In vitro biological dosimeter modeling of the glioblastoma response to radiation delivered by the Gamma Knife: Laboratory investigation (original) (raw)
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Journal of Physics: Conference Series, 2009
The BANG™ polymer gel dosimeter was used to evaluate 3D absorbed dose distributions in tissue delivered with Gamma Knife stereotactic radiosurgery systems. We compared dose distributions calculated with Leksell GammaPlan (LGP) treatment-planning software with dose distributions measured with the polymer gel dosimeter for single-shot irradiations. Head-sized spherical glass vessels filled with the polymer gel were irradiated with Gamma Knife. The phantoms were scanned with a 1.0T MRI scanner. The Hahn spin-echo sequence with two echoes was used for the MRI scans. Calibration relations between the spin-spin relaxation rate and the absorbed dose were obtained by using small cylindrical vials, which were filled with the polymer gel from the same batch as for the spherical phantom. We made voxel-by-voxel comparisons of measured and calculated dose distributions for 31 × 31 × 31 dose matrix elements. With the 3D dose data we calculated the tumor control probability (TCP) and normal tissue complication probability (NTCP) for a simple model. For the maximum dose of 100 Gy, the mean and one standard deviation of differences between the measured and the calculated doses were the following:-0.38±4.63 Gy, 1.49±2.77 Gy, and-1.03±4.18 Gy for 8-mm, 14-mm, and 18-mm collimators, respectively. Tumor control probability values for measurements were smaller than the calculations by 0% to 7%, whereas NTCP values were larger by 7% to 24% for four of six experiments.
Cellular radiosensitivity of a rat brain tumor
Cancer, 1975
The response of a model brain tumor system in the rat to single doses of x irradiation has been studied. Solid tumors were exposed in situ, removed, dissociated into single cells, and grown in tissue culture. The fraction of surviving clonogenic cells was determined as a function of x-ray dose level for tumors irradiated in anesthetized, air-breathing rats, and for tumors irradiated in rats killed 5 minutes prior to irradiation by nitrogen gas asphyxiation. The parameters of the survival curve for tumors irradiated in air-breathing rats were: Do = 295 rads; D, = 350 rads; and n = 3.0. Similarly, the survival parameters for tumors irradiated in nitrogen gas asphyxiated rats were: Do = 625 rads; D, = 675 rads; and n = 3.0. The survival curve of these tumor cells when assayed in in vitro tissue culture only has parameters of: Do = 225 rads; D, = 350 rads; and n = 4.7. Data from the in vivo to in vitro tumor cell survival curves suggest that there is no significant hypoxic fraction in this brain tumor. Cancer 3 5 : 154 5-1 5 50, 1 9 75. HE MALIGNANT TUMORS ARISING IN BRAIN T and spinal cord are rarely curable by radiation therapy.31 T h e question of why such tumors appear so resistant to radiation treatment would appear to be a n important area of investigation. In this regard, it would be desirable to obtain information on the cellular survival characteristics of such tumors after exposure to ionizing radiation. A n experimental brain tumor model system has been d e~e l o p e d ,~ and we have used this Presented in part at the 16th Annual hleeting of the .\merican Society of 'Therapeutic Radiologists, Key 8iscayne, FL. October 30-November 3 , 1974.
Biological Tissue Modeling with Agar Gel Phantom for Radiation Dosimetry of <sup>99m</sup>Tc
Open Journal of Radiology, 2014
The biological tissue has been mimicked and replaced by other materials, which have shown certain radiological similarity determined by attenuation coefficient (μ), density and atomic number. Specifically, in molecular imaging and radiation therapy have been developed multifunctional radiopharmaceuticals which contain beta/gamma and/or light emitters to chronic degenerative diseases treatment. Therefore, it is necessary to develop phantoms that allow optical and radiometric characterization. Since the agar gel has shown to be a medium which allows to model biological tissue in phototherapy studies, the aim of this study is to determine whether the agar gel may be used as biological tissue substitutes in 99m Tc dosimetry. Agar gel was prepared to 1% and 2.3% (water:agar) and its radiologicalproperties as: linear attenuation coefficient obtained by narrow beam geometry and XCOM software, density and effective atomic number (Z eff) were determined. Using the determined μ, photontransmission was calculated by Monte Carlosimulation. The 99m Tc source region was immersed in a water phantom, two source regions were used, one source region was filled with water and another with agar gel. For both cases; the cumulated activity ( A) by conjugate view method, the absorbed doseper unitcumulated activity (S) and absorbed dose (D) were determined. The 2.3% concentration gel consistency facilitated its handling during a bigger irradiation time. A 0.151 0.02 1 cm
Development of a phantom for dose distribution verification in Stereotactic Radiosurgery
Physica Medica, 2013
A geometric acrylic phantom was designed and built for dose distribution verification in Stereotactic Radiosurgery. Acrylic objects representing the tumor tissue, (target volume (TV)), and the organ at risk (OAR), the brainstem, were inserted inside this phantom. The TV is represented by two semi-spheres of acrylic with a diameter of 13.0 mm, both having a central cavity for accommodation of a TLD-100 detector and a small radiochromic Gafchromic EBT film. The OAR is represented by the two parts of a 38.0 mm length acrylic cylinder with a diameter 18.0 mm and cavities along the cylinder central axis able to accommodate 5 TLD e 100 detectors and another of EBT film between the two cylinder parts. This experimental setup was submitted to a radiosurgical treatment, after which the TL dosimeters were evaluated and their responses were compared with the planned dose values. The radiochromic EBT films showed the dose distributions. The linear accelerator used was a Varian 2300 C/D, generating a 6 MV photon beam. The investigated phantom system was able to check the accuracy of dose delivery to predetermined points and the dose distribution due to stereotactic radiosurgery treatments and proved to be a good tool for quality control in these situations.
Gamma Knife irradiation method based on dosimetric controls to target small areas in rat brains
Medical Physics, 2015
Purpose: Targeted and whole-brain irradiation in humans can result in significant side effects causing decreased patient quality of life. To adequately investigate structural and functional alterations after stereotactic radiosurgery, preclinical studies are needed. The purpose of this work is to establish a robust standardized method of targeted irradiation on small regions of the rat brain. Methods: Euthanized male Fischer rats were imaged in a stereotactic bed, by computed tomography (CT), to estimate positioning variations relative to the bregma skull reference point. Using a rat brain atlas and the stereotactic bregma coordinates obtained from CT images, different regions of the brain were delimited and a treatment plan was generated. A single isocenter treatment plan delivering ≥100 Gy in 100% of the target volume was produced by Leksell GammaPlan using the 4 mm diameter collimator of sectors 4, 5, 7, and 8 of the Gamma Knife unit. Impact of positioning deviations of the rat brain on dose deposition was simulated by GammaPlan and validated with dosimetric measurements. Results: The authors' results showed that 90% of the target volume received 100 ± 8 Gy and the maximum of deposited dose was 125 ± 0.7 Gy, which corresponds to an excellent relative standard deviation of 0.6%. This dose deposition calculated with GammaPlan was validated with dosimetric films resulting in a dose-profile agreement within 5%, both in X-and Z-axes. Conclusions: The authors' results demonstrate the feasibility of standardizing the irradiation procedure of a small volume in the rat brain using a Gamma Knife. C 2015 American Association of Physicists in Medicine. [http://dx.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005
The goal of this project is to determine the feasibility of utilizing colloidal gold as a marker for C6 glioblastoma cells implanted into rat brain as an appropriate model for volumetric measurements of tumors using absorption edge subtraction (AES). Phase sensitive X-ray imaging is combined with KES to give good soft tissue contrast. Current methods for volumetric measurements of implanted C6 glioblastoma tumors in rat brains using MRI technology are inadequate due to the small size of the tumor (2.5-4 mm in diameter) and the thickness of the MRI slice (1-1.5 mm). Previously, our group has shown that AES detection of colloidal gold labeled C6 glioblastoma cells implanted into a rat brains may be feasible. The long-term goal for this project is to establish a method, which would allow the researcher to monitor the development of a tumor over time. Most importantly, this technique should allow researchers to accurately determine the potency of a treatment on the size and growth rate for a C6 implanted tumors. In addition, we plan to challenge the hypothesis that tumors of the glioma type do not metastasize outside of the brain. A sensitive technique for the detection of C6 cells, such as that using colloidal gold and AES/DEI, should enable researchers to detect C6 cells, which have metastasized and migrated to different areas of the body. The ability to detect implanted C6 cells followed by the development of the tumor, the possible migration of the cells and the ability to accurately measure the effects of treatments on the volume of the tumor would be of the utmost importance to brain tumor research. r
Medical Physics, 2009
Polymer gel dosimeters offer a practical solution to 3D dose verification for conventional radiotherapy as well as intensity-modulated and stereotactic radiotherapy. In this study, EGSnrc calculated and PAGAT polymer gel dosimeter measured dose volume histograms ͑DVHs͒ for single-shot irradiations of the Gamma Knife ͑GK͒ unit were used to investigate the effects of the presence of inhomogeneities on 3D dose distribution. The head phantom was a custom-built 16 cm diameter Plexiglas sphere. Inside the phantom, there is a cubic cutout for inserting the gel vials and another cutout for inserting the inhomogeneities. Following irradiation with the GK unit, the polymer gel phantoms were scanned with a 1.5 T MRI scanner. Comparing the results of measurement in homogeneous and heterogeneous phantoms revealed that inserting inhomogeneities inside the homogeneous phantom did not cause considerable disturbances on dose distribution in irradiation with 8 mm collimator within low isodose levels ͑Ͻ50%͒, which is essential for the dose sparing of sensitive structures. The results of simulation for homogeneous and inhomogeneous phantoms in irradiation with 18 mm collimator of the GK unit showed 23.24% difference in DVH within 90%-100% relative isodose level and also revealed that a significant part of the target ͑28.56%͒ received relative doses higher than the maximum dose, which exceeds the acceptance criterion ͑5%͒. Based on these results it is concluded that the presence of inhomogeneities inside the phantom can cause considerable errors in dose calculation within high isodose levels with respect to LGP prediction which assumes that the target is a homogeneous material. Moreover, it is demonstrated that the applied MC code is an accurate and stand-alone tool for 3D evaluation of dose distribution in irradiation with the GK unit, which can provide important, 3D plan evaluation criteria used in clinical practice.
Impact of decaying dose rate in gamma knife radiosurgery: in vitro study on 9L rat gliosarcoma cells
Journal of radiosurgery and SBRT, 2012
Purpose Leksell Gamma Knife (LGK) installations replace their Co-60 sources every 5-10 years corresponding to one two Co-60 half-lives. Between source replacements the dose rate gradually declines. The purpose of this study was to assess whether the decreasing dose rates associated with radioactive decay of Co-60 may affect the radiobiological response of a given dose delivered to 9L rat gliosarcoma cells. Method and Materials 9L rat gliosarcoma cells were irradiated using LGK U, LGK 4C, and LGK Perfexion providing three different dose rates of 0.770 Gy/ min (sources reloaded 12.0 years ago), 1.853 Gy/min (sources reloaded 5.0 years ago) and 2.937 Gy/min (sources reloaded 1.6 years ago), respectively. After irradiation of cell samples to 4.0 Gy, 8.0 Gy and 16.0 Gy using each of the LGK units, the irradiated cells were plated into petri dishes. Two weeks later cell colonies with greater than 50 cells were counted. The survival of cells was plotted as a function of dose over the range...
The British journal of radiology, 2019
OBJECTIVE: Small animal radiotherapy research platforms such as XStrahl's SARRP enable more precise irradiation of tumours and normal tissues in pre-clinical models of cancer. Using an orthotopic G7 glioblastoma xenograft model we studied the impact of four different radiotherapy plans on tumour and normal tissue dosimetry. METHODS: Plans were created using four different approaches (single beam, parallel opposed pair, single plane arcs, couch rotation arcs) and dose volume histograms (DVH) for the tumour and the relevant organs at risk (OARs) (mouth, ipsilateral brain, contralateral brain, brain stem) were compared for a sample mouse subject. To evaluate the accuracy of delivery, treatment plans were recreated in solid-water phantoms and delivered to radiochromic film. RESULTS: Favourable tumour dosimetry was achieved by all plans. DVH analysis showed that different plans could be used to spare specific OARs depending on the objectives of the study. The delivery accuracy of the...