Design of a light and fast energy degrader for a compact superconducting gantry with large momentum acceptance

Liu, Xu; Wang, Wei; Liang, Zhikai; Zhao, Runxiao; Liu, Kaifeng; Qin, Bin

doi:10.1016/j.ejmp.2020.04.008

Cited by 6 publications

(7 citation statements)

References 12 publications

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“…According to momentum calculations, the therapeutic energy (70-218 MeV) of the LMA-SC gantry is divided into three energy bands in Table 1. 19 Switching energy bands takes 10 s, whereas switching energy within one band only takes 16 ms per step (around 5 mm water depth) using current fast servo linear motors. 19,28,29 And the speed of spot switching and line switching is 30.0 and 9.0 mm/ms, respectively.…”

Section: Parameters Of Lma-sc Gantrymentioning

confidence: 99%

“…19 Switching energy bands takes 10 s, whereas switching energy within one band only takes 16 ms per step (around 5 mm water depth) using current fast servo linear motors. 19,28,29 And the speed of spot switching and line switching is 30.0 and 9.0 mm/ms, respectively. 22 Using the Monte Carlo simulation, the transport efficiency of the beam increases with the proton energy, ranging from 0.7% to 80.0%, as illustrated in Table 1.…”

Section: Parameters Of Lma-sc Gantrymentioning

confidence: 99%

“…A novel beamline based on superconducting (SC) magnets, enabling rapid energy-layer switching, has been developed. [18][19][20][21][22][23] SC magnets offer several advantages over normal conducting magnets, including smaller volume, lighter weight, and, importantly, a larger momentum acceptance (dp/p = −10% to +10%). 20,21 In bending magnets, the trajectory of the proton beam is dependent on its momentum.…”

Section: Introductionmentioning

confidence: 99%

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Feasibility study of multiple‐energy Bragg peak proton FLASH on a superconducting gantry with large momentum acceptance

Zeng,

Li,

Wang

et al. 2024

Medical Physics

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BackgroundWhile the Bragg peak proton beam (BP) is capable of superior target conformity and organs‐at‐risk sparing than the transmission proton beam (TB), its efficacy in FLASH‐RT is hindered by both a slow energy switching process and the beam current. A universal range shifter (URS) can pull back the high‐energy proton beam while preserving the beam current. Meanwhile, a superconducting gantry with large momentum acceptance (LMA‐SC gantry) enables fast energy switching.PurposeThis study explores the feasibility of multiple‐energy BP FLASH‐RT on the LMA‐SC gantry.Method and MaterialsA simultaneous dose and spot map optimization algorithm was developed for BP FLASH‐RT treatment planning to improve the dose delivery efficiency. The URS was designed to be 0–27 cm thick, with 1 cm per step. BP plans using the URS were optimized using single‐field optimization (SFO) and multiple‐field optimization (MFO) for ten prostate cancer patients and ten lung cancer patients. The plan delivery parameters, dose, and dose rate metrics of BP plans were compared to those of TB plans using the parameters of the LMA‐SC gantry.ResultsCompared to TB plans, BP plans significantly reduced MUs by 42.7% (P < 0.001) with SFO and 33.3% (P < 0.001) with MFO for prostate cases. For lung cases, the reduction in MUs was 56.8% (P < 0.001) with SFO and 36.4% (P < 0.001) with MFO. BP plans also outperformed TB plans by reducing mean normal tissue doses. BP‐SFO plans achieved a reduction of 56.7% (P < 0.001) for prostate cases and 57.7% (P < 0.001) for lung cases, while BP‐MFO plans achieved a reduction of 54.2% (P < 0.001) for the prostate case and 40.0% (P < 0.001) for lung cases. For both TB and BP plans, normal tissues in prostate and lung cases received 100.0% FLASH dose rate coverage (>40 Gy/s).ConclusionsBy utilizing the URS and the LMA‐SC gantry, it is possible to perform multiple‐energy BP FLASH‐RT, resulting in better normal tissue sparing, as compared to TB plans.

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Section: Parameters Of Lma-sc Gantrymentioning

confidence: 99%

Section: Parameters Of Lma-sc Gantrymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Feasibility study of multiple‐energy Bragg peak proton FLASH on a superconducting gantry with large momentum acceptance

Zeng,

Li,

Wang

et al. 2024

Medical Physics

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“…But, it increases the transverse beam emittance and momentum spread, which eventually leads to beam loss 29,30 . To minimize these side effects, several groups have optimized the geometry structure and used materials with low atomic numbers and high density 31,32 . Moreover, Maradia et al.…”

Section: Introductionmentioning

confidence: 99%

“…29,30 To minimize these side effects, several groups have optimized the geometry structure and used materials with low atomic numbers and high density. 31,32 Moreover, Maradia et al developed a beamline that transports a larger emittance beam (100 π⋅mm⋅mrad) using asymmetric collimators. 33 The beamline resulted in the overall transmission increased by 40%, especially for the 70 MeV beam, where the transmission was improved from 0.13% to 0.72%.…”

Section: Introductionmentioning

confidence: 99%

Improving delivery efficiency using spots and energy layers reduction algorithms based on a large momentum acceptance beamline

et al. 2023

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BackgroundIntensity‐modulated proton therapy (IMPT) is a well‐known delivery method of proton therapy. Besides higher plan quality, reducing the delivery time is also essential to IMPT plans. It can enhance patient comfort, reduce treatment costs, and improve delivery efficiency. From the perspective of treatment efficacy, it contributes to mitigating the intra‐fractional motions and improving the accuracy of radiotherapy, especially for moving tumors.PurposeHowever, there is a tradeoff problem between the plan quality and delivery time. We consider the potential of a large momentum acceptance (LMA) beamline and apply the spots and energy layers reduction method to reduce the delivery time.MethodsThe delivery time for each field consists of the energy layer switching time, spot traveling time, and dose delivery time. The larger momentum spread and higher intensity beam offered by the LMA beamline contribute to reducing the total delivery time compared to the conventional beamline. In addition to the dose fidelity term, an L1 and logarithm items were added to the objective function to increase the sparsity of the low‐weighted spots and energy layers. After that, the low‐weighted spots and layers were iteratively excluded in the reduced plan, which reduced the energy layer switching time and spot traveling time. We used the standard, reduced, and LMA‐reduced plans to validate the proposed method and tested it on prostate and nasopharyngeal cases. Then, we compared and evaluated the plan quality, treatment time, and plan robustness against delivery uncertainty.ResultsCompared with the standard plans, the number of spots in the LMA‐reduced plans was on average reduced by 13 400 (95.6%) for prostate cases and by 48 300 (80.7%) for nasopharyngeal cases and the number of energy layers was on average reduced by 49 (61.3%) for prostate cases and by 97 (50.5%) for nasopharyngeal cases. And, the delivery time of the LMA‐reduced plans was shortened from 34.5 to 8.6 s for prostate cases and from 163.8 to 53.6 s for nasopharyngeal cases. The LMA‐reduced plans had comparable robustness to the spot monitor unit (MU) error compared with the standard plans, but the LMA‐reduced plans became more sensitive to spot position uncertainty.ConclusionThe delivery efficiency can be significantly improved using the LMA beamline and spots and energy layers reduction strategies. The method is promising to improve the efficiency of motion mitigation strategies for treating moving tumors.

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Biological‐equivalent‐dose‐based integrated optimization framework for fast‐energy‐switching Bragg peak FLASH‐RT using single‐beam‐per‐fraction

Zeng,

Li,

Zhang

et al. 2024

Medical Physics

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BackgroundsWhen comparing the delivery of all beams per fraction (ABPF) to single beam per fraction (SBPF), it is observed that SBPF not only helps meet the FLASH dose threshold but also mitigates the uncertainty with beam switching in the FLASH effect. However, SBPF might lead to a higher biological equivalent dose in 2 Gy (EQD2) for normal tissues.PurposeThis study aims to develop an EQD2‐based integrated optimization framework (EQD2‐IOF), encompassing robust dose, delivery efficiency, and beam orientation optimization (BOO) for Bragg peak FLASH plans using the SBPF treatment schedule. The EQD2‐IOF aims to enhance both dose sparing and the FLASH effect.MethodsA superconducting gantry was employed for fast energy switching within 27 ms, while universal range shifters were utilized to improve beam current in the implementation of FLASH plans with five Bragg peak beams. To enhance dose delivery efficiency while maintaining plan quality, a simultaneous dose and spot map optimization (SDSMO) algorithm for single field optimization was incorporated into a Bayesian optimization‐based auto‐planning algorithm. Subsequently, a BOO algorithm based on Tabu search was developed to select beam angle combinations (BACs) for 10 lung cases. To simultaneously consider dose sparing and FLASH effect, a quantitative model based on dose‐dependent dose modification factor (DMF) was used to calculate FLASH‐enhanced dose distribution. The EQD2‐IOF plan was compared to the plan optimized without SDSMO using BAC selected by a medical physicist (Manual plan) in the SBPF treatment schedule. Meanwhile, the mean EQD2 in the normal tissue was evaluated for the EQD2‐IOF plan in both SBPF and ABPF treatment schedules.ResultsNo significant difference was found in D2% and D98% of the target between EQD2‐IOF plans and Manual Plans. When using a minimum DMF of 0.67 and a dose threshold of 4 Gy, EQD2‐IOF plans showed a significant reduction in FLASH‐enhanced EQD2mean of the ipsilateral lung and normal tissue by 10.5% and 11.5%, respectively, compared to Manual plans. For normal tissues that received a dose greater than 70% of the prescription dose, using a minimum DMF of 0.7 for FLASH sparing compensated for the increase in EQD2mean resulting from replacing ABPF with SBPF schedules.ConclusionsThe EQD2‐IOF can automatically optimize SBPF FLASH‐RT plans to achieve optimal sparing of normal tissues. With an energy switching time of 27 ms, the loss of fractionate repairing using SBPF schedules in high‐dose regions can be compensated for by the FLASH effect. However, when an energy switching time of 500 ms is utilized, the SBPF schedule needs careful consideration, as the FLASH effect diminishes with longer irradiation time.

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Design of a light and fast energy degrader for a compact superconducting gantry with large momentum acceptance

Cited by 6 publications

References 12 publications

Feasibility study of multiple‐energy Bragg peak proton FLASH on a superconducting gantry with large momentum acceptance

Feasibility study of multiple‐energy Bragg peak proton FLASH on a superconducting gantry with large momentum acceptance

Improving delivery efficiency using spots and energy layers reduction algorithms based on a large momentum acceptance beamline

Biological‐equivalent‐dose‐based integrated optimization framework for fast‐energy‐switching Bragg peak FLASH‐RT using single‐beam‐per‐fraction

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