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- Hagmarker, Linn, et al.
(författare)
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Characterisation of a planar dosimetry method estimating the absorbed dose to the bone marrow during 177Lu-DOTATATE treatment
- 2016
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Ingår i: European Journal of Nuclear Medicine and Molecular Imaging. - : Springer. - 1619-7070 .- 1619-7089.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Aim: An image based method for bone marrow dosimetry, earlier presented by our research group, has shown a significant correlation between the absorbed dose to the bone marrow and haematological toxicity in 177Lu-DOTATATE treatment. The aim of this study was to further evaluate and optimise the method. Materials and Methods: 46 patients with advanced neuroendocrine tumours were treated with 177Lu -DOTATATE on 2-6 occasions. The patients were evaluated using the 4 planar gamma camera images collected at 2, 24, 48 and 168 hours after injection. The whole body was divided into a high- and a low uptake compartment, using a threshold based segmentation tool in the image platform PhONSAi, developed in-house. The segmentation tool starts by including the highest uptake focus and then gradually includes foci with lower and lower uptakes until a threshold is reached where the number of foci escalates. The threshold determines the proportion of the foci that is included in the two compartments. Visual inspection was used to determine the threshold valuewhere all high uptake tissues (i.e. kidney, spleen, liver and tumours) were included in the high uptake compartment. For thresholds around this value the activity in the two compartments was determined by the conjugate view method and the bonemarrow dose was calculated as a sum of the self and cross dose in the low uptake compartment and the cross dose from the high uptake compartment. Results: The visual analysis implies a threshold value of 10%of the maximum number of foci. A correlation was found between the absorbed bone marrow dose and haematological toxicity with p-values ranging from 0.001 to 0.02 for thresholds between 2 % and 25 %, the strongest correlation was found at 15 %. The mean absorbed bone marrow dose were 0.20-0.22 Gy per 7.4 GBq for threshold values between 10-25 %, and increased to 0.28 Gy for the lower values. No significant difference was observed in coefficient of variation (8.2-8.7 %) for the individual mean absorbed doses when varying the threshold value. Conclusion: The individual variation in absorbed dose is maintained at a low level when varying the threshold value for the determination of the compartment sizes. This implies that the method is stable for estimation of bone marrow doses and its correlation to haematological toxicity.
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- Hemmingsson, Jens, 1986, et al.
(författare)
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Simulation of 90Y microspheres in selective internal radiation therapy (SIRT) reveals different heterogeneity profiles for glass and resin microspheres.
- 2016
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Ingår i: European Journal of Nuclear Medicine and Molecular Imaging. 43 (Suppl 1): 1. - : Springer Science and Business Media LLC. - 1619-7070 .- 1619-7089.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Aim: Selective internal radiation therapy (SIRT) can supply normal tissue in the liver with radiation doses exceeding tolerance without causing toxicity, an effect possibly explained by microsphere clustering causing heterogeneity in the distribution. Using a simulation of microspheres transported through a simplified arterial structure, the aim of this study has been to evaluate how the number of injected microspheres affect the dose distribution. Materials and methods: The simulation was based on observations in biopsies and autoradiographies from resected liver tissue receiving 90YSIRT. Individual microspheres, with diameter and density from literature, were followed through a simplistic bifurcations model in which three parameters were introduced and optimised to obtain results consistent with observations: an artery coefficient of variation, a reduction parameter for the arterial diameter and a distribution volume parameter for the arterial tree. In the model the arterial diameter decreases for higher artery generations and the probability of microsphere clustering increases successively in the artery tree. After simulation a 90Y dose kernel was applied to the 940 cm3 sized 3D-matrix of microspheres and the dose distribution throughout the matrix was evaluated using varying resolutions and computing the coefficient of variation (CV). A smaller number of simulated microspheres (10^5) corresponds to the higher activity/sphere found in glass spheres while a larger number (10^7) resembles resin spheres. Results: As the number of microspheres increase from thousands to 106 the CV of the absorbed dose decrease from over 80 % to 32 % in a volume corresponding to a lobuli (2 mm^3) and at 106 microspheres a plateau was reached. The simulation was consistent with biopsy and autoradiography observations regarding the formation of clusters. A large majority of the clusters contain few microspheres and a minority of the clusters are significantly more numerous in microspheres. Conclusion: For the high microsphere concentrations used with resin microspheres the CVof the absorbed doses was constant (32 %) while for the lower microsphere concentrations used for glass spheres the CV varied between 90 % and 40 %. These results implies that small scale dosimetry for 90Y-SIRT differs between resin and glass spheres.
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- Högberg, Jonas, 1976, et al.
(författare)
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On the dose heterogeneity in normal liver tissue due to treatment of liver tumors with yttrium-90 microspheres
- 2012
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Ingår i: 25th Annual Congress on European Association of Nuclear Medicine, Milano, Italy, October 27-31, 2012. European Journal of Nuclear Medicine and Molecular Imaging. - : Springer Science and Business Media LLC. - 1619-7070 .- 1619-7089. ; 39:suppl 2
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Aim: When treating patients with primary or metastatic liver cancer, applying external radiotherapy, an absorbed dose of 30 - 35 Gy to the whole normal liver tissue volume is associated with a 5 % risk of radiation-induced hepatitis. If less than half of the normal liver volume is being exposed, the threshold for a 5 % risk of hepatitis is increased to above 60 Gy for both primary and metastatic liver cancer. Experience with patients treated with SIR-Spheres® (Sirtex Medical Ltd.), resin microspheres aggregated with yttrium-90, has shown that most patients tolerate an average absorbed dose to normal liver tissue higher than 60 Gy. The high tolerance for this treatment procedure can probably be explained by the resulting heterogenic distribution of radioactivity. It is of interest to study the degree of heterogeneity in the distribution of radioactivity in normal liver tissue, in order to explain or even predict the tolerance to radiation. The aim of this study was to describe the degree of heterogeneity by comparing the relative standard deviations of the radioactivity concentration for different sample mass categories. Materials and Methods: Two patients with cholangiocarcinoma were planned for a combined treatment with yttrium-90-aggregated SIR-Spheres followed by surgery 9 days after radiotherapy. According to standard protocol for treatments with SIR-Spheres, the therapies were preceded by Tc-99m-labled Macro aggregated albumin (Tc-99m-MAA) distribution studies for pre-therapeutic dosimetry and lung shunting evaluations. After surgery the resected tissue, containing both tumour and normal tissue, was studied regarding the distribution of radioactivity. Several small circular samples of normal liver tissue were punched out from 2 mm thick slices of resected tissue, deliberately varying the sizes, and thus the masses of the tissue samples (from 6 to 102 mg). The samples were weighed and categorized in two (first patient) and three (second patient) groups, depending on sample mass. After this the radioactivity was measured with a NaI(Tl) detector. The relative standard deviations (SD/Median) for the radioactivity concentration for each sample mass group were determined and compared. Results: The relative standard deviation for the radioactivity concentration was decreasing rapidly with increasing sample mass. Conclusion: The results indicate a considerable degree of heterogeneity in the distribution of microspheres. One probable explanation for this heterogeneity is clustering of microspheres in the blood vessels.
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