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An overview of the recent operations and the main results of cesium injection in the Source for the Production of Ions of Deuterium Extracted from Rf plasma (SPIDER) negative ion source are described in this contribution. In experiments without cesium injection, all SPIDER plants were tested to verify the basic expectations on the operational parameters (e.g., electron cooling effectiveness of magnetic filter field) and to determine its operational region. For beam properties, it was shown that the current density varies across the beam in the vertical direction. In preliminary cesium experiments, the expected increase of negative ion current and simultaneous decrease of co-extracted electrons were found, along with the influence of the control parameters (polarization of the plasma electrodes, magnetic filter field) on the SPIDER beam uniformity in the horizontal and vertical directions. It was shown that non-Gaussian tails can be identified in the angular distribution on the plane perpendicular to the beam propagation direction. Stray particles, nonhomogeneous beam and large divergence might result in unexpected heat and particle loads over ITER neutral beam injector (NBI) accelerator grids; it is the goal of SPIDER to assess and possibly to identify suitable methods for controlling these beam features. A major shutdown, planned for late 2021, to solve the issues identified during the operation and to carry out scheduled modifications, is outlined. Such improvements are expected to allow SPIDER to pursue the ITER requirements in terms of negative ion current, electron-to-ion ratio, and beam duration.

ITER envisages the use of two heating neutral beam injectors plus an optional one as part of the auxiliary heating and current drive system, to reach the desired performances during its various phases of operation. The 16.5 MW expected neutral beam power per injector is several notches higher than worldwide existing facilities.In order to enable such development, a Neutral Beam Test Facility (NBTF) was established at Consorzio RFX, exploiting the synergy of two test beds, called SPIDER and MITICA. SPIDER is dedicated developing and char-acterizing large efficient negative ion sources at relevant parameters in ITER-like conditions: source and accel-erator located in the same vacuum where the beam propagates, immunity to electromagnetic interferences of multiple radio-frequency (RF) antennas, avoidance of RF-induced discharges on the outside of the source. Three years of experiments on SPIDER have addressed to the necessary design modifications to enable full perfor-mances. The source is presently under a long shut-down phase to incorporate learnings from the experimental campaign, in particular events/issues occurred during operation, which led to the identification of improvement opportunities/necessities (e.g. RF discharges, local burns, water leaks, other damages, configuration/design upgrades to maximize chances/margin to quest target parameters).Parallelly, developments on MITICA, the full-scale prototype of the ITER Neutral Beam Injector (NBI) featuring a 1 MV accelerator and ion neutralization, are underway including manufacturing of the beam source, accel-erator and the beam line components, while power supplies and auxiliary plants, already installed, are under final testing and commissioning.Integration, commissioning and tests of the 1 MV power supplies are essential for this first-of-kind system, unparalleled both in research and industry field. 1.2 MV dc insulating tests of high voltage components were successfully completed. The integrated test to confirm 1 MV output by combining invertor systems, DC gener-ators and transmission lines extracted errors/accidents in some components. To realize a concrete system for ITER, said events have been addressed and solutions for the repair and the improvement of the system were developed.Hence, NBTF is emerging as a necessary facility, due to the large gap with existing injectors, effectively dedicated to identify issues and find solutions to enable successful ITER NBI operations in a time bound fashion. The lessons learned during the implementation on NBTF and future perspectives are here discussed.

Source for production of ion of deuterium extracted from rf plasma (SPIDER) is the 100 keV negative ion source prototype of the ITER neutral beam injector. The cooling plant is one of the SPIDER auxiliary systems where ultrapure water (UPW) is used as the cooling media, thanks to its advantageous properties such as good cooling performance and high resistivity. Water resistivity needs to be maintained above certain values during SPIDER operation to enable the electrical insulation of in-vessel components that operate at different voltages. Nonetheless, degradation of water resistivity was observed in some circuits during operation. Water resistivity degradation had a negative impact on the SPIDER experimental campaign since it limits cooling plant availability. To understand the cause for the observed water degradation, sampling points were installed to sample water during operation. Ad hoc experiments have been performed on the worst affected circuit, and water samples were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Circulation experiments were conducted at constant temperature, pressure, and flow rate to assess water degradation by monitoring water conductivity increase. ICP-MS analyses on water from the worst affected circuit revealed the presence of Cu in relevant quantities and Zn. Corrosion induced by the presence of a non-compatible component with SPIDER requirements was found. The identified component was made of a galvanized steel plate, carbon steel, and brass. This was found responsible for the contamination of the cooling loop and its water properties' degradation.

PURPOSE To assess the dosimetric advantages of apertures in intracranial single fraction proton radiosurgery. MATERIALS AND METHODS Six neuroma and 10 meningioma patients were investigated. For each patient, six plans were computed, with two spot spacing and three aperture settings (no apertures, 5 and 8 mm margin between aperture and clinical target volume [CTV]). All plans were optimized on the CTV with the same beam arrangement and the same single-field robust optimization (2 mm setup errors, 3.5% range uncertainties). Robustness analysis was performed with 0.5 and 1.0 mm systematic setup errors and 3.5% range uncertainties. CTV coverage in the perturbed scenarios and healthy brain tissue sparing in the surrounding of the CTV were compared. RESULTS Meningiomas were larger and at a shallow depth than neuromas. In neuromas, spot spacing did not affect OAR doses or the robustness of CTV coverage and the apertures reduced brain dose without any significant impact on CTV robustness. In meningiomas, smaller spot spacing produced a reduction in brain V5Gy and improved robustness of CTV coverage; in addition, an 8 mm margin aperture reduced low and medium brain tissue doses without affecting robustness in the 0.5 mm perturbed scenario. A 5 mm margin aperture caused a reduction of plan robustness. CONCLUSION The optimal use of apertures is a trade-off between sparing of low and medium dose to the healthy brain and robustness of target coverage, also depending on size and depth of the lesion.

The first ever built full-scale prototype of the ITER heating neutral beam injector is the MITICA experiment at PRIMA-NBTF (Neutral Beam Test Facility), under realization in Padua, Italy. The MITICA experiment includes many auxiliary plants; this paper is focused on the simulation and verification of the air cooling system of the High Voltage Power Supply (−1 MVdc), hosted in a Faraday cage (HVD1, High Voltage Deck1) inside a dedicated Building (High Voltage Hall, HVH) at PRIMA-NBTF. The HVD1 hosts the MITICA ISEPS (Ion Source Power Supply) in a two-floor cage, air insulated to ground for -1MVdc, with huge dimensions 12.5 m (L) × 8.4 m (W) × 9.6 m (H). Severe cleanliness constraints are required in the HVH hosting the HVD1, due to the high voltage operative conditions (the −1 MVdc Faraday cage is air insulated). The thermal behavior and air distribution in HVH are investigated as described in this paper.

The first ever built full-scale prototype of the ITER heating neutral beam injector is the MITICA experiment at PRIMA Neutral Beam Test Facility, under realization in Padova, Italy. This experiment consists of several in-vessel components: most of them are actively cooled by a large Cooling Plant, still under construction. Coolant is deionized water produced by a Chemical Control System (CCS). In the PRIMA facility, a cryogenic plant (currently in manufacturing phase) is also foreseen to serve the cryopumps to be installed in the MITICA Beam Line Vessel. During the installation of cooling plant and the design phase of cryogenic plant, two different issues came into evidence: waste water (produced by the CCS during operations) could not be delivered directly into the public network and the warm compressor of the cryogenic plant, originally air-cooled, changed to a water-cooled system. For the first issue the solution was found in a Water Treatment Unit (WTU) that requires the supply of hot water to distil the wastewater and to concentrate it. The second issue and the need to balance the heat loads and the cost and space constraints lead to an innovative system: it is essentially based on a high temperature water-water heat pump, by means of which the heat rejected by the warm compressor is used to heat up the WTU. Moreover this will reduce the operational costs by introducing a significant energy saving.

Purpose To design and implement a new protontherapy planning method for the treatment of shallow lesions with PBS and to compare it to the standard method. Methods In order to treat tumors located at depths lower than our minimum range available (4.1 cm), a pre-absorber is needed (Range Shifter – RS). The RS also causes scatter, so it is associated to some dose degradation, which should be minimized. We studied three tumor localizations (pelvic, H&N and Cranio-Spinal-Irradiation) requiring RS and we created three plans for each case: one is the standard method with the RS always used as close as possible to the patient, one with the RS used only for the shallow part of the tumor but completely retracted (Figure a) and the third as the second but with the RS as close as possible to the patient (Figure b). We called these last two Range Shifter Optimization (RSO) techniques. We compared those plans in terms of dose distribution quality, delivery time and patient QA results. Results In tables dosimetric results and delivery time are reported. A very good sparing of OARs are obtained when the RSO technique is used with the RS extended toward the patient with no significative loss in terms of target coverage. Patient QA gave very good results in terms of γ Passing Rate (PR) (3%,3 mm) for both RSO techniques (mean 98.09%, minimum 93.75%) while the standard had some very low PR (minimum 81.09%) while the average was still good (97.73%). The delivery time increased but was still acceptable in terms of patient compliance. Conclusions We developed a new planning technique for shallow lesions and we demonstrated its superiority (plan quality and patient specific QA results) with respect to the standard method. This technique is now routinely used to treat patients in our centre. Download : Download high-res image (448KB) Download : Download full-size image Download : Download high-res image (680KB) Download : Download full-size image Download : Download high-res image (440KB) Download : Download full-size image

To reach fusion conditions and control the plasma configuration in ITER, the next step in tokamak fusion research, two neutral beam injectors (NBIs) will supply 16.5 MW each, by neutralizing accelerated negative hydrogen or deuterium ions. The requirements of ITER NBIs (40A/1 MeV D- ions for ≤1 h, 46A/870 keV H- ions for ≤1000 s) have never been simultaneously attained. So in the Neutral Beam Test Facility (NBTF, Consorzio RFX, Italy) the operation of the full-scale ITER NBI prototype (MITICA) will be tested and optimised up to full performances, focussing on accelerator (including voltage holding), beam optics, neutralisation, residual ion removal. The NBTF includes also the full-scale prototype of the ITER NBI source with 100 keV particle energy (SPIDER), for early investigation of: negative ion production and extraction, source uniformity, negative ion current density and beam optics. This paper will describe the main results of the first two years of SPIDER operation, devoted to characterizing plasma and beam parameters, including investigation of RF-plasma coupling efficiency and magnetic filter field effectiveness in reducing co-extracted electrons. SPIDER is progressing towards the first caesium injection, which aims at increasing the negative ion density. A major shutdown, planned for 2021, to solve the issues identified during the operation and to carry out programmed modifications, will be outlined. The installation of each MITICA power supply and auxiliary system is completed; in-vessel mechanical components are under procurement by Fusion for Energy (F4E). Integration, commissioning and test of the power supplies, procured by F4E and QST, as the Japanese Domestic Agency (JADA), will be presented. In particular, 1.0MV insulating tests were carried out step-by-step and successfully completed. In 2020 integrated tests of the power supplies on the accelerator dummy load started, including the assessment of their resilience to accelerator grid breakdowns using a short-circuit device located in vacuum. The aggressive programme, to validate the NBI design at NBTF and to meet ITER schedule (requiring NBIs in operation in 2032), will be outlined. Unfortunately, in 2020 the coronavirus disease infection affected the NBTF activities. A solution to proceed with integrated power tests despite the coronavirus is presented.

Corrosion-erosion phenomena occurred in the cooling circuits of primary heat transfer systems of the prototype of the ITER-like ion source named SPIDER, in particular during the first phase of the experiment activity which began in May 2018. Demineralised water circulating in cooling channels of components subjected to high heat loads reacts with inner channel surfaces made of copper alloys, aluminium, and stainless steel thus producing thinning of cooling channel walls. Then, resistivity degradation phenomenon of the demineralised water occurred and resistivity was measured before and after a working cycle to plan water treatment operations in order to maintain maximum availability of the SPIDER plants. This degradation was observed to be particularly fast during experimental campaigns: despite predictions, this effect is more significant in the less complex cooling circuit linked to Ion Source and Extraction Power Supply (ISEPS), feeding the Ion Source polarized to ground at -100 kV dc. Corrosion-erosion phenomena were investigated considering dissolved O2 and CO2, pH, flow velocity and turbulence, galvanic corrosion at dissimilar metal junctions, leakage current through high voltage cooling breaks, temperature, and water conductivity. This paper presents the first data of water parameters, monitored during experimental sessions by using the Cooling Plant and ISEPS Local Control Systems. Basing on collected data, some hypotheses were put forward on the behaviour of circuits and components, in order to propose possible mitigation actions and to reduce the frequency at which the cooling water should be renewed to keep the resistivity value in the required operative range.

Aims: During and after re-irradiation of relapsed high-grade gliomas (rHGG) variation of edema (ED) is a common event and may translate into neurological symptoms, clinical deterioration and steroid use modi- fication. In magnetic resonance imaging (MRI), ED is usually evaluated with T2 or fluid-attenuated inversion recovery (FLAIR) sequences. Aim of the study was to report a quantitative analysis of radiation-induced ED during and after proton therapy (PT) re-irradiation of rHGG.ty-one patients (pts) with rHGG were re-irradiated with PT at our institution. 22 pts underwent MRI early before, during, at the end as well as 1 month after the treatment and were included in the analysis. All pts received 36 GyRBE in 18 fractions. ED was evaluated and contoured on 88 MRI scans using T2 and FLAIR sequences (5 mm thickness). ED volume (in cc) was Gross Tumor Volume. We analyzed the temporal change of ED.Results: Eighteen pts were treated for recurrent glioblastoma and 4 for anaplastic gliomas. Median (Med) CTV was 78,48 cc (range, 12-259 cc). Med ED volume at the baseline, mid-therapy, at the end, and 1 month after treatment was 63 cc (range, 7-265), 83 (range, 9-242), 85 (range 10-194), 69 (range 9-200), respectively. During treatment ED increased in 16 pts (72%) and decreased in 6 (27%). Such increase of ED volume was associated with mild symptoms only in 8 pts (50%) and was controlled with modification of steroids dose. One month after treatment ED decreased in 10 pts (45%), increased in 7 (32%) and was stable in 5 (23%). Six out of 7 pts (86%) with increased ED needed modification of steroids dose. During follow up 2 pts (9%) developed radionecrosis (RN - diagnosed at imaging) with mild symptoms controlled with steroids. In pts who presented RN, ED volume increased of 130% during treatment. In pts who registered increased ED without RN, the mean ED volume increase during the treatment was of 82%. Pts who presented RN had a mean CTV volume of 67.39 cc. ciated with increase of ED volume during treat- ment. Such variation often does not need modification of steroid use. ED volume seems to decrease after the end of the treatment. ED volume during treatment sig- nificantly increase in pts who experience RN after re- irradiation and could predict the development of RN. CTV volume does not seems to predict the development of RN.

Purpose To develop normal tissue complication probability (NTCP) models for radiation-induced alopecia (RIA) in brain tumor patients treated with proton therapy (PT). Methods and materials We analyzed 116 brain tumor adult patients undergoing scanning beam PT (median dose 54 GyRBE; range 36–72) for CTCAE v.4 grade 2 (G2) acute (≤90 days), late (>90 days) and permanent (>12 months) RIA. The relative dose-surface histogram (DSH) of the scalp was extracted and used for Lyman-Kutcher-Burman (LKB) modelling. Moreover, DSH metrics (Sx: the surface receiving ≥ X Gy, D2%: near maximum dose, Dmean: mean dose) and non-dosimetric variables were included in a multivariable logistic regression NTCP model. Model performances were evaluated by the cross-validated area under the receiver operator curve (ROC-AUC). Results Acute, late and permanent G2-RIA was observed in 52%, 35% and 19% of the patients, respectively. The LKB models showed a weak dose-surface effect (0.09 ≤ n ≤ 0.19) with relative steepness 0.29 ≤ m ≤ 0.56, and increasing tolerance dose values when moving from acute and late (22 and 24 GyRBE) to permanent RIA (44 GyRBE). Multivariable modelling selected S21Gy for acute and S25Gy, for late G2-RIA as the most predictive DSH factors. Younger age was selected as risk factor for acute G2-RIA while surgery as risk factor for late G2-RIA. D2% was the only variable selected for permanent G2-RIA. Both LKB and logistic models exhibited high predictive performances (ROC-AUCs range 0.86–0.90). Conclusion We derived NTCP models to predict G2-RIA after PT, providing a comprehensive modelling framework for acute, late and permanent occurrences that, once externally validated, could be exploited for individualized scalp sparing treatment planning strategies in brain tumor patients.

The in-vessel actively cooled components of the SPIDER Beam Source shall be drained and dried in case of major maintenance to limit as much as possible atmospheric corrosion inside the circuits and components, to prevent water spreading, and to allow the execution of vacuum leak tests of the circuits before re-installation inside the vacuum vessel. These operations are needed after the first phase of experiment exploitation of SPIDER begun in May 2018. Drying system consists of evaporation by mass transport of coolant from dead volumes to the dried nitrogen. The drying system capabilities are set for ranges of gas pressure 2-8 bar(a) and heating temperature (70-110 °C) consistently with design and manufacturing in accordance with the Sound Engineering Practice (low hazard level without CE marking applying the Pressure Equipment Directive). On the other hand, the maximum drying temperature is careful evaluations to avoid risks of damage due to excessive thermal deformations, in particular at joints between dissimilar materials and ceramic breaks. Heating up calculations demonstrate the need to increase the gas inlet pressure up to the maximum allowable value in order to decrease the time required for heating: the estimated time to heat up the Electron Dump decreases from about 10 to 3 minutes by increasing the nitrogen pressure from 2.0 bar(a) to 8.0 bar(a). Drying out calculations show that the evaporation capacity of nitrogen increases with the gas inlet temperature; moreover, higher pressures will reduce the drying out duration from about 11 minutes at 2.0 bar(a) to about 3 minutes at 8.0 bar(a). All the calculated values demonstrate the feasibility of the drying system with parameters to be monitored, in particular the gas humidity at the inlet and at the outlet of the component to be dried. A dedicated procurement was set for the realization of the Drying System as a portable skid.

SPIDER is a 100 kV negative hydrogen/deuterium ion beam source, under operation at Consorzio RFX, which will be exploited for assessment and optimization of the radio frequency source that will be employed in the ITER Neutral Beam Injectors. The in-vessel actively cooled components shall be drained in case of major maintenance to limit as much as possible atmospheric corrosion inside the circuits and components, to prevent water spreading, and finally to allow the execution of vacuum leak tests of the circuits before re-installation of the Beam Source inside the Vacuum Vessel. Draining of hydraulic circuits is first foreseen by gravity after opening of the end connections of hydraulic circuits and then by blowing-out with inert gas. Injection of pressurized nitrogen is simulated by means of one-dimensional models to perform transient two-phase analyses of the blowing-out process with identification of flow regimes. Moreover, three-dimensional transient two-phase analyses are used to deeply investigate the behaviour of components made of complex geometries. Parametric simulations as function of the inlet pressure are carried out to characterize the blowing-out process in terms of flow rate, evacuation time and draining efficiency. The gas and water flow rates are evaluated recognising Rayleigh-Taylor instabilities which occur when the light nitrogen is pushing the heavy water. The maximum allowable pressure for blowing out, in accordance with the Pressure Equipment Directive (PED), is fixed to 1.1 MPa in order to stay in the Sound Engineering Practice category (low hazard level without CE marking). Among all the applied draining pressures, the range between 0.15-0.4 MPa is considered to perform the blowing out process in order to limit the gas speed and take into account possible pressure fluctuations. The analyses were fundamental to design a blowing-out system capable of satisfying the requirements of the different components belonging to the SPIDER Beam Source.

Background: Different modern radiation therapy treatment solutions for breast cancer (BC) and regional nodal irradiation (RNI) have been proposed. In this study, we evaluate the potential reduction in radiation-induced skin morbidity obtained by intensity modulated proton therapy (IMPT) compared with intensity modulated photon therapy (IMXT) for left-side BC and RNI. Material and Methods: Using CT scans from 10 left-side BC patients, treatment plans were generated using IMXT and IMPT techniques. A dose of 50 Gy (or Gy [RBE] for IMPT) was prescribed to the target volume (involved breast, the internal mammary, supraclavicular, and infraclavicular nodes). Two single filed optimization IMPT (IMPT1 and IMPT2) plans were calculated without and with skin optimization. For each technique, skin dose-metrics were extracted and normal tissue complication probability (NTCP) models from the literature were employed to estimate the risk of radiation-induced skin morbidity. NTCPs for relevant organs-at-risk (OARs) were also considered for reference. The non-parametric Anova (Friedman matched-pairs signed-rank test) was used for comparative analyses. Results: IMPT improved target coverage and dose homogeneity even if the skin was included into optimization strategy (HIIMPT2 = 0.11 vs. HIIMXT = 0.22 and CIIMPT2 = 0.96 vs. CIIMXT = 0.82, p < .05). A significant relative skin risk reduction (RR = NTCPIMPT/NTCPIMXT) was obtained with IMPT2 including the skin in the optimization with a RR reduction ranging from 0.3 to 0.9 depending on the analyzed skin toxicity endpoint/model. Both IMPT plans attained significant OARs dose sparing compared with IMXT. As expected, the heart and lung doses were significantly reduced using IMPT. Accordingly, IMPT always provided lower NTCP values. Conclusions: IMPT guarantees optimal target coverage, OARs sparing, and simultaneously minimizes the risk of skin morbidity. The applied model-based approach supports the potential clinical relevance of IMPT for left-side BC and RNI and might be relevant for the setup of cost-effectiveness evaluation strategies based on NTCP predictions, as well as for establishing patient selection criteria.

Heating neutral beam (HNB) injectors, necessary to achieve burning conditions and to control plasma instabilities in ITER, are characterized by such demanding parameters that a neutral beam test facility (NBTF) dedicated to their development and optimization is being realized in Padua (Italy) with direct contributions from the Italian government (through Consorzio RFX as the host entity) and the ITER international organization (with kind contributions from the ITER domestic agencies of Europe, Japan and India) and technical and scientific support from various European laboratories and universities. The NBTF hosts two experiments: SPIDER, devoted to ion source optimization for the required source performance, and MITICA, the full-size prototype of the ITER HNB, with an ion source identical to SPIDER. This paper gives an overview of the progress towards NBTF realization, with particular emphasis on issues discovered during this phase of activity and on solutions adopted to minimize the impact on the schedule and maintain the goals of the facilities. The realization of MITICA is well advanced; operation is expected to start in 2023 due to the long procurement time of the in-vessel mechanical components. The beam source power supplies, operating at 1 MV, are in an advanced phase of realization; all high-voltage components have been installed and the complex insulation test phase began in 2018. At the same time, construction and installation of SPIDER plant systems was successfully completed with their integration into the facility. The mechanical components of the SPIDER ion source were installed inside the vessel and connected to the plants. Integrated commissioning with the control, protection and safety systems ended positively and the first experimental phase has begun. The first results of the SPIDER experiment, with data from operational diagnostics, and the plans for the 1 MV insulation tests on the MITICA high-voltage components are presented.

Purpose To present an advanced junction concept in craniospinal irradiation (CSI) by proton pencil beam scanning (PBS). Materials and methods In PBS CSI, whole brain irradiation (WBI) is commonly delivered by opposed lateral-beams, whereas spine irradiation is delivered by posterior entrances. Since lateral-beams would cross a large portion of the patient at the shoulder level, the junction between WBI and spine irradiation cannot extend below that level, thus the size of the lateral-beams needs to be limited and the number of required isocenters can increase. To overcome such limitation, a pseudo-junction was introduced below the posterior fossa, to turn in this region the WBI beam arrangement to a single posterior beam pointed at the same isocenter, that was matched to the posterior spinal beam more caudally, below shoulder level, in the true-junction. After assessing robustness of the technique to range and setup uncertainties, twenty-three treated patients were reviewed to estimate the percentage that might benefit of being treated by two instead of three isocenters. Results Target coverage at the junction levels resulted robust, with D95% > 95% on pseudo-junction and D95% > 90% on the true-junction. By the advanced junction concept, 91% of patients might by treated with only two isocenters, whereas, by the conventional method, 83% of patients required three isocenters. Conclusion With the presented junction concept the number of isocenters can be reduced, with a consequent relevant reduction of treatment time, which is particularly valuable in the management of pediatric patients under anesthesia.

Rosette-forming glioneuronal tumors (RGNTs) are rare, grade I, central nervous system (CNS) tumors typically localized to the fourth ventricle. We describe a 9-year-old girl with dizziness and occipital headache. A magnetic resonance imaging (MRI) revealed a large hypodense posterior fossa mass lesion in relation to the vermis, with cystic component. Surgical resection of the tumor was performed. A RGNT diagnosis was made at the histopathological examination. During follow-up, the patient experienced a first relapse, which was again surgically removed. Eight months after, MRI documented a second recurrence at the local level. She was a candidate for the proton beam therapy (PBT) program. Three years after the end of PBT, the patient had no evidence of disease recurrence. This report underlines that, although RGNTs are commonly associated with an indolent course, they may have the potential for aggressive behavior, suggesting the need for treatment in addition to surgery. Controversy exists in the literature regarding effective management of RGNTs. Chemotherapy and radiation are used as adjuvant therapy, but their efficacy management has not been adequately described in the literature. This is the first case report published in which PBT was proposed for adjuvant therapy in place of chemotherapy in RGNT relapse.

Background Proton therapy has proven to be effective and safe in the treatment of radioresistant skull base tumors such as chordomas. Thanks to the peculiar physical properties of the proton beam, radiation energy is delivered in a narrow space called the Bragg peak and the surrounding normal tissues receive a minimal amount of the radiation dose. This is important to lower the risk of radiation-induced damage, especially in children. However, local adverse effects in proximity to the target volume may occur. In particular, the development of moyamoya syndrome (MMS) has been rarely reported in children receiving proton beam therapy for brain tumors. Case Description We report on a child who developed rapidly progressive MMS after proton beam therapy for a clivus chordoma. A combined indirect revascularization procedure by encephalo-duro-arterio-synangiosis and encephalo-myo-synangiosis was performed with good neuroradiologic and clinical outcome. Conclusions Regardless of the presence of known risk factors for MMS, strict neuroimaging surveillance is indicated in all patients treated with radiotherapy including those receiving proton beam therapy. We suggest that an early revascularization procedure should be considered in patients with worsening symptoms and/or sign of neuroradiologic progression of cerebral vasculopathy. This management of MMS could lower the risk of permanent neurologic deficits and improve patients' quality of life.

Purpose Proton therapy for the treatment of breast cancer is acquiring increasing interest, due to the potential reduction of radiation-induced side effects such as cardiac and pulmonary toxicity. While several in silico studies demonstrated the gain in plan quality offered by pencil beam scanning (PBS) compared to passive scattering techniques, the related dosimetric uncertainties have been poorly investigated so far. Methods Five breast cancer patients were planned with Raystation 6 analytical pencil beam (APB) and Monte Carlo (MC) dose calculation algorithms. Plans were optimized with APB and then MC was used to recalculate dose distribution. Movable snout and beam splitting techniques (i.e. using two sub-fields for the same beam entrance, one with and the other without the use of a range shifter) were considered. PTV dose statistics were recorded. The same planning configurations were adopted for the experimental benchmark. Dose distributions were measured with a 2D array of ionization chambers and compared to APB and MC calculated ones by means of a γ analysis (agreement criteria 3%, 3 mm). Results Our results indicate that, when using proton PBS for breast cancer treatment, the Raystation 6 APB algorithm does not allow obtaining sufficient accuracy, especially with large air gaps. On the contrary, the MC algorithm resulted into much higher accuracy in all beam configurations tested and has to be recommended. Conclusions Centers where a MC algorithm is not yet available should consider a careful use of APB, possibly combined with a movable snout system or in any case with strategies aimed at minimizing air gaps.

In June 2018 the SPIDER device, which is the full-size prototype of the negative ion source and extractor for the ITER Heating Neutral Beam has entered the first operation phase at the Neutral Beam Test Facility (NBTF) in Padova, Italy. This paper describes the present status of the device, the experimental plans and the results obtained during the first experimental campaign of the radio-frequency driven plasma source.

The ITER tokamak requires two injectors of neutral beams resulting from the neutralisation of accelerated negative hydrogen/deuterium ions. To optimise the source operation, a specific test facility ("PRIMA") was established in Padova, comprising the experiment SPIDER (full-size negative ion source with 40A beam, 100keV particle energy). The design of SPIDER accelerator was based on the most advanced numerical codes available for the investigation of the expected beam properties. Several diagnostic systems will characterise source and beam during the experiments. In view of the operation, this paper describes the preparation of the experiments by means of numerical simulations of the accelerator. The simulations provide also estimates of the current and power deposited onto the accelerator grids and will be the basis for further work aimed at computing the expected measurements by the various beam diagnostics.

Purpose The gradient-optimized methods are overcoming the traditional feathering methods to plan field junctions in craniospinal irradiation. In this note, a new gradient-optimized technique, based on the use of a background dose, is described. Methods Treatment planning was performed by RayStation (RaySearch Laboratories, Stockholm, Sweden) on the CT scans of a pediatric patient. Both proton (by pencil beam scanning) and photon (by volumetric modulated arc therapy) treatments were planned with three isocenters. An ‘in silico’ ideal background dose was created first to cover the upper-spinal target and to produce a perfect dose gradient along the upper and lower junction regions. Using it as background, the cranial and the lower-spinal beams were planned by inverse optimization to obtain dose coverage of their relevant targets and of the junction volumes. Finally, the upper-spinal beam was inversely planned after removal of the background dose and with the previously optimized beams switched on. Results In both proton and photon plans, the optimized cranial and the lower-spinal beams produced a perfect linear gradient in the junction regions, complementary to that produced by the optimized upper-spinal beam. The final dose distributions showed a homogeneous coverage of the targets. Discussion Our simple technique allowed to obtain high-quality gradients in the junction region. Such technique universally works for photons as well as protons and could be applicable to the TPSs that allow to manage a background dose.

The ITER project requires at least two Neutral Beam Injectors (NBIs), each accelerating to 1MV a 40A beam of negative deuterium ions, to deliver to the plasma a power of about 33 MW for one hour as additional heating.Since these requirements have never been experimentally met, it was recognized necessary to build-up a test facility, named PRIMA (Padova Research on ITER Megavolt Accelerator), in Italy, including both a 100 kV full-size negative ion source (SPIDER - Source for Production of Ion of Deuterium Extracted from Rf plasma) and a prototype of the whole 1 MV ITER injector (MITICA - Megavolt ITER Injector & Concept Advancement).The mission of SPIDER is to increase the understanding of the source operation and to optimize the source performance in terms of extracted current density, current uniformity and duration.The SPIDER experiment needs a dedicated Cooling Plant to remove up to 10 MW heat loads applied during the one hour pulses to the beam source, the beam dump/calorimeter and the power supplies. The total water flow rate necessary to remove the heat and guarantee the optimal control of temperatures is about 150 kg/s at full operational conditions.The plant is widespread over the whole PRIMA site area and is characterized by several physical interfaces with the SPIDER experiment, the related power supplies and control system and finally with PRIMA buildings and civil plants. A well-equipped system of sensors and feed-back control system is also present to guarantee the correct performances of the plant during different operational phases.The paper deals with the installation and testing phases of the plant under execution, with particular emphasis on integration problems, electrical insulation, tests of immunity to electromagnetic interference, vibration issues, monitoring and safety issues for possible activated water and finally the acceptance tests before integrated commissioning.

SPIDER is one of two projects of the ITER Neutral Beam Test Facility under construction in Padova, Italy, at the Consorzio RFX premises. It will have a 100 keV beam source with a full-size prototype of the radiofrequency ion source for the ITER neutral beam injector (NBI) and also, similar to the ITER diagnostic neutral beam, it is designed to operate with a pulse length of up to 3600 s, featuring an ITER-like magnetic filter field configuration (for high extraction of negative ions) and caesium oven (for high production of negative ions) layout as well as a wide set of diagnostics. These features will allow a reproduction of the ion source operation in ITER, which cannot be done in any other existing test facility. SPIDER realization is well advanced and the first operation is expected at the beginning of 2018, with the mission of achieving the ITER heating and diagnostic NBI ion source requirements and of improving its performance in terms of reliability and availability. This paper mainly focuses on the preparation of the first SPIDER operations - integration and testing of SPIDER components, completion and implementation of diagnostics and control and formulation of operation and research plan, based on a staged strategy

The ITER Neutral Beam Test Facility (NBTF), called PRIMA (Padova Research on ITER Megavolt Accelerator), is hosted in Padova, Italy and includes two experiments: MITICA, the full-scale prototype of the ITER heating neutral beam injector, and SPIDER, the full-size radio frequency negative-ions source. The NBTF realization and the exploitation of SPIDER and MITICA have been recognized as necessary to make the future operation of the ITER heating neutral beam injectors efficient and reliable, fundamental to the achievement of thermonuclear-relevant plasma parameters in ITER. This paper reports on design and R&D carried out to construct PRIMA, SPIDER and MITICA, and highlights the huge progress made in just a few years, from the signature of the agreement for the NBTF realization in 2011, up to now - when the buildings and relevant infrastructures have been completed, SPIDER is entering the integrated commissioning phase and the procurements of several MITICA components are at a well advanced stage

Neutral beam injection is one of the most important methods of plasma heating in thermonuclear fusion experiments, allowing the attainment of fusion conditions as well as driving the plasma current. Neutral beams are generally produced by electrostatically accelerating ions, which are neutralised before injection into the magnetised plasma. At the particle energy required for the most advanced thermonuclear devices and particularly for ITER, neutralisation of positive ions is very inefficient so that negative ions are used. The present paper is devoted to the description of the phenomena occurring when a high-power multi-ampere negative ion beam travels from the beam source towards the plasma. Simulation of the trajectory of the beam and of its features requires various numerical codes, which must take into account all relevant phenomena. The leitmotiv is represented by the interaction of the beam with the background gas. The main outcome is the partial neutralisation of the beam particles, but ionisation of the background gas also occurs, with several physical and technological consequences. Diagnostic methods capable of investigating the beam properties and of assessing the relevance of the various phenomena will be discussed. Examples will be given regarding the measurements collected in the small flexible NIO1 source and regarding the expected results of the prototype of the neutral beam injectors for ITER. The tight connection between measurements and simulations in view of the operation of the beam is highlighted.

BACKGROUND Stereotactic radiosurgery (SRS) is an important treatment option for intracranial lesions and several photon-SRS techniques have been developed. Proton therapy (PT) has special characteristics that allow normal tissues to be spared better as well as greater homogeneity than with the use of photons, but limited data are available for proton-SRS. Nowadays, PT-SRS is delivered only with passive scattering technique while active pencil beam scanning (PBS) that is considered the most advanced proton technique has not been reported for SRS treatments yet. Here we report early clinical outcomes of PBS PT SRS. MATERIAL AND METHODS Between June 2017 and January 2019, 14 patients (pts) with 20 lesions underwent PBS PT SRS at our institution. Median age was 62 years (range, 28–87). Median Karnofsky performance status was 90 (range, 70–100). Six were male. Tumors included 16 meningiomas (MG) and 4 vestibular schwannomas (VS). Median GTV was 1.05 cc (range, 0.2–2.71). Dose prescription was 12 Gy radiobiologic equivalent (RBE) in one fraction for VS and 15 GyRBE in one fraction for MG. Pts were immobilized using a frameless system: Type-S proton overlay and Type-S proton mask (CIVCO medical solutions, Kalona, IA, USA) together with Moldcare headrest (Q-Fix systems, Avondale, PA, USA). All pts were treated with PBS PT using 2–3 fields with single field optimization technique, and using min-max robust robust optimization (2 mm setup errors, 3.5% range uncertainties), with a Monte Carlo algorithm and 1 mm grid size. Toxicity was assessed using Common Terminology Criteria for Adverse Events version 4.0. RESULTS Median follow-up (FU) was 9 months (range, 3–22). All pts completed the treatment with excellent compliance and no side effects were registered during the procedure. Registered acute side effects include grade 1 (14%) fatigue, grade 2 (7%) headache, and grade 2 (28%) alopecia. There were no grade 3 or higher acute toxicities. Registered late side effects include grade 1 (7%) headache, and grade 1 (14%) alopecia. There were no grade 3 or higher late toxicities. Currently, absolute tumor control is 100% regardless the type of tumor. Despite the short FU radiological reduction was registered in 9 lesions (45%). CONCLUSION PBS PT SRS is a feasible and safe treatment in pts with MG or VS. A high radiological response rate was observed. Longer FU is necessary to assess definitive safety and efficacy.

Purpose Proton therapy reduces lung dose and mean heart dose in breast cancer irradiation in adjuvant breast cancer, in particular with nodal involvement [1] . In this work we compare 10 selected intensity modulated photon therapy (IMXT) treatment cases selected from the sending institution with PBS proton therapy. Methods and materials The eligibly criteria of the sending institution were: poor coverage of the target volumes, unfavourable dose volume histograms (DVH) to the organs at risk (OAR) lung and heart or wide irradiated volume (IV) with static IMXT. The type of case were heterogeneous as shown in Table 1. All plans were performed on the CT and volumes send applying a class solution of 3 proton field with range shifter with treatment planning system (TPS) Raystation. All plans were performed in robust Single Field Optimization technique (rSFO) optimizing the target and the OAR heart and the ipsilateral lung. The optimization was done with clinical pencil beam algorithm and 5 mm geometrical robust optimization tool provided by the TPS. No robust optimization of the range was applied. Results Comparing the proton and photon plans there was a significant improvement in at least one of the following parameter: IV, DVH of lung, DVH of heart for each case (e.g. Fig. 1). Conclusion The results of this study are promising. The heuristic eligibility method provide positive answer in 100% of the cases. Further work are necessary to assess role of range errors of proton peak.

To investigate the range errors made in treatment planning due to the presence of the immobilization devices along the proton beam path.The measured water equivalent thickness (WET) of selected devices was measured by a high-energy spot and a multi-layer ionization chamber and compared with that predicted by treatment planning system (TPS). Two treatment couches, two thermoplastic masks (both un-stretched and stretched) and one headrest were selected. At TPS, every immobilization device was modelled as being part of the patient. The following parameters were assessed: CT acquisition protocol, dose-calculation grid-sizes (1.5 and 3.0mm) and beam-entrance with respect to the devices (coplanar and non-coplanar). Finally, the potential errors produced by a wrong manual separation between treatment couch and the CT table (not present during treatment) were investigated.In the thermoplastic mask, there was a clear effect due to beam entrance, a moderate effect due to the CT protocols and almost no effect due to TPS grid-size, with 1mm errors observed only when thick un-stretched portions were crossed by non-coplanar beams. In the treatment couches the WET errors were negligible (0.3mm) regardless of the grid-size and CT protocol. The potential range errors produced in the manual separation between treatment couch and CT table were small with 1.5mm grid-size, but could be0.5mm with a 3.0mm grid-size. In the headrest, WET errors were negligible (0.2mm).With only one exception (un-stretched mask, non-coplanar beams), the WET of all the immobilization devices was properly modelled by the TPS.

SPIDER is one of the two projects of the ITER Neutral Beam Test Facility (NBTF) under construction in Padova, Italy, at Consorzio RFX premises; it is the full-size prototype of the radiofrequency (RF) ion source for ITER Neutral Beam Injector (NBI), with beam energy of 100keV, designed to operate with pulse length up to 3600 s, featuring ITER-like filter field configuration, caesium oven layout and a wide set of diagnostics. These features will allow reproducing the ion source operation like in ITER as cannot be done in any other existing test facility. SPIDER realization is well advanced and the first operation is expected at the beginning of 2018, with the mission to prove the possibility of achieving the ITER NBI ion source target requirements and of improving its performance in terms of reliability and availability. This paper mainly focuses on the preparation of the first SPIDER operations: integration and testing of SPIDER components, completion and implementation of diagnostics and control and workout of operation and research plan, based on a staged strategy.

Megavolt ITER Injector Concept Advancement is the full scale prototype of the heating and current drive neutral beam injectors for ITER, to be built at Consorzio RFX (Padova). The engineering design of its components is challenging: the total heat loads they will be subjected to (expected between 2 and 19 MW), the high heat fluxes (up to 20 MW/m(2)), and the beam pulse duration up to 1 h, set demanding requirements for reliable active cooling circuits. In support of the design, the thermo-hydraulic behavior of each cooling circuit under steady state condition has been investigated by using one-dimensional models. The final results, obtained considering a number of optimizations for the cooling circuits, show that all the requirements in terms of flow rate, temperature, and pressure drop are properly fulfilled.

PRIMA (Padova Research Injector Megavolt Accelerated) is the name of the ITER neutral beam facility currently under construction at the RFX Consortium located in Padua – Italy. PRIMA consists of two injectors which will test at the same time the ion source (SPIDER) and the whole system (MITICA). Both injectors accelerate negative deuterium and hydrogen ions with a maximum energy of 1 MeV for MITICA and 100 keV for SPIDER, with a maximum beam current of 40 A. Accelerated ions are stopped on a CuCrZr alloy calorimeter. Operation in deuterium leads to production of an intense neutron flux through D–D and D–T reactions on the calorimeter panels which is likely to activate materials and components around the injectors, among which the corrosion products formed in the cooling loops; the radioactivity of the activated corrosion products (ACPs) may persist even after injector shutdown, representing a relevant radiation protection issue during repair and inspection activities. In the present paper the occupational radiation exposure (ORE) is evaluated. The total amount of radioactivity produced inside the cooling loops is calculated under different operative conditions and the radiation dose received by workers carrying out maintenance activities on the injector is also assessed for both experiments.

The ITER torus and neutral beam cryopumps are complex vacuum pumps which will be designed to the build-to-print level stage for the call for tender for manufacturing. Although being completely different in size, the pumps share the same concept of cryosorption on activated charcoal. Thus, the design procedure itself can follow the same generic workflow. The requirements on the pumps are summarized and the status of design evolution is described. Both design packages require specific R&D for experimental clarification and design validation. Two examples for this approach are given, namely the characterization of the closing forces of the torus pump inlet valve, and the measurement of hydraulic resistance coefficients of hydroformed components.

This paper presents a proposal of Cooling Plant for two new Neutral Beam experiments called MITICA and SPIDER to be realized in Padova (Italy). A large amount of Power (up to 70 MW) has to be removed from in-vessel components and auxiliary systems belonging to these two experiments. Different experimental scenarios (pulse duration ranging from few seconds up to 3600 s), requirements for operating temperature, coolant quality and voltage holding are taken into account in this conceptual design proposal. To reduce the radiological risks due to possible presence of activated corrosion products (ACP) in some water cooled components suitable design choices have been analysed. This work was carried out by considering carefully a lot of different aspects like operability, standardization of components, maintenance and repair, optimization of the installed power and the overall costs of the plant. Experiment components with similar requirements are grouped in the same primary circuits where fine temperature regulation, water quality monitoring and calorimetric measurements are the main characteristics. Each primary circuit (PC) is connected to secondary circuits which allow thermal dissipation and, in some cases, also component preheating. Secondary circuits are connected to two large basins the water of which is cooled down by active cooling rejection system such as cooling towers and air coolers. In this way the requirement for impulsive heat dissipation is fulfilled by the water basins allowing to install a less powerful active rejection system and so reducing the total costs. A large effort was done to guarantee good plant integration with the Experiment Main Hall (in which MITICA and SPIDER are located) and other technical supplies, buildings and areas. Other special requirements for stand-alone systems like Draining and Drying System, Pressure Test System and Chemical Control System are also part of this work.

BACKGROUND: To report preliminary results of re-irradiation with proton therapy (PT) with or without chemotherapy (CHT) in difficult-to-treat recurrent glioblastoma (rGBM): patients (pts) were selected for PT because of the large tumor size or proximity to dose-limiting organs at risk that previously had received near-maximum dose tolerance during the first radiation course MATERIAL AND METHODS: Between January 2015 and January 2018, 34 pts with rGBM were re-irradiated with PT. All pts had been previously treated with Stupp regimen. Twenty-nine (85%) were re-irradiated at first relapse/progression, 5 at the second/third one. Nine pts (26%) were re-irradiated after partial tumor resection. Median (med) age and KPS at re-irradiation were 56 years and 90%, respectively. Med time between prior radiotherapy and PT was 13 months. Target definition was based on CT, MR, and 18F-DOPA PET imaging. Gross Tumor Volume (GTV) included any area of contrast enhancement after contrast medium administration plus any pathological PET uptake regions. Clinical Target Volume (CTV) was generated by adding to GTV a 3-mm margin. Med CTV volume was 47 cc (range, 13–153 cc). All pts received 36 GyRBE in 18 fractions. PT was delivered with or without chemotherapy as follows: eight (23.5%) pts (Group 1) also received concomitant TMZ (75 mg/m2/die, 7 days/week); 4 (12%) pts (Group 2) also received concomitant (as above) and adjuvant TMZ (150–200 mg/m2/die, 5 days/month); 9 (26.5%) pts (Group 3) received PT only; 13 (38%) pts (Group 4) received PT followed by CHT (different regimens/drugs). All pts were treated with active pencil beam scanning PT. Registered side effects were graded according to Common Terminology Criteria for Adverse Events (CTCAE) version 4.0. Treatment response was assessed according to Response Assessment in Neuro-Oncology criteria. Survival and progression-free survival after re-irradiation were calculated from initiation of PT until tumor progression or death (by any cause), using the Kaplan Meier method RESULTS: All pts completed the treatment without breaks. There were no grade 3 or higher acute toxicities. One pts developed TMZ-related grade 1 neutropenia. There were no grade 3 or higher late toxicities. During follow-up five pts (15%) developed radionecrosis (diagnosed at imaging) with mild symptoms controlled with steroids. The med progression-free survival (PFS) was 6.3 months, while 6-month PFS rate was 60%. The med PFS was 6.8, 4.3, 5.4, and 5.5 for Group 1-2-3-4, respectively. Med overall survival (OS) after PT was 10.7 months CONCLUSION: PT re-irradiation of difficult-to-treat rGBM showed to be feasible and safe even with concomitant and adjuvant chemotherapy administration. Despite the small number of patients of this series and the retrospective nature of the study PFS and OS rates are promising and deserve further evaluation in a larger pts sample to assess the most effective strategy

BACKGROUND: To report preliminary results of active beam scanning proton therapy (PT) for large skull base benign meningiomas. MATERIAL AND METHODS: Thirty-three patients (pts) with large skull base meningiomas were treated with PT between January 2015 and February 2018. Median age was 53 years (range, 28–82) while KPS ranged between 60 and 100 (median 90); 26 were female (79%), and 7 were male (21%). Twelve pts (36%) had histologically proven World Health Organization (WHO) Grade I tumors. In remaining pts diagnosis was based on the typical imaging appearance of benign meningioma. All patients received PT for residual, progressive or non-operable lesions. Newly diagnosed tumors received total dose of 50 GyRBE (RBE: relative biologic effectiveness) while progressing meningiomas 54 GyRBE. All the treatments were delivered at 2 GyRBE per fraction. Treatment planning was based on morphological magnetic resonance imaging (MRI) with contrast enhancement medium administration. All pts received also 68-Ga-DOTATOC-PET. Any area of contrast enhancement on MRI was used to identify the gross tumor volume. We used the pathological distribution of 68Ga-DOTATOC in brain tissue to identify the so-called Biological Tumor Volume. Gross tumor volume ranged from 21 to 107 cc. Toxicity was assessed according to Common Terminology Criteria for Adverse Events version 4.0. Median follow-up time was 9 months (range, 3–37). RESULTS: All pts completed the treatment without breaks. Acute side effects include grade 1 (21%) and grade 2 (9%) skin erythema, grade 1 (9%) and grade 2 (9%) alopecia, grade 1 (48%) fatigue, grade 1 (6%) and grade 2 (15%) conjunctivitis, grade 1 (15%) pain, grade 1 (15%) blurred vision, grade 1 (15%) headache, and grade 2 (15%) skin hyperpigmentation. One pt experienced grade 3 pain. There were no further grade 3 or higher acute toxicities. Late side effects include grade 1 (9%) and grade 2 (9%) alopecia, grade 1 (21%) fatigue, grade 1 (9%) and grade 2 (6%) headache, grade 1 (6%) dizziness, grade 1 (6%) blurred vision, grade 1 (6%) and grade 2 (6%) pain, grade 1 (6%) dry eye, and grade 1 (15%) skin hyperpigmentation. One pts experienced grade 3 pain. There were no further grade 3 or higher late toxicities. One pts (3%) with cavernous sinus meningioma experienced complete obstruction of intracavernous carotid artery with mild transient symptoms that resolved in few days and brain tissue ischemia detected at MRI (grade 2). Before irradiation this pts already had a meningioma-related near-complete obstruction of the intracavernous carotid artery and received a vascular surgery evaluation. Currently, absolute tumor control is 100%. Moreover, relief of symptoms recorded before irradiation occurred in 24% of pts. CONCLUSION: PT is feasible and safe treatment for pts with large skull base benign meningiomas. Longer follow-up is necessary to assess definitive efficacy.

In the framework of the strategy for the development and the procurement of the NB systems for ITER, it has been decided to build in Padova a test facility, including two experimental devices: a full size plasma source with low voltage extraction and a full size NB injector at full beam power (1 MV). These two different devices will separately address the main scientific and technological issues of the 17 MW NB injector for ITER. In particular the full size plasma source of negative ions will address the ITER performance requirements in terms of current density and uniformity, limitation of the electron/ion ratio and stationary operation at full current with high reliability and constant performances for the whole operating time up to 1 h. The required negative ion current density to be extracted from the plasma source ranges from 290 A/m2 in D2 (D−) and 350 A/m2 in H2 (H−) and these values should be obtained at the lowest admissible neutral pressure in the plasma source volume, nominally at 0.3 Pa. The electron to ion ratio should be limited to less than 1 and the admissible ion inhomogeneity extracted from the grids should be better than 10% on the whole plasma cross-section having a surface exposed to the extraction grid of the order of 1 m2. The main design choices will be presented in the paper as well as an overview of the design of the main components and systems.