Frozen Hybrid Kernelised Expectation Maximisation For Bremsstrahlung SPECT Reconstruction

Background: Selective internal radiation therapy with Yttrium-90 microspheres is an effective therapy for liver cancer and liver metastases. Yttrium-90 is mainly a high-energy beta particle emitter. These beta particles emit Bremsstrahlung radiation during their interaction with tissue making post-therapy imaging of the radioactivity distribution feasible. Nevertheless, image quality and quantification is difficult due to the continuous energy spectrum which makes resolution modelling, and attenuation and scatter estimation challenging. Methods: In this study, a modified hybrid kernelised expectation maximisation is used to improve resolution and contrast and reduce noise. The iterative part of the kernel was frozen at the 72nd sub-iteration to avoid over-fitting of noise and background. A NEMA phantom with spherical inserts was used for the optimisation and validation of the algorithm, and data from 5 patients treated with Selective internal radiation therapy were used as proof of clinical relevance of the method. Results: The results suggest a maximum improvement of 56% for region of interest mean recovery coefficient at fixed coefficient of variation and better identification of the hot volumes in the NEMA phantom. Similar improvements were achieved with patient data, showing 47% mean value improvement over the gold standard used in hospitals. Conclusions: Such quantitative improvements could facilitate improved dosimetry calculations with SPECT when treating patients with Selective internal radiation therapy, as well as provide a more visible position of the cancerous lesions in the liver.

Stochastic parametric skeletal dosimetry model for humans: General approach and application to active marrow exposure from bone-seeking beta-particle emitters

The objective of this study is to develop a skeleton model for assessing active marrow dose from bone-seeking beta-emitting radionuclides. This article explains the modeling methodology which accounts for individual variability of the macro- and microstructure of bone tissue. Bone sites with active hematopoiesis are assessed by dividing them into small segments described by simple geometric shapes. Spongiosa, which fills the segments, is modeled as an isotropic three-dimensional grid (framework) of rod-like trabeculae that “run through” the bone marrow. Randomized multiple framework deformations are simulated by changing the positions of the grid nodes and the thickness of the rods. Model grid parameters are selected in accordance with the parameters of spongiosa microstructures taken from the published papers. Stochastic modeling of radiation transport in heterogeneous media simulating the distribution of bone tissue and marrow in each of the segments is performed by Monte Carlo methods. Model output for the human femur at different ages is provided as an example. The uncertainty of dosimetric characteristics associated with individual variability of bone structure was evaluated. An advantage of this methodology for the calculation of doses absorbed in the marrow from bone-seeking radionuclides is that it does not require additional studies of autopsy material. The biokinetic model results will be used in the future to calculate individual doses to members of a cohort exposed to 89,90Sr from liquid radioactive waste discharged to the Techa River by the Mayak Production Association in 1949–1956. Further study of these unique cohorts provides an opportunity to gain more in-depth knowledge about the effects of chronic radiation on the hematopoietic system. In addition, the proposed model can be used to assess the doses to active marrow under any other scenarios of 90Sr and 89Sr intake to humans.

A model for calculating beta exposure doses to tracheobronchial cells during movement of a point source

The article describes a model and method for calculating beta-exposure doses to secretory and basal cells of the tracheobronchial part of the respiratory tract when a point source of 1 Bq activity moves along the inner surface of respiratory formations. The calculations, that used for proposed model, were performed by using a 90Y point source as an example. The dose calculation model takes into account the speed o f movement of the radiation source in each respiratory formation, the size of the respiratory formations, and the depth of the secretory and basal cells. The dose calculation is based on the dose rate attenuation functions published by W. G. Cross et al. (DOI: 10.1097/00004032-199208000-00002). The calculations were performed for a cylindrical model of a respiratory formation. Two kinds of cells were considered for the dose estimation: cells irradiated without beta-particle exit into bronchial lumen (type 1 cells) and cells irradiated due to beta-par­ticle exit into bronchial lumen (type 2 cells). The results of calculations showed, that as far as the generation number increasing, the average irradiation doses of the type 1 cells are 10 or more times greater than those of the type 2 cells. With increasing generation number in the tracheobronchial tree, doses per cells increase by several orders of magnitude. The highest doses are formed in bronchioles of generations 9-15, reaching units and tens of mGy. In spite of the fact that the number of generation increases, the total number of irradiated cells decreases, the collective doses of irradiated cells (sum of doses to all cells of the respiratory formation) in the last generations are 30-50 times higher than the doses of the first generations. Thus, in case of a single point source, there is a significant (by many orders of magnitude) scatter of doses to individual cells in indi­vidual respiratory formation, as well as significant differences in average doses of trachea, individual bronchi and bronchioles.

RADIOECOLOGICAL SITUATION ON THE TERRITORY OF BORODULIKHA VILLAGE OF BORODULIKHA DISTRICT, EAST KAZAKHSTAN REGION

As part of the research work on the topic «Development of scientific and methodological foundations for minimizing the environmental burden, medical support, social protection and health improvement of the population of environmentally unfavorable territories of the Republic of Kazakhstan», the Research Institute of Radiation Medicine and Ecology carried out radioecological studies on the territory of Borodulikha village of Borodulikha district of East Kazakhstan region in May 2018. Radiation parameters of the environmental situation (MED, radon concentration, alpha and beta particle flux densities, the content of radioactive elements in environmental objects).

RADIOECOLOGICAL SITUATION ON THE TERRITORY OF KARAUL VILLAGE OF ABAYSKY DISTRICT OF EAST KAZAKHSTAN REGION

As part of the research work on the topic «Development of scientific and methodological foundations for minimizing the environmental burden, medical support, social protection and health improvement of the population of environmentally unfavorable territories of the Republic of Kazakhstan», the Research Institute of Radiation Medicine and Ecology carried out radioecological studies in the Karaul village of Abay district of East Kazakhstan region. The radiation situation of Karaul village was formed in the 50s of the last century by local contamination of this settlement from nuclear explosions carried out at the Semipalatinsk Nuclear Test Site. Measurements of radiation parameters of the current environmental situation on the ground and sampling of environmental objects that carried out in the period of May 2018. The radiation parameters of the environmental situation (MED, radon concentration, alpha and beta particle flux densities, and the content of radioactive elements in environmental objects) on the territory of the village are within the established standards

Characterization Of A Single Pixel Beta Detector For Guidance In Breast-Conserving Surgery

Breast-conserving surgery (BCS) is a challenging surgical procedure due to the lack of intraoperative image guidance available to surgeons. One potential method of intra-operative guidance would be radio-guided surgery with adiopharmaceutical emitting beta particles. In this thesis, a single pixel beta sensitive detector was constructed and characterized for intra-operative guidance during BCS. The thickness of the scintillation element of the detector was optimized to obtain a superior beta to gamma detection ratio. A computer model of the detector response was derived from an empirically measured, two-dimensional (2D) detector response. An in silico study evaluated whether the novel single pixel beta detector could detect less than 1 mm² deposits of cancer at the cut edge of the surgically excised cancerous tissue, with a sensitivity and specificity of 95%. A thickness of 0.5 mm for a CaF₂(Eu) scintillator was found to be optimal for a beta to gamma detection ratio. Additionally, according to an in silico study it is expected that with an acquisition time of 30 seconds, a tumour-to-background ratio of 5 or higher, and a normal breast tissue activity of 1.69 kBq/ml, detection of cancerous deposits of less than 1 mm² is possible. The result of this thesis demonstrate that radio-guided BCS, with a CaF₂(Eu) scintillation beta particle detector, can intra-operatively assess the tumour margin involvement, which would help surgeons in determining resection margins.