Beam properties within the momentum acceptance of a clinical gantry beamline for proton therapy

Giovannelli, Anna Chiara; Maradia, Vivek; Meer, D.; Safai, Sairos; Psoroulas, S.; Togno, Michele; Bula, C.; Weber, Damien Charles; Lomax, Anthony; Fattori, Giovanni

doi:10.1002/mp.15449

Cited by 11 publications

(16 citation statements)

References 55 publications

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“…In addition, because of the spill cycle used by synchrotrons the energy layer switching time (ELST) is greater. In a recent publication reported values of ELST from a selection of proton therapy centers range from 0.2 to 2 s for synchrotrons and from 0.08 to 0.9 s for cyclotrons 23 . At our center the average ELST is approximately 0.9 s. The minimum value of 0.2 s reported for synchrotrons is achieved through the use of a multi‐energy extraction (MEE) system that allows a single spill of protons to be used for multiple energy layers.…”

Section: Discussionmentioning

confidence: 99%

“…The current study investigates the use of a MRF in a cyclotron system with an ESS, which has a different beam production and delivery mechanism and therefore a different relationship between the spot map and beam delivery time. In particular, the energy layer switching time (ELST) is dramatically longer for synchrotrons 23 . Another important difference between synchrotron and cyclotron systems is the shape of the Bragg peak, particularly for low‐energy beams.…”

Section: Introductionmentioning

confidence: 99%

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The use of a mini‐ridge filter with cyclotron‐based pencil beam scanning proton therapy

et al. 2023

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Background: Pencil beam scanning (PBS) proton therapy allows for far superior dose conformality compared with passive scattering techniques. However, one drawback of PBS is that the beam delivery time can be long, particularly when treating superficial disease. Minimizing beam delivery time is important for patient comfort and precision of treatment delivery. Mini-ridge filters (MRF) have been shown to reduce beam delivery time for synchrotron-based PBS. Given that cyclotron systems are widely used in proton therapy it is necessary to investigate the potential clinical benefit of mini-ridge filters in such systems. Purpose: To demonstrate the clinical benefit of using a MRF to reduce beam delivery time for patients with large target volumes and superficial disease in cyclotron-based PBS proton therapy. Methods: A MRF beam model was generated by simulating the effect of a MRF on our clinical beam data assuming a fixed snout position relative to the isocenter. The beam model was validated with a series of measurements. The model was used to optimize treatment plans in a water phantom and on six patient DICOM datasets to further study the effect of the MRF and for comparison with physician-approved clinical treatment plans. Beam delivery time was measured for six plans with and without the MRF to demonstrate the reduction achievable. Plans with and without MRF were reviewed to confirm clinical acceptability by a radiation oncologist. Patient-specific QA measurements were carried out with a two-dimensional ionization chamber array detector for one representative patient's plan optimized with the MRF beam model. Results: Results show good agreement between the simulated beam model and measurements with mean and maximum deviations of 0.06 mm (0.45%) and 0.61 mm (4.9%). The increase in Bragg peak width (FWHM) ranged from 2.7 mm at 226 MeV to 6.1 mm at 70 MeV. The mean and maximum reduction in beam delivery time observed per field was 29.1 s (32.2%) and 79.7 s (55.3%). Conclusion: MRFs can be used to reduce treatment time in cyclotron-based PBS proton therapy without sacrificing plan quality. This is particularly beneficial for patients with large targets and superficial disease such as in breast cancer where treatment times are generally long, as well as patients treated with deep inspiration breath hold (DIBH).

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The use of a mini‐ridge filter with cyclotron‐based pencil beam scanning proton therapy

et al. 2023

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“…Although the distal fall‐off of the dose distribution has some dependence on the momentum spread used, the momentum spectrum at the isocenter is expected to have a negligible change due to these losses as they will only occur in the tails of the momentum distribution. In this respect, it is important that, due to the achromatic beam optics, the lateral beam size at the isocenter is independent of the momentum spread of the beam 18 . As such it would make it interesting to add the momentum spread as one of the parameters to be optimized in the treatment planning.…”

Section: Discussionmentioning

confidence: 99%

“…In this respect, it is important that, due to the achromatic beam optics, the lateral beam size at the isocenter is independent of the momentum spread of the beam. 18 As such it would make it interesting to add the momentum spread as one of the parameters to be optimized in the treatment planning.…”

Section: Discussionmentioning

confidence: 99%

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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“…For cyclotron-based facilities, the energy change time ranges from 80 to 900 ms (Giovannelli et al 2022). However, for most synchrotron-based facilities, it is even slower ranging from 200 to 2000 ms (Giovannelli et al 2022). Thus, reducing the number of energy layers would improve the beam delivery efficiency.…”

Section: Introductionmentioning

confidence: 99%

Universal and dynamic ridge filter for pencil beam scanning particle therapy: a novel concept for ultra-fast treatment delivery

et al. 2022

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Objective In pencil beam scanning (PBS) particle therapy, a short treatment delivery time is paramount for the efficient treatment of moving targets with motion mitigation techniques (such as breath-hold, rescanning, and gating). Energy and spot position change time are limiting factors in reducing treatment time. In this study, we designed a universal and dynamic energy modulator (ridge filter, RF) to broaden the Bragg peak, to reduce the number of energies and spots required to cover the target volume, thus lowering the treatment time. Approach Our RF unit comprises two identical RFs placed just before the isocenter. Both RFs move relative to each other, changing the Bragg peak’s characteristics dynamically. We simulated different Bragg peak shapes with the RF in Monte Carlo simulation code (TOPAS) and validated them experimentally. We then delivered single-field plans with 1Gy/fraction to different geometrical targets in water, to measure the dose delivery time using the RF and compare it with the clinical settings. Main results Aligning the RFs in different positions produces different broadening in the Bragg peak; we achieved a maximum broadening of 2.5 cm. With RF we reduced the number of energies in a field by more than 60%, and the dose delivery time by 50%, for all geometrical targets investigated, without compromising the dose distribution transverse and distal fall-off. Significance Our novel universal and dynamic RF allows for the adaptation of the Bragg peak broadening for a spot and/or energy layer based on the requirement of dose shaping in the target volume. It significantly reduces the number of energy layers and spots to cover the target volume, and thus the treatment time. This RF design is ideal for ultra-fast treatment delivery within a single breath-hold (5-10 sec), efficient delivery of motion mitigation techniques, and small animal irradiation with ultra-high dose rates (FLASH).

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Beam properties within the momentum acceptance of a clinical gantry beamline for proton therapy

Cited by 11 publications

References 55 publications

The use of a mini‐ridge filter with cyclotron‐based pencil beam scanning proton therapy

The use of a mini‐ridge filter with cyclotron‐based pencil beam scanning proton therapy

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

Universal and dynamic ridge filter for pencil beam scanning particle therapy: a novel concept for ultra-fast treatment delivery

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