6 results on '"Grimm, Jimm"'
Search Results
2. Fitting NTCP models to SBRT dose and carotid blowout syndrome data.
- Author
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Mavroidis P, Grimm J, Cengiz M, Das S, Tan X, Yazici G, and Ozyigit G
- Subjects
- Carotid Arteries pathology, Head and Neck Neoplasms radiotherapy, Humans, Models, Biological, Radiotherapy Dosage, Retrospective Studies, Carotid Arteries radiation effects, Radiation Dosage, Radiosurgery adverse effects
- Abstract
Purpose: To estimate the radiobiological parameters of three popular NTCP models, which describe the dose-response relations of carotid blowout syndrome (CBOS) after stereotactic body radiotherapy (SBRT). To evaluate the goodness-of-fit and the correlation of those models with CBOS., Methods: The study included 61 patients with inoperable locally recurrent head and neck cancer treated with SBRT using CyberKnife (Accuray, Sunnyvale, CA) at the Department of Radiation Oncology, Hacettepe University, Ankara, Turkey between June 2007 and March 2011. The dose-volume histograms of the internal carotid were exported from the plans of all the patients. The follow-up results regarding the end point of carotid blowout syndrome were collected retrospectively. Initially, univariable analyses (Wilcoxon rank-sum or Chi-square tests) and a multivariate logistic regression analysis were performed between the outcome data and a list of clinical and treatment factors to identify significant correlations. Additionally, the Lyman-Kutcher-Burman (LKB), Relative Seriality (RS), and Logit NTCP models were used to fit the clinical data. The fitting of the different models was assessed through the area under the receiver operating characteristic curve (AUC), Akaike information criterion (AIC), and Odds Ratio methods., Results: The clinical/treatment factors that were found to have a significant or close to significant correlations with acute CBOS were Age at the time of CK (P-value = 0.03), Maximum carotid dose (P-value = 0.06), and CK prescription dose (P-value = 0.08). Using D
max , physical DVH, and EQD2 Gy -DVH as the dosimetric metrics in the NTCP models, the derived LKB model parameters were: (a) D50 = 45.8 Gy, m = 0.24, n = n/a; (b) D50 = 44.8 Gy, m = 0.28, n = 0.01; and (c) D50 = 115.8 Gy, m = 0.45, n = 0.01, respectively. The AUC values for the dosimetric metrics were 0.70, 0.68, and 0.61, respectively. The differences in AIC between the different models were less than 2 and ranged within ±0.9., Conclusion: The maximum dose to the internal carotid less than 34 Gy appears to significantly reduce the risk for CBOS. Age at the time of CK, Maximum carotid dose, and CK prescription dose were also found to correlate with CBOS. The values of the parameters of three NTCP models were determined for this endpoint. A threshold of gEUD <34.5 Gy appears to be significantly associated with lower risks of CBOS., (© 2018 American Association of Physicists in Medicine.)- Published
- 2018
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3. The dosimetric impact of the prescription isodose line (IDL) on the quality of robotic stereotactic radiosurgery (SRS) plans.
- Author
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Xu Q, Fan J, Grimm J, LaCouture T, Asbell S, Park JH, and Kubicek G
- Subjects
- Brain Neoplasms radiotherapy, Humans, Organs at Risk radiation effects, Quality Control, Radiometry, Radiotherapy Dosage, Retrospective Studies, Radiation Dosage, Radiosurgery, Radiotherapy Planning, Computer-Assisted methods, Robotic Surgical Procedures
- Abstract
Purpose: There is no consensus on the optimal prescription isodose line (IDL) in CyberKnife (CK) SRS. We designed a strategy to search for optimal CK plans at different levels of IDLs and investigated the dosimetric impact on the quality of CK plans., Methods and Materials: The retrospective study consisted of 13 CK patients with 16 brain tumors. The mean volume and size of the tumors was 9.7 ± 10.4 cc and 30.3 ± 10.9 mm, respectively. Four shells were created at distances of 2-3 mm to 60 mm from the target. The constraint dose of the innermost shell (D1) was the primary optimization parameter. For isolated brain tumors, D1 started from the prescription dose and gradually reduced after optimization started over. The optimal plans were reached when the coverage started to degrade and the desired IDL was achieved. For eight tumors abutting an OAR, both the D1 and constraint dose to the OAR were gradually pushed until an optimal plan was reached for the desired IDL., Results: For the isolated tumors, the V5 Gy, V10 Gy, V15 Gy, V20 Gy, and V25 Gy of low IDL (49.6 ± 2.1%) plans were on average 23.6%, 28.6%, 33.8%, 26.2%, and 10.6% lower, respectively, comparing to the high IDL (88.6 ± 1.3%) plans. The Conformality Index (CI) of the low IDL plans outperformed the high IDL plans (mean: 1.15 vs. 1.24), except for a lesion under 0.5 cc. The quality of the middle IDL plans (69.6 ± 1.5%) was close to the low IDL plans. Similar results were observed for tumors abutting an OAR., Conclusions: Low IDL plans outperformed high IDL plans for all metrics in tumors > 0.5 cc. The lower dose exposure of normal brain tissue and better CI could potentially reduce radiation necrosis while the higher maximum dose could improve local control., (© 2017 American Association of Physicists in Medicine.)
- Published
- 2017
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4. Small field dose measurements using plastic scintillation detector in heterogeneous media.
- Author
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Xue J, McKay JD, Grimm J, Cheng CW, Berg R, Grimm SL, Xu Q, Subedi G, and Das IJ
- Subjects
- Humans, Monte Carlo Method, Phantoms, Imaging, Photons, Plastics, Radiometry
- Abstract
Purpose: The purpose of this study was to evaluate a plastic scintillation detector for the measurement of small field dosimetry and to verify the accuracy of measured dose in comparison with Monte Carlo calculation in a heterogeneous medium., Methods: The study is performed with CyberKnife planning and delivery system. The setup consists of a custom made solid lung phantom with the insert of an Exradin W1 scintillation detector or an Exradin A16 ion chamber. The measurement was done for a series of cone sizes from 5 mm to 60 mm, and the dose was calculated by Monte Carlo algorithm in MultiPlan workstation. The difference between measurement and calculation was reported., Results: Our preliminary results demonstrated the applicability of plastic scintillation detectors in the measurement of small field dosimetry in a heterogeneous medium. The difference between the calculated and measured output factors was less than 3% for all cone sizes from 60 mm down to 5 mm. Without any corrections, the measured dose from the scintillation detector calibrated to the ion chamber reading was also within 3% of the Monte Carlo calculation in the lung phantom for cone sizes 20 mm or larger., Conclusions: Small field dosimetry is particularly relevant to stereotactic radiation treatment. The accuracy of dose calculation for small static beams is critical to dose planning so would potentially affect the treatment outcomes in a heterogeneous medium. Our results have shown good agreement with plastic scintillation detector in both homogeneous and heterogeneous medium., (© 2017 American Association of Physicists in Medicine.)
- Published
- 2017
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5. Factors that may determine the targeting accuracy of image-guided radiosurgery.
- Author
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Subedi G, Karasick T, Grimm J, Jain S, Xue J, Xu Q, Chen Y, Asbell S, Pahlajani N, and LaCouture T
- Subjects
- Algorithms, Quality Control, Robotics, Surgery, Computer-Assisted instrumentation, Surgery, Computer-Assisted methods
- Abstract
Purpose: The AAPM TG-135 report is a landmark recommendation for the quality assurance (QA) of image-guided robotic radiosurgery. The purpose of this paper is to present results pertaining to intentionally offsetting the phantom as recommended by TG-135 and to present data on targeting algorithm accuracy as a function of imager parameters in less than ideal circumstances, which had not been available at the time of publication of TG-135., Methods: All tests in this study were performed at the Cooper University Hospital CyberKnife Center in Mt. Laurel, NJ. For intentional offsets, initial tests were performed on the Accuray-supplied anthropomorphic head and neck phantom, whereas for subsequent tests, the Accuray-supplied alignment quality assurance (AQA) phantom was used. To simulate the effects of imager parameters for larger patients, slabs of Blue Water (Standard Imaging, Inc., Middleton, WI) were added to attenuate the x-ray images in some of the tests. In conjunction with attenuated x-ray tests, the number of fiducials was varied by systematically deselecting them one at a time at the CyberKnife console., Results: Tests using the AQA phantom verified that submillimeter alignments were consistently achieved even with intentional shifts and rotations of up to 10.0 mm and 1.0°, respectively. An analysis of 17 months of daily QA alignment tests showed that submillimeter alignments were achieved more than 99% of the time even with such intentional shifts and rotations of the phantom. When additional slabs of Blue Water were added to simulate patient attenuation of the x-ray images, targeting errors could be induced depending on imager parameters and the amount of Blue Water used. A series of consecutive tests showed that two helpful variables to ensure good accuracy of the system were (1) the fiducial extraction confidence level (FECL) system parameter and (2) the number of targeted fiducials. When fewer than four fiducials were used, the FECL reported by the CyberKnife was sometimes high even when a false lock occurred, so using multiple fiducials helped to ensure reliable targeting., Conclusions: Radiosurgery requires the highest degree of targeting accuracy, and in our experience, the CyberKnife has been able to maintain submillimeter accuracy consistently. It has been verified that our CyberKnife can correct for phantom shifts of up to 10.0 mm and rotations of up to 1.0°. It has also been discovered that false locks are more likely to occur with a single fiducial than with multiple fiducials. Although targeting accuracy can only be measured on a phantom, the insight gained from analyzing the QA tests can help us in devising better strategies for achieving the best treatment for our patients.
- Published
- 2015
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6. Dosimetric investigation of accelerated partial breast irradiation (APBI) using CyberKnife.
- Author
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Xu Q, Chen Y, Grimm J, Fan J, An L, Xue J, Pahlajani N, and Lacouture T
- Subjects
- Breast Neoplasms surgery, Female, Humans, Monte Carlo Method, Phantoms, Imaging, Radiometry, Retrospective Studies, Breast surgery, Mastectomy, Segmental methods, Radiosurgery methods
- Abstract
Purpose: To investigate the dosimetric feasibility of accelerated partial breast irradiation (APBI) using CyberKnife., Methods: Fourteen previously treated patients with early-stage breast cancer were selected for a retrospective study. Six of these patients had been treated to 38.5 Gy in 10 fractions in a phase III accelerated partial breast trial and the rest of the patients were treated to 50.4 Gy in 28 fractions. In this planning study, the guidelines in the protocol for the phase III partial breast trial were followed for organ delineation and CyberKnife planning. The achievable dosimetric parameters from all CyberKnife plans were compared to Intensity-modulated radiation therapy (IMRT) and 3D-CRT methods. The reproducibility of the dose delivery with and without respiratory motion was assessed through delivering a patient plan to a breast phantom. Different dose calculation algorithms were also compared between ray tracing and Monte Carlo., Results: For all the patients in the study, the dosimetric parameters met the guidelines from the NSABP B39∕RTOG 0413 protocol strictly. The mean PTV volume covered by 100% of the prescription dose was 95.7 ± 0.7% (94.7%-97.1%). The mean maximal dose was 104 ± 2% of the prescription dose. The mean V(50%) and mean V(100%) to the ipsilateral normal breast were 23.1 ± 11.6% and 9.0 ± 5.8%, respectively. The conformity index of all plans was 1.14 ± 0.04. The maximum dose to the contralateral breast varied from 1.3 cGy to 111 cGy. The mean V(5%) and mean V(30%) to the contralateral and ipsilateral lungs were 1.0 ± 1.6% and 1.3 ± 1.2%, respectively. In our study, the mean V(5%) to the heart was 0.2 ± 0.5% for right-sided tumors and 9.4 ± 10.1% for left-sided tumors. Compared with IMRT and 3D-CRT planning, the PTV coverage from CyberKnife planning was the highest, and the ratio of V(20%) to V(100%) of the breast from CyberKnife planning was the smallest. The heart and lung doses were similar in all the techniques except that the V(5%) for the lung and heart in CyberKnife planning was slightly higher., Conclusions: The dosimetric feasibility of APBI using CyberKnife was investigated in this retrospective study. All the dosimetric parameters strictly met the guidelines from the NSABP B39∕RTOG 0413 protocol. With advanced real-time tracking capability, CyberKnife should provide better target coverage and spare nearby critical organs for APBI treatment.
- Published
- 2012
- Full Text
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