Towards FLASH proton therapy: the impact of treatment planning and machine characteristics on achievable dose rates

Water, Steven van de; Safai, Sairos; Schippers, Jacobus Maarten; Weber, Damien Charles; Lomax, Anthony

doi:10.1080/0284186x.2019.1627416

Cited by 135 publications

(187 citation statements)

References 21 publications

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“…SDDRO is generally applicable to the scenario of multiple proton energies. However, only one proton energy is considered in this study (and also other studies [7,8]). This choice was mainly made because multiple proton energies can significantly increase the number of proton spots and thereby decrease the proton weights, which will subsequently decrease the minimum MU threshold and thus the dose rate.…”

Section: Discussionmentioning

confidence: 99%

“…The dose influence matrix A was generated using MatRad [21] with 229 MeV proton energy only, 5 mm spot width (in both directions), 3 mm lateral spot spacing and 3 mm longitudinal spot spacing on 3 mm 3 dose grid. 229MeV was chosen since a higher energy leads to higher maximum beam intensity and 229MeV was the highest energy for which the theoretical maximum beam intensity was available in [7]. The beam angles were equally sampled with no couch kick, starting from 0º, e.g., "3 Beams" had 3 beam angles 0º, 120º, and 240º.…”

Section: Methodsmentioning

confidence: 99%

“…While each spot has a spatial dose and dose-rate distribution, all spots can be optimized jointly to form the desirable dose and dose rate distribution. However, currently available treatment plan optimization method only optimizes the dose distribution and does not directly optimize the dose rate [7,8].…”

Section: Accepted Articlementioning

confidence: 99%

“…The tissue-receiving dose rate constraint in Eq. (1) is based on dose-averaged dose rate (DADR) [7],…”

Section: The Dose Distribution D Is Determined By X Via Dose Influencmentioning

confidence: 99%

“…The key simulation parameters were: minimum dose rate threshold γ 0 =40 Gy/s for the ROI=CTV_10mm (the ring sandwiched by 10mm outer and inner expansion of CTV boundary), minimum MU threshold G min = 5×10 6 protons, minimum spot duration t=3 ms, and I max =1.2×10 12 protons/s at 229MeV [7].…”

Section: Accepted Articlementioning

confidence: 99%

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Simultaneous dose and dose rate optimization (SDDRO) for FLASH proton therapy

Gao

Lin

et al. 2020

Medical Physics

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Purpose: FLASH radiotherapy (RT) can potentially reduce normal tissue toxicity while preserving tumoricidal effectiveness to improve the therapeutic ratio. The key of FLASH for sparing normal tissues is to irradiate Accepted Article This article is protected by copyright. All rights reserved tissues with an ultra-high dose rate (i.e., ≥40Gy/s), for which proton RT can be used. However, currently available treatment plan optimization method only optimizes the dose distribution and does not directly optimize the dose rate. The contribution of this work to FLASH proton RT is the development of a novel treatment optimization method, i.e., simultaneous dose and dose rate optimization (SDDRO), to optimize tissue-receiving dose rate distribution as well as dose distribution. Methods: Distinguished from existing methods, SDDRO accounts for dose rate constraint and optimizes dose rate distribution. In terms of mathematical formulation, SDDRO is a constrained optimization problem with dose-volume constraint on dose distribution, minimum dose rate constraint on dose-averaged tissue-receiving dose rates, minimum monitor-unit constraint on spot weight, and maximum intensity constraint on beam intensity. In terms of optimization algorithm, SDDRO is solved by iterative convex relaxation and alternating direction method of multipliers. SDDRO algorithms are presented for both scenarios with either constant or variable beam intensity. Results: SDDRO was compared with intensity modulated proton therapy (IMPT) (dose optimization alone, and no dose rate optimization) using three lung cases. SDDRO substantially improved the dose rate distribution compared to IMPT, e.g., increasing of the region-of-interest (ROI) volume (ROI=CTV_10mm: the ring sandwiched by 10mm outer and inner expansion of CTV boundary) receiving at least 40Gy/s from ~30-50% to at least 98%, and the lung volume receiving at least 40Gy/s from ~30-40% to ~70-90%. Moreover, both dose and dose rate distributions from SDDRO were further considerably improved via the combined use of hypofractionation and multiple beams. Conclusions: We have developed a joint dose and dose rate optimization method for FLASH proton RT, namely SDDRO, which is first-of-its-kind to the best of our knowledge. The results suggest that (1) SDDRO can substantially improve the FLASH-dose-rate coverage (e.g., in terms of dose-rate volume histogram) compared to IMPT for the purpose of normal tissue sparing while preserving the dose distribution and (2) the combination of hypofractionation and multiple beams can further considerably improve the SDDRO plan quality in terms of both dose and dose rate distribution.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Accepted Articlementioning

confidence: 99%

“…The tissue-receiving dose rate constraint in Eq. (1) is based on dose-averaged dose rate (DADR) [7],…”

Section: The Dose Distribution D Is Determined By X Via Dose Influencmentioning

confidence: 99%

Section: Accepted Articlementioning

confidence: 99%

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Simultaneous dose and dose rate optimization (SDDRO) for FLASH proton therapy

Gao

Lin

et al. 2020

Medical Physics

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Commissioning and initial validation of Eclipse eMC algorithm for the electron FLASH research extension (FLEX) system for pre‐clinical studies

Oh,

Gallagher,

Yan

et al. 2024

J Applied Clin Med Phys

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PurposeTo investigate the feasibility of commissioning the 16 MeV electron FLASH Extension (FLEX) in the commercial treatment planning system (TPS) for biomedical research with cell and mouse models, and in silico treatment planning studies.MethodsTo commission the FLEX system with the electron Monte Carlo (eMC) algorithm in the commercial TPS, radiochromic film was used to measure the vendor‐recommended beam data. Once the beam model was generated for the eMC algorithm, supplemental measurements were collected for validation purposes and compared against the TPS‐calculated results. Additionally, the newly commissioned 16 MeV FLASH beam was compared to the corresponding 16 MeV conventional electron beam.ResultsThe eMC algorithm effectively modeled the FLEX system. The eMC‐calculated PDDs and profiles for the 16 MeV electron FLASH beam agreed with measured values within 1%, on average, for 6 × 6 cm2 and 10 × 10 cm2 applicators. Flatness and symmetry deviated by less than 1%, while FWHM and penumbra agreed within 1 mm for both eMC‐calculated and measured profiles. Additionally, the small field (i.e., 2‐cm diameter cutout) that was measured for validation purposes agreed with TPS‐calculated results within 1%, on average, for both the PDD and profiles. The FLASH and conventional dose rate 16 MeV electron beam were in agreement in regard to energy, but the profiles for larger field sizes began to deviate (>10 × 10 cm2) due to the forward‐peaked nature of the FLASH beam. For cell irradiation experiments, the measured and eMC‐calculated in‐plane and cross‐plane absolute dose profiles agreed within 1%, on average.ConclusionsThe FLEX system was successfully commissioned in the commercial TPS using the eMC algorithm, which accurately modeled the forward‐peaked nature of the FLASH beam. A commissioned TPS for FLASH will be useful for pre‐clinical cell and animal studies, as well as in silico FLASH treatment planning studies for future clinical implementation.

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A framework for defining FLASH dose rate for pencil beam scanning

et al. 2020

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To develop a method of (a) calculating the dose rate of voxels within a proton field delivered using pencil beam scanning (PBS), and (b) reporting a representative dose rate for the PBS treatment field that enables correspondence between multiple treatment modalities. This method takes into account the unique spatiotemporal delivery patterns of PBS FLASH radiotherapy. Methods: The dose rate at each voxel of a PBS radiation field is approximately the quotient of the voxel's dose and "effective" irradiation time. Each voxel's "effective" irradiation time starts when the cumulative dose rises above a chosen threshold value, and stops when its cumulative dose reaches its total dose minus the same threshold value. The above calculation yields a distribution of dose rates for the voxels within a PBS treatment field. To report a representative dose rate for the PBS field, we propose a user-selectable parameter of pth percentile of the dose rate distribution, such that (100 − p) % of the field is above the corresponding dose rate. To demonstrate the method described above, we design FLASH transmission fields using 250 MeV protons and calculate the PBS dose rate distributions in both two-dimensional (2D) and three-dimensional (3D) models. To further evaluate the formalism, we provide an example of a clinical PBS treatment field. Results: With the 2D PBS transmission field, it is demonstrated that the time to accumulate the total dose at a voxel is limited to a fraction of the delivery time of the entire field. In addition, the spatial distributions of dose and dose rate are quite different within the field. For the 10 × 10 cm 2 PBS field irradiating a 3D water phantom, the prescribed dose of 10 Gy at 10 cm depth is delivered in 1.0 s. The dose rate decreases in the irradiated volume with increasing depth (until the Bragg peak) due to increase of beam spot size by Coulomb scattering. For example, 95% of the irradiated volume between 0 and 10 cm depth receive >40 Gy/s, whereas between 0-20 cm and 0-30 cm depth, 95% of the irradiated volume received >36 Gy/s and >24 Gy/s, respectively. For the clinical PBS treatment field, the scanning pattern conforms to the PTV. PBS dose rate data are presented for the PTV and adjacent normal organs. Conclusion: We have developed a method of calculating the dose rate distribution of a PBS proton field and have recommended nomenclature for reporting PBS treatment dose rate. We believe that standardizing the method for calculating and reporting PBS treatment dose rates, in a manner that corresponds with other treatment modalities, will advance the research and potential application of PBS FLASH radiotherapy.

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Towards FLASH proton therapy: the impact of treatment planning and machine characteristics on achievable dose rates

Cited by 135 publications

References 21 publications

Simultaneous dose and dose rate optimization (SDDRO) for FLASH proton therapy

Simultaneous dose and dose rate optimization (SDDRO) for FLASH proton therapy

Commissioning and initial validation of Eclipse eMC algorithm for the electron FLASH research extension (FLEX) system for pre‐clinical studies

A framework for defining FLASH dose rate for pencil beam scanning

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