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Home » Page 959

Replacing LED light bulbs before they fail may be greener

Households can reduce their energy bills and cut their contribution to greenhouse gas emissions by switching to more efficient lighting, but what’s the best strategy to maximize savings in cost, energy and emissions? Should we buy our new bulbs today or wait for further improvements to the technology? Having considered the options in detail, researchers based at the University of Michigan, US, have drawn up a list of household lighting guidelines to help us make the right decision.

All incandescent and halogen light bulbs should be replaced immediately with compact fluorescent lamps or LED versions, they found, assuming an average use of 3 hours per day. But if you are already using compact fluorescent lamps then the next step depends on several factors.

“If your main goal is to reduce overall carbon dioxide emissions, then you should switch to LEDs now,” Lixi Liu told environmentalresearchweb. “However, if you are aiming to minimize costs or energy consumption overall then waiting until LEDs are available that use even less energy and are more affordable may be the most desirable option.”

The group, which also includes Gregory Keoleian and Kasu Saitou, based its analysis on 60 W-equivalent light bulbs, a common choice in US households.

Their replacement model considers not just the type of lamp currently in use – incandescent, halogen, compact fluorescent or LED – but also examines how lighting technologies could evolve over coming years as well as future changes in the composition of the electricity grid.

The researchers note that lamps used most often should be replaced first to maximize energy savings, and suggest that households shouldn’t necessarily wait until the bulb has blown before installing a new lamp.

“Replacing a light bulb before it burns out seems wasteful, but this study shows that you can save more energy by replacing the bulb earlier,” said Liu. “Replacing LED-based lamps before they burn out should be considered because cheaper models that use less energy are likely to become available long before the current ones burn out.”

Based on this finding, the scientists suggest that manufacturers should focus on making LED bulbs more energy efficient before making them longer lasting. In addition, the team advocates recycling programmes for household lamps as well as pursuing strategies to dematerialize and modularize designs for ease of disassembly and component replacement.

Liu and colleagues published their results in Environmental Research Letters (ERL).

Innovation: patent applications review

A round-up of the latest international patent applications in radiation therapy.

MRI-PET radiotherapy system verifies dose deposition

Alberta Health Services has devised a radiotherapy system that can determine the in vivo dose deposition of a treatment beam in real time (WO/2018/023195). The system includes a bi-planar MRI apparatus, comprising a pair of magnets with a hole in the centre of one of them. The beam source is positioned to transmit the treatment beam through the hole in the magnet, while a patient support positions the patient so that the treatment target is proximal to the beam. The set-up also includes a PET detector between the magnets, positioned so that the target lies between opposing portions of the detector. The PET detector uses annihilation photons generated when the treatment beam interacts with the patient (either directly, for proton beams, or from an injected radiotracer, for photons) to obtain dose information.

Focused ultrasound modulates peripheral nerves

Researchers from Columbia University have developed techniques for modulating peripheral nerves using focused ultrasound (FUS). In patent application WO/2018/022902, they describe methods for locating a peripheral nerve in a subject using an imaging probe, delivering FUS with one or more ultrasound parameters adjusted to target a location on the peripheral nerve, and modulating the peripheral nerve. The methods can further include eliciting and measuring a physiological response from the FUS modulation, generating tissue deformation in the vicinity of the FUS modulation, and imaging the nerve and tissue deformation simultaneously with the modulation.

Respiratory guidance minimizes normal tissue dose

A team at The Catholic University of Korea has invented a method for obtaining an optimized irradiation time point during radiotherapy, by determining the point in the patient’s respiratory period at which normal tissue is irradiated the least (WO/2018/004052). This is achieved by defining a 3D geometric relationship between peripheral tissue and a target volume, using biological characteristics of normal tissue such as oesophagus or the spine, and an overlap volume histogram. The associated irradiation method involves determining the irradiation timing using the radiation sensitivity of at least one organ within a predetermined distance from the tumour and the degree of geometric overlap between this organ and the tumour. The tumour is then irradiated using this timing, wherein the radiation sensitivity and the geometric overlapping degree may vary according to the patient’s respiration.

Robotic system controls intraoperative radiation therapy

Sensus Healthcare has developed a robotic system for intraoperative radiation therapy (IORT), a treatment that involves irradiation of a tumour bed exposed during surgical excision (WO/2018/013846). The IORT system includes a robotic arm with a number of movable joints and a treatment head, which generates therapeutic X-rays, attached to its distal end. At least one patient motion sensor detects the patient’s breathing movement. A control system dynamically controls the position of the treatment head by varying the position of at least one of the robotic arm’s movable joints. This movement is managed to minimize the relative motion between the treatment head and the internal tumour bed during radiation treatment.

Ultrasound guides partial breast irradiation

A team from The University of Texas System has described devices and methods for 3D volumetric ultrasound guidance of prone partial breast irradiation treatments (WO/2018/023001). In some embodiments, the portable ultrasound apparatus comprises a reservoir with an interior compartment having a central axis and containing a liquid. The reservoir is configured to receive a portion of a patient’s breast into the compartment through an opening. A cradle coupled to the reservoir rotates around its central axis and is also coupled to an ultrasound transceiver such that the transceiver is fixed in at least one degree-of-freedom relative to the cradle. According to the filing, the system provides high-quality volumetric images of breast tissue in treatment planning and patient positioning during radiation treatments.

Motion tracking for focused ultrasound therapy

INSIGHTEC has published details of a method for tracking the motion of a target or other objects of interest in real time during an image-guided treatment procedure such as focused ultrasound (WO/2017/212336). Motion is tracked based upon the comparison of treatment images against a library of reference images, such as MR images, for example. The images are acquired prior to treatment for the anticipated range of motion and processed to identify the location of the target or other object(s) therein. Complementary information associated with the stage of the target motion during treatment is also used for the motion tracking.

Heaviest element could have fascinating atomic and nuclear spectra

In 2002, a team of Russian and American scientists created the first ever atom of oganesson, which is the heaviest chemical element ever recorded to date. With an atomic number of 118, oganesson filled the final gap in the seventh period of the periodic table as a noble gas. However, the chemical and physical properties of the new element have proven incredibly difficult to explore. Making oganesson atoms is an arduous process, and even when synthesized, they had a half-life of just around 1 µs.

A team of physicists led by Paul Jerabek at Massey University in New Zealand has now predicted the atomic structure of oganesson with the help of computer simulations. Their calculations take account of relativistic and quantum theories to explore the structures of the oganesson nucleus and its orbiting electrons, revealing fascinating properties that are not observed in lighter elements. Their work could make it easier for experimentalists to measure the properties of other superheavy elements.

Both the atomic electrons, and the protons and neutrons inside the nucleus, are arranged in shells. These shells can be calculated using “fermion localization functions”, which map the density of electrons and nucleons. For lighter atoms, these calculations will reveal electron shells that are dense and distinct, separated with low-density bands. In much heavier atoms, however, the calculation becomes more complicated.

Exotic structures

In their study, Jerabek’s team used fermion localization functions to simulate the exotic structures they believed would be seen in oganesson. For the electron structure, the researchers assumed that the large electrostatic forces originating from the highly positively-charged nucleus would cause electron energy levels to overlap, forcing electron shells to become much smoother and less well-defined. Electrons passing close to the nucleus would also need to move faster to escape its electrostatic forces, introducing the need for relativistic effects.

To account for these effects, Jerabek and his colleagues created an electron localization function for their simulations – a modified form of a fermion localization function. Using the function, they compared the electronic structures of lighter noble gases – xenon and radon – with that of oganesson. They found that the distinction between electron shells become almost imperceptible. Instead, the electrons form a uniform-density “gas” around the nucleus. Practically, this would make oganesson highly polarizable, meaning there would be strong Van der Waals forces between atoms.

Opposing the strong force

Inside an oganesson nucleus, Jerabek’s team predict that electrostatic forces between protons, combined with those from orbiting electrons, would act against the strong nuclear force keeping the nucleus together. Again, the researchers concluded that these effects would smooth out the clearly-defined shell structure. Constructing a separate nucleon localization function to account for these unusual properties, Jerabek’s team again mapped the structure of an oganesson nucleus, comparing it with the nuclei of xenon and radon. Much like the electrons, the superheavy nucleus forms a uniform-density gas of protons and neutrons.

As well as representing a significant advance towards understanding the atomic structures of superheavy elements, the work could inspire new theoretical research into the strange physical and chemical properties which emerge for elements at the bottom of the periodic table. As technology improves, it could also help experimentalists to create instruments that measure the properties of superheavy atoms.

The simulations are described in Physical Review Letters

Bendable nanowires capture bacteria in blood

A new dialyzer made from 3D carbon foam pre-grafted with nanowires could more efficiently remove bacteria and other pathogens from blood than existing technologies. The device, which is inspired by the Venus flytrap, might be used to create a nanotechnology platform for making artificial kidneys in the future.

Bacteria in the bloodstream can cause serious, potentially life-threatening infectious diseases, such as sepsis. Broad-spectrum antibiotics are usually used to treat these diseases, but they are less effective than “blood-cleansing” therapeutics that target specific microbes or antibiotic-resistant pathogens. Such therapies include filtering blood using microfluidic devices and magnetic nanoparticles, but these techniques are not very efficient since bacteria can “fall off” the devices and particles due to the shearing force of the bloodstream.

Researchers led by Tie Wang of the Chinese Academy of Sciences in Beijing made their new dialyzer by grafting bendable polycrystalline nanowires containing ligand receptors on 3D carbon foam. The nanowires, which are straight and point outwards, act as “claws” when they sense targeted bacteria and then bend to trap these pathogens. This is just like the Venus flytrap that opens widely and snaps shut, trapping its prey.

97% capture efficiency

“These bendable nanowires simultaneously satisfy two requirements of an ideal dialyzer substrate,” explains Wang. “First, they hardly deform at high fluid flow velocities so are very sensitive o targeted microorganisms. Second, they can significantly bend at their tip under weak carbohydrate-protein forces to that immobilized bacteria cannot desorb – even in a fluid bloodstream.”

In experiments in a bloodstream with a velocity of 10 cm/s, the researchers measured that the devices were able to capture bacteria with an efficiency of 97%. To compare, devices made from carbon foam alone had a 10% capture efficiency, and unbendable single-crystalline nanowires on carbon foam a 40% capture efficiency.

Nano-biotechnology platform

“As well as bacteria, our proof-of-concept device might also be used to trap other microorganisms, such as viruses, and even circulating cancer cells,” Wang tells nanotechweb.org. “It might thus be used to create a nano-biotechnology platform for fabricating multifunctional artificial kidneys.”

There is still much work to do though to improve the nanowire dialyzer, he adds. “At the moment, it can only capture bacteria and cannot release them, so we will need to integrate a mechanical response into the device so that this can be done under fluid shear stress.”

The dialyzer is detailed in Nature Communications doi:10.1038/s41467-018-02879-9.

Of graphs and giggles

In recent years, there seems to have been a boom in science stand-up and theatre – indeed, last year we reviewed three physics-themed plays, not to mention a host of other similar events at the Edinburgh Festival Fringe. While this is a pleasing trend, the term “stand-up mathematician” threw me, not to mention the name of the show Just for Graphs. The cheesy wordplay did make me laugh, but could actual scientific graphs, plots or diagrams ever be inherently funny? I didn’t think so, but I was pleased to be proved wrong by the geeky comedy trio who make up Festival of the Spoken Nerd and claim to “feed your brain, tickle your ribs and light your Bunsen burner”.

Physics songstress Helen Arney (pictured, right), experimentalist Steve Mould (left) and the aforementioned stand-up mathematician Matt Parker (centre) are a talented bunch for whom science and humour go hand in hand. Performing together since their first tour – Full Frontal Nerdity – in 2014, the three deliver shows that are funny, clever and sometimes downright silly, but always scientifically sound. Although each of them regularly appears independently on shows such as Discovery’s Outrageous Acts of Science, BBC’s QI and The One Show, they work best together. Apart from a long list of science festivals in the UK, the trio have performed in Las Vegas, in New York, in London’s Science Museum and at Shakespeare’s Globe Theatre.

Just for Graphs was their sell-out 2015 show that toured 36 locations across the UK, and has just been released on DVD and for digital download. The 92-minute show was filmed live, and this works well in their favour, considering the excellent audience interaction and participation throughout the show. There are 13 chapters, with perplexing titles such as “Flame tube” and “You can’t graph love”, to take you on an amusing, rapid-fire tour of everything from standing waves and Venn diagrams to space probes and sudoku anarchism (also described as “recreational mathematics” by Parker). Throughout the show, Mould, Arney and Parker each do three or four individual “bits”, aided, abetted and heckled by the other two.

I’ve always enjoyed Arney’s physics-y songs, and her one about Rosetta’s Philae comet-landing probe was particularly charming, as was her song about our indignant Sun. Even though the tracks are a bit off-piste, they serve as a nice break from the more maths-related stuff. But my favourite bit of the show (and trust me, I’m as surprised by this as you may be) was Mould’s chapter on “Venn vs Euler”. Now, Venn diagrams we all know and, yes, they are good for making all kinds of funny and pointed jokes. But Mould then introduces the Euler diagram. This is based on set theory too but unlike a Venn diagram, which shows all possible logical relationships between a collection of sets, an Euler diagram only shows relevant relationships, and leaves out any voids.

You may at first wonder why you need an Euler diagram at all. But Mould swiftly makes his case by showing the audience how complicated (and difficult to decipher) Venn diagrams become when you try to, say, represent the geographical and political divisions of the British Isles. Switch instead to the Euler version and suddenly the data become much clearer. At this stage, just in case you are not convinced and wondering what’s funny about this, Mould brings out the big guns – a “five-way Venn diagram” that gives you a visual depiction of the chorus of the song “Girls and boys” by Blur.

With their topical jokes, flaming antics and solid science, Just for Graphs (and indeed any show by Festival of the Spoken Nerd) is sure to delight nerds, non-nerds and everyone in-between. Can you picture the Euler diagram yet?

  • Festival of the Spoken Nerd: Just for Graphs Laughing Stock Studio/Trunkman Productions 2017 £10.07 (DVD)

100% renewables – a fantasy?

“Electricity comprises just one fifth of annual energy demand in the UK, so creating a 100% renewable energy economy would be an order of magnitude more difficult than the already challenging task of powering our existing electricity grid with 100% renewable sources.” So says a report from the Policy Exchange, putting the case for small modular reactors (SMRs). It’s a familiar line – 100% for power will be very tough, 100% for all energy impossible.

The Policy Exchange claims that “The diffuse and intermittent nature of solar and wind means that we cannot rely on them for 100% of our energy needs – for example, January typically sees at least one week where virtually no electricity is produced by either wind or solar compared with what is needed. Buying in electricity through interconnectors from other Western European nations will be increasingly difficult as our neighbours also turn to wind and solar and so have less capacity to export, while the battery storage capability to back up renewables could cost up to £1 trillion. We need a reliable and affordable low carbon form of energy – small modular reactors have the potential to be that technology.”

Citing David McKay’s views, it says “There are two main challenges with moving to a 100% renewable energy system. The first is simply in producing enough electricity from sources of energy that are very diffuse. Powering a country by wind, water and biomass, for example, would require hundreds of times more land (or sea) than doing so with fossil fuels or especially nuclear power. The second challenge is in coping with the intermittent nature of wind and solar power.” And it develops these views in some detail.

However, this is all going over old ground. There have been many global and national studies suggesting that it is possible to reach near 100% of electricity by 2050 and some saying 100% of all energy is possible by then, without significant land-use conflicts. The most notable of the latter is the 139 country study by a team from Stanford University led by Mark Jacobson. But there are many more. The most recent is the global and regional study from LUT in Finland/EWG in Germany.

The Policy Exchange report seeks to discredit studies like this by citing studies by Heard et al, and an Energy Innovation Reform Project (EIRP) report, which looked at some of them (initially 24, and 30, respectively). The Heard review rejects many such studies on the basis of their failure to meet the criteria it sets for credibility, including grid balancing, although it accepts that some studies do address that. Its main concern (apart from the absence of nuclear in the scenarios) seems to be that there is too much optimism about the role of storage.

Certainly, while short-term flexible balancing is being achieved and batteries can help with that, long-term storage to deal with the occasional long-term lulls in renewables is only now taking off seriously. Though storage of surplus output from wind and PV, converted to storable hydrogen, and then maybe methane, looks like a winner. However, it will take time to deploy widely. But then so would the new nuclear options and, given varying demand, they too will at times have surpluses to deal with, so to some extent it’s really just a matter of which supply option you like. The supply variations would be different with renewables, with short-term variations being the most obvious, but smart grid demand management could help deal with these, and reduce demand peaks. The longer-term lulls are also mostly unique to renewables, although nuclear plants can also go offline suddenly. Given proper balancing and top-ups from supergrid imports/exports, it’s not clear (see below) if a system based on renewables would be any less robust or costly than one based on nuclear.

The EIRP report disagrees. It reviews 30 deep decarbonization studies that were published since 2014. It says there was a consensus that near 100% decarbonization is much more challenging than making it to 50–70%: “While it is theoretically possible to rely primarily (or even entirely) on variable renewable energy resources such as wind and solar, it would be significantly more challenging & costly than pathways that employ a diverse portfolio of resources. In particular, including dispatchable low-carbon resources in the portfolio such as nuclear energy or fossil energy with carbon capture and storage would significantly reduce the cost and technical challenges of deep decarbonization.”

However, there are studies suggesting that, with flexible smart grid balancing/supergrid trade, which could avoid some losses by better matching supply and demand, a diverse renewables-based system could be just as reliable and also possibly less costly. Indeed one study claims that “flexibility can significantly reduce the integration cost of intermittent renewables, to the point where their whole-system cost makes them a more attractive expansion option than CCS and/or nuclear”. At the very least, with a large renewable capacity, sufficient to meet most demand most of the time, there would be some surpluses that, if stored, could meet demand when renewables were low and/or demand was high, with the export of some of these surpluses providing an income that could offset the cost of the system. Basically we are looking to a new more efficient system, with lowered costs. Not much need for big inflexible nuclear then, or CCS, with, given proper attention to energy efficiency, renewables able to supply all power by around 2040. With enough to spare, in time, to also meet most heat and transport fuels needs, directly or via surpluses, in a balanced system. See my next post.

However, the Policy Exchange report sees it very differently – SMRs can step in. “SMRs could offer a number of advantages in a flexible power system, including the potential for dual output, producing other useful services in addition to electricity, like hydrogen or heat. SMRs could, for example, provide a demand/grid management solution by redirecting the power from an SMR to hydrogen production when renewable output is high.”

It is not at all clear if SMRs will be any more flexible than conventional nuclear plants. It is claimed that some types might be – molten salt reactor systems, for example. But they are decades away. Most current designs are just smaller versions of standard reactors, e.g. NuScale’s mini PWR. Being smaller might make them easier to fit into gaps and niches, including for local heat supply. However, the SMR “combined heat and power” heat supply concept assumes SMRs can be in or near cities, which may not be acceptable, given safety and security issues. Indeed, the Policy Exchange report notes that 62% of those asked in a recent YouGov UK survey said they would be unhappy living within 5 miles of one. The economics are also far from certain. Being able to sell heat as well as power would seem vital, but even that may not make SMRs economically viable, although mass production might improve the situation, if enough sites could be found.

But as it stands, SMRs look likely to be expensive. Moreover, given the government’s low level of support, that may not change soon. Only £4m has been allocated initially for R&D on new reactor types, although maybe £40m later on, plus £7m for assessment. In which case the timetable in this ETI report, with SMR start up in 2030, may be very unrealistic.

All this would also seem to make the Policy Exchange report’s recommendation that “when the UK leaves the EU it should abandon renewable energy targets” very unwise. We are going to need as much as we can get, and targets help. And with the UK likely to get to 50% of power by 2035,  near 100% by 2050 wouldn’t be a bad one, with 100% for most energy as the next hurdle. See my next post.

Physics of ski jackets, the eerie sound of thin ice, how figure skaters linger in mid-air

 

By Michael Banks and Hamish Johnston

Probably with an eye on the Winter Olympics, which starts today, two firms have just released new ranges of high-tech ski jackets. The Swiss technology business Osmotex and the Swiss Federal Laboratories for Materials Science and Technology premiered their new ski jacket at the sport and sportwear international (ISPO) trade fair in Munich. It contains an “electro-osmotic” membrane called HYDRO_BOT in the fabric so that when membrane is switched on with a conventional battery it speeds up the transfer of salt ions across the membrane, taking them away from your sweaty skin. The creators claim it can pump out 10 litres of liquid per square metre per hour. For more details, see the video above.

(more…)

Polar bears lose weight as climate bites

To survive, polar bears need to gain weight, not lose it. With a longer summer and less sea ice, it’s a lot harder to do that.

Polar bears may be having a harder time than anybody thought. Biologists who monitored the hunting habits of the Arctic’s iconic predator found that bears have a faster metabolism – that is, they need high-energy foods more often – and are likely to lose weight just when they should be getting fat and ready for the winter.

Ursus maritimus is famous for going without food for long periods and then making up for it when the going is good. And for a polar bear, the going only gets good when there is a lot of sea ice and rich pickings among the seal population.

But US Geological Survey scientists who fitted monitors and video cameras to nine female polar bears for periods of 8 to 11 days and then tracked them on the ice of the Beaufort Sea, north of Alaska, report that five of their “volunteers” had lost weight.

Four of them had lost 10% of their body mass: that is, they could not catch seals often enough to put on weight. One had even lost muscle tissue.

The study confirms that bears are vulnerable to climate change. Sea ice minimum levels are falling at the rate of 14% a decade in the Arctic, and polar bears have been feeling the loss.

But because the bear is a sit-and-wait predator, hunting ringed seals or bearded seals for preference as they haul out onto the ice, biologists had assumed that a resting bear would have a low metabolic rate. Not so, according to a new study in the journal Science.

The bears are active about one third of the time and use energy swimming and walking. The tests and observations were made during the period from April to July when bears catch most of their prey to store up the body fat they need.

In fact the instrument readings and tests of urine and blood samples told the scientists that the metabolic rate of a bear was more than 50% above previous calculations.

So a female seal out on the ice in the polar spring would need to eat one adult ringed seal, or three subadults, or 19 newborn seal pups, every 10 or 12 days just to stay as she was, at the same bodyweight.

Fall explained

But to succeed and breed in the winter, a female would ideally need to consume so much seal blubber that her fat levels matched her lean body mass. In April on the Beaufort Sea between 2014 and 2016, the bears in the test study had no great luck.

“We found that polar bears actually have much higher energy demands than predicted. They need to be catching a lot of seals,” said Anthony Pagano, a doctoral researcher from the University of California Santa Cruz, and a wildlife biologist with the US Geological Survey, who led the research.

Bear population in the Beaufort Sea has fallen by about 40% in the last decade. Now, biologists are beginning to see why.

“We now have the technology to learn how they are moving on the ice, their activity patterns and their energy needs, so we can better understand the implications of these changes we are seeing on the sea ice,” he said. – Climate News Network

• This report was first published in Climate News Network

Protons plus photons: the optimal combination

Proton therapy is a limited resource that’s available to relatively few cancer patients. But as more cancer centres install single-room proton systems into their radiotherapy clinics, combined proton–photon therapy could provide a practical alternative. The question then becomes: “how can a given number of proton therapy slots be used optimally in a proton–photon treatment?”

In previous studies of combined treatments, intensity-modulated radiotherapy and proton therapy (IMRT and IMPT) plans were optimized separately and then simply combined. Now, a research team headed by Jan Unkelbach from University Hospital Zürich has demonstrated that simultaneous optimization of the two modalities can capitalize better on proton therapy’s ability to reduce normal tissue dose (Radiother. Oncol. 10.1016/j.radonc.2017.12.031).

“In this work, we specifically look at treatment sites where a certain number of fractions is needed to protect dose-limiting normal tissues within or near the target volume,” Unkelbach explained. “These can only be protected through fractionation, and hence both proton and photon fractions should deliver the same dose to these tissues.”

However, parts of the gross tumour volume (GTV) may be eligible for hypofractionation. In this case, most of the dose to the GTV can be delivered with protons. Thereby, healthy tissues away from the target volume benefit from an overall reduction of the photon dose bath.

Case study

Unkelbach and co-authors demonstrated this concept for a sacral chordoma patient in whom the GTV abuts the rectum, bowel and bladder. Chordomas require high radiation doses to achieve local control, and are treated with simple proton–photon combinations at some institutions (such as MGH in Boston). For this patient, most of the GTV could be hypofractionated with protons, however, protecting the rectum, bowel and bladder required fractionation.

To account for fractionation effects, the researchers simultaneously optimized IMPT and IMRT plans based on their cumulative biologically effective dose (BED). While traditional plan optimization evaluates objective and constraint functions for physical dose, in this approach, these same functions are instead evaluated for cumulative BED.

To quantify the benefit of optimized proton–photon treatments, the researchers initially optimized a 30-fraction IMRT plan and a 30-fraction IMPT plan, based on the same set of objectives. They used these single-modality plans to generate a reference plan representing a simple proportional combination, in which the two modalities deliver the same target dose.

The team also created two optimized proton–photon plans: combination 1, which used the same objectives as the single-modality plans; and combination 2, which emphasized integral dose reduction by increasing the weighting for objectives that minimize dose to OARs and remaining healthy tissue.

Dose comparisons

Optimized combination 1, with 10 IMPT and 20 IMRT fractions, generated a conformal treatment plan that delivered the prescribed BED to the target volume. The proton and photon fractions in this plan delivered similar doses to the bowel and rectum overlaying the target, thus protecting these normal tissues through fractionation.

In the GTV, on the other hand, photon fractions delivered a mean dose of 1.7 Gy while proton fractions delivered 3.6 Gy, thereby lowering the integral dose to the gastrointestinal tract compared with the reference plan.

The mean BED4 (assuming an α/β ratio of 4 for healthy tissues) to the bowel was 13.12 Gy for a 30-fraction IMRT plan and 4.85 Gy for the IMPT plan. The reference plan, with 10 proton and 20 IMRT fractions, yielded a BED4 of 10.41 Gy, corresponding (as expected) to approximately one third of the dose reduction possible using protons alone. The optimized combination 1 plan delivered a mean BED4 of 8.63 Gy, corresponding to 54% of the reduction possible with IMPT.

As optimized combination 1 uses the same objective function as the single-modality plans, improvements over the reference plan are distributed over multiple objectives. By shifting most of the benefit to reducing integral dose, optimized combination 2 achieved 78% BED reduction compared with the reference plan, without degrading target coverage or conformity.

Dose-volume histograms showed that the five plans (IMRT, IMPT, reference and optimized combinations 1 and 2) delivered similar target coverage and were similar in the high-dose region of the bowel and rectum, which overlap with the PTV. The main difference was observed in the low-dose region of the bowel, where the optimized combinations improved upon the reference plan.

Finally, the researchers varied the number of proton fractions in a combined 30-fraction treatment from one to 20. The mean BED reduction in the bowel increased with increasing number of proton fractions. With five IMPT fractions, optimized combinations 1 and 2 achieved BED reductions of 36% and 66%, respectively, levels that would require 11 and 20 IMPT fractions in a simple proportional combination of plans.

Clinical options

The authors note that optimized proton–photon therapy could benefit many other clinical indications, such as spinal metastasis with epidural involvement, for example, or large liver tumours abutting the bowel, stomach or duodenum.

“As a next step towards implementation, we will look at the robustness of combined proton–photon treatments with respect to range and setup errors, and apply robust plan optimization techniques to mitigate such uncertainties,” Unkelbach told medicalphysicsweb.

Nanoparticles enable deep-brain manipulation

Optogenetics, in which neurons are engineered to be activated or inhibited by light, provides valuable insights into underlying mechanisms of brain function and holds promise for the treatment of neurological disorders. However, the blue-green wavelengths required to turn neurons on or off scatters strongly and cannot penetrate deep into the brain, necessitating the use of fibre probes to deliver the light.

To avoid this invasive approach, a research team headed up at the RIKEN Brain Science Institute is investigating the use of upconversion nanoparticles (UCNPs) to enable delivery of laser light from outside the skull. These UCNPs absorb near-infrared laser light, which can penetrate deeper into brain tissue, and emit the blue-green photons required for neural stimulation (Science 359 679).

“Optogenetics has been a revolutionary tool for controlling neurons in the lab, and hopefully someday in the clinic,” said research group leader Thomas McHugh. “Unfortunately, delivering light within brain tissue requires invasive optical fibres. Nanoparticles effectively extend the reach of our lasers, enabling the ‘remote’ delivery of light and potentially leading to non-invasive therapies.”

In tests in mice, the researchers demonstrated that the UCNPs could serve as optogenetic actuators of transcranial NIR light to turn on neurons in various brain areas. Electron microscopy showed that UCNPs injected into mouse brains remained localized in the injection area.

Non-invasive activation of neurons in the mouse brain
Non-invasive activation of neurons in the mouse brain

“The nanoparticles appear to be quite stable and biocompatible, making them viable for long-term use,” said McHugh. “Plus, the low dispersion means we can target neurons very specifically.”

In addition to activating neurons, the UCNPs could also be used for inhibition, for example to silence seizures. The researchers injected nanoparticles tuned to emit green light into the hippocampus and energized them with laser pulses at the surface of the skull. Hyperexcitable neurons were effectively silenced in these mice.

In another brain area, the medial septum, nanoparticle-emitted light contributed to synchronizing neurons in an important brain wave called the theta cycle. And in mice with learned fear memories, the freezing behaviour associated with these experiences was evoked by blue light-emitting UCNPs, also in the hippocampus.

These neural activation, inhibition and memory recall effects were only observed in mice that received nanoparticle-mediated optogenetic stimulation, not in control animals that received laser light without the UCNP injection.

The nanoparticles are compatible with various light-activated channels currently used in optogenetics and can be employed for neural activation or inhibition in many deep-brain structures. The authors note that the technique could, one day, complement or extend current approaches to deep-brain stimulation and therapies for neurological disorders in humans.

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