's contacts have been shortened. The third modified mD detector (mD_noChip) is the same as the standard version but the diamond chip with the sensitive volume has been removed. Output correction factors were calculated from the measured OR and simulated using the EGSnrc package. An adapted Monte Carlo user‐code has been used to study the underlying mechanisms of the field size‐dependent charge imbalance and to identify the detector's structural components contributing to this effect.

Results

At the smallest field size investigated, the OR measured using the standard mD detector is >3% higher than the OR obtained using the modified mD detector with reversed contact (mD_reversed). Combining the results obtained with the different versions of the detector, the OR have been corrected for the effect of radiation imbalance. The OR obtained using the modified mD detector with shortened contacts (mD_shortened) agree with the corrected OR, all showing an over‐response of less than 2% at the field sizes investigated. The discrepancy between the experimental and simulated output correction factors has been eliminated after accounting for the effect of charge imbalance.

Discussions and conclusions

The role of radiation‐induced charge imbalance on the dose–response of mD detector in small field dosimetry has been studied and quantified. It has been demonstrated that the effect is significant at small field sizes. Multiple methods were used to quantify the effect of charge imbalance with good agreement between Monte Carlo simulations and experimental results obtained with modified detectors. When this correction is applied to the Monte Carlo data, the discrepancy from experimental data is eliminated. Based on the detailed component analysis using an adapted Monte Carlo user‐code, it has been demonstrated that the effect of charge imbalance can be minimized by modifying the design of the detector's contacts.

Novel approaches to surgical site infections: what recommendations can be made?

INTRODUCTION

Surgical site infections (SSI) are one of the most frequent healthcare-associated infections worldwide, representing a substantial burden on the healthcare system and the individual patient. Various risk factors for SSI have been identified, which can be separated into patient-related, procedure-related and other risk factors. Areas covered: Other risk factors relevant for SSI are the season in which surgery is performed, the volume of surgeries in a department, the working atmosphere in the operating room and the indications for surgery. Overall, the risk of SSI is higher during summertime. Higher-volume departments appear to be protective against SSI as does a calm working atmosphere. The frequency of certain types of surgery differs greatly among European countries. The decision to perform surgery appears to be dependent on the patient's condition as well as the healthcare system and financial incentives. Expert commentary: When possible, elective surgery should not be executed during summertime but during cooler times of year. Departments with a high volume of surgical procedures should be given preference. The establishment of a calm working atmosphere is beneficial to a surgeon's performance and can reduce SSI rates. The indications for performing surgery should be carefully reevaluated whenever possible.

Volume Matters: Returning Home After Hip Fracture

OBJECTIVES

To examine the effect of the relationship between volume (number of hip fracture admissions during the 12 months before participant's fracture) and other facility characteristics on outcomes.

DESIGN

Prospective observational study.

SETTING

U.S. skilled nursing facilities (SNFs) admitting individuals discharged from the hospital after treatment for hip fracture between 2000 and 2007 (N = 15,439).

PARTICIPANTS

Community-dwelling fee-for-service Medi-care beneficiaries aged 75 and older admitted to U.S. hospitals for their first hip fracture and discharged to a SNF for postacute care from 2000 to 2007 (N = 512,967).

MEASUREMENTS

Successful discharge from SNF to community, defined as returning to the community within 30 days of hospital discharge to the SNF and remaining in the community without being institutionalized for at least 30 days, was examined using Medicare administrative data, propensity score matching, and instrumental variables.

RESULTS

The overall rate of successful discharge to the community was 31%. Of the 15,439 facilities, the facility interquartile range varied from 0% (25th percentile) to 42% (75th percentile). An important determinant of variation in discharge rate was SNF volume of hip fracture admissions. Unadjusted successful discharge from SNF to community was 43.7% in high-volume facilities (>24 admissions/year), versus 18.8% in low-volume facilities (1-6 admissions/year). This facility volume effect persisted after adjusting for participant and facility characteristics associated with outcomes (e.g., adjusted odds ratio = 2.06, 95% confidence interval = 1.91-2.21 for volume of 25 vs 3 admissions per year).

CONCLUSION

In community-dwelling persons with their first hip fracture, successful return to the community varies substantially according to SNF provider volume and staffing characteristics.

Volume effect of localized injection in functional MRI and electrophysiology

PURPOSE

The local injection of neurotransmitter agonists and antagonists to modulate recorded neurons in awake animals has long been an important and widely used technique in neuroscience. Combined with functional magnetic resonance imaging (fMRI) and simultaneous electrophysiology, local injection enables the study of specific brain regions under precise modulations of their neuronal activity. However, localized injections are often accompanied by mechanical displacement of the tissue, known as volume effect (VE), which can induce changes in electrophysiological recordings as well as artifacts that are particular to fMRI studies.

METHODS

We characterize the changes produced by VE in an agarose phantom as well as during stimulus-evoked and resting-state fMRI and simultaneously acquired electrophysiology in awake rabbits.

RESULTS

Our results demonstrate that localized injection can produce significant intensity changes in fMRI data, even while effects on electrophysiological recordings are minimized. These changes are localized to the vicinity of the injection needle and diminish over time due to diffusion of the injected volume.

CONCLUSION

Sufficient time should be allowed for drug diffusion to ensure stable results, particularly for resting-state fMRI experiments.