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Carlier B, Heymans SV, Nooijens S, Collado-Lara G, Toumia Y, Delombaerde L, Paradossi G, D’hooge J, Van Den Abeele K, Sterpin E, Himmelreich U. A Preliminary Investigation of Radiation-Sensitive Ultrasound Contrast Agents for Photon Dosimetry. Pharmaceuticals (Basel) 2024; 17:629. [PMID: 38794199 PMCID: PMC11125270 DOI: 10.3390/ph17050629] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2024] [Revised: 04/28/2024] [Accepted: 04/30/2024] [Indexed: 05/26/2024] Open
Abstract
Radiotherapy treatment plans have become highly conformal, posing additional constraints on the accuracy of treatment delivery. Here, we explore the use of radiation-sensitive ultrasound contrast agents (superheated phase-change nanodroplets) as dosimetric radiation sensors. In a series of experiments, we irradiated perfluorobutane nanodroplets dispersed in gel phantoms at various temperatures and assessed the radiation-induced nanodroplet vaporization events using offline or online ultrasound imaging. At 25 °C and 37 °C, the nanodroplet response was only present at higher photon energies (≥10 MV) and limited to <2 vaporization events per cm2 per Gy. A strong response (~2000 vaporizations per cm2 per Gy) was observed at 65 °C, suggesting radiation-induced nucleation of the droplet core at a sufficiently high degree of superheat. These results emphasize the need for alternative nanodroplet formulations, with a more volatile perfluorocarbon core, to enable in vivo photon dosimetry. The current nanodroplet formulation carries potential as an innovative gel dosimeter if an appropriate gel matrix can be found to ensure reproducibility. Eventually, the proposed technology might unlock unprecedented temporal and spatial resolution in image-based dosimetry, thanks to the combination of high-frame-rate ultrasound imaging and the detection of individual vaporization events, thereby addressing some of the burning challenges of new radiotherapy innovations.
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Affiliation(s)
- Bram Carlier
- Department of Oncology, KU Leuven-University of Leuven, 3000 Leuven, Belgium; (B.C.); (L.D.); (E.S.)
- Department of Imaging and Pathology, KU Leuven-University of Leuven, 3000 Leuven, Belgium
- Molecular Small Animal Imaging Center (MoSAIC), KU Leuven-University of Leuven, 3000 Leuven, Belgium
| | - Sophie V. Heymans
- Department of Physics, KU Leuven Campus Kortrijk—KULAK, Etienne Sabbelaan 53, 8500 Kortrijk, Belgium; (S.V.H.); (K.V.D.A.)
- Department of Cardiovascular Sciences, KU Leuven-University of Leuven, 3000 Leuven, Belgium; (S.N.); (J.D.)
| | - Sjoerd Nooijens
- Department of Cardiovascular Sciences, KU Leuven-University of Leuven, 3000 Leuven, Belgium; (S.N.); (J.D.)
| | - Gonzalo Collado-Lara
- Department of Cardiology, Erasmus MC University Medical Center, 3015 GD Rotterdam, The Netherlands;
| | - Yosra Toumia
- National Institute for Nuclear Physics, INFN Sezione di Roma Tor Vergata, 00133 Rome, Italy;
- Department of Chemical Science and Technologies, University of Rome Tor Vergata, 00133 Rome, Italy;
| | - Laurence Delombaerde
- Department of Oncology, KU Leuven-University of Leuven, 3000 Leuven, Belgium; (B.C.); (L.D.); (E.S.)
- Department of Radiotherapy, UH Leuven, 3000 Leuven, Belgium
| | - Gaio Paradossi
- Department of Chemical Science and Technologies, University of Rome Tor Vergata, 00133 Rome, Italy;
| | - Jan D’hooge
- Department of Cardiovascular Sciences, KU Leuven-University of Leuven, 3000 Leuven, Belgium; (S.N.); (J.D.)
| | - Koen Van Den Abeele
- Department of Physics, KU Leuven Campus Kortrijk—KULAK, Etienne Sabbelaan 53, 8500 Kortrijk, Belgium; (S.V.H.); (K.V.D.A.)
| | - Edmond Sterpin
- Department of Oncology, KU Leuven-University of Leuven, 3000 Leuven, Belgium; (B.C.); (L.D.); (E.S.)
- Particle Therapy Interuniversity Center Leuven—PARTICLE, 3000 Leuven, Belgium
| | - Uwe Himmelreich
- Department of Imaging and Pathology, KU Leuven-University of Leuven, 3000 Leuven, Belgium
- Molecular Small Animal Imaging Center (MoSAIC), KU Leuven-University of Leuven, 3000 Leuven, Belgium
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Collado-Lara G, Heymans SV, Rovituso M, Sterpin E, D'hooge J, Vos HJ, Abeele KVD, de Jong N. Analytic prediction of droplet vaporization events to estimate the precision of ultrasound-based proton range verification. Med Phys 2023. [PMID: 36856326 DOI: 10.1002/mp.16327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2022] [Revised: 02/14/2023] [Accepted: 02/20/2023] [Indexed: 03/02/2023] Open
Abstract
BACKGROUND The safety and efficacy of proton therapy is currently hampered by range uncertainties. The combination of ultrasound imaging with injectable radiation-sensitive superheated nanodroplets was recently proposed for in vivo range verification. The proton range can be estimated from the distribution of nanodroplet vaporization events, which is stochastically related to the stopping distribution of protons, as nanodroplets are vaporized by protons reaching their maximal LET at the end of their range. PURPOSE Here, we aim to estimate the range estimation precision of this technique. As for any stochastic measurement, the precision will increase with the sample size, that is, the number of detected vaporizations. Thus, we first develop and validate a model to predict the number of vaporizations, which is then applied to estimate the range verification precision for a set of conditions (droplet size, droplet concentration, and proton beam parameters). METHODS Starting from the thermal spike theory, we derived a model that predicts the expected number of droplet vaporizations in an irradiated sample as a function of the droplet size, concentration, and number of protons. The model was validated by irradiating phantoms consisting of size-sorted perfluorobutane droplets dispersed in an aqueous matrix. The number of protons was counted with an ionization chamber, and the droplet vaporizations were recorded and counted individually using high frame rate ultrasound imaging. After validation, the range estimate precision was determined for different conditions using a Monte Carlo algorithm. RESULTS A good agreement between theory and experiments was observed for the number of vaporizations, especially for large (5.8 ± 2.2 µm) and medium (3.5 ± 1.1 µm) sized droplets. The number of events was lower than expected in phantoms with small droplets (2.0 ± 0.7 µm), but still within the same order of magnitude. The inter-phantom variability was considerably larger (up to 30x) than predicted by the model. The validated model was then combined with Monte Carlo simulations, which predicted a theoretical range retrieval precision improving with the square-root of the number of vaporizations, and degrading at high beam energies due to range straggling. For single pencil beams with energies between 70 and 240 MeV, a range verification precision below 1% of the range required perfluorocarbon concentrations in the order of 0.3-2.4 µM. CONCLUSION We proposed and experimentally validated a model to provide a quick estimate of the number of vaporizations for a given set of conditions (droplet size, droplet concentration, and proton beam parameters). From this model, promising range verification performances were predicted for realistic perfluorocarbon concentrations. These findings are an incentive to move towards preclinical studies, which are critical to assess the achievable droplet distribution in and around the tumor, and hence the in vivo range verification precision.
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Affiliation(s)
- Gonzalo Collado-Lara
- Biomedical Engineering, Department of Cardiology, Erasmus MC University Medical Center, Rotterdam, The Netherlands
| | - Sophie V Heymans
- Biomedical Engineering, Department of Cardiology, Erasmus MC University Medical Center, Rotterdam, The Netherlands.,Department of Physics, KU Leuven Campus Kulak, Kortrijk, Belgium.,Department of Cardiovascular Sciences, Leuven KU, Leuven, Belgium
| | | | - Edmond Sterpin
- Department of Oncology, Leuven KU, Leuven, Belgium.,Center of Molecular Imaging, Radiotherapy and Oncology, IREC Institute, Université Catholique de Louvain, Brussels, Belgium
| | - Jan D'hooge
- Department of Cardiovascular Sciences, Leuven KU, Leuven, Belgium
| | - Hendrik J Vos
- Biomedical Engineering, Department of Cardiology, Erasmus MC University Medical Center, Rotterdam, The Netherlands
| | | | - Nico de Jong
- Biomedical Engineering, Department of Cardiology, Erasmus MC University Medical Center, Rotterdam, The Netherlands
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van der Heyden B, Heymans SV, Carlier B, Collado-Lara G, Sterpin E, D’hooge J. Deep learning for dose assessment in radiotherapy by the super-localization of vaporized nanodroplets in high frame rate ultrasound imaging. Phys Med Biol 2022; 67. [DOI: 10.1088/1361-6560/ac6cc3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Accepted: 05/04/2022] [Indexed: 11/12/2022]
Abstract
Abstract
Objective. External beam radiotherapy is aimed to precisely deliver a high radiation dose to malignancies, while optimally sparing surrounding healthy tissues. With the advent of increasingly complex treatment plans, the delivery should preferably be verified by quality assurance methods. Recently, online ultrasound imaging of vaporized radiosensitive nanodroplets was proposed as a promising tool for in vivo dosimetry in radiotherapy. Previously, the detection of sparse vaporization events was achieved by applying differential ultrasound (US) imaging followed by intensity thresholding using subjective parameter tuning, which is sensitive to image artifacts. Approach. A generalized deep learning solution (i.e. BubbleNet) is proposed to localize vaporized nanodroplets on differential US frames, while overcoming the aforementioned limitation. A 5-fold cross-validation was performed on a diversely composed 5747-frame training/validation dataset by manual segmentation. BubbleNet was then applied on a test dataset of 1536 differential US frames to evaluate dosimetric features. The intra-observer variability was determined by scoring the Dice similarity coefficient (DSC) on 150 frames segmented twice. Additionally, the BubbleNet generalization capability was tested on an external test dataset of 432 frames acquired by a phased array transducer at a much lower ultrasound frequency and reconstructed with unconventional pixel dimensions with respect to the training dataset. Main results. The median DSC in the 5-fold cross validation was equal to ∼0.88, which was in line with the intra-observer variability (=0.86). Next, BubbleNet was employed to detect vaporizations in differential US frames obtained during the irradiation of phantoms with a 154 MeV proton beam or a 6 MV photon beam. BubbleNet improved the bubble-count statistics by ∼30% compared to the earlier established intensity-weighted thresholding. The proton range was verified with a −0.8 mm accuracy. Significance. BubbleNet is a flexible tool to localize individual vaporized nanodroplets on experimentally acquired US images, which improves the sensitivity compared to former thresholding-weighted methods.
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Heymans SV, Collado-Lara G, Rovituso M, Vos HJ, D'hooge J, de Jong N, Van Abeele KD. Acoustic Modulation Enables Proton Detection With Nanodroplets at Body Temperature. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2022; 69:2028-2038. [PMID: 35385380 DOI: 10.1109/tuffc.2022.3164805] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Superheated nanodroplet (ND) vaporization by proton radiation was recently demonstrated, opening the door to ultrasound-based in vivo proton range verification. However, at body temperature and physiological pressures, perfluorobutane nanodroplets (PFB-NDs), which offer a good compromise between stability and radiation sensitivity, are not directly sensitive to primary protons. Instead, they are vaporized by infrequent secondary particles, which limits the precision for range verification. The radiation-induced vaporization threshold (i.e., sensitization threshold) can be reduced by lowering the pressure in the droplet such that ND vaporization by primary protons can occur. Here, we propose to use an acoustic field to modulate the pressure, intermittently lowering the proton sensitization threshold of PFB-NDs during the rarefactional phase of the ultrasound wave. Simultaneous proton irradiation and sonication with a 1.1 MHz focused transducer, using increasing peak negative pressures (PNPs), were applied on a dilution of PFB-NDs flowing in a tube, while vaporization was acoustically monitored with a linear array. Sensitization to primary protons was achieved at temperatures between [Formula: see text] and 40 °C using acoustic PNPs of relatively low amplitude (from 800 to 200 kPa, respectively), while sonication alone did not lead to ND vaporization at those PNPs. Sensitization was also measured at the clinically relevant body temperature (i.e., 37 °C) using a PNP of 400 kPa. These findings confirm that acoustic modulation lowers the sensitization threshold of superheated NDs, enabling a direct proton response at body temperature.
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Toumia Y, Pullia M, Domenici F, Facoetti A, Ferrarini M, Heymans SV, Carlier B, Van Den Abeele K, Sterpin E, D'hooge J, D'Agostino E, Paradossi G. Ultrasound-assisted carbon ion dosimetry and range measurement using injectable polymer-shelled phase-change nanodroplets: in vitro study. Sci Rep 2022; 12:8012. [PMID: 35568710 PMCID: PMC9107472 DOI: 10.1038/s41598-022-11524-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2022] [Accepted: 04/20/2022] [Indexed: 11/09/2022] Open
Abstract
Methods allowing for in situ dosimetry and range verification are essential in radiotherapy to reduce the safety margins required to account for uncertainties introduced in the entire treatment workflow. This study suggests a non-invasive dosimetry concept for carbon ion radiotherapy based on phase-change ultrasound contrast agents. Injectable nanodroplets made of a metastable perfluorobutane (PFB) liquid core, stabilized with a crosslinked poly(vinylalcohol) shell, are vaporized at physiological temperature when exposed to carbon ion radiation (C-ions), converting them into echogenic microbubbles. Nanodroplets, embedded in tissue-mimicking phantoms, are exposed at 37 °C to a 312 MeV/u clinical C-ions beam at different doses between 0.1 and 4 Gy. The evaluation of the contrast enhancement from ultrasound imaging of the phantoms, pre- and post-irradiation, reveals a significant radiation-triggered nanodroplets vaporization occurring at the C-ions Bragg peak with sub-millimeter shift reproducibility and dose dependency. The specific response of the nanodroplets to C-ions is further confirmed by varying the phantom position, the beam range, and by performing spread-out Bragg peak irradiation. The nanodroplets' response to C-ions is influenced by their concentration and is dose rate independent. These early findings show the ground-breaking potential of polymer-shelled PFB nanodroplets to enable in vivo carbon ion dosimetry and range verification.
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Affiliation(s)
- Yosra Toumia
- Department of Chemical Science and Technologies, University of Rome Tor Vergata, 00133, Rome, Italy.
- National Institute for Nuclear Physics, INFN Sez. Roma Tor Vergata, 00133, Rome, Italy.
| | - Marco Pullia
- Fondazione CNAO, The National Center of Oncological Hadrontherapy, 27100, Pavia, Italy
| | - Fabio Domenici
- Department of Chemical Science and Technologies, University of Rome Tor Vergata, 00133, Rome, Italy
- National Institute for Nuclear Physics, INFN Sez. Roma Tor Vergata, 00133, Rome, Italy
| | - Angelica Facoetti
- Fondazione CNAO, The National Center of Oncological Hadrontherapy, 27100, Pavia, Italy
| | - Michele Ferrarini
- Fondazione CNAO, The National Center of Oncological Hadrontherapy, 27100, Pavia, Italy
| | - Sophie V Heymans
- Department of Physics, KU Leuven Campus Kulak, Kortrijk, Belgium
- Department of Cardiovascular Sciences, KU Leuven, Leuven, Belgium
- Biomedical Engineering, Department of Cardiology, Erasmus MC University Medical Center, Rotterdam, The Netherlands
| | - Bram Carlier
- Department of Oncology, KU Leuven, Leuven, Belgium
| | | | | | - Jan D'hooge
- Department of Cardiovascular Sciences, KU Leuven, Leuven, Belgium
| | | | - Gaio Paradossi
- Department of Chemical Science and Technologies, University of Rome Tor Vergata, 00133, Rome, Italy
- National Institute for Nuclear Physics, INFN Sez. Roma Tor Vergata, 00133, Rome, Italy
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