Mixed Ion [Beams Could Enhance Particle Therapy Accuracy

Ion beam radiotherapy offers precision dose deposition, with a low entrance dose increasing to a maximum at the Bragg peak and then falling off sharply. This steep dose gradient, however, makes treatments such as carbon-ion therapy highly sensitive to range uncertainties. As such, there’s a clear need for improved treatment verification techniques.

One recent idea is to add a small amount of helium ions to a carbon-ion treatment beam to enable online monitoring during therapy. Fully stripped helium and carbon ions exhibit roughly the same mass/charge ratio, allowing their simultaneous acceleration in a synchrotron to the same energy-per-nucleon. As helium ions have about three times the range of carbon ions (at the same velocity) they travel straight through the patient and can be used for imaging while the carbon-ion beam provides the treatment.

To assess this proposed helium/carbon beam mixing method, a team headed up by Joao Seco at the German Cancer Research Centre (DKFZ) and Simon Jolly at University College London (UCL) has irradiated phantoms with beams of helium and carbon ions at the Heidelberg Ion-Beam Therapy Centre (HIT) (Phys. Med. Biol. 10.1088/1361-6560/ab6e52).

“We wanted to investigate whether the advantages offered by particle imaging could also be exploited for online treatment verification,” explains first author Lennart Volz, who worked on the project in close collaboration with UCL’s Laurent Kelleter. “Range uncertainty is a key challenge in particle therapy and any accurate method for online treatment verification could greatly benefit patients. The mixed beam could be ideal for this, as it would enable you to see what you treat.”

Detecting range modulation

Since the HIT synchrotron is not set up to deliver mixed beams, the researchers irradiated the phantoms sequentially with helium- and carbon-ion beams of similar energy-per-nucleon, using a 10:1 carbon-to-helium ratio. To monitor the range of the helium-ion beam and carbon-ion fragments, they used a novel range telescope developed at UCL, comprising a stack of thin plastic scintillator sheets read out by a flat-panel CMOS sensor.

Summing the scintillation light yield in each sheet and attributing it to the water-equivalent thickness at the centre of the sheet enabled the creation of depth–light curves. The curves of the carbon- and helium-ion beams were scaled 10:1 and then summed to produce a “mixed-beam” signal.

The researchers assessed the system’s sensitivity using a PMMA slab phantom containing different sized air slits. They used the difference between the measured light output signal and a reference measurement to quantify range changes. Irradiating phantoms with slits of 2 mm thickness and widths of 5 and 2 mm resulted in relative differences of 40% and 17% (from a solid phantom), respectively, in the residual beam range. This was expected as more of the 8 mm FWHM beam (55%) crosses the larger slit than the smaller one (22%). Even a 1 mm thick, 2 mm wide slit could be observed, with a relative difference of 8%.

Clinical scenarios
To examine a more clinically relevant scenario, the team used the ADAM pelvis phantom to study the effect of bowel gas movements on helium-ion beam range. They generated a prostate cancer treatment plan and irradiated the ADAM phantom using three spots from the plan (with the same energy), incident upon: the tumour isocentre, a spot near the rectum and a spot between the two. They inflated a rectal balloon inside the phantom to air volumes of 30, 45 and 60 ml.

For the spot near the rectum, even the smallest air volume in the balloon caused an observable change in helium range. For larger inflations, the team saw a drastic overshoot in helium range as the beam crossed into the rectum and rectal gas. Similarly, for the in-between spot, the two larger inflations created observable signal changes. At the isocentre, the team saw no significant change with balloon inflation. In a Monte Carlo simulation of the experiment, however, the two larger air volumes caused small changes.

Finally, to investigate the effect of small patient rotations on the observed signal, the team used the ADAM-PETer pelvis phantom. They irradiated the phantom rotated by 2° and 4° around its vertical axis. Both rotations led to a noticeable change in the measured mixed beam signal compared with the non-rotated state, with similar but slightly larger effects seen in simulations.

The findings reveal the potential of using a mixed helium/carbon beam to monitor intra-fractional anatomy changes. The ability to detect range modulation from a narrow air gap affecting less than a quarter of the beam demonstrates the method’s relative sensitivity. And for the more realistic cases, the mixed beam could help detect bowel gas movements and small patient rotations.

The researchers suggest that for anatomical sites subject to slow or non-periodic motion, sequential beams could provide useful information, provided that fast switching of ion sources or beam energy is technically feasible. But when treating moving targets with strong range changes, such as lung tumours, an actual mixed helium/carbon beam would be advantageous.

“Given the potential of the mixed helium/carbon beam, the next step is to generate a real mixed beam, which we are investigating in collaboration with the GSI Helmholtz Centre for Heavy Ion Research and HIT,” Volz tells Physics World. “Long-term, we would like to investigate generating high-resolution online helium radiographs with a mixed beam.”

Mixed ion beams could enhance particle therapy accuracy

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Key Components of Second HTR-PM Reactor Connected

The reactor pressure vessel, steam generator and hot gas duct of the second reactor at China’s demonstration high-temperature gas-cooled reactor plant (HTR-PM) have been successfully paired and connected, China National Nuclear Corporation (CNNC) announced today.

Construction of the demonstration HTR-PM unit at Shidaowan

Work began on the demonstration HTR-PM unit – which features two small reactors and a turbine – at China Huaneng’s Shidaowan site in Weihai city, in East China’s Shandong province, in December 2012. China Huaneng is the lead organisation in the consortium to build the demonstration units together with CNNC subsidiary China Nuclear Engineering Corporation (CNEC) and Tsinghua University’s Institute of Nuclear and New Energy Technology, which is the research and development leader. Chinergy, a joint venture of Tsinghua and CNEC, is the main contractor for the nuclear island. The pressure vessel of the first reactor was installed within the unit’s containment building in March 2016. The vessel – about 25 metres in height and weighing about 700 tonnes – was manufactured by Shanghai Electric Nuclear Power Equipment. The second reactor pressure vessel was installed later that year. CNNC said the “pairing of the key nodes” of the second reactor was completed on March 18. The pressure vessel, steam generator and hot gas duct, it said, have been “rigidly connected in the form of a flange to form a primary circuit system for the thermal energy transmission of the reactor, which constitutes a second barrier to prevent the leakage of radioactive materials.” The key node pairing creates “the necessary prerequisites for the subsequent reinstallation of the low-temperature helium riser of the steam generator, the installation of the main steam detachable pipe section and the installation of the main helium fan,” CNNC said. The demonstration plant’s twin HTR-PM reactors will drive a single 210 MWe turbine. Helium gas will be used as the primary circuit coolant. The steam generator transfers heat from helium coolant to a water/steam loop. The design temperature of the HTR-PM reaches 750 degrees Celsius. A further 18 such HTR-PM units are proposed at Shidaowan. Beyond HTR-PM, China proposes a scaled-up version called HTR-PM600, which sees one large turbine rated at 650 MWe driven by some six HTR-PM reactor units. Feasibility studies on HTR-PM600 deployment are under way for Sanmen, Zhejiang province; Ruijin, Jiangxi province; Xiapu and Wan’an, in Fujian province; and Bai’an, Guangdong province.

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Numerical Simulation for Operational State Switching Processes of CN HCCB TBS Helium Cooling System

Understanding the thermal hydraulic behaviors of switching processes between operational states is one of key issues in the design and optimization of the helium cooling system (HCS) of China helium cooled ceramic breeder test blanket system (CN HCCB TBS). The thermal hydraulic model of HCS considering the influence of heat structural and thermal insulation layer was established, and the main switching processes for the main operational states of HCS were simulated. The results present the dynamic changes of the thermal hydraulic parameters, including temperature, pressure, helium mass, power of heater, etc. The results indicate that the operation states and relative switching processes are reasonable: the designed operational states can be achieved by controlling the heater power and circulator mass flow rate; the time consumptions for state switching processes are far less than the reserved time according to the operation campaign schedule of international thermal-nuclear fusion reactor (ITER). The work presented in this paper demonstrates the operation of HCS, which provides an important foundation for further design and optimization of the HCS.

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A Message From The Editor

As your focal point for global industrial gas news, views and intelligence, as your eyes and ears, mouthpiece and partner, we are closely following the continued outbreak of Covid-19 (coronavirus) and the impact this is having on the markets.

More specifically, we’re monitoring the impact on you and your business, and how we can support you during these challenging times. We knew 2020 would be a significant year for our industry, for you. We knew that Helium Shortage 3.0 would continue to play out; we knew too that by the close of September 2020 we would have just one year left of the BLM Pipeline on the commercial helium market; we knew hydrogen and other alternative fuels would make great progress towards their necessary tipping points; and we expected that so many other key dynamics in the industry would continue to shape the year for us all. None of us could have foreseen, however, quite what a significant year this would prove to be for all the wrong reasons. Or, at the very least, all the challenging reasons. We have seen events fall by the wayside across the globe, including our own, business travel and trade restrictions enforced, and challenges in how we all conduct our business. This is the new normal for us all for the weeks and months ahead, and at gasworld we recognise that our conventional meetings in person will be severely limited in this period. Yet we remain committed – more than ever before – to providing the most effective and engaging platforms for our industry, to best support our clients and friends around the world. We continue to identify the means to help your business not just survive but thrive during these difficult days. Communication has never been more important – from the office to the remote worker, from the supplier to the customer, from producer to end-user, from one part of the world to another. Finding new means of communicating is the order of the day, while returning to those tried and tested – and trusted – channels is just as important. At gasworld we have those channels, from monthly magazines that deliver a promotional punch in print to up-to-the-minute digital newsletters and content delivery online, and our respected range of annual products – from Yearbooks to Directories. We’re determined to keep investing in those products, to keep innovating and adding value, and to keep giving you the best, most informative, most accessible and engaging promotional platform for your company. If you need information, we will have it. If you need intelligence, we can provide it. If your company needs a vehicle to deliver its own messages, then we are driving it. We don’t know how long this new normal will last, it may be weeks, it may be months. What we do know is that we keep to our deadlines, to our publishing frequencies, and we are committed to maintaining the level of service you expect from us. Our teams are already working remotely, and we have not seen any change in our delivery. We are more committed than ever before, at a time when using our proven platforms has never been more important. This is about the long haul, about the right fusion of new and proven means of communications, and we look forward to doing everything we can to support you in the months ahead. Don’t hesitate to contact us and see what we could do for you.

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Hydrogen Trapping in Tungsten: Impact of Helium Irradiation and Thermal Cycling

The impact of helium (He) plasma exposure with He fluxes relevant for ITER and WEST on the near-surface microstructure of polycrystalline tungsten (W) is investigated by coupling transmission electron microscopy (TEM) analysis and thermal desorption spectrometry (TDS) measurements. The samples were exposed in the PSI-2 linear plasma device to 75 eV He ions up to the fluence of 3 × 1023 He m−2 with the surface temperature in the range 1053–1073 K. The obtained He bubbles–enriched W samples are subsequently probed with sequences of low flux and low fluence 250 eV deuterium (D) ion implantations and TDS measurements in an ultra-high-vacuum setup to study the effects of the near-surface morphology changes due to the helium irradiation on fundamental mechanisms of deuterium retention. The results obtained for two different near-surface layer He bubbles morphologies revealed that the effects of He irradiation on D retention in W strongly depend on its subsequent thermal cycling. For annealing below 900 K, deuterium retention is similar to the one measured in pristine W. In contrast, for annealing above 1150 K, deuterium retention in the He bubbles-enriched W is increased 3–8 fold as compared to non-damaged W. Additionally, the deuterium desorption peak shifts from 540 to 450 K. This increase of D trapping in the He bubbles-enriched W annealed above 1150 K is presumably associated with a modification of the near-surface microstructure concurrent with an outgassing of He.

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