Dam removal Europe: refuting myths and supporting professionals

The removal of dams and weirs has been happening for decades. Since the 90’s a few countries have increased this tendency. USA has already removed at least 1,300 dams. What very few people know is that in Europe there have been over 3,500 barriers demolished already. In some European countries, like France, Sweden, Spain, Finland and UK dams are mainly being removed due to existing legislation, safety and security, the need to reach a good ecological status of their rivers for the Water Frame Directive and/or economical reasons. However, the lack of awareness, knowledge, support by decision makers and funding for dam removal are generally bottlenecks and most of the times is the cause of many dam removal failures. In addition, the Renewable Energy Directive requires the EU countries to fulfil at least 20% of its total energy needs with renewables by 2020, and amongst these renewables is hydropower. All this makes dam removal projects tremendously difficult to those who are willing to start removing old and useless dams, and automatically makes dam removal an uncomfortable subject to bring up for politicians. Europe requires a shift towards adaptive management of stream barriers, one that maximizes benefits and minimizes impacts, one that keeps efficient dams and removes obsolete and abandoned dams. The goals of Dam Removal Europe (www.damremoval.eu) are to improve citizens’ awareness about removing dams and refute myths, create a reference community of professionals, experts and starters, who generates and shares knowledge about dam removal and putting dam removal on the agenda of policy makers, directors and managers

Dam removal Europe: refuting myths and supporting professionals

The removal of dams and weirs has been happening for decades. Since the 90’s a few countries have increased this tendency. USA has already removed at least 1,300 dams. What very few people know is that in Europe there have been over 3,500 barriers demolished already. In some European countries, like France, Sweden, Spain, Finland and UK dams are mainly being removed due to existing legislation, safety and security, the need to reach a good ecological status of their rivers for the Water Frame Directive and/or economical reasons. However, the lack of awareness, knowledge, support by decision makers and funding for dam removal are generally bottlenecks and most of the times is the cause of many dam removal failures. In addition, the Renewable Energy Directive requires the EU countries to fulfil at least 20% of its total energy needs with renewables by 2020, and amongst these renewables is hydropower. All this makes dam removal projects tremendously difficult to those who are willing to start removing old and useless dams, and automatically makes dam removal an uncomfortable subject to bring up for politicians. Europe requires a shift towards adaptive management of stream barriers, one that maximizes benefits and minimizes impacts, one that keeps efficient dams and removes obsolete and abandoned dams. The goals of Dam Removal Europe (www.damremoval.eu) are to improve citizens’ awareness about removing dams and refute myths, create a reference community of professionals, experts and starters, who generates and shares knowledge about dam removal and putting dam removal on the agenda of policy makers, directors and managers

The effect of on-line position correction on the dose distribution in focal radiotherapy for bladder cancer

<p>Abstract</p> <p>Background</p> <p>The purpose of this study was to determine the dosimetric effect of on-line position correction for bladder tumor irradiation and to find methods to predict and handle this effect.</p> <p>Methods</p> <p>For 25 patients with unifocal bladder cancer intensity modulated radiotherapy (IMRT) with 5 beams was planned. The requirement for each plan was that 99% of the target volume received 95% of the prescribed dose. Tumor displacements from -2.0 cm to 2.0 cm in each dimension were simulated, using 0.5 cm increments, resulting in 729 simulations per patient. We assumed that on-line correction for the tumor was applied perfectly. We determined the correlation between the change in D_99%and the change in path length, which is defined here as the distance from the skin to the isocenter for each beam. In addition the margin needed to avoid underdosage was determined and the probability that an underdosage occurs in a real treatment was calculated.</p> <p>Results</p> <p>Adjustments for tumor displacement with perfect on-line position correction resulted in an altered dose distribution. The altered fraction dose to the target varied from 91.9% to 100.4% of the prescribed dose. The mean D_99%(± SD) was 95.8% ± 1.0%. There was a modest linear correlation between the difference in D_99%and the change in path length of the beams after correction (R²= 0.590). The median probability that a systematic underdosage occurs in a real treatment was 0.23% (range: 0 - 24.5%). A margin of 2 mm reduced that probability to < 0.001% in all patients.</p> <p>Conclusion</p> <p>On-line position correction does result in an altered target coverage, due to changes in average path length after position correction. An extra margin can be added to prevent underdosage.</p

4D CT amplitude binning for the generation of a time-averaged 3D mid-position CT scan.

The purpose of this study was to develop a method to use amplitude binned 4D-CT (A-4D-CT) data for the construction of mid-position CT data and to compare the results with data created from phase-binned 4D-CT (P-4D-CT) data. For the latter purpose we have developed two measures which describe the regularity of the 4D data and we have tried to correlate these measures with the regularity of the external respiration signal. 4D-CT data was acquired for 27 patients on a combined PET-CT scanner. The 4D data were reconstructed twice, using phase and amplitude binning. The 4D frames of each dataset were registered using a quadrature-based optical flow method. After registration the deformation vector field was repositioned to the mid-position. Since amplitude-binned 4D data does not provide temporal information, we corrected the mid-position for the occupancy of the bins. We quantified the differences between the two mid-position datasets in terms of tumour offset and amplitude differences. Furthermore, we measured the standard deviation of the image intensity over the respiration after registration (sigma(registration)) and the regularity of the deformation vector field ((Delta vertical bar J vertical bar) over bar) to quantify the quality of the 4D-CT data. These measures were correlated to the regularity of the external respiration signal (sigma(signal)). The two irregularity measures, (Delta vertical bar J vertical bar) over bar and sigma(registration), were dependent on each other (p <0.0001, R-2 = 0.80 for P-4D-CT, R-2 = 0.74 for A-4D-CT). For all datasets amplitude binning resulted in lower <(Delta vertical bar J vertical bar)over bar> and sigma(registration) and large decreases led to visible quality improvements in the mid-position data. The quantity of artefact decrease was correlated to the irregularity of the external respiratory signal. The average tumour offset between the phase and amplitude binned midposition without occupancy correction was 0.42 mm in the caudal direction (10.6% of the amplitude). After correction this was reduced to 0.16 mm in caudal direction (4.1% of the amplitude). Similar relative offsets were found at the diaphragm. We have devised a method to use amplitude binned 4D-CT to construct motion model and generate a mid-position planning CT for radiotherapy treatment purposes. We have decimated the systematic offset of this midposition model with a motion model derived from P-4D-CT. We found that the A-4D-CT led to a decrease of local artefacts and that this decrease was correlated to the irregularity of the external respiration signa

Registration accuracy and image quality of time averaged mid-position CT scans for liver SBRT.

The purpose was to validate the accuracy of motion models derived from deformable registration from four-dimensional computed tomography (4DCT) and breath-hold contrast enhanced computed tomography (BHCCT) scans for liver SBRT. Additionally, the image quality of the time averaged mid-position (MidP) CT constructed using the detected motion model was assessed. 4DCT and BHCCT liver scans of 11 patients were acquired with 1 or 2 fiducial markers. Using parametric sampling the markers were digitally removed. Phase-based optical flow was used to register the 4D frames and the BHCCT, and create MidP data. We compared the deformable registration of the markerless scans with the actual displacement of the markers to assess registration accuracy. The noise levels of the MidP scans were compared to those of the 4DCT and BHCCT data. We found an average misregistration of 1.8mm (± 0.5mm). The constructed MidPCT scan contained around three times less noise than the original 4D scan. The residual error between the MidPCT and the BHCCT was 3.0mm (± 0.9 mm). High precision deformable image registration of 4DCT and BHCCT liver cancer patients was achieved and used to create motion compensated MidPCT scans, with increased contrast-to-noise (CNR) levels. This improved visualisation of tumours and anatomy, facilitates radiotherapy treatment plannin

Adaptive margin radiotherapy for patients with prostate carcinoma: what's the benefit?

With daily portal images and repeated CT scans from 20 patients with gold markers (GM) an adaptive margin radiotherapy strategy (AMRT) was simulated and compared to traditional bony anatomy (BA) and standard GM verification protocols. AMRT is comparable with BA. GM protocols are superio

PET motion compensation for radiation therapy using a CT-based mid-position motion model: methodology and clinical evaluation.

PURPOSE: Four-dimensional positron emission tomography (4D PET) imaging of the thorax produces sharper images with reduced motion artifacts. Current radiation therapy planning systems, however, do not facilitate 4D plan optimization. When images are acquired in a 2-minute time slot, the signal-to-noise ratio of each 4D frame is low, compromising image quality. The purpose of this study was to implement and evaluate the construction of mid-position 3D PET scans, with motion compensated using a 4D computed tomography (CT)-derived motion model. METHODS AND MATERIALS: All voxels of 4D PET were registered to the time-averaged position by using a motion model derived from the 4D CT frames. After the registration the scans were summed, resulting in a motion-compensated 3D mid-position PET scan. The method was tested with a phantom dataset as well as data from 27 lung cancer patients. RESULTS: PET motion compensation using a CT-based motion model improved image quality of both phantoms and patients in terms of increased maximum SUV (SUV(max)) values and decreased apparent volumes. In homogenous phantom data, a strong relationship was found between the amplitude-to-diameter ratio and the effects of the method. In heterogeneous patient data, the effect correlated better with the motion amplitude. In case of large amplitudes, motion compensation may increase SUV(max) up to 25% and reduce the diameter of the 50% SUV(max) volume by 10%. CONCLUSIONS: 4D CT-based motion-compensated mid-position PET scans provide improved quantitative data in terms of uptake values and volumes at the time-averaged position, thereby facilitating more accurate radiation therapy treatment planning of pulmonary lesions

Behavior of lipiodol markers during image guided radiotherapy of bladder cancer.

Purpose: To investigate the stability of a novel type of markers used in partial bladder tumor irradiation and tumor deformation as indicated by the markers. Materials and Methods: In 15 patients with solitary bladder cancer, lipiodol was injected in the bladder wall during flexible cystoscopy to identify the tumor. A planning CT scan was made, followed by daily cone-beam CT (CBCT) scans during treatment. To study the accuracy of using these markers for image guidance, uncertainties U1 and U2 were calculated, which were defined as the difference between submask registration (covering single marker) and the average of all submask registrations and the difference between the submask registration and the general mask registration (including all markers), respectively. Finally, to study tumor deformation, the relative movement of each marker pair was correlated with the relative bladder volume (RBV). Results: The analyzed patients had 2.3 marker injections on average. The lipiodol spot size was 0.72 +/- 1.1 cm(3). The intensity of spots in both CT and CBCT was significantly higher than the surrounding bladder tissue. The uncertainties U1 and U2 were comparable, and the uncertainties in left-right direction (0.14-0.19 cm) were smaller than those in cranial-caudal and anterior-posterior directions (0.19-0.32 cm). The relative marker movement of within-zone marker pairs was much smaller (and has less dependence on the RBV) than across-zones marker pairs. Conclusions: Lipiodol markers are a feasible method to track bladder tumor by using online CBCT. Tumor deformation is observed, especially for tumors that cross the defined bladder zones. (C) 2010 Elsevier In

Position verification for the prostate: effect on rectal wall dose.

Purpose: To evaluate the effect of gold marker (GM)-based position correction on the cumulative dose in the anorectal wall compared with traditional bony anatomy (BA)-based correction, taking into account changes in anorectal shape and position. Methods and Materials: A total of 20 consecutive prostate cancer patients, treated with curative external beam radiotherapy, were included. Four fiducial GMs were implanted in the prostate. Positioning was verified according to the shift in BA and GMs on daily electronic portal images. Position corrections were determined using on- and off-line position verification protocols according to the position of the GMs (GM-on and GM-off) and BA (BA-off). For all patients, intensity-modulated radiotherapy plans were made for the GM (8-mm planning target volume margin) and BA (10-mm planning target volume margin) protocols. The dose distribution was recomputed on 11 repeat computed tomography scans to estimate the accumulated dose to the prostate and anorectal wall while considering internal organ motion. Results: The dose that is at least received by 99% of the prostate was, on average, acceptable for all protocols. The individual patient data showed the best coverage for both GM protocols, with >95% of the prescribed dose for all patients. The anorectal wall dose was significantly lower for the GM protocols. The dose that is at least received by 30% of the rectal wall was, on average, 54.6 Gy for GM-on, 54.1 Gy for GM-off, and 58.9 Gy for BA-off (p <.001). Conclusion: Position verification with GM and reduced planning target volume margins yielded adequate treatment of the prostate and a lower rectal wall dose, even when accounting for independent movement of the prostate and anorectal wall. (C) 2011 Elsevier In