Multiple common garden experiments suggest lack of local adaptation in an invasive ornamental plant

Aims: Adaptive evolution along geographic gradients of climatic conditions is suggested to facilitate the spread of invasive plant species, leading to clinal variation among populations in the introduced range. We investigated whether adaptation to climate is also involved in the invasive spread of an ornamental shrub, Buddleja davidii, across western and central Europe. Material and Methods: We combined a common garden experiment, replicated in three climatically different central European regions, with reciprocal transplantation to quantify genetic differentiation in growth and reproductive traits of 20 invasive B. davidii populations. Additionally, we compared compensatory regrowth among populations after clipping of stems to simulate mechanical damage. Important findings: Our results do not provide evidence for clinal variation among invasive B. davidii populations: populations responded similarly to the different environments, and trait values were not correlated to climatic conditions or geographic coordinates of their home sites. Moreover, we did not detect differences in the compensatory ability of populations. We suppose that the invasive spread of B. davidii has been facilitated by phenotypic plasticity rather than by adaptation to climate, and that continent-wide shuffling of cultivars due to horticultural trade may have limited local adaptation so far

FBG-based sensing for real-time needle tracking during MR-guided brachytherapy

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An automated optimization tool for high-dose-rate (HDR) prostate brachytherapy with divergent needle pattern

International audienceFocal High-Dose-Rate (HDR) for prostate cancer has gained an increasing interest as an alternative to whole gland therapy as it may contribute to reduction of treatment related toxicity. For focal treatment, optimal needle guidance and placement is warranted. This can be achieved under MRI guidance. However, MRI-guided needle placement is currently not possible due to space restrictions in the closed MR bore. To overcome this problem, a MR-compatible, single-divergent needle-implant robotic device is under development at the University Medical Centre, Utrecht (UMCU): placed between the legs of the patient inside the MR bore, this robot will tap the needle in a divergent pattern from a single rotation point into the tissue. This rotation point is just beneath the perineal skin to have access to the focal prostate tumor lesion. Currently, there is no treatment planning system commercially available which allows optimization of the dose distribution with such needle arrangement. The aim of this work is to develop an automatic inverse dose planning optimization tool for focal HDR prostate brachytherapy with needle insertions in a divergent configuration. A complete optimizer workflow is proposed which includes the determination of (1) the position of the center of rotation, (2) the needle angulations and (3) the dwell times. Unlike most currently used optimizers, no prior selection or adjustment of input parameters such as minimum or maximum dose or weight coefficients for treatment region and organs at risk is required. To test this optimizer, a planning study was performed on 10 patients (treatment volumes ranged from 8.5cm 3 to 23.3cm 3 ) by using 2 to 14 needle insertions. The total computation time of the optimizer workflow was below 20 minutes and a clinically acceptable plan was reached on average using only four needle insertions

Adaptive planning strategy for high dose rate prostate brachytherapy—a simulation study on needle positioning errors

The development of magnetic resonance (MR) guided high dose rate (HDR) brachytherapy for prostate cancer has gained increasing interest for delivering a high tumor dose safely in a single fraction. To support needle placement in the limited workspace inside the closed-bore MRI, a single-needle MR-compatible robot is currently under development at the University Medical Center Utrecht (UMCU). This robotic device taps the needle in a divergent way from a single rotation point into the prostate. With this setup, it is warranted to deliver the irradiation dose by successive insertions of the needle. Although robot-assisted needle placement is expected to be more accurate than manual template-guided insertion, needle positioning errors may occur and are likely to modify the pre-planned dose distribution.In this paper, we propose a dose plan adaptation strategy for HDR prostate brachytherapy with feedback on the needle position: a dose plan is made at the beginning of the interventional procedure and updated after each needle insertion in order to compensate for possible needle positioning errors. The introduced procedure can be used with the single needle MR-compatible robot developed at the UMCU. The proposed feedback strategy was tested by simulating complete HDR procedures with and without feedback on eight patients with different numbers of needle insertions (varying from 4 to 12). In of the cases tested, the number of clinically acceptable plans obtained at the end of the procedure was larger with feedback compared to the situation without feedback. Furthermore, the computation time of the feedback between each insertion was below 100 s which makes it eligible for intra-operative use

The effect of catheter displacement and anatomical variations on the dose distribution in MRI-guided focal HDR brachytherapy for prostate cancer

PURPOSE: The aim of this study was to analyze the effect of catheter displacement and anatomical variations of prostate and organs at risk on dose distribution in MRI-guided 19 Gy single fraction focal high-dose-rate brachytherapy (HDR-BT) of the prostate. METHODS AND MATERIALS: Seventeen patients with localized prostate cancer were enrolled in a prospective trial investigating focal HDR-BT in a 1.5 T MRI-HDR-BT facility. The diagnostic MRI delineations were registered with intraoperative MR scan, and a single fraction of 19 Gy was applied to the visible tumor. Self-anchoring umbrella catheters were used for HDR-BT delivery. A 1.5 T MRI was performed directly after ultrasound (US)-guided catheter placement for treatment planning. After treatment and before removal of catheters, a posttreatment 1.5 T MRI was performed. Regions of interest were also delineated on the posttreatment MR images and the catheters of 17 patients were reconstructed. The dose plan was constructed for the posttreatment MRI scan to assess the influence of catheter migration and anatomical variation on the dose delivered to the target and the organs at risk. Also on the posttreatment MRI, the complete catheter reconstruction was reassessed, to correct for, for example, bending of the catheters. The displacement of catheters between the MRI scans was determined by comparing the catheter tip positions on the treatment planning and posttreatment 1.5 T MRI scans. RESULTS: The displacements of 241 catheters were investigated. Average (range) displacements of the umbrella catheters are 0.6 (0-2.9) mm in the x-direction, 0.5 (0-2.1) mm in the y-direction, and 0.9 (0-5.5) mm in the z-direction. In 3 patients, the displacement was >4 mm and up to 5.5 mm. This occurred in respectively 1/13, 1/16, and 1/18 catheters in these patients. The dosimetric differences between the intraoperative treatment and the posttreatment plans were in most patients less than 1.5 Gy. In 4 patients, a dose difference in clinical target volume D95 of >2 Gy up to 5.8 Gy was reported. No discrimination can be made between dose differences due to catheter displacement and/or organ movement/anatomy changes. CONCLUSIONS: In general, catheter displacements were in the order of a mm and differences in dose to the clinical target volume and the organs at risk between the treatment and posttreatment plans smaller than 1.5 Gy. In some patients, dose differences up to 5.8 Gy were determined, due to either individual larger catheter displacement and/or anatomy changes. A longer followup is necessary to assess the clinical implications of individual large dose differences

Fiber Bragg gratings-based sensing for real-time needle tracking during MR-guided brachytherapy

PURPOSE: The development of MR-guided high dose rate (HDR) brachytherapy is under investigation due to the excellent tumor and organs at risk visualization of MRI. However, MR-based localization of needles (including catheters or tubes) has inherently a low update rate and the required image interpretation can be hampered by signal voids arising from blood vessels or calcifications limiting the precision of the needle guidance and reconstruction. In this paper, a new needle tracking prototype is investigated using fiber Bragg gratings (FBG)-based sensing: this prototype involves a MR-compatible stylet composed of three optic fibers with nine sets of embedded FBG sensors each. This stylet can be inserted into brachytherapy needles and allows a fast measurement of the needle deflection. This study aims to assess the potential of FBG-based sensing for real-time needle (including catheter or tube) tracking during MR-guided intervention. METHODS: First, the MR compatibility of FBG-based sensing and its accuracy was evaluated. Different known needle deflections were measured using FBG-based sensing during simultaneous MR-imaging. Then, a needle tracking procedure using FBG-based sensing was proposed. This procedure involved a MR-based calibration of the FBG-based system performed prior to the interventional procedure. The needle tracking system was assessed in an experiment with a moving phantom during MR imaging. The FBG-based system was quantified by comparing the gold-standard shapes, the shape manually segmented on MRI and the FBG-based measurements. RESULTS: The evaluation of the MR compatibility of FBG-based sensing and its accuracy shows that the needle deflection could be measured with an accuracy of 0.27 mm on average. Besides, the FBG-based measurements were comparable to the uncertainty of MR-based measurements estimated at half the voxel size in the MR image. Finally, the mean(standard deviation) Euclidean distance between MR- and FBG-based needle position measurements was equal to 0.79 mm(0.37 mm). The update rate and latency of the FBG-based needle position measurement were 100 and 300 ms, respectively. CONCLUSIONS: The FBG-based needle tracking procedure proposed in this paper is able to determine the position of the complete needle, under MR-imaging, with better accuracy and precision, higher update rate, and lower latency compared to current MR-based needle localization methods. This system would be eligible for MR-guided brachytherapy, in particular, for an improved needle guidance and reconstruction