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RadCalc innovations reinforce the benefits of independent QA

While the coronavirus pandemic wreaks havoc across national healthcare systems and the global economy, many technology companies have bunkered down and spent a good chunk of 2020 focusing on what they do best: relentless product innovation. A case study in this regard is the development team behind RadCalc QA secondary check software, a suite of widely deployed quality-assurance (QA) tools that provides medical physicists and dosimetrists with fully automated and independent dosimetric verification of their radiotherapy treatment planning systems (TPS).

Among a raft of advanced RadCalc features unveiled this year, top billing goes to the addition of automated 3D dose-volume verification – a result of the successful integration of Monte Carlo and collapsed-cone dose calculation algorithms into the platform. That 3D capability is reinforced by a continuous-improvement mindset – aligned with the evolving operational priorities of end-users at more than 2500 clinics worldwide – which ensures that automation, speed and workflow efficiency remain hard-wired into the RadCalc develop-and-release programme.

3D thinking

“For the past 20 years, we have provided independent QA software that’s fast, easy-to-use and accurate when it comes to identifying TPS dose errors,” explains Jim Dube, president and co-founder of the RadCalc software portfolio, part of LAP’s growing QA product line in radiotherapy. As such, the addition of automated 3D dose verification represents a natural progression for RadCalc, ensuring enhanced QA accuracy for harder-to-treat cases – for example, metastatic brain tumours or small tumour targets surrounded by lung heterogeneities – as well as an independent check for a range of advanced treatment modalities, including intensity-modulated radiation therapy (IMRT), volumetric modulated-arc therapy (VMAT), stereotactic radiosurgery (SRS), stereotactic body radiotherapy (SBRT) plus hypofractionation and ultrahypofractionation.

Jim Dube
Jim Dube: “Independent verification is, and will remain, a big deal for medical physicists and for the radiotherapy equipment vendors.”

Under the hood, RadCalc’s 3D Monte Carlo module exploits the well-established BEAMnrc dose engine in tandem with proprietary machine modelling acquired from the medical physics team at McGill University, Canada. The collapsed-cone convolution superposition algorithm is the result of a separate acquisition covering the source code and related patents of a product called DosimetryCheck (purchased from US radiological software specialist Math Resolutions back in 2017). “Our investment in Monte Carlo and collapsed-cone algorithms gives users a higher degree of certainty in their QA 3D dose calculations,” adds Dube. “That certainty translates into improved targeting accuracy and dose distribution accuracy – and ultimately better patient outcomes.”

If accuracy is a given for 3D dose verification, so too are automation and speed. Put simply, says Dube, all the physicist has to do is export a treatment plan via their DICOM RT and RadCalc will automatically verify the plan using either a Monte Carlo or collapsed-cone algorithm, generating results in minutes. “If the treatment plan doesn’t pass versus preset criteria,” he adds, “RadCalc will prompt the user to investigate what’s going on using a suite of dose analysis tools. They can slice-and-dice the plan just about any way they want to see where the hot or cold spot is and figure out what to do from there.”

Buy vs subscribe

Functionality aside, there’s also significant innovation to report on the RadCalc commercial model – most notably the availability of subscription licensing for radiation oncology clinics in North America. In terms of specifics, end-users can now select from four preconfigured packages – Essential, 3D Premium, 3D Gold and 3D Unlimited – and add functional modules to meet their changing clinical needs. “We are constantly working on new features, new releases and the optimization of the software platform,” says Dube. “With a subscription, users can access all the latest features to ensure they are always up to date.”

Annual and multiyear RadCalc subscription packages are available, all with technical support and maintenance included. The financial driver here is that even in the best of times – let alone the middle of a pandemic – the upfront capital outlay on a traditional QA software licence can prove a blocker for smaller clinics, many of which struggle to accommodate spending spikes outside their annual budgeting cycle.

The RadCalc subscription model offers customers a fast-track workaround, spreading their software investment over an extended timeframe. “Subscription packages provide 70% lower upfront spend compared to traditional licence fees,” claims Dube. “It’s a win–win, with the client getting much-improved visibility and certainty about their QA software spending over time.”

Listening to the user

Right now, the RadCalc team is hard at work fleshing out the development roadmap for 2021 and beyond, including the release of 3D EPID-based functionality to underpin true measurement-based IMRT QA and in vivo verification. In short, RadCalc will import the necessary EPID data/image files, process them, and then send to the collapsed-cone dose engine to calculate the dose.

Ongoing requirements-gathering and prioritization are built upon what Dube calls “dialogue at scale” with the clinical user base – though he concedes that “it’s suddenly not so easy to gather ideas from customers in a face-to-face setting” as the main scientific conferences and tradeshows go virtual.

All things considered, though, it seems the collective conversation on RadCalc is in good shape, with the technical support and sales teams very much the “eyes and ears” for customer feedback and new feature requests. “Our annual customer survey is another fantastic channel to inform our product development,” says Dube, “and very much in the spirit of ‘what are we doing well, what could we do better, what can we do to make your life easier?’”

Operationally, RadCalc’s incorporation into the LAP group (in January 2019) has also opened up new growth opportunities through the latter’s global customer base. LAP laser systems are used worldwide for patient positioning in radiotherapy, both in the imaging and treatment unit. More broadly, the company is focused on delivering the enabling technologies for next-generation radiation therapy with ongoing innovation across its QA and multileaf-collimator product lines.

Capitalizing on that access, Dube concludes, starts and ends with RadCalc’s core value proposition to the radiation oncology community: “Independent verification is, and will remain, a big deal for medical physicists and for the radiotherapy equipment vendors. Why wouldn’t they want independent QA providing a double-check of their treatment plans?”

‘Mutual detectability’ will improve the search for extraterrestrial civilizations

The search for extraterrestrial intelligence (SETI) is slowly evolving from a fringe endeavor to a more mainstream one thanks to improvements in the capability of astronomical surveys, detector sensitivity, and greater philanthropic financial support. Still, because of the vastness of the universe and the scarcity of resources, scientists must develop strategies around where, when, and how to discover alien civilizations.

Much of SETI involves trying to receive signals broadcast by other civilizations. However, it could be that every civilization in the universe has decided that transmitting messages for other civilizations to receive is unwise or dangerous, but that listening for messages sent by others is a safe and worthwhile pursuit.

This “SETI Paradox” would leave all SETI efforts doomed to failure because for any civilization’s SETI efforts to succeed, some other civilization must engage in messaging extraterrestrial intelligence (METI). One important question is how two civilizations should coordinate their efforts to discover each other, given that they are not certain about each other’s existence. Another is which civilization should send a message, and which should listen.

Onus to transmit

In a recent preprint, astronomer Eamonn Kerins of the UK’s University of Manchester has developed a game-theory framework that determines not only how and where civilizations should target their efforts, but also which of two such civilizations has the onus to send a message, and which should be listening for that message.

As Jason Wright, professor of astronomy and astrophysics at Penn State, summarizes, “Kerins’ idea is that the symmetry that keeps us all from transmitting can be broken by recognizing that some species have access to more information about other planets, and that the ‘onus to transmit’ should lie with them”. He adds, “It’s a neat approach and suggests that there are systems towards which we have the onus to transmit and should be contacting, while other [planets] are better targets for listening. If other species are following the same logic, then this should make SETI programs more efficient and likely to succeed.”

Kerins considers the scenario in which both civilizations can gather data that suggests the existence of the other. Ideally, each civilization should gather similar data because only when the data are comparable would the civilizations possess “mutual” information – which is key to Kerins’ framework. Because the civilizations may vastly differ in their technological capabilities, it is important that they both consider the simplest possible evidence of the other’s existence.

“Common denominator information”

Kerins proposes that civilizations should use “common denominator information” (CDI) to find potential SETI/METI targets. CDI is evidence that both parties can recognize, and that is independent of either party’s particular method of acquiring information. Kerins offers the example of the amount of starlight blocked by a planet as it transits across its host star – which is called the transit’s signal strength.

This quantity is simple enough that any civilization engaged in SETI/METI efforts should be capable of measuring it, and it is also independent of how the measurement is made. In this sense, a transit’s signal strength is “intrinsic” and therefore can be compared by two civilizations who are looking for one another. Crucially, each party should be able to determine not only their own signal strength as the other party would measure it, but also the signal strength of the other planet. Then, each party would know what the other knows, and therefore both parties know who has the superior evidence about the other’s potential existence.

Kerins argues that whichever party has superior information has the greater incentive to send a message to the other – the onus to transmit – while the party with inferior information should listen for a signal.

On where and how to implement his game-theory framework, Kerins points to planets in the “Earth’s transit zone” (ETZ), a slice of space in which an observer can watch Earth transit the Sun. “From the basic idea of transits, and with technology comparable to ours, [extraterrestrial civilizations in the ETZ]  can work out that we are a potentially habitable planet,” says Kerins. “The transit method is among the first methods that any civilization capable of finding other planets would establish. Therefore, if there are SETI-capable civilizations out there, by using the transit method, we’ll hopefully embrace most of them, because they’ll also have knowledge of the transit method. The situation in which we’re looking at a region of the sky where we can see them in transit and they can see us in transit maximizes our chances of success.”

The preprint has been accepted for publication in The Astronomical Journal.

Achieving a healthy work–life balance as a graduate student

As a PhD student in physics, I’ve learned that the work–life balance during your graduate career can look different from how it did in your undergraduate life. Graduate school in physics is hard, and it’s extremely important to make sure that you’re giving yourself time to enjoy things outside of work to recharge yourself.

During the first few years this might be a little difficult with all the classes and, depending on your programme, research and service work. I definitely struggled to balance everything. But finding a balance is critical because the stress of doing work all the time can start to have negative effects on you. Sometimes they’re tangible and sometimes they’re not.

Since stress affects people in different ways, it’s important to recognize what happens to you. For me, during my first few years as a postgraduate student, I mostly felt like I was going through the motions. I was extremely busy with classes and qualifying exams, and the workload started to take its toll on me. I started to sleep extremely poorly. I would get eight hours of sleep and feel like I got four.

Luckily, my fellowship at West Virginia University in the US required service work, and I found a volunteer opportunity coaching soccer (football), which I really enjoy. Growing up I had watched my brothers play soccer and had eventually started playing too. I played throughout high school and into university until suffering an injury. Through the network I created by coaching, I also began playing soccer again, something I hadn’t done in years.

Carving out time for yourself

Even if classes and research seem to take up all of your time, sometimes you have to make time. During my first few years of graduate school, I made a point of taking one day off a week when I didn’t do anything except what I wanted to, be it video games, hanging out with my family, or reading. I also started asking my friends for help on homework if I was stuck. When I struggled through problems alone, I would start to doubt myself and feel like I didn’t belong in the field. I found that I could better understand the material if I laid out the steps of the problems with my friends, which reduced my stress.

Photo of Amber Lenon and some of her fellow football (soccer) players
Team player The author (seated, third from left) started coaching and playing soccer during her studies at West Virginia University in the US. (Courtesy: Amber Lenon)

It’s astounding to look back at my work–life balance during my undergraduate career, when for a period of time I wasn’t sleeping or eating well. Since then I’ve learned how my body reacts under too much stress and when I need to better balance my work and life. I realized what brought me peace and allowed me to re-centre myself, and that occurred because I started to understand who I was as a person. Now I know that I’m balancing my work and life well when on my days off I’m not worrying about what I have to do during the week.

If I have to work on weekends (for conferences, research and the like), then I take an equivalent amount of time off during the week. This is a valuable bit of advice I learned from one of my mentors. Although this is easier to do once you’ve finished classes and have a little bit more flexibility with your schedule, it’s always an important strategy for preventing burnout. It also makes me more productive, not less. When I start to burn out, sometimes it feels like I am giving 100%, but it’s only about 50% of what I can do when I’m not burned out.

When to take a break

Today my schedule is built around what works for me. I treat graduate school more like a 9-to-5 job, where I work only during specific hours. I make time to work out every day, because it allows me to focus on myself. My family is extremely important to me, and we are very close, so I try to talk with them almost every day, and once a week we play Dungeons and Dragons together remotely. We grew up playing that together in person, so it’s great to continue the tradition. After working, I try to spend part of my time every night reading, and I’ve recently found a lot of joy in cooking. Pursuing the things that bring you joy outside of work will help you maintain your mental health.

Sometimes, though, even with a good work–life balance, you may find that you’re struggling to stay motivated. At that point, it might be a good idea to take a break and step back from research, classes, and work things, kind of like a holiday. You can discuss this with your adviser and find out how it will affect your progress in your programme. This happened to me about a year ago. I went through something traumatic, and at the time I thought I was handling it fine. But after conversations with my mentors, I realized I needed to take a total break. Afterward it was like a huge weight was lifted off my shoulders, and I felt at peace and motivated to start up research again. The trauma that I went through didn’t just disappear; it was something I dealt with even after my break, and it was the reason I ended up transferring from West Virginia to Syracuse University. I struggled a lot with making the decision to transfer, but I realized it was ultimately the best decision for me. Sometimes things just don’t work out in one area, and that’s okay.

Recognizing when I needed to take a break came hand in hand with evaluating my mental health. There are certain signs for me – getting nauseous while eating or not being able to determine what my emotions are – that mean I am in dire need of a break. If I can recognize the signs before I get to the point where I need a long break of a month or more, I can combat them by taking off just a few days to a week. Taking a break might make you feel like you’re going to fall behind and not be able to catch up, but I promise that won’t happen. You’ll feel revitalized and be more motivated to keep going.

Deep learning transforms standard CT scans towards spectral images

Virtual monoenergetic images
Top row: benchmark virtual monoenergetic (VM) images from dual-energy CT projection data reconstructed at 80 and 110 keV, respectively. Bottom row: corresponding VM images produced at the same energies from only 140-kVp images, using a deep learning approach. (Courtesy: Wenxiang Cong, Yan Xi, Paul Fitzgerald, Bruno De Man and Ge Wang)

Computed tomography (CT) is a popular medical imaging tool, visualizing and quantifying internal structures for screening, diagnosis, therapy planning and treatment monitoring. Conventional clinical CT scans generate a spectrally integrated attenuation image that shows tissue morphology, but does not directly provide any information regarding tissue composition.

Dual-energy CT (DECT) systems, which acquire two spectrally distinct datasets, can reconstruct virtual monoenergetic (VM) and material-specific images that provide information about tissue composition. Compared with conventional CT, however, DECT is more expensive and complex, and often requires an increased radiation dose.

For patients without access to DECT scans, a way to approximate the information provided by DECT using a single-spectrum CT scan could improve clinical diagnoses. With this aim, Wenxiang Cong and a team led by Ge Wang at Rensselaer Polytechnic Institute demonstrated a deep-learning approach that can produce VM images from single-spectrum CT scans.

“With traditional CT, you take a greyscale image, but with dual-energy CT you take an image with two colours,” explains Wang. “With deep learning, we try to use the standard CT machine to do the job of dual-energy CT imaging. We hope that this technique will help extract more information from a regular single-spectrum X-ray CT scan, make it more quantitative and improve diagnosis.”

Wang and his team – in collaboration with Shanghai First-Imaging Tech and GE Research – modified a residual neural network (ResNet) to transform clinical single-spectrum CT images to VM counterparts. After training the network on clinical DECT images, they used it to produce VM images at two energy levels (80 and 110 keV) from single-spectrum images. These VM images showed excellent agreement with those produced by DECT reconstruction using two different spectra.

The model was able to produce high-quality approximations to linear attenuation coefficients with a relative error of less than 2%. The structural similarity between the two types of VM images was up to 0.99, showing that structural information, especially texture features, was well preserved by the machine learning method.

Next, the team used the deep-learning-based VM images to generate material-specific images of three tissue types: adipose, muscle and bone. The resulting images were of high quality and closely approximated those produced by DECT using projection datasets from two X-ray spectra.

The researchers note that the bone image could be clearly separated from the VM images. Notably, a calcification in the abdominal aorta that was inconspicuous in the original polychromatic image was visible in the synthesized VM image and in the bone image. This reveals one of the potential clinical utilities of the DL method.

Having demonstrated that a conventional CT dataset coupled with deep learning can deliver a close approximation of DECT images, the researchers suggest that it is potentially feasible to use conventional CT to perform some important tasks currently achieved using DECT – thereby eliminating the hardware cost associated with a DECT scanner.

One example application is the determination of proton stopping power for use in proton therapy planning, where it is important to accurately represent material concentrations of common tissues along the therapeutic beam. The team also highlight deep-learning-based VM imaging as an alternative to photon-counting micro-CT for in vivo preclinical applications.

The full details of the research are published in Patterns.

Hypofractionation: pushing the boundaries of MLC performance

The clinical upside of hypofractionated radiation therapy has been evident for some time, with cancer patients benefiting from increased dose per fraction such that they can complete their course of radiotherapy much faster than is possible with conventional treatment schedules – and just as safely and effectively. Think fewer hospital visits, a speedier return to family and, for some indications, enhanced treatability and outcomes. Equally compelling is the long-term opportunity for healthcare providers, with higher dose per fraction (and fewer fractions) translating into significant workflow efficiencies, lower cost of care and, ultimately, increased patient throughput – all of which looks even more compelling against a backdrop of growing cancer incidence worldwide and the perfect storm of the coronavirus pandemic.

Right now, though, the challenge for radiotherapy OEMs and the wider supply chain is to come up with the enabling technologies and treatment protocols to realize these clinical and economic outcomes at scale. For starters, the radiation oncology team needs the ability to maintain submillimetre accuracy and precision throughout treatment delivery – identifying the target location in the body; automatically detecting, tracking and correcting for target motion (due to breathing and peristalsis, for example); and accurately repointing the beam in real-time to support the clinical use of smaller margins to reduce the side-effects of treatment.

With this in mind, a German R&D initiative is aiming to realize a “new gold standard” in the performance of the so-called multileaf collimator (MLC), a core building block of the radiotherapy linacs used for cutting-edge cancer treatments like hypofractionation and ultrahypofractionation. The industry–academia joint venture, which earlier this year received backing from the Bavarian regional government, brings together laser and radiotherapy QA specialist LAP with the Institute for Medical Engineering of the Ostbayerische Technische Hochschule (OTH) Amberg-Weiden. Their goal: a next-generation drive and control unit that promises an order-of-magnitude improvement in the speed and precision of the MLC subsystem – and specifically the array of independently controlled tungsten “leaves” (typically between 120 and 160) used to shape and vary the intensity of the treatment beam as it addresses the tumour volume.

Innovation meets pragmatism

The commercial imperative for MLC development is a mix of technology push and market pull, claims Stefan Ueltzhöffer, who heads up LAP’s MLC and radiotherapy QA business. “We follow the market closely,” he explains, “and maintain an ongoing dialogue with the radiotherapy equipment supply chain, the clinical user base and our academic partners. It’s clear from those conversations that emerging treatment modalities like hypofractionation and MR-guided radiotherapy (MR/RT) will benefit from MLC innovation, creating opportunities for subsystem suppliers like us to set new standard in terms of MLC performance.”

Stefan Ueltzhöffer
Stefan Ueltzhöffer: “From a commercial and clinical perspective, we want MLCs that are more stable, more serviceable and easier to manufacture.” (Courtesy: LAP)

From that starting point, argues Ueltzhöffer, two questions inform the development roadmap for LAP’s MLC product line. First, how does LAP address the evolving needs of its customers (the radiotherapy OEMs) and customers’ customer (the radiation oncology clinics)? Second, what does differentiation of that MLC offering look like to enable LAP to gain market-share versus its competition? The answer, it seems, is a next-generation MLC that will consolidate the outcomes of various in-house development projects with the efforts of this latest collaboration with OTH. “Ultimately,” adds Ueltzhöffer, “I believe we will be talking about multiples of improvement in terms of MLC speed and precision, after pretty much only incremental changes in the technology over the past 20 years.”

Yet while LAP is clearly pushing for a step-function breakthrough in MLC performance, it’s also a given that any advanced capabilities must deliver against strict cost/performance criteria. “Pragmatism is key – the MLC is no longer a toy only for physicists,” notes Ueltzhöffer. “From a commercial and clinical perspective, we want MLCs that are more stable, more serviceable and easier to manufacture. As such, the innovations we are evaluating will enhance performance without sacrificing the considerable progress made on cost and machinability over the past decade.”

Play to your strengths

If that’s the commercial context, what of the technical progress to date? According to Ueltzhöffer, several advanced MLC technologies are already in the works and shaping up well in proof-of-concept demonstrators at LAP. One particular area of focus right now is the MLC drive, with a simplified set-up expected to yield significant outcomes in terms of reduced footprint, weight and designed-in MR compatibility (to minimize the need for shielding in MR/RT treatment systems).

“The MLC drive has always been quite cumbersome in terms of the size of the motors and associated sensors,” says Ueltzhöffer. “As such, we are looking at easier-to-integrate modules that could lead to a lot more degrees of freedom in designing the MLC subsystem – and maybe even make it possible to get rid of some of the transmission mechanisms.”

Another development track is evaluating the use of laser-based sensors to provide optical encoding and tracking of the MLC leaves – a traditional pain-point for today’s MLC designs which rely on cameras, other optical sensors or potentiometers to do that job. “It’s a no-brainer,” says Ueltzhöffer. “We’re applying diverse laser technologies and specialist domain knowledge from the wider LAP group to support our MLC innovation programme.”

If the technology end-point is clear – a new generation of MLCs and a “big leap forward” in capability – the commercial outcome appears more fluid and nuanced. On the one hand, LAP intends to grow its market-share by supplying turnkey MLC units for OEM equipment vendors to integrate directly into their radiotherapy machines. Equally, Ueltzhöffer also plans to license key MLC technologies – for example, drives, sensors and controllers – to those OEM equipment vendors who prefer to build their own MLC subsystems.

“More broadly,” concludes Ueltzhöffer, “LAP remains focused on delivering the enabling technologies for next-generation radiotherapy – in particular, emerging modalities like hypofractionation and MR/RT – through ongoing innovation across its MLC, QA and laser positioning product lines.”

Further reading

See also the LAP webinars Maximizing QA accuracy and efficiency with RadCalc in a challenging environment and Commissioning and QA workflows of MR-linac with the Thales 3D MR scanner.

Measures of success: how to thrive as a student in physics

For a long time, I used to think success in physics mainly meant winning accolades, getting institutional recognition, and having an ingenious understanding of the subject. And to some degree, these factors do qualify for what it means to be a successful physics student.  I was the first person in my family to pursue a degree in physics, and in time I realized that my measures of success as a student were completely different from what I expected. I found that being a successful student actually requires a strong foundational work ethic, persistent determination and communal support.

As the only daughter of two immigrant parents, and growing up in a typical Caribbean household, success was the only option. My grades were always expected to be 95% or above. The terms “I don’t know” and “I can’t” never existed in my vocabulary, and if I chose to embark on a new task, I was expected to finish it. My parents are the embodiment of hard work, dedication and a strong work ethic, as they left their native countries to have a better life for themselves in the US. Their resilience inspired me to be as hard-working, which was an essential factor in my success as a student. My parents knew my potential to attain the impossible, because they had done the impossible themselves.

When I decided to pursue physics as one of my majors at Mount Holyoke College, although my parents were unfamiliar with the subject, they were completely supportive of my decision. They became my emotional support in the mornings when I had to get up early to attend classes; provided a listening ear at night when I felt hopeless and lost about taking courses out of my league, such as electromagnetic theory or quantum mechanics; and were my biggest fans when I graduated from college magna cum laude.  I was a successful student because of them – their unconditional support, love and work ethic led me to graduate with high honours in physics; write a senior thesis; and advocate for resources that were conducive to my well-being as a Black woman in physics.

Physics’ academic culture does not mirror the multifaceted identities of its Black students

If physics has taught me anything, it’s determination. I learned from early on that it is not an easy subject. For many Black students, when we first begin studying physics, we are often reminded that we are seeing and learning this material for the first time. We recognize and know that the culture, vernacular and coursework of physics disregard the vocabulary and syntax used throughout the Black community. Physics’ academic culture does not mirror the multifaceted identities of its Black students – rather, it exists in a world where Black students often do not have access to learning or becoming familiar with the material at a young age. Therefore, it usually takes us twice as long and requires twice the effort to complete assignments or gain a basic understanding of the subject.

When I find myself in these situations, struggling to keep up, I remind myself of the reasons I fell in love with physics: attending the free science museum days and learning about the solar system, or riding the subway system in New York and wondering how the trains worked. The curiosity I held as a child influenced my success as a student. While I never noticed that I was often the only Black girl running around the science exhibits, I remember how tenacious I felt doing physics and how determined I was to find the answers to every scientific question that I asked. As a student, I made sure to hold on to those same skill sets that I had developed as a child, which included having a natural inclination to wonder about the world and a genuine interest in scientific investigation.

However, the real secret to my success as a student is my community. That includes friends and other Black physicists who I have collaborated with and learned from along the way. Their support allowed me to see how I was impacting my community in real time. Towards the end of my undergraduate experience was the first time I felt I had finally found my place as a physics student and understood what it truly felt like to succeed. For much of my undergraduate experience and a short period during graduate school, I found myself isolated and doing physics alone. This situation was unfamiliar to me, as my earlier educational experience consisted of constant collaboration. When I began working with mentors from my community, who looked like me and were doing research that reflected who I was as a student, I realized how that increased my self-efficacy.

Collaborating with other Black students validated my existence in the field and made my experience more meaningful. As a result, my own research focused on the intersection of identity and performing arts of Black physicists. My collaborators and I collected and analysed the physics experiences of 13 Black physicists, and found themes in the ways that their participation in the performing arts supported their experiences in the field as Black physicists (ComPADRE PERC2018 Williams). For so long, I was under the perception that I would be the only Black student I knew pursuing a degree in physics. My research allowed me to find and connect with my community, which became crucial for my identity as a student.

In academia, our success is rooted in our passion for physics, our family and the community that supports us. We succeed regardless of how difficult or challenging the work may be. The more I learn, the more I realize there is no guide or beginner’s manual on how to be a successful student; the only real success is what you determine it to be.

On the road less travelled: a Black physicist’s journey in academia

Photo of Brooke Russell
Trailblazer Brooke Russell is the first Black woman to receive a doctorate in physics from Yale University. (Courtesy: Brooke Russell)

This past May I earned my doctorate in physics, becoming the first Black woman to do so at Yale University. There are very few Black women with doctorates in physics. Approximately 100 Black women have received a PhD in a physics-related field in the US.

With such a dearth in numbers, at times I experience a sense of loneliness and isolation in physics. Some people are taken aback by my presence in research settings. On a number of occasions, I have been mistaken for janitorial staff in physics departments, in national laboratories and at conferences. This is a common experience among my Black physics colleagues. Anecdotally, the anonymity of e-mail and conference calls smooths over some of the stilted behaviour I otherwise experience working with new colleagues face-to-face. An initial encounter may be awkward, but in time, as new colleagues become familiar with my physics acumen, preconceived notions fade away.

Physicists hail from all socioeconomic and cultural backgrounds. I have had the good fortune of working closely with physicists from all over the world. When we rally around the physics questions at hand, differences in background don’t seem to matter. Close collaboration in physics requires trust, openness and transparency. With these keystones to a relationship established in the physics setting, the pivot to get to know and understand my colleagues on a more personal level is eased. Even though making a groundbreaking measurement or establishing a revolutionary new theory is ultimately what many of us are after as researchers, close relationships developed along our journeys are the sustenance that keeps us going.

A mentor’s impact

As an undergraduate studying physics at Princeton University, I had the great fortune of working with Frank Calaprice. The experience fundamentally changed the trajectory of my life. But for this connection, I would not be in the position I find myself in today. As my senior thesis adviser, Calaprice suggested a topic, in situ purification for liquid-argon dark-matter detectors, that I could actively work on in the laboratory over the course of my senior year. Apparently pleased with my work, Calaprice offered me a position to continue working with him the summer following graduation. I continued on with Calaprice for the next two-plus years. During that time, I worked closely with Princeton PhD students and postdoctoral associates, travelled internationally to work at Gran Sasso National Laboratory in Italy, and developed the confidence to pursue a doctorate in physics.

Funding agencies should invest in making physics research opportunities available to the unconventional candidate

Years later, Princeton held a celebration for Calaprice marking his many contributions to the field. Among the attendees were a physics Nobel laureate and many prominent professors of physics and national laboratory staff scientists. Over the course of the event programme, I learned about the trials and tribulations Calaprice had encountered over his decades-long career. What struck me most was the continued mentorship he had carried out over the years. There were many people just like me whom Calaprice had taken under his wing and worked closely with in their development as scientists. These mentees hailed from all backgrounds. Our common denominator was our interest in physics. We would all like to leave our mark on the field with a groundbreaking discovery, but in many ways each of us can leave the field better than we found it through the people we develop and the connections we make.

Not everyone is blessed with a Frank Calaprice in their life. However, the fostering of a constructive environment like the one I found myself in can and should be replicated to help bring new people into the field, especially those who otherwise initially think they do not have a place in physics. In my view, funding agencies should invest in making physics research opportunities available to the unconventional candidate – perhaps a student who returns to academia later in life, or a student who lacks a sterling academic record, or a military veteran, or a young parent, and so on – to broaden the base of potential graduate school applicants. Burgeoning young scientists can be found within this talent pool, including up-and-coming Black scientists. The assumption that deciding to pursue a career in physics should occur during one’s undergraduate years is not necessarily well founded. In my case, life experiences helped prompt my path toward physics.

Breaking down walls

Much has been written about the scarcity of Black people with undergraduate and doctoral degrees in physics. It is encouraging that awareness of the issue is becoming more prevalent and that many universities are constructing action plans to rectify the situation. I believe mentorship and investment in people will aid in turning the tide on the flatlined numbers of Black students pursuing physics degrees. Further, by our rallying around the physics, cultural walls and divisions can crumble. We should embrace our common physics interests in order to work through and better understand our differences. By the numbers, Black physicists today are trailblazers, in that few have tread our current path. It’s on all of us to clear the way for people of all backgrounds to follow.

New optical connections for trapped ions could lead to better quantum computers

An important step towards creating a scalable quantum computer based on trapped ions has been made by two independent research groups in the US and Switzerland. The teams have developed the optics needed to manipulate multiple trapped ions that are integrated onto single chips.

The first practical implementation of quantum gates – the fundamental components of a quantum computer — was made in 1995 by Chris Monroe and David Wineland at the US National Institute for Standards and Technology in Colorado. The researchers trapped beryllium ions in a vacuum chamber and controlled their electronic energy levels using lasers. The energy level of the ions was coupled to their motional state, which – owing to the electromagnetic interaction between ions – made the state of one ion conditional on the state of another.

Since then quantum gates have been created using various other systems as quantum bits (qubits). These include Rydberg atoms, impurities in diamond and superconducting circuits – the latter being used in state-of-the-art quantum computers built by Google and Intel. Commenting on superconductor-based systems, Monroe (now at the University of Maryland, College Park) says, “They use similar tools [to today’s computers], all of the chips are on a two-dimensional surface and you have to wire them together. People are familiar with those basic fabrication tools.” In contrast, he says, trapped-ion qubit technology requires more unfamiliar technology: “It has lasers, it has optics, it has individual atoms in a vacuum chamber.”

Prone to imperfections

Despite their current popularity, progress has recently slowed in the development of superconducting quantum computers, and some researchers are skeptical they will ever scale to thousands of qubits or beyond. This is because, whereas isolated atoms in free space are guaranteed to be identical by the laws of quantum mechanics and can therefore maintain coherent entangled states reliably, manufactured circuit elements are inherently prone to imperfections and almost impossible to isolate from noise.

Several research groups and commercial companies are therefore focusing on developing the technology needed to scale up trapped-ion systems. Around 15 years ago, says John Chiaverini of Massachusetts Institute of Technology, researchers began fabricating ion traps on chips. Mastering this basic technology of holding different atoms in different places allows researchers to “utilize some of the other stuff that the [semiconductor] industry has built up over 50 or 60 years and put other things in those ion trap chips, like integrated electronics and integrated photonics,” he says. “That work has really only started in earnest in the last five or six years.”

Now, two papers published side by side in Nature – one from the MIT researchers led by Chiaverini and colleague Jeremy Sage, the other from scientists at ETH Zurich – present complementary advances in manipulation of trapped ions using integrated photonics. Both teams fabricated waveguides on chips to deliver the light necessary to excite specific transitions in their chosen ions — the ETH Zurich group used calcium and the MIT researchers chose strontium.

The ETH chip
Integrated waveguides: laser light is fed into the ETH chip via the optical fibres on the right. (Courtesy: K Metha/ETH Zurich)

Using a commercial foundry, the Swiss group fabricated chips with eight waveguides, allowing them to inject light at the wavelengths necessary for initializing their qubits (bringing them into the desired states) and controlling them (switching between the two states). Their trap holds two ions, and the researchers produced a quantum gate by entangling their states. The chip itself needs to be cryogenically cooled and placed in high vacuum to keep the ions in the trap. This requires quite large apparatus, much as the dilution refrigerator around a superconducting quantum computer is tens of centimetres in scale. However, ETH Zurich team leader Karan Mehta explains that a multi-qubit processor would only require one cryostat: “Think about scaling a desktop computer,” he says, “It doesn’t really matter how big the tower is: it matters how powerful the processor is.”

The MIT researchers focused on just one qubit but performed a wider variety of operations. Using their dedicated research foundry, they produced chips able to carry six different wavelengths of light through four different waveguides, allowing them to ionize a neutral strontium atom, load an ion into the trap and cool it before preparing, controlling and reading out its state.

Essentially opaque

The need to generate and inject light at specific frequencies is one of principal challenges for integrating photonics into trapped ion quantum computing: “All the materials systems that people have used for integrated photonics in the past are essentially opaque to the light that we need,” explains Sage, “A lot of what we have been working on is to develop high-performance integrated optics that works at the wavelengths required by trapped ion systems.”

The research demonstrates a single trapped ion qubit isolated a fraction of a millimetre above a classical, solid-state control system: “A lot of people speculating about the feasibility of making a larger quantum system assume that, if it’s not solid state, then they can’t,” says MIT’s Robert Niffenegger, the paper’s first author: “This is starting to bring those things closer together.”

“It’s a great step, because you don’t have to align the laser beams – that’s a big deal,” says Monroe. “The next step for both groups – and something the rest of the community really wants to do – is to deploy these techniques in a system and make it reliable.”

Physics in the pandemic: ‘This coronavirus has created an employment crisis across the country’

In February, I had just completed my master’s degree in medical physics and an internship at Kidwai Memorial Institute of Oncology, and I was searching for a job from my home in Kannur, Kerala.

While staying at home I realized several things. With an increasing number of coronavirus cases, the government locked down transport services, closed all public and private offices and factories, and restricted mobilization. The use of face masks was promoted, and schools and colleges were closed. All religious groups were told to cancel gatherings to encourage social distancing and reduce the spread of COVID-19. People were only allowed out of their houses to provide essential services or buy essential goods. Police officers regularly patrolled public places and markets to make sure that people stayed apart and to inform people about the importance of social distancing and wearing masks and gloves.

For students at the juncture of their academic career or professional courses, as well as for their parents, the lockdown heightened their anxiety, as it affected their education and job opportunities. Educational institutes had been forced to depend on online learning. I was using social media to get connected and communicating via mobile phone.

This lethal coronavirus pandemic has not just created a medical emergency but also an employment crisis across the country. Since the outbreak of COVID-19, so many hospitals cancelled job interviews. They were not ready to employ new staff and were trying to manage with the existing workforce. The absence of flights, trains and other modes of public transport during the lockdown made it impossible anyway.

Six months after my course completion, two vacancies were advertised for medical physicists at SMS Medical College and Hospitals in Jaipur. The interview was scheduled for 7 July. The main problem that I faced was attending the interview on that day as there was no proper transportation during that time. Travelling from one state to another state was a big deal. Also, different states had different travel rules according to their current COVID-19 situation.

At that time, the only way to reach Jaipur was by flying. Airline services were very few and there were so many procedures to carry out to get cleared for interstate travel. The first mandatory step before flying was to install Aarogya Setu, a central government app that uses location trackers and Bluetooth technology to assess the risk of the user catching COVID-19. Airlines won’t allow passengers on flights if the app shows their status as red. Temperature checks were carried out at all entry points, and self-check in and remote bag drops were mandated to avoid clustering of people.

On the day of my interview, the hospital administration conducted the interview according to the COVID-19 protocol. All candidates attended their interviews with face masks and maintained social distancing. After the interview, I was not able to go back home due to lack of airline services.

According to the Kerala government guidelines for air travellers coming into the state at that time, all should be home quarantined for 14 days from their date of arrival. The guidelines stated that all passengers had to register their details with the COVID-19 Jagratha web portal. After undergoing medical screening for any COVID-19 symptoms, asymptomatic persons must undergo home quarantine.

After reaching home, I was in quarantine for 14 days and my family members were not supposed to visit me. Health workers used to come to my home every day and inspect everything. Police officers also visited daily for inspections and I was asked to call them for requirements including groceries. After these days of quarantine, I joined SMS Medical College and Hospitals as a senior demonstrator (medical physicist) on 4 August.

The distance from my home in Kannur to Jaipur is nearly 3000 km. During my initial days at work, one of my major problems was speaking in Hindi, the local language in Jaipur.  My mother tongue is Malayalam and understanding Hindi spoken by people wearing face masks was a challenge. With time, I adjusted and my interaction with colleagues and patients improved a lot. Accommodation, food and daily travel to the department were also concerns, but I found accommodation near to the hospital within a week, which also solved the commuting problem.

The COVID-19 situation has made me more conscious of personal and public hygiene. The rituals of washing hands and sanitizing things before use, which started as a compulsion, slowly became a habit. At this time, there are no specific vaccines or treatments for COVID-19. However, there are many ongoing clinical trials evaluating potential treatments. And WHO is continuously providing updates and necessary information.

Patient QA: prioritizing accuracy, efficiency and throughput in the SRS/SBRT workflow

The myQA SRS detector will eliminate patient QA bottlenecks associated with high-precision stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT) treatments, allowing medical physicists to compare dose distributions – measured versus calculated – in minutes rather than hours and significantly enhancing patient throughput in the process. That’s the claim of IBA Dosimetry, a German supplier of specialist QA products and services to radiation oncology clinics, ahead of the official unveiling of myQA SRS at the virtual ASTRO 2020 Annual Meeting this week.

For context, SRS has generated significant traction – and clinical success – in the treatment of single and metastatic tumours in the brain. By exploiting multiple narrow beams from different directions, SRS is able to deliver conformal, high-dose radiation in one or a few fractions while minimizing collateral damage to surrounding healthy tissue and organs at risk. Similar progress is evident in the stereotactic treatment of tumours elsewhere in the body – for example, in the lungs, liver and spine, where these techniques are referred to collectively as SBRT.

Notwithstanding the growing clinical adoption of stereotactic treatment systems, the extreme physics of SRS/SBRT – focusing high-dose radiation very precisely on a small lesion and having it fall off as quickly as possible – represents a non-trivial dosimetric and QA challenge for the medical physics team. Put simply: it’s not easy to confirm targeting accuracy and dose-distribution accuracy when the stereotactic treatment volume can be as small as a few millimetres in diameter – and doubly so when the existing QA options for SRS/SBRT are unsatisfactory, claims Sandra Kos, product manager for patient QA solutions at IBA Dosimetry.

“While film provides excellent precision in terms of dose resolution,” she explains, “it is cumbersome to use, time-consuming and temperamental, owing to the uncertainties in handling, calibration and development. On the other hand, 2D diode arrays and ion-chamber arrays are able to generate results rapidly, but lack the necessary spatial resolution and error-detection sensitivity for SRS/SBRT QA.” With myQA SRS, Kos argues, that accuracy versus efficiency trade-off no longer applies. “We have created a unique SRS/SBRT QA solution that delivers film-class resolution along with the proven workflow efficiency of a digital detector.”

QA reimagined

If that’s the back-story, what of the device-level innovation? The core sensor in myQA SRS exploits a silicon complementary metal-oxide-semiconductor (CMOS) technology platform, which enables a compact design, fast read-out and high pixel density along the x and y coordinates (with each pixel representing a radiation-sensitive element comprising a photodiode, capacitor and three transistors). All of which yields a significantly enhanced digital detector for stereotactic patient QA.

In the clinic, that patient QA process demands a spatial resolution comparable to film (approximately 0.4 mm) in order to detect and analyse errors in SRS/SBRT treatment plans. While ion chambers, for example, have a proven QA track-record supporting standard radiotherapy techniques – including intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) – they lack the resolution needed to deal with the extreme dose gradients characteristic of SRS/SBRT beam delivery.

Typical SRS QA detector arrays seen in clinical use today offer a pitch (distance between measurement points) of 2.5 mm or larger and have limited field sizes. In SRS/SBRT, that granularity is insufficient and necessitates dose interpolation to fill in the “dead points” between pixels – estimates that, in turn, can lead to dose-peak errors. “With the myQA SRS we can decrease the pitch by a factor of 10 [versus standard arrays] and multiply the total number of channels by a factor of 100,” explains Arianna Giuliacci, a nuclear engineer who heads up the testing programme for myQA SRS within IBA Dosimetry. As such, the myQA SRS provides a spatial resolution of 0.4 mm, with more than 100,000 pixels across a large active area of 12×14 cm2.

Right now, Giuliacci and her colleagues in Schwarzenbruck, Germany, are focused on physical characterization of the myQA SRS detector versus key performance metrics like thermal stability, measurement precision, reliability and robustness. Using IBA’s in-house clinical set-up, the team has also evaluated dosimetric response of the detector at clinical photon fields and compared performance to ionizing chambers – including measurements of small-field beam output factors and percentage depth-dose curves. “In parallel,” Giuliacci adds, “we have integrated the detector in a treatment planning system, with subsequent irradiation of clinical plans and gamma analysis yielding high pass rates.”

QA best practice

With the in-house testing programme well advanced and third-party clinical evaluation to follow by year-end, myQA SRS is being lined up for full commercial release in the second quarter of next year. Even now, though, the potential upsides for clinical end-users are evident. For starters, the active area of the device (at 12×14 cm2) promises significant time savings in the QA of patients with several treatment volumes, helping medical physicists to confirm that planned SRS treatments are delivered accurately versus the complex dose distributions required for single-isocentre, simultaneous irradiation of multiple lesions.

“There is no need for the physicist to prepare multiple plans or choose which targets they want to QA, as everything can fit in one QA plan and one irradiation session,” explains Kos. “The size of the detector clearly helps to verify mono-isocentric plans with multiple targets.”

Ease of use and reliability also underpin the custom development of a cylindrical SRS/SBRT phantom that’s compatible with static and rotational treatment delivery. As a result, the combined detector–phantom assembly removes uncertainties in set-up, calibration and QA checks, notes Kos, while the QA plans can be verified and cross-checked independently in the same phantom using the myQA SRS detector, different ionization chambers and film. At the same time, the detector’s wireless Gantry Sensor+ provides accurate measurement of linac rotation angles to support rotational treatment plans.

For Kos, the enhanced capabilities of myQA SRS are part of the bigger picture in which independent QA plays a pivotal role in the validation of SRS/SBRT treatments. “Independence is a fundamental requirement for successful QA,” she concludes. “We can check patient QA outcomes without being influenced by possible malfunctions in the radiotherapy equipment chain, and we can ensure peace of mind and confidence that our customers are doing QA in the right way.”

As such, myQA SRS is compatible with all commercial SRS/SBRT treatment systems, including C arm, O-shaped or robotic linacs in a range of clinical set-ups.

Small-field innovation

myQA SRS detector
IBA Dosimetry unveiled its work-in-progress myQA SRS detector at the virtual ASTRO 2020 Annual Meeting this week. (Courtesy: IBA Dosimetry)

SRS/SBRT target volumes can be as small as few mm diameter and are treated with field sizes of 1×1 cm2 or less. The myQA SRS detector (shown left, with phantom) uses silicon CMOS technology to measure the dose distribution of such a 1×1 cm2 field with 625 measurement points (illustrated in the visualization, right). The schematic shows there is no need for interpolation between measurement points, ensuring unprecedented accuracy for the high dose gradients typical of SRS/SBRT treatment plans. In addition, the myQA SRS offers more than 100 measurement points for a 5 mm stereotactic cone plan.

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