Optimierung der Anbautechnik bei der Weißen Lupine im ökologischen Landbau

Im Rahmen eines Projektes wurden von 2016 bis 2019 an der Bayerischen Landesanstalt für Landwirtschaft zusammen mit den Landwirtschaftlichen Lehranstalten in Triesdorf zwei-ortige Feldversuche zur Optimierung der Produktionstechnik bei der Weißen Lupine durchgeführt. Geprüft wurden drei verschiedene Saatstärken und zusätzlich zum Blindstriegeln drei Varianten der Beikrautregulierung: ein weiterer Striegeldurchgang (Reihenabstand 12,5 cm), Hacken und eine Kombination aus Hacke und Striegel (jeweils ein Arbeitsgang, Reihenabstand 25 cm). Eine Reduzierung der Saatstärke von 60 auf 40 Körner/m² wirkte sich negativ auf den Kornertrag der Weißen Lupine aus. Die einzelnen Pflanzen konnten die Reduzierung trotz einer günstigeren Standraumzuteilung und einem verbesserten Hülsenansatz nicht kompensieren. Eine erhöhte Saatstärke (80 vs. 60 Körner/m²) brachte keinen höheren Ertrag. Deshalb wird eine Saatstärke von 60 Körnern/m² für den Anbau der Weißen Lupine empfohlen. In den Versuchen war der Beikrautdruck gering und der enge Reihenabstand (12,5 cm) mit reinem Striegeleinsatz erbrachte Mehrerträge im Vergleich zum weiteren Reihenabstand mit Hacktechnik

Evaluation of an adaptive radiation therapy workflow for hypofractionated prostate cancer treatment based on synthetic cone-beam computed tomography

Hypofractionated stereotactic body radiation therapy of prostate cancer has experienced an increasing use during the last years, requiring higher accuracy during every treatment fraction. This can be achieved by harnessing the full potential of daily acquired images such as cone-beam computed tomography (CBCT) which are currently limited by insufficient image quality. Hence, the aim of this work was to overcome this drawback by generating synthetic CT (sCT) from CBCT based on a novel cycle-generative adversarial network and validating the accuracy of the obtained pelvic synthetic CT model for the following core components of an online adaptive workflow: image quality, image segmentation and dose calculation. Having been priorly trained with an independent collective of prostate cancer patients’ pelvic CT data, the neural network-based model allowed for a conversion of CBCT into sCT in 30±3 s for 15 tested patients. It accomplished image uncertainties being close to the related treatment planning CT with mean errors of 5.4±4.6 Hounsfield units. Afterwards, image segmentation was performed with a deformable image registration-based method that provided a structure set within 30 ±5 s, showing a satisfying mean dice similarity coefficient of 85.9±3.3 % for the prostate compared to manual references. Dose calculations on sCT were determined as sufficiently accurate with dosimetric deviations not exceeding ±1.5% and ±1.0% for target and organ-at-risk structures. Based on this validation, different adaptive replanning strategies were evaluated in respect of dosimetric benefits over conventional image-guided radiation therapy and regarding clinical feasibility. Three different replanning approaches on sCT ranging from segment aperture morphing-based warm start optimization with segment-weights and additional segment-shape modification to a full re-optimization were analyzed for the hypofractionated treatment regimen of the PACE-C trial for 32 patients each having 5 CBCT. All three replanning approaches were proven to gain substantial dosimetric benefits over the image-guided approach, especially for the planning target volume and rectum. Additional plan quality scoring revealed that dosimetric benefits were either focused on increasing target coverage or sparing organs-at-risk, thus guiding the decision on the most suitable adaptation strategy. With all evaluated approaches being executable within 7.1±1.8 min in one software environment, crucial steps towards the clinical implementation of online adaptive radiation therapy methods at CBCT-based C-arm linear accelerators were accomplished. If combined with techniques of online quality assurance and intrafractional tracking, the presented image conversion, segmentation and replanning approaches are ready for use in clinical routine

Characterization and clinical evaluation of a novel 2D detector array for conventional and flattening filter free (FFF) IMRT pre-treatment verification

Background and purpose: The novel MatriXXFFF (IBA Dosimetry, Germany) detector is a new 2D ionization chamber detector array designed for patient specific IMRT-plan verification including flattening-filter-free (FFF) beams. This study provides a detailed analysis of the characterization and clinical evaluation of the new detector array. Material and methods: The verification of the MatriXXFFF was subdivided into (i) physical dosimetric tests including dose linearity, dose rate dependency and output factor measurements and (ii) patient specific IMRT pre-treatment plan verifications. The MatriXXFFF measurements were compared to the calculated dose distribution of a commissioned treatment planning system by gamma index and dose difference evaluations for 18 IMRT-sequences. All IMRT-sequences were measured with original gantry angles and with collapsing all beams to 0° gantry angle to exclude the influence of the detector's angle dependency. Results: The MatriXXFFF was found to be linear and dose rate independent for all investigated modalities (deviations ≤0.6%). Furthermore, the output measurements of the MatriXXFFF were in very good agreement to reference measurements (deviations ≤1.8%). For the clinical evaluation an average pixel passing rate for γ(3%,3 mm) of (98.5 ± 1.5)% was achieved when applying a gantry angle correction. Also, with collapsing all beams to 0° gantry angle an excellent agreement to the calculated dose distribution was observed (γ(3%,3 mm) = (99.1 ± 1.1)%). Conclusions: The MatriXXFFF fulfills all physical requirements in terms of dosimetric accuracy. Furthermore, the evaluation of the IMRT-plan measurements showed that the detector particularly together with the gantry angle correction is a reliable device for IMRT-plan verification including FFF

Dosimetric benefits of daily treatment plan adaptation for prostate cancer stereotactic body radiotherapy

Background!#!Hypofractionation is increasingly being applied in radiotherapy for prostate cancer, requiring higher accuracy of daily treatment deliveries than in conventional image-guided radiotherapy (IGRT). Different adaptive radiotherapy (ART) strategies were evaluated with regard to dosimetric benefits.!##!Methods!#!Treatments plans for 32 patients were retrospectively generated and analyzed according to the PACE-C trial treatment scheme (40 Gy in 5 fractions). Using a previously trained cycle-generative adversarial network algorithm, synthetic CT (sCT) were generated out of five daily cone-beam CT. Dose calculation on sCT was performed for four different adaptation approaches: IGRT without adaptation, adaptation via segment aperture morphing (SAM) and segment weight optimization (ART1) or additional shape optimization (ART2) as well as a full re-optimization (ART3). Dose distributions were evaluated regarding dose-volume parameters and a penalty score.!##!Results!#!Compared to the IGRT approach, the ART1, ART2 and ART3 approaches substantially reduced the V!##!Conclusion!#!Treatment plan adaptation was demonstrated to adequately restore relevant dose criteria on a daily basis. While for SAM adaptation approaches dosimetric benefits were realized through ensuring sufficient target coverage, a full re-optimization mainly improved OAR sparing which helps to guide the decision of when to apply which adaptation strategy

Surface guidance compared with ultrasound-based monitoring and diaphragm position in cone-beam computed tomography during abdominal stereotactic radiotherapy in breath-hold

Background and purpose: Spirometry induced deep-inspiration-breath-hold (DIBH) reduces intrafractional motion during upper abdominal stereotactic body radiotherapy (SBRT). The aim of this prospective study was to evaluate whether surface scanning (SGRT) is an adequate surrogate for monitoring residual internal motion during DIBH. Residual motion detected by SGRT was compared with experimental 4D-ultrasound (US) and an internal motion detection benchmark (diaphragm-dome-position in kV cone-beam computed tomography (CBCT) projections). Materials and methods: Intrafractional monitoring was performed with SGRT and US in 460 DIBHs of 12 patients. Residual motion detected by all modalities (SGRT (anterior-posterior (AP)), US (AP, craniocaudal (CC)) and CBCT (CC)) was analyzed. Agreement analysis included Wilcoxon signed rank test, Maloney and Rastogi’s test, Pearson’s correlation coefficient (PCC) and interclass correlation coefficient (ICC). Results: Interquartile range was 0.7 mm (US(AP)), 0.8 mm (US(CC)), 0.9 mm (SGRT) and 0.8 mm (CBCT). SGRT(AP) vs. CBCT(CC) and US(CC) vs. CBCT(CC) showed comparable agreement (PCCs 0.53 and 0.52, ICCs 0.51 and 0.49) with slightly higher precision of CBCT(CC). Most agreement was observed for SGRT(AP) vs. US(AP) with largest PCC (0.61) and ICC (0.60), least agreement for SGRT(AP) vs. US(CC) with smallest PCC (0.44) and ICC (0.42). Conclusions: Residual motion detected during spirometry induced DIBH is small. SGRT alone is no sufficient surrogate for residual internal motion in all patients as some high velocity motion could not be detected. Observed patient-specific residual errors may require individualized PTV-margins