A new emittance selection system to maximize beam transmission for low‐energy beams in cyclotron‐based proton therapy facilities with gantry

Maradia, Vivek; Meer, D.; Weber, Damien Charles; Lomax, Anthony; Schippers, Jacobus Maarten; Psoroulas, S.

doi:10.1002/mp.15278

Cited by 20 publications

(27 citation statements)

References 59 publications

(89 reference statements)

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“…This produces large losses [i.e. >99% of the beam can be lost ( 66 )] especially when selecting lower energies, resulting in a radioactive hot spot and a beam with a very large distribution of energies, not suitable for precise 3D conformal dose delivery. Therefore, an ESS usually follows the energy degrader, consisting of several devices (degraders i.e.…”

Section: Limitations and Avenues For Improvementsmentioning

confidence: 99%

Future Developments in Charged Particle Therapy: Improving Beam Delivery for Efficiency and Efficacy

2021

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The physical and clinical benefits of charged particle therapy (CPT) are well recognized. However, the availability of CPT and complete exploitation of dosimetric advantages are still limited by high facility costs and technological challenges. There are extensive ongoing efforts to improve upon these, which will lead to greater accessibility, superior delivery, and therefore better treatment outcomes. Yet, the issue of cost remains a primary hurdle as utility of CPT is largely driven by the affordability, complexity and performance of current technology. Modern delivery techniques are necessary but limited by extended treatment times. Several of these aspects can be addressed by developments in the beam delivery system (BDS) which determines the overall shaping and timing capabilities enabling high quality treatments. The energy layer switching time (ELST) is a limiting constraint of the BDS and a determinant of the beam delivery time (BDT), along with the accelerator and other factors. This review evaluates the delivery process in detail, presenting the limitations and developments for the BDS and related accelerator technology, toward decreasing the BDT. As extended BDT impacts motion and has dosimetric implications for treatment, we discuss avenues to minimize the ELST and overview the clinical benefits and feasibility of a large energy acceptance BDS. These developments support the possibility of advanced modalities and faster delivery for a greater range of treatment indications which could also further reduce costs. Further work to realize methodologies such as volumetric rescanning, FLASH, arc, multi-ion and online image guided therapies are discussed. In this review we examine how increased treatment efficiency and efficacy could be achieved with improvements in beam delivery and how this could lead to faster and higher quality treatments for the future of CPT.

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Section: Limitations and Avenues For Improvementsmentioning

confidence: 99%

Future Developments in Charged Particle Therapy: Improving Beam Delivery for Efficiency and Efficacy

2021

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“…However, we have shown in another study that the transport of 100 π*mm*mrad emittance in both transversal planes could bring an increase in overall transmission (cyclotron to isocenter) by almost a factor 6 compared to transporting 30 π*mm*mrad for low energy beams. 7 Therefore, the solution shown in this article, together with larger emittance transported from the cyclotron to the CP, could strongly enhance the beam currents reached at isocenter in cyclotron‐based gantries.…”

Section: Discussionmentioning

confidence: 90%

“…For cyclotron‐based proton therapy facilities, and for low energy beams, the beam emittance after the energy degrader is typically to be in the order of a few hundred π*mm*mrad. 7 In fact, the emittance accepted by the gantry determines the maximum emittance that is transported through the fixed beamline between the cyclotron and the gantry, and hence also affects the achievable beam intensity at the isocenter. A gantry's emittance acceptance is determined by both the gantry beam optics and the beam phase space at the coupling point (CP), whilst the imaging factor obtained in the beam optics of the gantry, together with the beam phase space at the CP, 7 , 8 , 9 determine the beam size at isocenter.…”

Section: Introductionmentioning

confidence: 99%

“… 7 In fact, the emittance accepted by the gantry determines the maximum emittance that is transported through the fixed beamline between the cyclotron and the gantry, and hence also affects the achievable beam intensity at the isocenter. A gantry's emittance acceptance is determined by both the gantry beam optics and the beam phase space at the coupling point (CP), whilst the imaging factor obtained in the beam optics of the gantry, together with the beam phase space at the CP, 7 , 8 , 9 determine the beam size at isocenter. In this work, we have investigated how improvements on the emittance acceptance and imaging factor can achieve improved beam intensities (dose rates) at the isocenter, whilst also allowing for a range of beam sizes.…”

Section: Introductionmentioning

confidence: 99%

“…Due to the typically used beam emittances of ≤30 π*mm*mrad, this, in turn, results in large beam divergences (angular spread within the beam) in the gantry, increasing the possibility of beam losses along the gantry as the beam envelope approaches the beam pipe. For instance, for PSI's Gantry 2, by transporting 30 π*mm*mrad emittance (3 mm beam size and 10 mrad divergence at the CP) with 1:1 imaging, a transmission of 57% is achieved for lower energies (70–100 MeV) 7 , 8 (transmission through the gantry is defined as the ratio of beam current at isocenter to the beam current at the CP). However, to achieve higher intensity for lower energy beams, it is desirable to transport a higher emittance through both the beamline and gantry.…”

Section: Introductionmentioning

confidence: 99%

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Increase of the transmission and emittance acceptance through a cyclotron‐based proton therapy gantry

et al. 2022

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Purpose In proton therapy, the gantry, as the final part of the beamline, has a major effect on beam intensity and beam size at the isocenter. Most of the conventional beam optics of cyclotron‐based proton gantries have been designed with an imaging factor between 1 and 2 from the coupling point (CP) at the gantry entrance to the isocenter (patient location) meaning that to achieve a clinically desirable (small) beam size at isocenter, a small beam size is also required at the CP. Here we will show that such imaging factors are limiting the emittance which can be transported through the gantry. We, therefore, propose the use of large beam size and low divergence beam at the CP along with an imaging factor of 0.5 (2:1) in a new design of gantry beam optics to achieve substantial improvements in transmission and thus increase beam intensity at the isocenter. Methods The beam optics of our gantry have been re‐designed to transport higher emittance without the need of any mechanical modifications to the gantry beamline. The beam optics has been designed using TRANSPORT, with the resulting transmissions being calculated using Monte Carlo simulations (BDSIM code). Finally, the new beam optics have been tested with measurements performed on our Gantry 2 at PSI. Results With the new beam optics, we could maximize transmission through the gantry for a fixed emittance value. Additionally, we could transport almost four times higher emittance through the gantry compared to conventional optics, whilst achieving good transmissions through the gantry (>50%) with no increased losses in the gantry. As such, the overall transmission (cyclotron to isocenter) can be increased by almost a factor of 6 for low energies. Additionally, the point‐to‐point imaging inherent to the optics allows adjustment of the beam size at the isocenter by simply changing the beam size at the CP. Conclusion We have developed a new gantry beam optics which, by selecting a large beam size and low divergence at the gantry entrance and using an imaging factor of 0.5 (2:1), increases the emittance acceptance of the gantry, leading to a substantial increase in beam intensity at low energies. We expect that this approach could easily be adapted for most types of existing gantries.

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A new emittance selection system to maximize beam transmission for low‐energy beams in cyclotron‐based proton therapy facilities with gantry

et al. 2021

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In proton therapy, the potential of using high-dose rates in the cancer treatment is being explored. High-dose rates could improve efficiency and throughput in standard clinical practice, allow efficient utilization of motion mitigation techniques for moving targets, and potentially enhance normal tissue sparing due to the so-called FLASH effect. However, high-dose rates are difficult to reach when lower energy beams are applied in cyclotron-based proton therapy facilities, because they result in large beam sizes and divergences downstream of the degrader, incurring large losses from the cyclotron to the patient position (isocenter). In current facilities, the emittance after the degrader is reduced using circular collimators; however, this does not provide an optimal matching to the acceptance of the following beamline, causing a low transmission for these energies. We, therefore, propose to use a collimation system, asymmetric in both beam size and divergence, resulting in symmetric emittance in both beam transverse planes as required for a gantry system. This new emittance selection, together with a new optics design for the following beamline and gantry, allows a better matching to the beamline acceptance and an improvement of the transmission. Methods: We implemented a custom method to design the collimator sizes and shape required to select high emittance, to be transported by the following beamline using new beam optics (designed with TRANSPORT) to maximize acceptance matching. For predicting the transmission in the new configuration (new collimators + optics), we used Monte Carlo simulations implemented in BDSIM, implementing a model of PSI Gantry 2 which we benchmarked against measurements taken in the current clinical scenario (circular collimators + clinical optics). Results: From the BDSIM simulations, we found that the new collimator system and matching beam optics results in an overall transmission from the cyclotron to the isocenter for a 70 MeV beam of 0.72%. This is an improvement of almost a factor of 6 over the current clinical performance (0.13% transmission). The new optics satisfies clinical beam requirements at the isocenter. Conclusions: We developed a new emittance collimation system for PSI's PROSCAN beamline which, by carefully selecting beam size and divergence asymmetrically, increases the beam transmission for low-energy beams in current state-of -the-art cyclotron-based proton therapy gantries. With theseThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

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A new emittance selection system to maximize beam transmission for low‐energy beams in cyclotron‐based proton therapy facilities with gantry

Cited by 20 publications

References 59 publications

Future Developments in Charged Particle Therapy: Improving Beam Delivery for Efficiency and Efficacy

Future Developments in Charged Particle Therapy: Improving Beam Delivery for Efficiency and Efficacy

Increase of the transmission and emittance acceptance through a cyclotron‐based proton therapy gantry

A new emittance selection system to maximize beam transmission for low‐energy beams in cyclotron‐based proton therapy facilities with gantry

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