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Khan S, Bassenne M, Wang J, Manjappa R, Melemenidis S, Breitkreutz DY, Maxim PG, Xing L, Loo BW, Pratx G. Multicellular Spheroids as In Vitro Models of Oxygen Depletion During FLASH Irradiation. Int J Radiat Oncol Biol Phys 2021; 110:833-844. [PMID: 33545301 DOI: 10.1016/j.ijrobp.2021.01.050] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Revised: 12/15/2020] [Accepted: 01/26/2021] [Indexed: 12/15/2022]
Abstract
PURPOSE The differential response of normal and tumor tissues to ultrahigh-dose-rate radiation (FLASH) has raised new hope for treating solid tumors but, to date, the mechanism remains elusive. One leading hypothesis is that FLASH radiochemically depletes oxygen from irradiated tissues faster than it is replenished through diffusion. The purpose of this study was to investigate these effects within hypoxic multicellular tumor spheroids through simulations and experiments. METHODS AND MATERIALS Physicobiological equations were derived to model (1) the diffusion and metabolism of oxygen within spheroids; (2) its depletion through reactions involving radiation-induced radicals; and (3) the increase in radioresistance of spheroids, modeled according to the classical oxygen enhancement ratio and linear-quadratic response. These predictions were then tested experimentally in A549 spheroids exposed to electron irradiation at conventional (0.075 Gy/s) or FLASH (90 Gy/s) dose rates. Clonogenic survival, cell viability, and spheroid growth were scored postradiation. Clonogenic survival of 2 other cell lines was also investigated. RESULTS The existence of a hypoxic core in unirradiated tumor spheroids is predicted by simulations and visualized by fluorescence microscopy. Upon FLASH irradiation, this hypoxic core transiently expands, engulfing a large number of well-oxygenated cells. In contrast, oxygen is steadily replenished during slower conventional irradiation. Experimentally, clonogenic survival was around 3-fold higher in FLASH-irradiated spheroids compared with conventional irradiation, but no significant difference was observed for well-oxygenated 2-dimensional cultured cells. This differential survival is consistent with the predictions of the computational model. FLASH irradiation of spheroids resulted in a dose-modifying factor of around 1.3 for doses above 10 Gy. CONCLUSIONS Tumor spheroids can be used as a model to study FLASH irradiation in vitro. The improved survival of tumor spheroids receiving FLASH radiation confirms that ultrafast radiochemical oxygen depletion and its slow replenishment are critical components of the FLASH effect.
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Affiliation(s)
- Syamantak Khan
- Department of Radiation Oncology, Stanford University, Stanford, California
| | - Maxime Bassenne
- Department of Radiation Oncology, Stanford University, Stanford, California
| | - Jinghui Wang
- Department of Radiation Oncology, Stanford University, Stanford, California
| | - Rakesh Manjappa
- Department of Radiation Oncology, Stanford University, Stanford, California
| | | | | | - Peter G Maxim
- Department of Radiation Oncology, Indiana University, Indianapolis, Indiana
| | - Lei Xing
- Department of Radiation Oncology, Stanford University, Stanford, California
| | - Billy W Loo
- Department of Radiation Oncology, Stanford University, Stanford, California
| | - Guillem Pratx
- Department of Radiation Oncology, Stanford University, Stanford, California.
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Simiele EA, Breitkreutz DY, Capaldi DPI, Liu W, Bush KK, Skinner LB. Precision radiotherapy using monochromatic inverse Compton x-ray sources. Med Phys 2020; 48:366-375. [PMID: 33107049 DOI: 10.1002/mp.14552] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Revised: 09/28/2020] [Accepted: 10/02/2020] [Indexed: 11/10/2022] Open
Abstract
PURPOSE The dosimetric properties of inverse Compton (IC) x-ray sources were investigated to determine their utility for stereotactic radiation therapy. METHODS Monte Carlo simulations were performed using the egs brachy user code of EGSnrc. Nominal IC source x-ray energies of 80 and 150 keV were considered in this work. Depth-dose and lateral dose profiles in water were calculated, as was dose enhancement in the bone. Further simulations were performed for brain and spine treatment sites. The impact of gold nanoparticle doping was also investigated for the brain treatment site. Analogous dose calculations were performed in a clinical treatment planning system using a clinical 6 MV photon beam model and were compared to the Monte Carlo simulations. RESULTS Both 80 and 150 keV IC beams were observed to have sharp 80-20 penumbra (i.e., < 0.1 mm) with broad low-dose tails in water. For reference, the calculated penumbra for the 6 MV clinical beam was 3 mm. Maximum dose enhancement factors in bone of 3.1, 1.4, and 1.1 were observed for the 80, 150 keV, and clinical 6 MV beams, respectively. The plan quality for the single brain metastasis case was similar between the IC beams and the 6 MV beam without gold nanoparticles. As the concentration of gold within the target increased, the V12 Gy to the normal brain tissue and D max within the target volume significantly decreased and the conformity significantly improved, which resulted in superior plan quality over the clinical 6 MV beam plan. In the spine cases, the sharp penumbra and enhanced dose to bone of the IC beams produced superior plan quality (i.e., better conformity, normal tissue sparing, and spinal cord sparing) as compared to the clinical 6 MV beam plans. CONCLUSIONS The findings from this work indicate that inverse Compton x-ray sources are well suited for stereotactic radiotherapy treatments due to their sharp penumbra and dose enhancement around high atomic number materials. Future work includes investigating the properties of intensity-modulated inverse Compton x-ray sources to improve the homogeneity within the target tissue.
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Affiliation(s)
- Eric A Simiele
- Department of Radiation Oncology, Stanford University, Stanford, CA, 94305, USA
| | - Dylan Y Breitkreutz
- Department of Radiation Oncology, Stanford University, Stanford, CA, 94305, USA
| | - Dante P I Capaldi
- Department of Radiation Oncology, Stanford University, Stanford, CA, 94305, USA
| | - Wu Liu
- Department of Radiation Oncology, Stanford University, Stanford, CA, 94305, USA
| | - Karl K Bush
- Department of Radiation Oncology, Stanford University, Stanford, CA, 94305, USA
| | - Lawrie B Skinner
- Department of Radiation Oncology, Stanford University, Stanford, CA, 94305, USA
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Breitkreutz DY, Renaud MA, Seuntjens J, Weil MD, Zavgorodni S, Bazalova-Carter M. Inverse optimization of low-cost kilovoltage x-ray arc therapy plans. Med Phys 2018; 45:5161-5171. [PMID: 30152125 DOI: 10.1002/mp.13153] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Revised: 06/28/2018] [Accepted: 08/17/2018] [Indexed: 12/30/2022] Open
Abstract
PURPOSE The objective of this work was to investigate the benefits of using inverse optimization treatment planning for kilovoltage arc therapy (KVAT) and to assess the dosimetric limitations of KVAT. METHODS Monte Carlo (MC) calculated, inversely optimized KVAT plans of spherical, idealized breast, lung, and prostate lesions were calculated using the EGSnrc/BEAMnrc and DOSXYZnrc MC codes. The dose delivered with the KVAT system, which generates 200-225 kV photon beamlets, was calculated and inversely optimized using an optimization framework developed at McGill University. KVAT dose distributions were compared with inversely optimized and MC generated megavoltage (MV) volumetric modulated arc therapy (VMAT) plans as a reference. Prescription doses delivered to 95% of the planning target volume (PTV) were 38.5 (10 fractions), 60 (30 fractions) and 73.8 (41 fractions) Gy for the breast, lung and prostate patients, respectively. Dose distributions, dose volume histograms, and PTV homogeneity indices were used to evaluate KVAT and VMAT plans based on RTOG protocols. RESULTS All organ-at-risk (OAR) doses were within prescribed dose limits for KVAT and VMAT plans. Generally, KVAT plans delivered higher doses to OARs. For example, due to the lower energy of KVAT, 50% of the rib volume received 12.9 Gy from KVAT while only receiving 2.5 Gy from VMAT. OAR doses were especially high for the KVAT prostate plan due to the presence of large volumes of bony anatomy, which illustrates a limitation of the KVAT system. The KVAT treatment times per fraction for the breast, lung and prostate patients were 2.8, 2.6 and 5.5 min, respectively. CONCLUSIONS The inversely optimized KVAT plans presented in this work have demonstrated the ability of our novel low-cost, kilovoltage x-ray therapy system to safely treat deep-seated spherical lesions in breast and lung patients while meeting RTOG dose constraints on OARs.
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Affiliation(s)
- Dylan Y Breitkreutz
- Department of Physics and Astronomy, University of Victoria, PO Box 1700 ST CSC, Victoria, BC, V8W 2Y2, Canada
| | - Marc-André Renaud
- Department of Oncology, Medical Physics Unit, McGill University, 1001 boul. Décarie, Montréal, QC, H4A 3J1, Canada
| | - Jan Seuntjens
- Department of Oncology, Medical Physics Unit, McGill University, 1001 boul. Décarie, Montréal, QC, H4A 3J1, Canada
| | - Michael D Weil
- Sirius Medicine LLC, PO Box 414, Half Moon Bay, CA, 94019, USA
| | - Sergei Zavgorodni
- Department of Physics and Astronomy, University of Victoria, PO Box 1700 ST CSC, Victoria, BC, V8W 2Y2, Canada.,Vancouver Island Centre - BC Cancer Agency, 2410 Lee Ave, Victoria, BC, V8R 6V5, Canada
| | - Magdalena Bazalova-Carter
- Department of Physics and Astronomy, University of Victoria, PO Box 1700 ST CSC, Victoria, BC, V8W 2Y2, Canada
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Breitkreutz DY, Weil MD, Zavgorodni S, Bazalova-Carter M. Monte Carlo simulations of a kilovoltage external beam radiotherapy system on phantoms and breast patients. Med Phys 2017; 44:6548-6559. [DOI: 10.1002/mp.12619] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2017] [Revised: 08/18/2017] [Accepted: 09/25/2017] [Indexed: 11/08/2022] Open
Affiliation(s)
- Dylan Y. Breitkreutz
- Department of Physics and Astronomy; University of Victoria; PO Box 1700 ST CSC Victoria BC V8W 2Y2 Canada
| | | | - Sergei Zavgorodni
- Vancouver Island Centre - BC Cancer Agency; 2410 Lee Ave Victoria BC V8R 6V5 Canada
| | - Magdalena Bazalova-Carter
- Department of Physics and Astronomy; University of Victoria; PO Box 1700 ST CSC Victoria BC V8W 2Y2 Canada
- Vancouver Island Centre - BC Cancer Agency; 2410 Lee Ave Victoria BC V8R 6V5 Canada
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Breitkreutz DY, Fallone BG, Yahya A. Effect of J coupling on 1.3-ppm lipid methylene signal acquired with localised proton MRS at 3 T. NMR Biomed 2015; 28:1324-1331. [PMID: 26314546 DOI: 10.1002/nbm.3387] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2015] [Revised: 07/10/2015] [Accepted: 07/30/2015] [Indexed: 06/04/2023]
Abstract
The purpose of this work was to investigate the effect of J-coupling interactions on the quantification and T2 determination of 1.3-ppm lipid methylene protons at 3 T. The response of the 1.3-ppm protons of hexanoic, heptanoic, octanoic, linoleic and oleic acid was measured as a function of point-resolved spectroscopy (PRESS) and stimulated echo acquisition mode (STEAM) TE. In addition, a narrow-bandwidth refocusing PRESS sequence designed to rewind J-coupling evolution of the 1.3-ppm protons was applied to the five fatty acids, to corn oil and to tibial bone marrow of six healthy volunteers. Peak areas were plotted as a function of TE, and data were fitted to monoexponentially decaying functions to determine Mo (the extrapolated area for TE = 0 ms) and T2 values. In phantoms, rewinding J-coupling evolution resulted in 198%, 64%, 44%, 20% and 15% higher T2 values for heptanoic, octanoic, linoleic and oleic acid, and corn oil, respectively, compared with those obtained with standard PRESS. The narrow-bandwidth PRESS sequence also resulted in significant changes in Mo , namely -77%, -22%, 28%, 23% and 28% for heptanoic, octanoic, linoleic and oleic acid, and corn oil, respectively. T2 values obtained with STEAM were closer to the values measured with narrow-bandwidth PRESS. On average, in tibial bone marrow (six volunteers) rewinding J-coupling evolution resulted in 21% ± 3% and 9 % ± 1% higher Mo and T2 values, respectively. This work demonstrates that the consequence of neglecting to consider scalar coupling effects on the quantification of 1.3-ppm lipid methylene protons and their T2 values is not negligible. The linoleic and oleic acid T2 results indicate that T2 measures of lipids with standard MRS techniques are dependent on lipid composition.
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Affiliation(s)
| | - B Gino Fallone
- Department of Oncology, University of Alberta, Edmonton, AB, Canada
- Department of Medical Physics, Cross Cancer Institute, Edmonton, AB, Canada
| | - Atiyah Yahya
- Department of Oncology, University of Alberta, Edmonton, AB, Canada
- Department of Medical Physics, Cross Cancer Institute, Edmonton, AB, Canada
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