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Apr 12, 2024

India sets its sights on linac innovation

India’s research scientists and engineers are pursuing diverse lines of enquiry to drive down the cost of radiotherapy treatment systems, while scaling up ambitious R&D efforts on multipurpose proton

India’s research scientists and engineers are pursuing diverse lines of enquiry to drive down the cost of radiotherapy treatment systems, while scaling up ambitious R&D efforts on multipurpose proton accelerators. Amit Roy evaluates the latest progress.

The estimated annual global incidence of new cancer cases was upwards of 19 million in 2020, with more than 70% of people suffering from the disease resident in low- and middle-income countries (JCO Global Oncology 2022 8 e2100358). What’s more, according to forecasts from the International Atomic Energy Agency published on World Cancer Day in February 2022, the total number of cancer deaths worldwide is forecast to rise by 60% over the next two decades – to 16 million people a year – with those same low- and middle-income countries suffering the brunt of the escalation. India finds itself in the eye of this healthcare storm, with the domestic burden of cancer cases projected at between 1.9 and 2 million in 2022 – a burden, moreover, that’s also projected to increase over time.

Fundamentally, this is a question of supply (high-quality cancer treatment) versus demand (rising cancer incidence) for India – not least when it comes to the challenges associated with rolling out accessible and affordable radiation therapy facilities at the national level. Right now, there are around 545 clinical radiotherapy units across India (180 60Co-based teletherapy systems and 365 electron linacs). Most of the e-linacs are supplied by commercial manufacturers, with 50% of these systems located in private hospitals – and therefore beyond the reach of the majority of Indian citizens.

To drive down the cost of radiotherapy treatment, while simultaneously opening up access to more cancer patients, the Society for Applied Microwave Electronics Engineering and Research (SAMEER) in Mumbai has been prioritising technology innovation in e-linacs for several decades (with financial support from the central government’s Ministry of Electronics and Information Technology, also known as MeitY).

A case study in this regard is the medical electronics division of SAMEER, which initiated an R&D programme for a 4 MeV e-linac for cancer therapy in the late 1980s. The initial outcome: an S-band, side-coupled linac (operating at π/2 mode at 2.998 GHz) developed for electron acceleration. The SAMEER development team later integrated the linac with other core subsystems in collaboration with the Central Scientific Instruments Organisation, Chandigarh, and the Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, with the completed linac commissioned at PGIMER in 1991.

This original machine was called Jeevan Jyoti-I. SAMEER engineers went on to build three more e-linac variations on the Jeevan Jyoti-I theme, with all units duly commissioned and operating in hospitals. Subsequently, under the Indian government’s Jai Vigyan initiative, SAMEER built six more radiotherapy units (with an increased energy of 6 MV) and installed these systems in hospitals. One more machine is being commissioned in 2022 – initially using commercial microwave sources from SAMEER (though these will eventually be replaced with a domestically developed 2.6 MW magnetron).

India’s Department of Atomic Energy (DAE) plans to exploit the country’s rich natural sources of thorium to bolster the domestic nuclear energy programme, simultaneously exploring new methods for dealing with high-level nuclear waste as well as the at-scale production of medical radioisotopes for the diagnosis and treatment of cancer.

Consider the so-called accelerator-driven subcritical reactor (ADSR), a next-generation nuclear reactor design formed by coupling a substantially subcritical nuclear reactor core (using thorium as fuel) with a high-intensity, high-energy proton accelerator. The latter generates a copious beam of spallation neutrons to sustain the fission process – activating the thorium without needing to make the reactor critical (i.e. turning off the proton beam results in immediate and safe shut-down of the reactor). Another benefit of the ADSR scheme is the relatively short half-lives of the waste products.

Within this context, DAE’s R&D laboratories have started work on a high-current 1 GeV proton accelerator (see “Collective endeavour” figure). In the first phase of construction of a 20 MeV normal-conducting linac at Bhabha Atomic Research Centre (BARC), scientists accelerated a 2 mA proton beam from an ion source using a four-vane RF quadrupole (generating a 3 MeV proton beam with 65% transmission). Earlier this year, the BARC team boosted the proton energy to 6.8 MeV through the first drift-tube linac (with a peak beam current of 2.5 mA and an average beam current of 1 μA with 93% transmission). At Raja Ramanna Centre for Advanced Technology (RRCAT), meanwhile, several warm-front-end ion sources and associated subsystems are under construction (including low-energy beam transport, RF quadrupoles, medium-energy beam transport and a drift-tube linac).

Operationally, collaboration is a defining theme of India’s R&D effort on proton accelerators – not least through its scientists’ direct participation in the Proton Improvement Plan II (PIP-II), an essential upgrade and ambitious reimagining of the Fermilab accelerator complex in the US. Several Indian institutions are front-and-centre in the PIP-II initiative, designing and developing room-temperature and superconducting magnets, superconducting RF cavities, cryomodules and RF amplifiers for the PIP-II project team.

BARC and the Inter-University Accelerator Centre (IUAC) in New Delhi, for example, initially supplied two single-spoke-resonator cavities for testing at Fermilab, while end-to-end infrastructure for niobium-cavity fabrication and testing has been established at RRCAT. Several niobium superconducting cavities – required in both the PIP-II project and the Indian proton accelerator programme – have since been fabricatedand tested successfully.

One thing is clear: India’s e-linac R&D effort continues to gather momentum. The next step is to enhance the technology for dual photon energies (6 and 15 MeV) from the same linac, along with multiple electron energies (from 6 to 18 MeV) for treatment. A prototype of a novel dual-energy linac has already been put through its paces, delivering beam-on-target at SAMEER. The energy is varied by introducing a plunger in the coupling cavity in the acceleration section. Industry partners are being sought as the system undergoes final quality assurance and control checks.

Parallel technology programmes – covering both e-linacs and proton cyclotrons – are also underway to support domestic production of medical radioisotopes used in the diagnosis and treatment of cancer. For example, a 30 MeV, 5–10 kW linac project (incorporating two 15 MeV sections) is being lined up for the production of 99mTc from 99Mo (the former being required in a nuclear imaging procedure called single-photon-emission computerised tomography, commonly known as SPECT). The 99Mo will be produced from 100Mo using Bremsstrahlung photons, with the latter emitted after accelerated electrons are incident on a target. Tests of the first accelerating structure (15 MeV) are in progress and the full energy of 30 MeV is expected to come online next year.

Following India’s associate membership at CERN from 2017, the country’s scientists and engineers continue to build on a rich and diverse legacy of contributions spanning core accelerator technologies and participation in front-line high-energy physics experiments. This is a legacy that extends across more than 50 years of collaboration. In the 1990s, for example, the RRCAT contributed to LEP, while the Indian High-Energy Heavy Ion Physics Team contributed to the WA93 experiment at the CERN-SPS. An international cooperation agreement between India’s Department of Atomic Energy (DAE) and CERN was signed in 1992 to deepen ties and extend the scientific and technical cooperation between India and CERN. Those developments, in turn, paved the way for the decision (in 1996) of India’s Atomic Energy Commission to take part in the construction of the LHC – specifically, to contribute to the development of the CMS and ALICE detectors. India became a CERN Observer State in 2002, and the success of the DAE–CERN partnership on the LHC led to a new cooperation on novel accelerator technologies, shaping DAE’s participation in CERN’s Linac4, SPL and CTF3 projects.

Elsewhere, the Variable Energy Cyclotron Centre (VECC) in Kolkata is leading a project to build an 18 MeV medical cyclotron – a machine that will reduce the cost of production for positron-emitting radioisotopes. In terms of operational specifics: the system will accelerate negative hydrogen ions (H–) from an external, multicusp volume ion source, while a carbon stripper foil will alter the charge state of the ions from negative to positive ahead of extraction. Progress to date is encouraging: engineering design of the main magnet is complete and a 1 mA current has been extracted from the H– ion source.

Further technology innovation is evident in the field of hadron therapy, which uses proton or ion beams to deliver precision tumour targeting with zero exit dose – a capability that clinicians estimate could improve therapeutic outcomes in 15–20% of cancer patients who receive radiotherapy. Recognising the potential here, Indian clinics have recently purchased and installed two 230 MeV proton cyclotrons, supplied by Belgian equipment maker IBA, in a pivot towards next-generation cancer treatments.

Further progress has been reported by a collaboration between SAMEER and KEK, Japan’s High-Energy Accelerator Research Organisation. Jointly, the two partners have completed conceptual design studies for a multi-ion therapy machine based on a novel digital accelerator concept. The system is basically a fast-cycling induction synchrotron with a specialised beam-handling capability. (For context, the accelerating devices of a conventional synchrotron, such as RF cavities, are replaced with induction devices in an induction synchrotron.) It is possible, for example, to inject particles at nearly 200 kV DC directly into the main ring and, as such, the induction synchrotron does not need a separate injector.

In a related initiative, the Tata Memorial Centre Mumbai, and Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, have come up with a preliminary design for a 2 MeV injector and a 70–250 MeV proton synchrotron that may also be suitable for variable-energy beam delivery and other ion-beam therapies.