Fetal Dose Evaluation for Pregnant Patients on Leksell Gamma Knife Perfexion/Icon.

INTRODUCTION: It is a normal procedure to avoid the application of ionizing radiation during pregnancy. In very rare occasions, treatment can be performed, but doses to the fetus must be evaluated and reported, and the patient must sign informed consent. There can occur two types of damage caused by ionizing radiation - deterministic and stochastic effects. Deterministic effects may occur after reaching a certain threshold (100 mGy for this study); meanwhile, stochastic effects have no limit and their probability rises with dose. This study focuses on deterministic effects. CASE PRESENTATIONS: This study compares the dose measured on phantom for the area of the pelvis and the dose measured on 3 patients with dosimeters positioned on the pelvis irradiated on Leksell Gamma Knife Perfexion/Icon. The mean dose for measurement on phantom for the pelvis was 0.73 ± 0.76 mGy, and for the patients, it was 1.28 mGy, 0.493 mGy, and 0.549 mGy which is 80 times lower, 200 times lower, and 180 times lower than the threshold for deterministic effects, respectively. CONCLUSION: The measurement carried on phantom served as the base for drafting informed consent and provided initial proof that treatment can be safely delivered. Measurements performed on patients only confirmed that irradiation of pregnant patients on Leksell Gamma Knife Perfexion/Icon is safe relative to the deterministic effects. Nevertheless, pregnant patients should be treated with ionizing radiation only in very extraordinary situations.

The process, outcomes and context of the sanitation change induced by the Swachh Bharat Mission in rural Jharkhand, India.

BACKGROUND: The Indian Swachh Bharat Mission (SBM) was launched in 2014 with the goal to make India open defecation (OD) free by October 2019. Although it is known that the ambitious goal was not achieved, the nature of the sanitation change brought about by the SBM in different parts of India is poorly understood. One reason is a dearth of case studies that would shed light on the performance of the SBM simultaneously across its different domains. This article provides an example of such study. Employing a Process, Outcomes, Context approach, the objective is to understand the process and outcomes of the SBM-induced sanitation change in a specific context of rural Jharkhand. METHODS: The study utilizes data collected through field research conducted in the rural areas of Ranchi district, Jharkhand, a state in east-central India. This data was obtained via repeated cross-sectional household surveys conducted at the beginning and at the end of the SBM, supplemented by key informant interviews with SBM stakeholders. FINDINGS: We identified political support of SBM implementation and its acceptance amongst the population. Female community workers became key agents of SBM implementation at local level. The SBM increased toilet coverage in the study area from 15% to 85% and lowered the OD rate from 93% to 26%. It substantially reduced structural inequalities in access to toilets, furthered social sanitation norms, improved some of the attitudes towards toilet use, but impacted less on hygiene and sanitation knowledge. The implementation mainly concentrated on the construction of subsidized toilets but less on improving public understanding of safe sanitation practices. CONCLUSIONS: Although the SBM reduced sanitation inequalities in access to toilets in the study area, the behaviour change component was underplayed, focusing more on spreading normative sanitation messages and less on public education. Sustainability of the observed sanitation change remains a key question for the future. This article calls for more systematic production of geographically situated knowledge on the performance of sanitation interventions.

Promotion of market-based sanitation in Ethiopia: a case study from Wolaita zone.

Ethiopia increased the availability of latrines notably, but the sanitation facilities rarely meet hygienic standards. Therefore, the market-based sanitation (MBS) programme has been implemented across the country for nearly a decade to expand the market and boost the demand for hygienic sanitation products and services. While it does not seem that the MBS would bring any notable change in sanitation conditions so far, its implementation challenges are not adequately understood. To address this gap, this article delves into the grassroots-level implementation of MBS in the Wolaita zone. The study relies on qualitative data gathered through interviews with various stakeholders, examining both demand- and supply-side challenges. Some issues identified were external to MBS implementation, such as high inflation and an unstable political and security situation in Ethiopia. Additionally, the study reveals that more general deficiencies of the Ethiopian health extension program, including the stress and discouragement of local change agents (health extension workers, health development army members) due to workloads and low remuneration, have adversely impacted MBS delivery. The implementation of MBS has also not effectively addressed the affordability of hygienic sanitation products. On the supply side, economic constraints and organizational inefficiencies have hindered the development of the sanitation market, preventing it from reaching a critical mass. Our research suggests that MBS alone will not suffice to improve sanitation in Ethiopia.

Household-level sanitation in Ethiopia and its influencing factors: a systematic review.

BACKGROUND: Within the past two decades, Ethiopia has achieved one of the fastest reductions of open defecation worldwide. This change can be attributed to the implementation of a national sanitation strategy that focused on facilitating community demand for latrine adoption and use of basic self-constructed latrines but less on other preconditions of hygienic sanitation. Recognition of sanitation by policymakers also catalyzed primary research in this area. As such, the synthesis of the available evidence is both warranted and possible. In this article, we thus decided to assess available primary evidence on the household-level sanitation in Ethiopia and its influencing factors. METHODS: We searched primary studies that present findings on the role of factors influencing household-level sanitation outcomes in Ethiopia. We typologically classified sanitation outcomes analyzed in identified literature and computed pooled estimates for the most prevalent ones (measures of latrine availability and use). We characterized thematic types (themes and sub-themes) of influential sanitation drivers and used network analysis to examine the relational patterns between sanitation outcomes and their influencing factors. FINDINGS: We identified 37 studies that met our inclusion criteria-all but one published after 2009. The general latrine coverage pooled across 23 studies was 70% (95% CI: 62-77%), the share of improved latrines pooled across 15 studies was 55% (95% CI: 41-68%), and latrine use pooled across 22 studies was 72% (95% CI: 64-79%). Between-study heterogeneity was high, and no time trends were identified. The identified sanitation outcomes were classified into eight types and factors reported to influence these outcomes were classified into 11 broader themes and 43 more specific sub-themes. Factors around the quality of latrines represented the most frequent sub-theme of consequential drivers. We found that the available research focused predominantly on outcomes concerning the initial adoption and use of basic latrines, emulating the main focus of national sanitation strategy. By contrast, research on drivers of the sustainability of sanitation change and, in particular, on the upgrading of latrines, has been rare despite its urgency. There is a high need to redirect the focus of sanitation research in Ethiopia towards understanding these factors on both the demand and supply side.

A System Using Artificial Intelligence to Detect and Scare Bird Flocks in the Protection of Ripening Fruit.

Flocks of birds may cause major damage to fruit crops in the ripening phase. This problem is addressed by various methods for bird scaring; in many cases, however, the birds become accustomed to the distraction, and the applied scaring procedure loses its purpose. To help eliminate the difficulty, we present a system to detect flocks and to trigger an actuator that will scare the objects only when a flock passes through the monitored space. The actual detection is performed with artificial intelligence utilizing a convolutional neural network. Before teaching the network, we employed videocameras and a differential algorithm to detect all items moving in the vineyard. Such objects revealed in the images were labeled and then used in training, testing, and validating the network. The assessment of the detection algorithm required evaluating the parameters precision, recall, and F1 score. In terms of function, the algorithm is implemented in a module consisting of a microcomputer and a connected videocamera. When a flock is detected, the microcontroller will generate a signal to be wirelessly transmitted to the module, whose task is to trigger the scaring actuator.

Risk of radiation-associated intracranial malignancy after stereotactic radiosurgery: a retrospective, multicentre, cohort study.

BACKGROUND: A major concern of patients who have stereotactic radiosurgery is the long-term risk of having a secondary intracranial malignancy or, in the case of patients with benign tumours treated with the technique, the risk of malignant transformation. The incidence of stereotactic radiosurgery-associated intracranial malignancy remains unknown; therefore, our aim was to estimate it in a population-based study to assess the long-term safety of this technique. METHODS: We did a population-based, multicentre, cohort study at five international radiosurgery centres (Na Homolce Hospital, Prague, Czech Republic [n=2655 patients]; Ruber International Hospital, Madrid, Spain [n=1080], University of Pittsburgh Medical Center, Pittsburgh, PA, USA [n=1027]; University of Virginia, Charlottesville, VA, USA [n=80]; and NYU Langone Health System, New York, NY, USA [n=63]). Eligible patients were of any age, and had Gamma Knife radiosurgery for arteriovenous malformation, trigeminal neuralgia, or benign intracranial tumours, which included vestibular or other benign schwannomas, WHO grade 1 meningiomas, pituitary adenomas, and haemangioblastoma. Patients were excluded if they had previously had radiotherapy or did not have a minimum follow-up time of 5 years. The primary objective of the study was to estimate the incidence of stereotactic radiosurgery-associated intracranial malignancy, including malignant transformation of a benign lesion or development of radiation-associated secondary intracranial cancer, defined as within the 2 Gy isodose line. Estimates of age-adjusted incidence of primary CNS malignancies in the USA and European countries were retrieved from the Central Brain Tumor Registry of the United States (CBTRUS) and the International Agency for Research on Cancer (IARC) Global Cancer statistics. FINDINGS: Of 14 168 patients who had Gamma Knife stereotactic radiosurgery between Aug 14, 1987, and Dec 31, 2011, in the five contributing centres, 4905 patients were eligible for the analysis (had a minimum follow-up of 5 years and no history of previous radiation therapy). Diagnostic entities included vestibular schwannomas (1011 [20·6%] of 4905 patients), meningiomas (1490 [30·4%]), arteriovenous malformations (1089 [22·2%]), trigeminal neuralgia (565 [11·5%]), pituitary adenomas (641 [13·1%]), haemangioblastoma (29 [0·6%]), and other schwannomas (80 [1·6%]). With a median follow-up of 8·1 years (IQR 6·0-10·6), two (0·0006%) of 3251 patients with benign tumours were diagnosed with suspected malignant transformation and one (0·0002%) of 4905 patients was considered a case of radiosurgery-associated intracranial malignancy, resulting in an incidence of 6·87 per 100 000 patient-years (95% CI 1·15-22·71) for malignant transformation and 2·26 per 100 000 patient-years (0·11-11·17) for radiosurgery-associated intracranial malignancy. Two (0·0004%) of 4905 patients developed intracranial malignancies, which were judged unrelated to the radiation field. Overall incidence of radiosurgery-associated malignancy was 6·80 per 100 000 patients-years (95% CI 1·73-18·50), or a cumulative incidence of 0·00045% over 10 years (95% CI 0·00-0·0034). The overall incidence of 6·8 per 100 000, which includes institutions from Europe and the USA, after stereotactic radiosurgery was found to be similar to the risk of developing a malignant CNS tumour in the general population of the USA and some European countries as estimated by the CBTRUS and IARC data, respectively. INTERPRETATION: These data show that the estimated risk of an intracranial secondary malignancy or malignant transformation of a benign tumour in patients treated with stereotactic radiosurgery remains low at long-term follow-up, and is similar to the risk of the general population to have a primary CNS tumour. Although prospective cohort studies with longer follow-up are warranted to support the results of this study, the available evidence suggests the long-term safety of stereotactic radiosurgery and could support physicians counselling patients on Gamma Knife stereotactic radiosurgery. FUNDING: None.

Comprehending practitioners' assessments of community-led total sanitation.

Around 2.3 billion people in developing countries still lack access to improved sanitation facilities and almost one billion practice open defecation (OD). The Community-Led Total Sanitation (CLTS) has recently become a particularly popular approach used in more than 60 countries. CLTS is a behavior-change approach that aims to ignite community action and make OD socially unacceptable without providing any external financial or material support to individual households. CLTS is sometimes perceived as a revolutionary approach that has proven to be highly cost-effective in abolishing OD. However, it has been criticized for its use of unethical practices and questioned with respect to the sustainability of its outcomes and the limited health benefits it can generate. Based on semi-structured interviews with development workers experienced in the implementation of CLTS in 14 different countries, this paper seeks to examine practical views on the issues surrounding this approach. We found that despite acknowledging some of the controversies and the possibly limited sustainability of results, CLTS is generally considered an effective and satisfactory tool for improving sanitation conditions. Practitioners first of all accentuate the normative importance of the elimination of OD attained through CLTS without weighting on (the absence of) evidence on the longer term effects or impacts on health. However, a need for various modifications of CLTS according to local social and natural environments was strongly expressed, including changes that go against the core principles of CLTS like no subsidies and no technical assistance principles.

The Potential of Utilizing Air Temperature Datasets from Non-Professional Meteorological Stations in Brno and Surrounding Area.

An increasing number of individuals and institutions own or operate meteorological stations, but the resulting data are not yet commonly used in the Czech Republic. One of the main difficulties is the heterogeneity of measuring systems that puts in question the quality of outcoming data. Only after a thorough quality control of recorded data is it possible to proceed with for example a specific survey of variability of a chosen meteorological parameter in an urban or suburban region. The most commonly researched element in the given environment is air temperature. In the first phase, this paper focuses on the quality of data provided by amateur and institutional stations. The following analyses consequently work with already amended time series. Due to the nature of analyzed data and their potential use in the future it is opportune to assess the appropriateness of chronological and possibly spatial interpolation of missing values. The evaluation of seasonal variability of air temperature in the scale of Brno city and surrounding area in 2015-2017 demonstrates, that the enrichment of network of standard (professional) stations with new stations may significantly refine or even revise the current state of knowledge, for example in the case of urban heat island phenomena. A cluster analysis was applied in order to assess the impact of localization circumstances (station environment, exposition, etc.) as well as typological classification of the set of meteorological stations.

Gamma knife radiosurgery for local recurrence of glioblastoma.

OBJECTIVE: Local recurrence of glioblastoma is observed in most patients after standard oncologic treatment (surgery, chemotherapy and radiotherapy). Stereotactic radiosurgery with the Leksell Gamma Knife (SRS with LGK) was used to treat recurrent tumors in selected cases, and retrospective analysis of treatment outcome was performed. METHODS: Altogether 126 patients were treated for glioblastoma at our center from 1992-2014. Sixty-nine patients (55%) were male and 57 (45%) female, with a median age of 56 years (range 17-80 years). Prior to LGK radiosurgery, 123 (98%) underwent surgery, 126 (100%) radiotherapy and 116 (92%) chemotherapy. The median Karnofsky score before LGK radiosurgery was 90% (range 50-100), and the median time from GBM diagnosis to LGK radiosurgery was 12 months (range 1-96 months). The median tumor volume was 3.75 cm3 (range 0.04-37.10 cm3). LGK radiosurgery was performed in a single fraction with a median minimal tumor dose of 12 Gy (range 10-25 Gy) on a median 50% (range 40-86%) isodose line. Two and more LGK radiosurgeries were performed in 19 (15%) cases, a median interval of 9.6 months (range 2-45 months) from the initial LGK radiosurgery. The median prescribed dose in these patients was 12.6 Gy (range 10-15 Gy), and the median volume 5.8 cm3 (range 0.1-13.7 cm3). RESULTS: The median survival from GBM diagnosis was 20 months (range 6-237 months). The median survival after LGK radiosurgery was 7 months (range 1-223 months). The one year survival after LGK radiosurgery was 27%, 2 years 8%, and more than 3 years 4%. Tumor regression on MR images was observed in 17% of patients at a median interval of 7 months. The median interval to tumor progression on MR images after LGK treatment was 8.5 months. No treatment-related radionecrosis with expansive behaviour was detected after radiosurgery. CONCLUSION: We show that LGK radiosurgery is a safe palliative treatment modality in patients with recurrent GBM.

Comparison of the Convolution algorithm with TMR10 for Leksell Gamma knife and dosimetric verification with radiochromic gel dosimeter.

The Convolution algorithm, implemented in Leksell GammaPlan® ver. Here, 10, is the first algorithm for Leksell Gamma Knife that takes heterogeneities into account and models dose build-up effects close to tissue boundaries. The aim of this study was preliminary comparison of the Convolution and TMR10 algorithms for real clinical cases and dosimetric verification of the algorithms, using measurements in a phantom. A total of 25 patients involved in comparison of the Convolution and TMR10 algorithms were divided into three groups: patients with benign tumors close to heterogeneities, patients with functional disorders, and patients with tumors located far from heterogeneities. Differences were observed especially in the group of patients with tumors close to heterogeneities, where the difference in maximal dose to critical structures for the Convolution algorithm was up to 15% compared to the TMR10 algorithm. Dosimetric verification of the algorithm was performed, using a radiochromic gel dosimeter based on Turnbull blue dye in a special heterogeneous phantom. Relative dose distributions measured with the radiochromic gel dosimeter agreed very well with both the TMR10 and Convolution calculations. We observed small discrepancies in the direction in which the largest inhomogeneity was positioned. Verification results indicated that the Convolution algorithm provides a different dose distribution, especially in regions close to heterogeneities and particularly for lower isodose volumes. However, the results obtained with gamma analyses in the gel dosimetry experiment did not verify the assumption that the Convolution algorithm provides more accurate dose calculation.

Two-year experience with the commercial Gamma Knife Check software.

The Gamma Knife Check software is an FDA approved second check system for dose calculations in Gamma Knife radiosurgery. The purpose of this study was to evaluate the accuracy and the stability of the commercial software package as a tool for independent dose verification. The Gamma Knife Check software version 8.4 was commissioned for a Leksell Gamma Knife Perfexion and a 4C unit at the University of Pittsburgh Medical Center in May 2012. Independent dose verifications were performed using this software for 319 radiosurgery cases on the Perfexion and 283 radiosurgery cases on the 4C units. The cases on each machine were divided into groups according to their diagnoses, and an averaged absolute percent dose difference for each group was calculated. The percentage dose difference for each treatment target was obtained as the relative difference between the Gamma Knife Check dose and the dose from the tissue maximum ratio algorithm (TMR 10) from the GammaPlan software version 10 at the reference point. For treatment plans with imaging skull definition, results obtained from the Gamma Knife Check software using the measurement-based skull definition method are used for comparison. The collected dose difference data were also analyzed in terms of the distance from the treatment target to the skull, the number of treatment shots used for the target, and the gamma angles of the treatment shots. The averaged percent dose differences between the Gamma Knife Check software and the GammaPlan treatment planning system are 0.3%, 0.89%, 1.24%, 1.09%, 0.83%, 0.55%, 0.33%, and 1.49% for the trigeminal neuralgia, acoustic neuroma, arteriovenous malformation (AVM), meningioma, pituitary adenoma, glioma, functional disorders, and metastasis cases on the Perfexion unit. The corresponding averaged percent dose differences for the 4C unit are 0.33%, 1.2%, 2.78% 1.99%, 1.4%, 1.92%, 0.62%, and 1.51%, respectively. The dose difference is, in general, larger for treatment targets in the peripheral regions of the skull owing to the difference in the numerical methods used for skull shape simulation in the GammaPlan and the Gamma Knife Check software. Larger than 5% dose differences were observed on both machines for certain targets close to patient skull surface and for certain targets in the lower half of the brain on the Perfexion, especially when shots with 70 and/or 110 gamma angles are used. Out of the 1065 treatment targets studied, a 5% cutoff criterion cannot always be met for the dose differences between the studied versions of the Gamma Knife Check software and the planning system for 40 treatment targets.

Dosimetric characteristics and quality control tests for the collimator sectors of the Leksell Gamma Knife(®) Perfexion(TM).

PURPOSE: The purpose of this study was to evaluate the dosimetric characteristics of each sector of the Leksell Gamma Knife Perfexion (LGK PFX) and to develop tests that can be done for the routine quality assurance checks of the sectors of the LGK PFX. METHODS: The following tests were performed to evaluate the dosimetric characteristics of the sectors: (1) Flash-radiation dose for the 16 mm collimator, (2) transit-radiation dose for the 8 and 4 mm collimators, (3) sector leakage within the radiation cavity and, (4) sector output uniformity. In these tests, the Elekta ABS phantom was used. A micropoint ion-chamber Exradin A16 was placed at the center of the phantom for all measurements. RESULTS: With the version 8.0 of the control software of the MCU in the LGK PFX, the average flash-radiation dose per sector for the 16 mm collimator was measured to be 0.423 ± 0.003 cGy, and the average transit-radiation dose per sector for the 8 and 4 mm collimators was measured to be 0.169 ± 0.0009 and 0.147 ± 0.020 cGy, respectively. The calibration dose rate on the day of measurements was 280.8 cGy/min. Here, the authors have introduced a new concept of "equivalent-time-duration" (ETD) to represent the time duration, during which the flash-radiation or the transit-radiation dose is delivered. The ETD is a quotient of the measured dose of the flash-radiation or the transit-radiation and the respective calibrated dose rate for the 16, 8, or 4 mm collimator. The ETD constancy is an indicator of the constancy of the sector movements. The average value of ETD per sector was measured to be 724 ± 6, 313 ± 2, and 311 ± 45 ms for the 16, 8, and 4 mm collimators, respectively. During monthly spot checks, the authors have been measuring the total ETD for the flash-radiation when all eight sectors are open with the 16 mm collimator. The average value of the total ETD of the last 40 consecutive months was measured to be 642 ± 10 ms. This number is a useful quality parameter for the LGK PFX, which can be used to establish the base-line performance of the collimators of the LGK PFX. The reader is alerted that with the newly introduced version 9.0 of the control software of the MCU in the LGK PFX, the flash-radiation and the transit-radiation doses have become practically zero due to the fact that the treatment time is now corrected to compensate for these radiation doses. The sector output uniformity for the 16, 8, and 4 mm collimators was determined to be 98.9%, 97.3%, and 96.6%, respectively. The total leakage radiation with in the radiation cavity from all sectors was measured to be 0.17% of the dose output for the 16 mm collimator. CONCLUSIONS: Our measurements show that the dosimetric characteristics of all sectors of the LGK PFX are satisfactory. The authors recommend that the sector performance of the LGK PFX be determined initially at the time of installation of the LGK PFX and thereafter, at least annually. Similarly, our recommendation is that the total flash-radiation dose for the 16 mm collimator and the corresponding ETD value be measured on a monthly basis. Should any change in the sector movement occur, it will be revealed by the sector performance and the measurement of ETD.

Assessment of variation in Elekta plastic spherical-calibration phantom and its impact on the Leksell Gamma Knife calibration.

PURPOSE: Traditionally, the dose-rate calibration (output) of the Leksell Gamma Knife (LGK) unit is performed using a 160 mm diameter plastic spherical phantom provided by the vendor of the LGK, Elekta Instrument AB. The purpose of this study was to evaluate variations in the Elekta spherical phantom and to assess its impact and use for the LGK calibration. METHODS: Altogether, 13 phantoms from six different centers were acquired, 10 of these phantoms were manufactured within the past 10 years and the last 3 approximately 15-20 years ago. To assess variation in phantoms, the diameter and mass densities were measured. To assess the impact on LGK calibration, the output of two models of LGK (LGK Perfexion and LGK 4C) were measured under identical irradiation conditions using all 13 phantoms for each LGK model. RESULTS: The mean measured deviation in diameter from expected nominal 160 mm for 13 phantoms was 0.51 mm (range of 0.09-1.51 mm). The mean measured phantom mass density for 13 phantoms was 1.066 +/- 0.019 g/cm3 (range of 1.046-1.102 g/cm3). The percentage deviation of output for individual phantom from mean of 13 phantom outputs ranged from -0.37% to 0.55% for LGK Perfexion. Similarly, the percentage deviation of output for individual phantom from mean of 13 phantom outputs ranged from -0.72% to 0.47% for LGK 4C. CONCLUSIONS: This study demonstrated that small variations in terms of phantom size and mass density of the phantom material do not have a significant impact on dose-rate measurements of the Leksell Gamma Knife. Also, date of manufacture of the phantom did not show up to be a significant factor in this study.

Persistent left superior vena cava connected through the left upper pulmonary vein to the left atrium: an unusual pathway for paradoxical embolization and a rare cause of recurrent transient ischaemic attack.

Ischaemic stroke, especially in the younger population, is an important cause of morbidity and mortality. When compared with the older population, the underlying aetiology of stroke in the young includes higher rates of cardioembolic disease and congenital heart anomalies. Paradoxical embolism may be an important cause of ischaemic cerebral events, which has to be ruled out in patients with no other evident stroke aetiology. A persistent left superior vena cava (PLSVC) that drains into the left atrium is a very rare congenital anomaly occurring in postnatal life and may be the cause of embolic events such as ischaemic stroke with potentially devastating consequences. For diagnostic purposes, we recommend the use of contrast transthoracic and transesophageal echocardiography with contrast agent application through the left arm peripheral intravenous line, which makes it possible to ascertain the presence of a right-to-left shunt. Computed tomography of the chest is recommended for a PLSVC with atypical left atrial drainage confirmation. Consequent endovascular occlusion of the PLSVC is feasible and can be performed with minimal procedural risk. If this cause of paradoxical embolism is not taken into consideration, the first manifestation of this clinical entity could be underestimated, increasing the likelihood of ischaemic stroke recurrence with potentially disabling or fatal consequences. We report the diagnosis and successful endovascular repair of this anomaly. This case report also aims to highlight the importance of close collaboration between neurologists, cardiologists and radiologists needed for accurate identification of stroke aetiology in young patients.

Unintended attenuation in the Leksell Gamma Knife Perfexion calibration-phantom adaptor and its effect on dose calibration.

The calibration of Leksell Gamma Knife Perfexion (LGK PFX) is performed using a spherical polystyrene phantom 160 mm in diameter, which is provided by the manufacturer. This is the same phantom that has been used with LGK models U, B, C, and 4C. The polystyrene phantom is held in irradiation position by an aluminum adaptor, which has stainless steel side-fixation screws. The phantom adaptor partially attenuates the beams from sectors 3 and 7 by 3.2% and 4.6%, respectively. This unintended attenuation introduces a systematic error in dose calibration. The overall effect of phantom-adaptor attenuation on output calibration of the LGK PFX unit is to underestimate output by about 1.0%.

Measurement of relative output factors for the 8 and 4 mm collimators of Leksell Gamma Knife Perfexion by film dosimetry.

Three types of films, Kodak EDR2, Gafchromic EBT, and Gafchromic MD-V2-55, were used to measure relative output factors of 4 and 8 mm collimators of the Leksell Gamma Knife Perfexion. The optical density to dose calibration curve for each of the film types was obtained by exposing the films to a range of known doses. Ten data points were acquired for each of the calibration curves in the dose ranges from 0 to 4 Gy, 0 to 8 Gy, and 0 to 80 Gy for Kodak EDR2, Gafchromic EBT, and Gafchromic MD-V2-55 films, respectively. For the measurement of relative output factors, five films of each film type were exposed to a known dose. All films were scanned using EPSON EXPRESSION 10000 XL scanner with 200 dpi resolution in 16 bit gray scale for EDR2 film and 48 bit color scale for Gafchromic films. The scanned images were imported in the red channel for both Gafchromic films. The background corrections from an unexposed film were applied to all films. The output factors obtained from film measurements were in a close agreement both with the Monte Carlo calculated values of 0.924 and 0.805 for 8 and 4 mm collimators, respectively. These values are provided by the vendor and used as default values in the vendor's treatment planning system. The largest differences were noted for the Kodak EDR 2 films (-2.1% and -4.5% for 8 and 4 mm collimators, respectively). The best agreement observed was for EBT Gafchromic film (-0.8% and +0.6% differences for 8 and 4 mm collimators, respectively). Based on the present values, no changes in the default relative output factor values were made in the treatment planning system.

A simple and effective method for validation and measurement of collimator output factors for Leksell Gamma Knife Perfexion.

Accurate determination of collimator output factors is important for Leksell Gamma Knife radiosurgery. The new Leksell Gamma Knife Perfexion system has a completely redesigned collimator system and the collimator output factors are different from the other Leksell Gamma Knife models. In this study, a simple method was developed to validate the collimator output factors specifically for Leksell Gamma Knife Perfexion. The method uses double-shot exposures on a single film to eliminate repeated setups and the necessity to acquire dose calibration curves required for the traditional film exposure method. Using the method, the collimator output factors with respect to the 16 mm collimator were measured to be 0.929 +/- 0.009 and 0.817 +/- 0.012 for the 8 mm and the 4 mm collimator, respectively. These values are in agreement (within 2%) with the default values of 0.924 and 0.805 in the Leksell Gamma Plan treatment planning system. These values also agree with recently published results of 0.917 (8 mm collimator) and 0.818 (4 mm collimator) obtained from the traditional methods. Given the efficiency of the method, measurement and validation of the collimator output factors can be readily adopted in commissioning and quality assurance of a Leksell Gamma Knife Perfexion system.

Radiosurgery for desmoplastic melanoma of the head and neck using the Leksell Gamma Knife Perfexion technology: a case report.

A 44-year-old male developed chronic cancer pain caused by a progressive desmoplastic melanoma involving the mandibular division of the trigeminal nerve. The patient had failed local resection, conformal radiation therapy and chemotherapy, but was eligible for stereotactic radiosurgery using a new technology. Intraoperative stereotactic magnetic resonance and computed tomography imaging were fused to define the tumor volume and to create a conformal radiosurgery dose plan. The radiosurgery target volume was 8.6 ml. A marginal dose of 17 Gy at the 50% isodose was prescribed. The entire procedure was performed on an outpatient basis. The Leksell Gamma Knife Perfexion technology increases the spectrum of treatable pathologies located in the cranial base and head and neck regions.

Efficiency and dose planning comparisons between the Perfexion and 4C Leksell Gamma Knife units.

AIMS: We analyzed the efficiency of the Leksell Gamma Knife Perfexion (LGK PFX) in the treatment of multiple metastases and benign tumors. We also compared treatment planning conformity between LGK PFX and LGK 4C for benign tumors. METHOD: Over a 6-week interval, 37 patients (21 with multiple brain metastases and 16 with benign tumors) underwent radiosurgery using LGK PFX at the University of Pittsburgh. We created dose plans for all patients using Leksell Gamma Plan for LGK PFX and LGK 4C. The same doses were prescribed for both LGK PFX and LGK 4C. RESULTS: No significant difference was observed between LGK 4C and LGK PFX for total beam-on time. The median reduction in setup time on the LGK PFX was 53 min per patient (range 19-125 min) for multiple metastases. The median reduction in setup time on the LGK PFX for benign tumors was 16 min per patient (range 5-53 min). There was no significant difference in the dose conformality between LGK 4C and LGK PFX. CONCLUSIONS: This study demonstrated that in addition to its enhanced cranial reach, LGK PFX provided a significant improvement in efficiency for patients with multiple brain metastases. For benign tumor radiosurgery LGK PFX provided improvement in efficiency without a significant difference in conformality.

Dosimetric comparison of the Leksell Gamma Knife Perfexion and 4C.

OBJECT: The recently introduced Leksell Gamma Knife (LGK) Perfexion is an entirely new system with a different beam geometry compared with the LGK 4C. The new Perfexion system has 192 cobalt-60 sources that are fixed on 8 sectors (each sector has 24 sources). Each sector can be moved independently of the others and can be set to 1 of 5 different positions: 3 positions defining collimator sizes of 4, 8, and 16 mm; an off position (sources are blocked); and a home position. The purpose of this study is to compare the dosimetric characteristics of the GK 4C and the Perfexion models. This comparison is important especially for the treatment of functional disorders when only a single shot with the 4- or 8-mm collimator is used. METHODS: A 160-mm-diameter spherical polystyrene phantom was used for all measurements and calculations. The irradiation geometry consisted of the placement of a single shot at the center of this phantom. Comparisons were made among different dosimetric parameters obtained from calculations performed using Leksell GammaPlan v. 8.0 and measurements performed using film dosimetry. The dosimetric parameters investigated were dose profiles for all collimators in all 3 stereotactic planes (x, y, and z) including the full width at half maximum and the penumbra for each profile, cumulative dose-volume histograms, the volume encompassed by the 50% isodose surface, the mean doses delivered to a defined matrix volume, and relative output factors for all collimator sizes. RESULTS: There was excellent agreement between the dosimetric parameters of GK 4C and Perfexion for the 4- and 8-mm collimators. CONCLUSIONS: The results of this study suggest that consistent treatments of functional disorders will be delivered using either GK 4C or Perfexion.