Optimization of hexagonal‐pattern minibeams for spatially fractionated radiotherapy using proton beam scanning

Zhou, Jun; Artz, Mark; Szalkowski, Gregory; Chang, Chung‐Cheng; Stanforth, Alexander; Lin, Liyong; Zhang, Rongxiao; Wang, C.‐K. Chris

doi:10.1002/mp.14192

Cited by 10 publications

(13 citation statements)

References 39 publications

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“…By doing this characterization, we can set up a beam model in our treatment planning system and have a set of reference values for subsequent quality assurance for that energy. This information is also essential for Monte Carlo applications, where beam characteristics are needed to set up the phase space parameters and run the simulations to avoid modeling the whole beamline [ 16 ].…”

Section: Introductionmentioning

confidence: 99%

Characterization of 250 MeV Protons from the Varian ProBeam PBS System for FLASH Radiation Therapy

Zhou

Chang

Zhu

et al. 2023

International Journal of Particle Therapy

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Shoot-through proton FLASH radiation therapy has been proposed where the highest energy is extracted from a cyclotron to maximize the dose rate (DR). Although our proton pencil beam scanning system can deliver 250 MeV (the highest energy), this energy is not used clinically, and as such, 250 MeV has yet to be characterized during clinical commissioning. We aim to characterize the 250-MeV proton beam from the Varian ProBeam system for FLASH and assess the usability of the clinical monitoring ionization chamber (MIC) for FLASH use. We measured the following data for beam commissioning: integral depth dose curve, spot sigma, and absolute dose. To evaluate the MIC, we measured output as a function of beam current. To characterize a 250 MeV FLASH beam, we measured (1) the central axis DR as a function of current and spot spacing and arrangement, (2) for a fixed spot spacing, the maximum field size that achieves FLASH DR (ie, > 40 Gy/s), and (3) DR reproducibility. All FLASH DR measurements were performed using an ion chamber for the absolute dose, and irradiation times were obtained from log files. We verified dose measurements using EBT-XD films and irradiation times using a fast, pixelated spectral detector. R90 and R80 from integral depth dose were 37.58 and 37.69 cm, and spot sigma at the isocenter were σx = 3.336 and σy = 3.332 mm, respectively. The absolute dose output was measured as 0.343 Gy*mm2/MU for the commissioning conditions. Output was stable for beam currents up to 15 nA and gradually increased to 12-fold for 115 nA. Dose and DR depended on beam current, spot spacing, and arrangement and could be reproduced with 6.4% and 4.2% variations, respectively. Although FLASH was achieved and the largest field size that delivers FLASH DR was determined as 35 × 35 mm2, the current MIC has DR dependence, and users should measure dose and DR independently each time for their FLASH applications.

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Section: Introductionmentioning

confidence: 99%

Characterization of 250 MeV Protons from the Varian ProBeam PBS System for FLASH Radiation Therapy

Zhou

Chang

Zhu

et al. 2023

International Journal of Particle Therapy

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“…It indicated that the application of the absorbable hydrogel spacer (TraceIT, Augmenix, Bedford, MA) to separate the head of the pancreas and duodenum could be useful in these cases ( 44 ). On the other hand, we should explore the feasibility of different-level dose escalation by increasing the probability of local target control while sparing the OARs utilizing new generation of treatment and planning techniques such as SPArc, minibeams, and functional image-guided dose painting ( 39 , 45 , 46 ).…”

Section: Discussionmentioning

confidence: 99%

Investigate the Dosimetric and Potential Clinical Benefits Utilizing Stereotactic Body Radiation Therapy With Simultaneous Integrated Boost Technique for Locally Advanced Pancreatic Cancer: A Comparison Between Photon and Proton Beam Therapy

et al. 2021

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PurposeTo investigate the potential clinical benefits of using stereotactic body radiation therapy (SBRT) with simultaneous integrated boost (SIB) technique for locally advanced pancreatic cancer (LAPC) among different treatment modalities and planning strategies, including photon and proton.MethodA total of 19 patients were retrospectively selected in this study: 13 cases with the tumor located in the head of the pancreas and 6 cases with the tumor in the body of the pancreas. SBRT-SIB plans were generated using volumetric modulated arc therapy (VMAT), two-field Intensity Modulated Proton Therapy (IMPT), and three-field IMPT. The IMPT used the robust optimization parameters of ± 3.5% range and 5-mm setup uncertainties. Root-mean-square deviation dose (RMSD) volume histograms were used to evaluate the target coverage robustness quantitatively. Dosimetric metrics based on the dose-volume histogram (DVH), homogeneity index (HI), and normal tissue complication probability (NTCP) were analyzed to evaluate the potential clinical benefits among different planning groups.ResultsWith a similar CTV and SIB coverage, two-field IMPT provided a lower maximum dose for the stomach (median: 18.6GyE, p<0.05) and duodenum (median: 32.62GyE, p<0.05) when the target was located in the head of the pancreas compared to VMAT and three-field IMPT. The risks of gastric bleed (3.42%) and grade ≥ 3 GI toxicity (4.55%) were also decreased. However, for the target in the body of the pancreas, VMAT showed a lower maximum dose for the stomach (median 30.93GyE, p<0.05) and toxicity of gastric bleed (median: 8.67%, p<0.05) compared to two-field IMPT and three-field IMPT, while other maximum doses and NTCPs were similar. The RMSD volume histogram (RVH) analysis shows that three-field IMPT provided better robustness for targets but not for OARs. Instead, three-field IMPT increased the Dmean of organs such as the stomach, duodenum, and intestine.ConclusionThe results indicated that the tumor locations could play a critical role in determining clinical benefits among different treatment modalities. Two-field IMPT could be a better option for LAPC patients whose tumors are located in the head of the pancreas. It provides lower severe toxicity for the stomach and duodenum. Nevertheless, VMAT is preferred for the body with better protection for the possibility of gastric bleed.

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“…In 1 cm depth of tissue they measured a beam width of 1.1 ± 0.05 mm (fwhm) and a PVDR value of about 6.5 [60]. While all above mentioned studies investigated planar collimator designs, the following works analyzed collimators generating mesh-or grid-like minibeam patterns [44,61,62].…”

Section: Minibeam Irradiation Methods -Collimation Versus Focusingmentioning

confidence: 99%

Preclinical Challenges in Proton Minibeam Radiotherapy: Physics and Biomedical Aspects

et al. 2020

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The concept of spatial fractionation in radiotherapy was developed for better sparing of normal tissue in the entrance channel of radiation. Spatial fractionation utilizing proton minibeam radiotherapy (pMBRT) promises to be advantageous compared to X-ray minibeams due to higher dose conformity at the tumor. Preclinical in vivo experiments conducted with pMBRT in mouse ear models or in rat brains support the prospects, but the research about the radiobiological mechanisms and the search for adequate application parameters delivering the most beneficial minibeam therapy is still in its infancy. Concerning preclinical research, we consider glioma, non-small cell lung cancer and hepatocellular carcinoma as the most promising targets and propose investigating the effects on healthy tissue, especially neuronal cells and abdominal organs. The experimental setups for preclinical pMBRT used so far follow different technological approaches, and experience technical limitations when addressing the current questions in the field. We review the crucial physics parameters necessary for proton minibeam production and link them to the technological challenges to be solved for providing an optimal research environment. We consider focusing of pencil or planar minibeams in a scanning approach superior compared to collimation due to less beam halos, higher peak-to-valley dose ratios and higher achievable dose rates. A possible solution to serve such a focusing system with a high-quality proton beam at all relevant energies is identified to be a 3 GHz radio-frequency linear accelerator. We propose using a 16 MeV proton beam from an existing tandem accelerator injected into a linear post-accelerator, boosted up to 70 MeV, and finally delivered to an imaging and positioning end-station suitable for small animal irradiation. Ion-optical simulations show that this combination can generate focused proton minibeams with sizes down to 0.1 mm at 18 nA mean proton current - sufficient for all relevant preclinical experiments. This technology is expected to offer powerful and versatile tools for unleashing structured and advanced preclinical pMBRT studies at the limits and also has the potential to enable a next step into precision tumor therapy.

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Optimization of hexagonal‐pattern minibeams for spatially fractionated radiotherapy using proton beam scanning

Cited by 10 publications

References 39 publications

Characterization of 250 MeV Protons from the Varian ProBeam PBS System for FLASH Radiation Therapy

Characterization of 250 MeV Protons from the Varian ProBeam PBS System for FLASH Radiation Therapy

Investigate the Dosimetric and Potential Clinical Benefits Utilizing Stereotactic Body Radiation Therapy With Simultaneous Integrated Boost Technique for Locally Advanced Pancreatic Cancer: A Comparison Between Photon and Proton Beam Therapy

Preclinical Challenges in Proton Minibeam Radiotherapy: Physics and Biomedical Aspects

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