•FLASH proton therapy provides a novel route for sparing healthy tissue in radiotherapy.•Delivering spot scanning FLASH proton therapy is extremely challenging.•Advances in accelerator, magnet and ...dosimetry technology will be necessary.•Each accelerator technology has specific challenges that must be addressed.•Combinations of 3D-printed ridge/pin filters and scanned beams show promise.
There is growing interest in the radiotherapy community in the application of FLASH radiotherapy, wherein the dose is delivered to the entire treatment volume in less than a second. Early pre-clinical evidence suggests that these extremely high dose rates provide significant sparing of healthy tissue compared to conventional radiotherapy without reducing the damage to cancerous cells. This interest has been reflected in the proton therapy community, with early tests indicating that the FLASH effect is also present with high dose rate proton irradiation.
In order to deliver clinically relevant doses at FLASH dose rates significant technical hurdles must be overcome in the accelerator technology before FLASH proton therapy can be realised. Of these challenges, increasing the average current from the present clinical range of 1–10 nA to in excess of 100 nA is at least feasible with existing technology, while the necessity for rapid energy adjustment on the order of a few milliseconds is much more challenging, particularly for synchrotron-based systems. However, the greatest challenge is to implement full pencil beam scanning, where scanning speeds 2 orders of magnitude faster than the existing state-of-the-art will be necessary, along with similar improvements in the speed and accuracy of associated dosimetry. Hybrid systems utilising 3D-printed patient specific range modulators present the most likely route to clinical delivery. However, to correctly adapt and develop existing technology to meet the challenges of FLASH, more pre-clinical studies are needed to properly establish the beam parameters that are necessary to produce the FLASH effect.
Roadmap: proton therapy physics and biology Paganetti, Harald; Beltran, Chris; Both, Stefan ...
Physics in medicine & biology,
02/2021, Letnik:
66, Številka:
5
Journal Article
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The treatment of cancer with proton radiation therapy was first suggested in 1946 followed by the first treatments in the 1950s. As of 2020, almost 200 000 patients have been treated with proton ...beams worldwide and the number of operating proton therapy (PT) facilities will soon reach one hundred. PT has long moved from research institutions into hospital-based facilities that are increasingly being utilized with workflows similar to conventional radiation therapy. While PT has become mainstream and has established itself as a treatment option for many cancers, it is still an area of active research for various reasons: the advanced dose shaping capabilities of PT cause susceptibility to uncertainties, the high degrees of freedom in dose delivery offer room for further improvements, the limited experience and understanding of optimizing pencil beam scanning, and the biological effect difference compared to photon radiation. In addition to these challenges and opportunities currently being investigated, there is an economic aspect because PT treatments are, on average, still more expensive compared to conventional photon based treatment options. This roadmap highlights the current state and future direction in PT categorized into four different themes, 'improving efficiency', 'improving planning and delivery', 'improving imaging', and 'improving patient selection'.
We report on test measurements using boron carbide (B4C) as degrader material in comparison with the conventional graphite, which is currently used in many proton therapy degraders. Boron carbide is ...a material of lower average atomic weight and higher density than graphite. Calculations predict that, compared to graphite, the use of boron carbide results in a lower emittance behind the degrader due to the shorter degrader length. Downstream of the acceptance defining collimation system we expect a higher beam transmission, especially at low beam energies. This is of great interest in proton therapy applications as it allows either a reduction of the beam intensity extracted from the cyclotron leading to lower activation or a reduction of the treatment time. This paper summarizes the results of simulations and experiments carried out at the PROSCAN facility at the Paul Scherrer Institute1. The simulations predict an increase in the transmitted beam current after the collimation system of approx. 30.5% for beam degradation from 250 to 84 MeV for a boron carbide degrader compared to graphite. The experiment carried out with a boron carbide block reducing the energy to 84 MeV yielded a transmission improvement of 37% compared with the graphite degrader set to that energy.
Higher dose rates, a trend for radiotherapy machines, can be beneficial in shortening treatment times for radiosurgery and mitigating the effects of motion. Recently, even higher doses (e.g., 100 ...times greater) have become targeted because of their potential to generate the FLASH effect (FE). We refer to these physical dose rates as ultra‐high (UHDR). The complete relationship between UHDR and the FE is unknown. But UHDR systems are needed to explore the relationship further and to deliver clinical UHDR treatments, where indicated. Despite the challenging set of unknowns, the authors seek to make reasonable assumptions to probe how existing and developing technology can address the UHDR conditions needed to provide beam generation capable of producing the FE in preclinical and clinical applications. As a preface, this paper discusses the known and unknown relationships between UHDR and the FE. Based on these, different accelerator and ionizing radiation types are then discussed regarding the relevant UHDR needs. The details of UHDR beam production are discussed for existing and potential future systems such as linacs, cyclotrons, synchrotrons, synchrocyclotrons, and laser accelerators. In addition, various UHDR delivery mechanisms are discussed, along with required developments in beam diagnostics and dose control systems.
PSI is still the only location in which proton therapy is applied using a dynamic beam scanning technique on a very compact gantry. Recently, this system is also being used for the application of ...intensity-modulated proton therapy (IMPT). This novel technical development and the success of the proton therapy project altogether have led PSI in Year 2000 to further expand the activities in this field by launching the project PROSCAN. The first step is the installation of a dedicated commercial superconducting cyclotron of a novel type. The second step is the development of a new gantry, Gantry 2. For Gantry 2 we have chosen an iso-centric compact gantry layout. The diameter of the gantry is limited to 7,5 m, less than in other gantry systems (∼10–12 m). The space in the treatment room is comfortably large, and the access on a fixed floor is possible any time around the patient table. Through the availability of a faster scanning system, it will be possible to treat the target volume repeatedly in the same session. For this purpose, the dynamic control of the beam intensity at the ion source and the dynamic variation of the beam energy will be used directly for the shaping of the dose.
PSI ist nach wie vor der einzige Ort, wo Protonentherapie mit einer dynamischen Scanning-Methode auf einer sehr kompakten Gantry appliziert wird. Dieses System wird seit kurzem für die Applikation von intensitätsmodulierter Therapie mit Protonen (IMPT) benützt. Diese neuartigen technischen Entwicklungen und der Erfolg des Projektes haben im Jahre 2000 das PSI dazu veranlasst, eine weitere Expansion der Aktivitäten in diesem Sektor zu beschließen. Der erste Schritt im neuen Projekt PROSCAN ist die Installation eines dedizierten kommerziellen supraleitenden Zyklotrons von neuem Typ. Der zweite Schritt ist die Realisation einer zweiten Gantry, Gantry 2. Für Gantry 2 haben wir ein isozentrisches kompaktes Layout gewählt. Der Durchmesser der Gantry ist auf 7,5 m begrenzt, weniger als in anderen Gantry-Anlagen (∼10–12 m). Die Platzverhältnisse im Bestrahlungsraum sind komfortabel groß und der Zugang zum Patiententisch ist ringsum über einen festen Boden jederzeit möglich. Durch die Verfügbarkeit eines schnelleren Scannings wird man das Zielvolumen mehrmals wiederholt in der gleichen Session behandeln können. Dazu wollen wir die dynamische Kontrolle der Intensität des Strahles in der Ionenquelle und die dynamische Variation der Energie des Strahles direkt zur Formgebung der Dosis benützen.
This paper provides an overview of the current developments in superconducting magnets for applications in proton and ion therapy. It summarizes the benefits and challenges regarding the utilization ...of these magnets in accelerating systems (e.g. superconducting cyclotrons) and gantries. The paper also provides examples of currently used superconducting particle therapy systems and proposed designs.
Proton therapy is a rapidly developing technique in cancer treatment since the radiation dose delivered to the target volume is maximized and the dose to surrounding healthy tissue is minimized. The ...3-D scanning-irradiation method is performed by means of fast sweeper magnets for transverse scanning, and the scanning in depth of the tumor is performed by fast energy changes in steps of 1% in less than 100 ms. Therefore, high magnetic field ramping speed is necessary. To aim the scanning beam from all directions to the tumor in the patient, the last part of the beam transport and scanning system are mounted on a rotatable gantry. The last bending magnet in the gantry is a major component that drives the weight, footprint, and costs of the whole machine. Superconducting magnets have the potential to reduce the facility weight and costs, maintaining at the same time a large scanning field size. The preliminary magnetic design of the superconducting dipole for a proton therapy gantry is presented in this paper. The design consists in four Nb 3Sn racetrack coils and considers the requirement of large aperture for the transverse scanning and low field at the patient location using an active shielding system.
The characterization of a scintillating GEM based gas detector for quality control of clinical radio-therapeutic beams is presented. Photons emitted by the Ar/CF 4 gas mixture are detected by means ...of a CCD camera; in addition, the charge is measured. The detector response has been studied as a function of alpha particle energy and dose rate. The measured signal underestimation, at the Bragg peak depth, is only few percent with respect to an air filled ionization chamber.
Polymetallic nodules (manganese nodules) have been formed on deep sea sediments over millions of years and are currently explored for their economic potential, particularly for cobalt, nickel, ...copper, and manganese. Here we explored microbial communities inside nodules from the northeastern equatorial Pacific. The nodules have a large connected pore space with a huge inner surface of 120 m2/g as analyzed by computer tomography and BET measurements. X-ray photoelectron spectroscopy (XPS) and electron microprobe analysis revealed a complex chemical fine structure. This consisted of layers with highly variable Mn/Fe ratios (<1 to >500) and mainly of turbostratic phyllomanganates such as 7 and 10 Å vernadites alternating with layers of Fe-bearing vernadite (δ-MnO2) epitaxially intergrown with amorphous feroxyhyte (δ-FeOOH). Using molecular 16S rRNA gene techniques (clone libraries, pyrosequencing, and real-time PCR), we show that polymetallic nodules provide a suitable habitat for prokaryotes with an abundant and diverse prokaryotic community dominated by nodule-specific Mn(IV)-reducing and Mn(II)-oxidizing bacteria. These bacteria were not detected in the nodule-surrounding sediment. The high abundance and dominance of Mn-cycling bacteria in the manganese nodules argue for a biologically driven closed manganese cycle inside the nodules relevant for their formation and potential degradation.
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