Jesper Kallehauge - Academia.edu (original) (raw)

Papers by Jesper Kallehauge

Research paper thumbnail of Contrast‐agent‐based perfusion MRI code repository and testing framework: ISMRM Open Science Initiative for Perfusion Imaging (OSIPI)

Magnetic Resonance in Medicine

PurposeSoftware has a substantial impact on quantitative perfusion MRI values. The lack of genera... more PurposeSoftware has a substantial impact on quantitative perfusion MRI values. The lack of generally accepted implementations, code sharing and transparent testing reduces reproducibility, hindering the use of perfusion MRI in clinical trials. To address these issues, the ISMRM Open Science Initiative for Perfusion Imaging (OSIPI) aimed to establish a community‐led, centralized repository for sharing open‐source code for processing contrast‐based perfusion imaging, incorporating an open‐source testing framework.MethodsA repository was established on the OSIPI GitHub website. Python was chosen as the target software language. Calls for code contributions were made to OSIPI members, the ISMRM Perfusion Study Group, and publicly via OSIPI websites. An automated unit‐testing framework was implemented to evaluate the output of code contributions, including visual representation of the results.ResultsThe repository hosts 86 implementations of perfusion processing steps contributed by 12 i...

Research paper thumbnail of Open Science Initiative for Perfusion Imaging (OSIPI): A community-led, open-source code library for analysis of DCE/DSC-MRI

ISMRM Annual Meeting

A lack of validated, open-source code reduces the reliability of perfusion MRI, resulting in dupl... more A lack of validated, open-source code reduces the reliability of perfusion MRI, resulting in duplicate development. To address this problem, the Open Science Initiative for Perfusion Imaging (OSIPI) established a taskforce to collect, validate and harmonise such code. To date, 74 code contributions have been collected, with 14 of these tested. Source code and tests are published in an open-access repository. The OSIPI DCE/DSC-MRI code collection constitutes a valuable resource for researchers, and will ultimately be developed into a standardised, community-driven open-source code library.

Research paper thumbnail of JS09.5.A Is Radiation Dose to Sleep-relevant Brain Structures Associated with Lower Sleep Quality in Adults with Primary Brain Tumors?

Neuro-oncology, Sep 1, 2022

Research paper thumbnail of Inclusion of functional information from perfusion SPECT improves predictive value of dose–volume parameters in lung toxicity outcome after radiotherapy for non-small cell lung cancer: A prospective study

Radiotherapy and Oncology, 2015

Background and purpose: To compare functional and standard dose-volume parameters as predictors o... more Background and purpose: To compare functional and standard dose-volume parameters as predictors of postradiation pulmonary toxicity in lung cancer patients undergoing curative chemo-radiotherapy (RT) studied prospectively. Material and methods: A total of 58 patients treated with Intensity Modulated RT (60-66 Gy) were analysed. Standard dose-volume parameters were extracted from treatment planning computed tomography (CT) scans. Corresponding functional dose-volume parameters were calculated from perfusion singlephoton emission computed tomography (SPECT). Primary end-point was radiation pneumonitis (RP) grade 2-5. Results: Functional mean lung dose (MLD) and lung volumes receiving 5, 10, 20 and 30 Gy (V5-V30, respectively) revealed high correlation with corresponding standard parameters (r > 0.8). Standard MLD, V20 and V30 were significantly higher in patients with RP (p = 0.01). All functional parameters were significantly higher in the RP patients (p < 0.03). In multivariate analysis functional parameters produced superior risk estimates, while all standard parameters, except V30, were not related to the risk of RP. Area under the curve (AUC) for functional metrics generally exceeded the AUC for corresponding standard parameters, but they were not significantly different from each other. Conclusion: SPECT-based functional parameters were better to predict the risk of RP compared to standard CT-based dose-volume parameters. Functional parameters may be useful to guide radiotherapy planning in order to reduce the risk of radiation-induced toxicity.

Research paper thumbnail of Diffusion Weighted MRI (DWI) for Brachytherapy in Locally Advanced Cervical Cancer - Determining the Degree of Distortion at 1.5T and 3T MRI

IFMBE Proceedings, 2011

Diffusion Weighted MRI (DWI) enables identification of tissue with high cellular density such as ... more Diffusion Weighted MRI (DWI) enables identification of tissue with high cellular density such as tumors. This makes DWI a potentially valuable tool in oncology imaging for both diagnostic imaging and monitoring of treatment. Locally advanced cervical cancer is usually treated with brachytherapy using an intracavitary applicator (Figure 1). MRI guided brachytherapy can be performed by imaging with the applicator in

Research paper thumbnail of OC-0376: FAZA PET/CT hypoxia imaging in patients with HNSCC treated with radiotherapy: results from the DAHANCA 24 trial

Radiotherapy and Oncology, 2014

distant control (DC) were compared between high vs. low pRT-Neu (the cutoff was determined based ... more distant control (DC) were compared between high vs. low pRT-Neu (the cutoff was determined based on OS outcome using restricted cubic splines method in the Cox model). Multivariate analysis (MVA) was used to confirm the prognostic value of pRT-Neu (continuous variable) for OS, LRC and DC. The prognostic value for OS and recurrence-free survival (RFS) was further explored in RT alone or CRT subgroups, and among non-smokers. Results: A total of 510 HPV(+) OPC were included. Median pRT-Neu count was 4.7 x 10 9 /L,of which 474 (93%) cases were within normal range (1.8-7.7 x 10 9 /L). Optimal cutoff for pRT-Neu count was 5.2 x 10 9 /L when the hazard ratio (HR) for OS was 1. This divided the group into low (n=325, 64%) and high (n=185, 36%) pRT-Neu cohorts, although the latter were mostly (153/185, 83%) within normal range. The high pRT-Neu cohort comprised more current smokers (44% vs 24%), T4 (27% vs 14%) or N3 disease (17% vs 5%) compared to the low cohort (all p<0.01). Median follow up was 5.1 years. The high pRT-Neu cohort had reduced 5-year OS (61% vs 80%), LRC (82% vs 90%), and DC (80% vs 88%) compared to the low cohort (all p<0.01). In MVA, every 10 9 /L increment in the pRT-Neu count (continuous variable) was associated with a lower OS (HR=1.2, p=0.02), LRC (HR=1.1, p=0.02),and DC (HR=1.2, p<0.01) after adjusting for age, smoking pack-years, T-, N-, and treatment. This association still existed in CRT (n=264) (HR=1.3 for OS, HR=1.2 for RFS) and RT alone subgroups (n=246) (HR=1.2 for both OS and RFS) separately (all p<0.01). Among 188 non-smokers, a higher pRT-Neu was also predictive for lower OS and RFS (both HR=1.2, p<0.01) after adjusting for age, T-, N-, and treatment in MVA. Conclusions: In this relatively large cohort, we identify that HPV(+) OPC patients with higher circulating pRT-Neu count (>5.2 x 10 9 /L) have inferior survival and increased risk of distant metastasis independent of smoking status or treatment modality, suggesting differential tumor activity associated with high circulating pRT-Neu. Circulating pRT-Neu may be an important and objective clinical factor for the selection of low risk cohorts for future HPV(+) OPC treatment de-intensification studies. Further study is needed to understand the biology of this observation and to potentially identify new therapeutic targets. OC-0375 Hypoxia dose-escalation with chemoradiation in head and neck cancer: planned interim analysis of a randomized study

Research paper thumbnail of Simulation of cervical cancer response to radiotherapy

Proceedings of the 2014 6th International Advanced Research Workshop on In Silico Oncology and Cancer Investigation - The CHIC Project Workshop (IARWISOCI), 2014

Research paper thumbnail of PD-0184: Diffusion weighted MRI and GTV at time of brachytherapy in locally advanced cervical cancer

Radiotherapy and Oncology, 2014

central and peripheral region. Regarding the small tumor size (≤3cm), it is not recommended to us... more central and peripheral region. Regarding the small tumor size (≤3cm), it is not recommended to use the threshold methods for tumor located in central region of lung.

Research paper thumbnail of Planning study comparing Bone marrow sparing IMRT against IMPT for para-aortic radiotherapy in gynecologic malignancies

Research paper thumbnail of Deformation field in plan selection strategy for bladder cancer patients

Research paper thumbnail of FAZE PET/CT hypoxia imaging in patients with HNSCC treated with radiotherapy: results from the DAHANCA 24 trial

Research paper thumbnail of Biomarker evaluation during an image-guided intracranial murine glioma study of radiation and sunitinib

Research paper thumbnail of Repeated Quantitative Functional MRI During Radiotherapy of Locally Advanced Cervical Cancer: PhD Dissertation

Research paper thumbnail of Model Parameter Correlation for DCE-MRI in Advanced Cervical Cancer

Purpose Recently it has been shown that stratifying patients by certain DCE-MRI parameters can di... more Purpose Recently it has been shown that stratifying patients by certain DCE-MRI parameters can distinguish between patients with better and poorer outcome for advanced cervical cancer. The results from Yuh et al. [1] showed the lowest 10 percentile of the RSI (Relative Signal Increase) to be the best stratifyer. Recent results from Halle et al. [2] have shown the 20-30 percentile of ABrix to be the best stratifyer. A number of these derived model parameters are highly correlated [3] and may thus be redundant. If such a correlation can be determined the computationally fastest and most robust approach could be chosen to enhance clinical use of these functional estimates for improving therapy.

Research paper thumbnail of An adaptive radiotherapy planning strategy for bladder cancer using deformation vector fields

Radiotherapy and Oncology, 2014

Purpose: Adaptive radiotherapy (ART) has considerable potential in treatment of bladder cancer du... more Purpose: Adaptive radiotherapy (ART) has considerable potential in treatment of bladder cancer due to large inter-fractional changes in shape and size of the target. The aim of this study was to compare our clinically applied method for plan library creation that involves manual bladder delineations (Clin-ART) with a method using the deformation vector fields (DVFs) resulting from intensity-based deformable image registrations (DVF-based ART). Materials and methods: The study included thirteen patients with urinary bladder cancer who had daily cone beam CTs (CBCTs) acquired for setup. In both ART strategies investigated, three plan selection volumes were generated using the CBCTs from the first four fractions; in Clin-ART boolean combinations of delineated bladders were used, while the DVF-based strategy applied combinations of the mean and standard deviation of patient-specific DVFs. The volume ratios (VRs) of the course-averaged PTV for the two ART strategies relative the non-adaptive PTV were calculated. Results: Both Clin-ART and DVF-based ART considerably reduced the course-averaged PTV, compared to non-adaptive RT. The VR for DVF-based ART was lower than for Clin-ART (0.65 vs. 0.73; p < 0.01). Conclusions: DVF-based ART for bladder irradiation has a considerable normal tissue sparing potential surpassing our already highly conformal clinically applied ART strategy.

Research paper thumbnail of Surface-sensitive conductance measurements on clean and stepped semiconductor surfaces: Numerical simulations of four point probe measurements

Surface Science, 2008

Recent progress in the development of microscopic four point probes permits surface-sensitive con... more Recent progress in the development of microscopic four point probes permits surface-sensitive conductivity measurements on semiconductor surfaces. It is, however, not straightforward to extract the actual values for the surface and space-charge layer conductivity. Here we present an approach to data analysis which is based on numerical finite-element simulations. The results of such simulations are compared to the known analytical

Research paper thumbnail of Thermal switching of the electrical conductivity of Si(111)(√3 × √3)Ag due to a surface phase transition

Journal of Physics: Condensed Matter, 2008

ABSTRACT Our recent paper on the surface conductivity of Si(111)(&amp;surd;3 × &amp;surd;... more ABSTRACT Our recent paper on the surface conductivity of Si(111)(&amp;surd;3 × &amp;surd;3)Ag [1] contains an error in the numerical simulation of the space charge layer conductance presented in figure 2(b) of the paper. A new version of the figure is presented here as figure 1. The incorrect version of this figure suggested that the space charge layer conductivity of Si(111)(&amp;surd;3 × &amp;surd;3)Ag is very similar to that of the clean Si(111)(7 × 7) surface but actually this is not the case. The space charge layer for Si(111)(7 × 7) becomes strongly insulating at low temperatures whereas it is rather conductive over the whole temperature range for Si(111)(&amp;surd;3 × &amp;surd;3)Ag. Figure 1 Figure 1. Experimental results (broken lines and markers) together with simulations (solid lines) of the conductance. The simulation in (b) has now been corrected, but the figure is otherwise the same as figure 2 from [1]. The model calculation shows the expected conductance of the bulk and space charge layer in (a) and (b) and for the expected conductance of a 3 ML Ag film with bulk properties in (c). The error in the calculation of the space charge layer conductivity has an impact on the interpretation of the low temperature measurements. Based on the incorrect calculation, it was concluded that the measurements are always surface sensitive, but this is not the case. In fact, the measured conductance in the low temperature regime is now quite similar to the conductance one could expect for the bulk and space charge layer.The interpretation of the data as a switching due to the surface phase transition is still consistent with results, especially since the transition in conductivity is much steeper than one would expect for a mechanism involving the freezing of carriers in the space charge region. However, we would also like to mention an alternative interpretation at this point. The free-electron like surface state on Si(111)(&amp;surd;3 × &amp;surd;3)Ag is unoccupied at zero temperature because the bottom of the band coincides with the Fermi energy [2]. At finite temperature, thermally excited carriers are present in the surface state band. It is therefore conceivable that the strong change in surface conductivity is caused by the thermal emptying of the surface state band as the temperature is lowered. At low temperature, the surface state band is devoid of carriers and only transport through the bulk and space charge layer can be observed. References [1] Wells J W, Kallehauge J F and Hofmann Ph 2007 J. Phys.: Condens. Matter 19 176008 [2] Crain J N, Gallagher M C, McChesney J L, Bissen M and Himpsel F J 2005 Phys. Rev. B 72 045312

Research paper thumbnail of PET hypoxia imaging with FAZA: reproducibility at baseline and during fractionated radiotherapy in tumour-bearing mice

European Journal of Nuclear Medicine and Molecular Imaging, 2012

Tumour hypoxia is linked to treatment resistance. Positron emission tomography (PET) using hypoxi... more Tumour hypoxia is linked to treatment resistance. Positron emission tomography (PET) using hypoxia tracers such as fluoroazomycin arabinoside (FAZA) may allow identification of patients with hypoxic tumours and the monitoring of the efficacy of hypoxia-targeting treatment. Since hypoxia PET is characterized by poor image contrast, and tumour hypoxia undergoes spontaneous changes and is affected by therapy, it remains unclear to what extent PET scans are reproducible. Tumour-bearing mice are valuable in the validation of hypoxia PET, but identification of a reliable reference tissue value (blood sample or image-derived muscle value) for repeated scans may be difficult due to the small size of the animal or absence of anatomical information (pure PET). Here tumour hypoxia was monitored over time using repeated PET scans in individual tumour-bearing mice before and during fractionated radiotherapy. Mice bearing human SiHa cervix tumour xenografts underwent a PET scan 3 h following injection of FAZA on two consecutive days before initiation of treatment (baseline) and again following irradiation with four and ten fractions of 2.5 Gy. On the last scan day, mice were given an intraperitoneal injection of pimonidazole (hypoxia marker), tumours were collected and the intratumoral distribution of FAZA (autoradiography) and hypoxia (pimonidazole immunohistology) were determined in cryosections. Tissue section analysis revealed that the intratumoral distribution of FAZA was strongly correlated with the regional density of hypoxic (pimonidazole-positive) cells, even when necrosis was present, suggesting that FAZA PET provides a reliable measure of tumour hypoxia at the time of the scan. PET-based quantification of tumour tracer uptake relative to injected dose showed excellent reproducibility at baseline, whereas normalization using an image-derived nonhypoxic reference tissue (muscle) proved highly unreliable since a valid and reliable reference value could not be determined. The intratumoral distribution of tracer was stable at baseline as shown by a voxel-by-voxel comparison of the two scans (R = 0.82, range 0.72-0.90). During treatment, overall tracer retention changed in individual mice, but there was no evidence of general reoxygenation. Hypoxia PET scans are quantitatively correct and highly reproducible in tumour-bearing mice. Preclinical hypoxia PET is therefore a valuable and reliable tool for the development of strategies that target or modify hypoxia.

Research paper thumbnail of 2039 POSTER Clinical Validation in Phantoms and Patients of a 4D-CT Based Method for Lung Ventilation Measurement

European Journal of Cancer, 2011

somewhat lower and much lower for systematic motion applied alone. In addition, anisotropic rando... more somewhat lower and much lower for systematic motion applied alone. In addition, anisotropic random motion provided stronger associations than the static DVH at high doses (70 Gy). Conclusion: A simple model for rectal motion has been presented and the corresponding motion-inclusive DVHs have been investigated in relation to rectal morbidity. The motion-inclusive DVHs provided a stronger association with rectal morbidity as compared to the static DVH alone.

Research paper thumbnail of Measurements of surface conductivity using micro four point probes

Page 1. Department of Physics and Astronomy University of Aarhus, Denmark Measurements of surface... more Page 1. Department of Physics and Astronomy University of Aarhus, Denmark Measurements of surface conductivity using micro four point probes Jesper F. Kallehauge Supervised by Philip Hofmann March, 2007 MASTER&amp;amp;amp;#x27;S THESIS Page 2. Page 3. ...

Research paper thumbnail of Contrast‐agent‐based perfusion MRI code repository and testing framework: ISMRM Open Science Initiative for Perfusion Imaging (OSIPI)

Magnetic Resonance in Medicine

PurposeSoftware has a substantial impact on quantitative perfusion MRI values. The lack of genera... more PurposeSoftware has a substantial impact on quantitative perfusion MRI values. The lack of generally accepted implementations, code sharing and transparent testing reduces reproducibility, hindering the use of perfusion MRI in clinical trials. To address these issues, the ISMRM Open Science Initiative for Perfusion Imaging (OSIPI) aimed to establish a community‐led, centralized repository for sharing open‐source code for processing contrast‐based perfusion imaging, incorporating an open‐source testing framework.MethodsA repository was established on the OSIPI GitHub website. Python was chosen as the target software language. Calls for code contributions were made to OSIPI members, the ISMRM Perfusion Study Group, and publicly via OSIPI websites. An automated unit‐testing framework was implemented to evaluate the output of code contributions, including visual representation of the results.ResultsThe repository hosts 86 implementations of perfusion processing steps contributed by 12 i...

Research paper thumbnail of Open Science Initiative for Perfusion Imaging (OSIPI): A community-led, open-source code library for analysis of DCE/DSC-MRI

ISMRM Annual Meeting

A lack of validated, open-source code reduces the reliability of perfusion MRI, resulting in dupl... more A lack of validated, open-source code reduces the reliability of perfusion MRI, resulting in duplicate development. To address this problem, the Open Science Initiative for Perfusion Imaging (OSIPI) established a taskforce to collect, validate and harmonise such code. To date, 74 code contributions have been collected, with 14 of these tested. Source code and tests are published in an open-access repository. The OSIPI DCE/DSC-MRI code collection constitutes a valuable resource for researchers, and will ultimately be developed into a standardised, community-driven open-source code library.

Research paper thumbnail of JS09.5.A Is Radiation Dose to Sleep-relevant Brain Structures Associated with Lower Sleep Quality in Adults with Primary Brain Tumors?

Neuro-oncology, Sep 1, 2022

Research paper thumbnail of Inclusion of functional information from perfusion SPECT improves predictive value of dose–volume parameters in lung toxicity outcome after radiotherapy for non-small cell lung cancer: A prospective study

Radiotherapy and Oncology, 2015

Background and purpose: To compare functional and standard dose-volume parameters as predictors o... more Background and purpose: To compare functional and standard dose-volume parameters as predictors of postradiation pulmonary toxicity in lung cancer patients undergoing curative chemo-radiotherapy (RT) studied prospectively. Material and methods: A total of 58 patients treated with Intensity Modulated RT (60-66 Gy) were analysed. Standard dose-volume parameters were extracted from treatment planning computed tomography (CT) scans. Corresponding functional dose-volume parameters were calculated from perfusion singlephoton emission computed tomography (SPECT). Primary end-point was radiation pneumonitis (RP) grade 2-5. Results: Functional mean lung dose (MLD) and lung volumes receiving 5, 10, 20 and 30 Gy (V5-V30, respectively) revealed high correlation with corresponding standard parameters (r > 0.8). Standard MLD, V20 and V30 were significantly higher in patients with RP (p = 0.01). All functional parameters were significantly higher in the RP patients (p < 0.03). In multivariate analysis functional parameters produced superior risk estimates, while all standard parameters, except V30, were not related to the risk of RP. Area under the curve (AUC) for functional metrics generally exceeded the AUC for corresponding standard parameters, but they were not significantly different from each other. Conclusion: SPECT-based functional parameters were better to predict the risk of RP compared to standard CT-based dose-volume parameters. Functional parameters may be useful to guide radiotherapy planning in order to reduce the risk of radiation-induced toxicity.

Research paper thumbnail of Diffusion Weighted MRI (DWI) for Brachytherapy in Locally Advanced Cervical Cancer - Determining the Degree of Distortion at 1.5T and 3T MRI

IFMBE Proceedings, 2011

Diffusion Weighted MRI (DWI) enables identification of tissue with high cellular density such as ... more Diffusion Weighted MRI (DWI) enables identification of tissue with high cellular density such as tumors. This makes DWI a potentially valuable tool in oncology imaging for both diagnostic imaging and monitoring of treatment. Locally advanced cervical cancer is usually treated with brachytherapy using an intracavitary applicator (Figure 1). MRI guided brachytherapy can be performed by imaging with the applicator in

Research paper thumbnail of OC-0376: FAZA PET/CT hypoxia imaging in patients with HNSCC treated with radiotherapy: results from the DAHANCA 24 trial

Radiotherapy and Oncology, 2014

distant control (DC) were compared between high vs. low pRT-Neu (the cutoff was determined based ... more distant control (DC) were compared between high vs. low pRT-Neu (the cutoff was determined based on OS outcome using restricted cubic splines method in the Cox model). Multivariate analysis (MVA) was used to confirm the prognostic value of pRT-Neu (continuous variable) for OS, LRC and DC. The prognostic value for OS and recurrence-free survival (RFS) was further explored in RT alone or CRT subgroups, and among non-smokers. Results: A total of 510 HPV(+) OPC were included. Median pRT-Neu count was 4.7 x 10 9 /L,of which 474 (93%) cases were within normal range (1.8-7.7 x 10 9 /L). Optimal cutoff for pRT-Neu count was 5.2 x 10 9 /L when the hazard ratio (HR) for OS was 1. This divided the group into low (n=325, 64%) and high (n=185, 36%) pRT-Neu cohorts, although the latter were mostly (153/185, 83%) within normal range. The high pRT-Neu cohort comprised more current smokers (44% vs 24%), T4 (27% vs 14%) or N3 disease (17% vs 5%) compared to the low cohort (all p<0.01). Median follow up was 5.1 years. The high pRT-Neu cohort had reduced 5-year OS (61% vs 80%), LRC (82% vs 90%), and DC (80% vs 88%) compared to the low cohort (all p<0.01). In MVA, every 10 9 /L increment in the pRT-Neu count (continuous variable) was associated with a lower OS (HR=1.2, p=0.02), LRC (HR=1.1, p=0.02),and DC (HR=1.2, p<0.01) after adjusting for age, smoking pack-years, T-, N-, and treatment. This association still existed in CRT (n=264) (HR=1.3 for OS, HR=1.2 for RFS) and RT alone subgroups (n=246) (HR=1.2 for both OS and RFS) separately (all p<0.01). Among 188 non-smokers, a higher pRT-Neu was also predictive for lower OS and RFS (both HR=1.2, p<0.01) after adjusting for age, T-, N-, and treatment in MVA. Conclusions: In this relatively large cohort, we identify that HPV(+) OPC patients with higher circulating pRT-Neu count (>5.2 x 10 9 /L) have inferior survival and increased risk of distant metastasis independent of smoking status or treatment modality, suggesting differential tumor activity associated with high circulating pRT-Neu. Circulating pRT-Neu may be an important and objective clinical factor for the selection of low risk cohorts for future HPV(+) OPC treatment de-intensification studies. Further study is needed to understand the biology of this observation and to potentially identify new therapeutic targets. OC-0375 Hypoxia dose-escalation with chemoradiation in head and neck cancer: planned interim analysis of a randomized study

Research paper thumbnail of Simulation of cervical cancer response to radiotherapy

Proceedings of the 2014 6th International Advanced Research Workshop on In Silico Oncology and Cancer Investigation - The CHIC Project Workshop (IARWISOCI), 2014

Research paper thumbnail of PD-0184: Diffusion weighted MRI and GTV at time of brachytherapy in locally advanced cervical cancer

Radiotherapy and Oncology, 2014

central and peripheral region. Regarding the small tumor size (≤3cm), it is not recommended to us... more central and peripheral region. Regarding the small tumor size (≤3cm), it is not recommended to use the threshold methods for tumor located in central region of lung.

Research paper thumbnail of Planning study comparing Bone marrow sparing IMRT against IMPT for para-aortic radiotherapy in gynecologic malignancies

Research paper thumbnail of Deformation field in plan selection strategy for bladder cancer patients

Research paper thumbnail of FAZE PET/CT hypoxia imaging in patients with HNSCC treated with radiotherapy: results from the DAHANCA 24 trial

Research paper thumbnail of Biomarker evaluation during an image-guided intracranial murine glioma study of radiation and sunitinib

Research paper thumbnail of Repeated Quantitative Functional MRI During Radiotherapy of Locally Advanced Cervical Cancer: PhD Dissertation

Research paper thumbnail of Model Parameter Correlation for DCE-MRI in Advanced Cervical Cancer

Purpose Recently it has been shown that stratifying patients by certain DCE-MRI parameters can di... more Purpose Recently it has been shown that stratifying patients by certain DCE-MRI parameters can distinguish between patients with better and poorer outcome for advanced cervical cancer. The results from Yuh et al. [1] showed the lowest 10 percentile of the RSI (Relative Signal Increase) to be the best stratifyer. Recent results from Halle et al. [2] have shown the 20-30 percentile of ABrix to be the best stratifyer. A number of these derived model parameters are highly correlated [3] and may thus be redundant. If such a correlation can be determined the computationally fastest and most robust approach could be chosen to enhance clinical use of these functional estimates for improving therapy.

Research paper thumbnail of An adaptive radiotherapy planning strategy for bladder cancer using deformation vector fields

Radiotherapy and Oncology, 2014

Purpose: Adaptive radiotherapy (ART) has considerable potential in treatment of bladder cancer du... more Purpose: Adaptive radiotherapy (ART) has considerable potential in treatment of bladder cancer due to large inter-fractional changes in shape and size of the target. The aim of this study was to compare our clinically applied method for plan library creation that involves manual bladder delineations (Clin-ART) with a method using the deformation vector fields (DVFs) resulting from intensity-based deformable image registrations (DVF-based ART). Materials and methods: The study included thirteen patients with urinary bladder cancer who had daily cone beam CTs (CBCTs) acquired for setup. In both ART strategies investigated, three plan selection volumes were generated using the CBCTs from the first four fractions; in Clin-ART boolean combinations of delineated bladders were used, while the DVF-based strategy applied combinations of the mean and standard deviation of patient-specific DVFs. The volume ratios (VRs) of the course-averaged PTV for the two ART strategies relative the non-adaptive PTV were calculated. Results: Both Clin-ART and DVF-based ART considerably reduced the course-averaged PTV, compared to non-adaptive RT. The VR for DVF-based ART was lower than for Clin-ART (0.65 vs. 0.73; p < 0.01). Conclusions: DVF-based ART for bladder irradiation has a considerable normal tissue sparing potential surpassing our already highly conformal clinically applied ART strategy.

Research paper thumbnail of Surface-sensitive conductance measurements on clean and stepped semiconductor surfaces: Numerical simulations of four point probe measurements

Surface Science, 2008

Recent progress in the development of microscopic four point probes permits surface-sensitive con... more Recent progress in the development of microscopic four point probes permits surface-sensitive conductivity measurements on semiconductor surfaces. It is, however, not straightforward to extract the actual values for the surface and space-charge layer conductivity. Here we present an approach to data analysis which is based on numerical finite-element simulations. The results of such simulations are compared to the known analytical

Research paper thumbnail of Thermal switching of the electrical conductivity of Si(111)(√3 × √3)Ag due to a surface phase transition

Journal of Physics: Condensed Matter, 2008

ABSTRACT Our recent paper on the surface conductivity of Si(111)(&amp;surd;3 × &amp;surd;... more ABSTRACT Our recent paper on the surface conductivity of Si(111)(&amp;surd;3 × &amp;surd;3)Ag [1] contains an error in the numerical simulation of the space charge layer conductance presented in figure 2(b) of the paper. A new version of the figure is presented here as figure 1. The incorrect version of this figure suggested that the space charge layer conductivity of Si(111)(&amp;surd;3 × &amp;surd;3)Ag is very similar to that of the clean Si(111)(7 × 7) surface but actually this is not the case. The space charge layer for Si(111)(7 × 7) becomes strongly insulating at low temperatures whereas it is rather conductive over the whole temperature range for Si(111)(&amp;surd;3 × &amp;surd;3)Ag. Figure 1 Figure 1. Experimental results (broken lines and markers) together with simulations (solid lines) of the conductance. The simulation in (b) has now been corrected, but the figure is otherwise the same as figure 2 from [1]. The model calculation shows the expected conductance of the bulk and space charge layer in (a) and (b) and for the expected conductance of a 3 ML Ag film with bulk properties in (c). The error in the calculation of the space charge layer conductivity has an impact on the interpretation of the low temperature measurements. Based on the incorrect calculation, it was concluded that the measurements are always surface sensitive, but this is not the case. In fact, the measured conductance in the low temperature regime is now quite similar to the conductance one could expect for the bulk and space charge layer.The interpretation of the data as a switching due to the surface phase transition is still consistent with results, especially since the transition in conductivity is much steeper than one would expect for a mechanism involving the freezing of carriers in the space charge region. However, we would also like to mention an alternative interpretation at this point. The free-electron like surface state on Si(111)(&amp;surd;3 × &amp;surd;3)Ag is unoccupied at zero temperature because the bottom of the band coincides with the Fermi energy [2]. At finite temperature, thermally excited carriers are present in the surface state band. It is therefore conceivable that the strong change in surface conductivity is caused by the thermal emptying of the surface state band as the temperature is lowered. At low temperature, the surface state band is devoid of carriers and only transport through the bulk and space charge layer can be observed. References [1] Wells J W, Kallehauge J F and Hofmann Ph 2007 J. Phys.: Condens. Matter 19 176008 [2] Crain J N, Gallagher M C, McChesney J L, Bissen M and Himpsel F J 2005 Phys. Rev. B 72 045312

Research paper thumbnail of PET hypoxia imaging with FAZA: reproducibility at baseline and during fractionated radiotherapy in tumour-bearing mice

European Journal of Nuclear Medicine and Molecular Imaging, 2012

Tumour hypoxia is linked to treatment resistance. Positron emission tomography (PET) using hypoxi... more Tumour hypoxia is linked to treatment resistance. Positron emission tomography (PET) using hypoxia tracers such as fluoroazomycin arabinoside (FAZA) may allow identification of patients with hypoxic tumours and the monitoring of the efficacy of hypoxia-targeting treatment. Since hypoxia PET is characterized by poor image contrast, and tumour hypoxia undergoes spontaneous changes and is affected by therapy, it remains unclear to what extent PET scans are reproducible. Tumour-bearing mice are valuable in the validation of hypoxia PET, but identification of a reliable reference tissue value (blood sample or image-derived muscle value) for repeated scans may be difficult due to the small size of the animal or absence of anatomical information (pure PET). Here tumour hypoxia was monitored over time using repeated PET scans in individual tumour-bearing mice before and during fractionated radiotherapy. Mice bearing human SiHa cervix tumour xenografts underwent a PET scan 3 h following injection of FAZA on two consecutive days before initiation of treatment (baseline) and again following irradiation with four and ten fractions of 2.5 Gy. On the last scan day, mice were given an intraperitoneal injection of pimonidazole (hypoxia marker), tumours were collected and the intratumoral distribution of FAZA (autoradiography) and hypoxia (pimonidazole immunohistology) were determined in cryosections. Tissue section analysis revealed that the intratumoral distribution of FAZA was strongly correlated with the regional density of hypoxic (pimonidazole-positive) cells, even when necrosis was present, suggesting that FAZA PET provides a reliable measure of tumour hypoxia at the time of the scan. PET-based quantification of tumour tracer uptake relative to injected dose showed excellent reproducibility at baseline, whereas normalization using an image-derived nonhypoxic reference tissue (muscle) proved highly unreliable since a valid and reliable reference value could not be determined. The intratumoral distribution of tracer was stable at baseline as shown by a voxel-by-voxel comparison of the two scans (R = 0.82, range 0.72-0.90). During treatment, overall tracer retention changed in individual mice, but there was no evidence of general reoxygenation. Hypoxia PET scans are quantitatively correct and highly reproducible in tumour-bearing mice. Preclinical hypoxia PET is therefore a valuable and reliable tool for the development of strategies that target or modify hypoxia.

Research paper thumbnail of 2039 POSTER Clinical Validation in Phantoms and Patients of a 4D-CT Based Method for Lung Ventilation Measurement

European Journal of Cancer, 2011

somewhat lower and much lower for systematic motion applied alone. In addition, anisotropic rando... more somewhat lower and much lower for systematic motion applied alone. In addition, anisotropic random motion provided stronger associations than the static DVH at high doses (70 Gy). Conclusion: A simple model for rectal motion has been presented and the corresponding motion-inclusive DVHs have been investigated in relation to rectal morbidity. The motion-inclusive DVHs provided a stronger association with rectal morbidity as compared to the static DVH alone.

Research paper thumbnail of Measurements of surface conductivity using micro four point probes

Page 1. Department of Physics and Astronomy University of Aarhus, Denmark Measurements of surface... more Page 1. Department of Physics and Astronomy University of Aarhus, Denmark Measurements of surface conductivity using micro four point probes Jesper F. Kallehauge Supervised by Philip Hofmann March, 2007 MASTER&amp;amp;amp;#x27;S THESIS Page 2. Page 3. ...