Microplastics contamination in pearl-farming lagoons of French Polynesia.

Pearl-farming is the second most important source of income in French Polynesia. However, tropical lagoons are fragile ecosystems with regard to anthropogenic pressures like plastic pollution, which threaten marine life and the pearl oyster-related economy. Here, we investigated the spatial distribution of microplastics (MP) and concentrations in surface water (SW), water column (WC) and cultivated pearl oyster (PO) from three pearl-farming atolls with low population and tourism. Microplastics were categorized by their size class, shape, colour and polymer type identified using FTIR spectroscopy. Widespread MP contamination was observed in every study site (SW, 0.2-8.4 MP m-3; WC, 14.0-716.2 MP m-3; PO, 2.1-125.0 MP g-1 dry weight), with high contamination in the WC highlighting the need to study the vertical distribution of MP, especially as this compartment where PO are reared. A large presence of small (< 200 µm) and fragment-shaped (> 70%) MP suggests that they result from the breakdown of larger plastic debris. The most abundant polymer type was polyethylene in SW (34-39%), WC (24-32%), while in PO, polypropylene (14-20%) and polyethylene were more evenly distributed (9-21%). The most common MP identified as black-grey polyethylene and polypropylene matches the polymer and colour of ropes and collectors questioning a pearl-farming origin.

4D-CT-based motion correction of PET images using 3D iterative deconvolution.

OBJECTIVES: Positron emission tomography acquisition takes several minutes representing an image averaged over multiple breathing cycles. Therefore, in areas influenced by respiratory movement, PET-positive lesions occur larger, but less intensive than they actually are, resulting in false quantitative assessment. We developed a motion-correction algorithm based on 4D-CT without the need to adapt PET-acquisition. METHODS: The algorithm is based on a full 3D iterative Richardson-Lucy-Deconvolution using a point-spread-function constructed using the motion information obtained from the 4D-CT. In a motion phantom study (3 different hot spheres in background activity), optimal parameters for the algorithm in terms of number of iterations and start image were estimated. Finally, the correction method was applied to 3 patient data sets. In phantom and patient data sets lesions were delineated and compared between motion corrected and uncorrected images for activity uptake and volume. RESULTS: Phantom studies showed best results for motion correction after 6 deconvolution steps or higher. In phantom studies, lesion volume improved up to 23% for the largest, 43% for the medium and 49% for the smallest sphere due to the correction algorithm. In patient data the correction resulted in a significant reduction of the tumor volume up to 33.3 % and an increase of the maximum and mean uptake of the lesion up to 62.1 and 19.8 % respectively. CONCLUSION: In conclusion, the proposed motion correction method showed good results in phantom data and a promising reduction of detected lesion volume and a consequently increasing activity uptake in three patients with lung lesions.

Radionuclide intake risks in the clinical administration of 223RaCl2.

An intake monitoring program covering more than half a year of clinical administration of Radium-223-dichloride for the palliative treatment of castration-resistant prostate cancer was carried out in the nuclear medicine department of the university hospital Bonn. Radioactivity in a total of 87 samples of gloves, air filters, faecal bioassays and face masks was measured and evaluated to assess the need for radiation protection measures for the medical staff. The main aim was to quantify or obtain an upper limit for the intake factor. An intake factor of 10-8 was measured when the preparation of patient doses took place in part in a laminar flow cabinet, which indicates an intake factor of 10-7 in more commonplace practice without a cabinet. The intake factor is therefore at the same level as other standard applications of unsealed sources in nuclear medicine. Our findings confirmed that masks are not required under any circumstances. However, the investigation also revealed that contamination risks, especially during the preparation of doses in syringes, should not be neglected.

68Ga-PSMA-PET/CT imaging of localized primary prostate cancer patients for intensity modulated radiation therapy treatment planning with integrated boost.

PURPOSE: The purpose of our study was to show the feasibility and potential benefits of using 68Ga-PSMA-PET/CT imaging for radiation therapy treatment planning of patients with primary prostate cancer using either integrated boost on the PET-positive volume or localized treatment of the PET-positive volume. The potential gain of such an approach, the improvement of tumor control, and reduction of the dose to organs-at-risk at the same time was analyzed using the QUANTEC biological model. METHODS: Twenty-one prostate cancer patients (70 years average) without previous local therapy received 68Ga-PSMA-PET/CT imaging. Organs-at-risk and standard prostate target volumes were manually defined on the obtained datasets. A PET active volume (PTV_PET) was segmented with a 40% of the maximum activity uptake in the lesion as threshold followed by manual adaption. Five different treatment plan variations were calculated for each patient. Analysis of derived treatment plans was done according to QUANTEC with in-house developed software. Tumor control probability (TCP) and normal tissue complication probability (NTCP) was calculated for all plan variations. RESULTS: Comparing the conventional plans to the plans with integrated boost and plans just treating the PET-positive tumor volume, we found that TCP increased to (95.2 ± 0.5%) for an integrated boost with 75.6 Gy, (98.1 ± 0.3%) for an integrated boost with 80 Gy, (94.7 ± 0.8%) for treatment of PET-positive volume with 75 Gy, and to (99.4 ± 0.1%) for treating PET-positive volume with 95 Gy (all p < 0.0001). For the integrated boost with 80 Gy, a significant increase of the median NTCP of the rectum was found, for all other plans no statistical significant increase in the NTCP neither of the rectum nor the bladder was found. CONCLUSIONS: Our study demonstrates that the use of 68Ga-PSMA-PET/CT image information allows for more individualized prostate treatment planning. TCP values of identified active tumor volumes were increased, while rectum and bladder NTCP values either remained the same or were even lower. However, further studies need to clarify the clinical benefit for the patients applying these techniques.

Assessment of Bone Metastases in Patients with Prostate Cancer-A Comparison between 99mTc-Bone-Scintigraphy and [68Ga]Ga-PSMA PET/CT.

PURPOSE: Bone scintigraphy is the standard of reference in bone metastases in prostate cancer patients. However, new radiotracers employed in prostate-specific membrane antigen (PSMA)-ligands has led to the growing importance of PET/CT as diagnostic tool. The aim of our study was to investigate the difference between bone scan and PSMA-PET/CT for the detection of bone metastases in prostate cancer. METHODS: Thirty patients with bone metastases originating from prostate cancer were examined by 99mTc-MDP bone scan and 68Ga-PSMA-PET/CT within an average of 21 days. Bone scans were analyzed visually according to the number of lesions and using the software package ExiniBONE by Exini Diagnostics. PET/CT data was analyzed visually. Numbers of detected lesions were compared for the different methods for the whole patient and for different regions. In addition, results were compared to serum prostate-specific antigen (PSA), alkaline phosphatase (ALP), bone alkaline phosphatase (bALP), pro gastrin releasing peptide (pGRP) and eastern cooperative oncology group (ECOG) performance status. RESULTS: In the bone scans, visual and semiautomatic lesion detection showed similar results with an average of 19.4 and 17.8 detected bone lesion per patient. However, in PSMA-PET/CT, on average double the numbers of lesions (40.0) were detected. The largest differences were found in the thorax and pelvis, which can be explained by the advantages of tomographic imaging. Bland-Altman analysis showed greater differences in patients with large numbers of bone metastases. CONCLUSION: No significant difference was found when using semiautomatic analysis compared to visual reading for bone scans. Fewer bone metastases were detected in bone scans than in PSMA-PET/CT. However, in none of our patients would the difference have led to clinical consequences. Therefore, it seems that for patients undergoing PSMA-PET/CT, there is no need to perform additional bone scans if the appropriate PET/CT protocols are applied.

Tumour delineation in oesophageal cancer - A prospective study of delineation in PET and CT with and without endoscopically placed clip markers.

PURPOSE: The objective was to analyse the value of F-18-fluorodesoxyglucose (FDG)-positron emission tomography/computed tomography (PET/CT) for delineation of the Gross Tumour Volumes (GTVs) in primary radiotherapy of oesophageal cancer. METHOD: 20 consecutive and prospective patients (13 men, 7 women) underwent FDG-PET/CT for initial staging and radiation treatment planning. After endoscopy-guided clipping of the tumour another CT study was acquired. The CT and the FDG-PET/CT were registered with a rigid and a non-rigid registration algorithm to compare the overlap between GTV contours defined with the following methods: manual GTV definition in (1) the CT image of the FDG-PET/CT, (2) the PET image of the FDG-PET/CT, (3) the CT study based on endoscopic clips (CT clip), and (4) in the PET-data using different semi-automatic PET segmentation algorithms including a gradient-based algorithm. The absolute tumour volumes, tumour length in cranio-caudal direction, as well as the overlap with the reference volume (CT-clip) were compared for all lesions and separately for proximal/distal tumours. RESULTS: In 6 of the patients, FDG-PET/CT discovered previously unknown tumour locations, which resulted in either altered target volumes (n=3) or altered intent of treatment from curative to palliative (n=3) by upstaging to stage IV. For tumour segmentation a large variability between all algorithms was found. For the absolute tumour volumes with CT-clip as reference, no single PET-based segmentation algorithm performed better compared to using the manual CT delineation alone. The best correlation was found between the CT-clip and the gradient based segmentation algorithm (PET-edge, R(2)=0.84) as well as the manual CT-delineation (CT-manual R(2)=0.89). Non-rigid registration between CT and image FDG-PET/CT did not decrease variability between segmentation methods compared to rigid registration statistically significant. For the analysis of tumour length no homogeneous correlation was found. CONCLUSION: Whereas FDG-PET was highly relevant for staging purposes, CT imaging with clipping of the tumour extension remains the gold standard for GTV delineation.