| 1. |
- Dasu, Alexandru, et al.
(författare)
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Dose painting by numbers - do the practical limitations of the technique decrease or increase the probability of controlling tumours?
- 2013
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Ingår i: IFMBE Proceedings. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 1680-0737 .- 1433-9277. ; 39, s. 1731-1734, s. 1731-1734
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Tidskriftsartikel (refereegranskat)abstract
- One of the important questions regarding the feasibility of dose-painting-by-numbers approaches for treatment planning concerns the influence of the averaging of the imaging techniques used and the resolution of the planned and achieved dose distributions. This study investigates the impact of these aspects on the probability of controlling dynamic tumours. The effectiveness of dose painting approaches to target tumour hypoxia has been investigated in terms of the predicted tumour control probabilities (TCP) for tumours with dynamic oxygenations. Several levels of resolution for the resistance of the tumour or the planned dose distributions have been investigated. A very fine heterogeneous dose distribution ideally calculated at voxel level for a high target TCP would fail to control a tumour with dynamic oxygenation during the course of fractionated radiotherapy as mismatches between hotspots in the dose distribution and resistant hypoxic foci would lead to a significant loss in TCP. Only adaptive treatment would lead to reasonably high TCP. A coarse resolution for imaging or for dose distributions might compensate microscale mismatches in dynamic tumours, but the resulting tumour control could still be below the target levels. These results indicate that there is a complex relationship between the resolution of the dose-painting-by-numbers approaches and the dynamics of tumour oxygenation. Furthermore, the clinical success of hypoxia targeting strategies in the absence of adaptive approaches might be explained by changes in tumour radiation resistance through reoxygenation.
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| 2. |
- Dasu, Alexandru, et al.
(författare)
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Impact of increasing irradiation time on the treatment of prostate cancers
- 2015
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Ingår i: World Congress on Medical Physics and Biomedical Engineering, June 7-12, 2015, Toronto, Canada. - Cham : Springer. - 9783319193861 - 9783319193878 ; 51, s. 490-493
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Konferensbidrag (refereegranskat)abstract
- This study aimed to investigate the expected impact of intrafraction repair during increasing irradiation times for the treatment of prostate cancers. Lengthy sessions are indeed expected for some advanced irradiation techniques capable to deliver the large fractional doses required by the increased fractionation sensitivity of the prostates. For this purpose, clinically-derived parameters characterizing repair rates and dose response curves for prostate tumors have been used to calculate the expected loss of effectiveness when increasing the irradiation time. The results have shown that treatment sessions lasting more than about 20 to 40 minutes could reduce the probability of biochemical control of prostate tumors by more than 20 to 30 percentage points. These results are in agreement with some observed clinical results and therefore they suggest that treatment durations in prostate radiation therapy should be carefully recorded in order to explicitly account for intrafraction repair, especially when irradiation techniques make use of multiple beams and imaging sessions. Failure to do so might overestimate the expected effectiveness of the treatment and could lead to disappointing clinical results precisely from the demanding treatment modalities expected to increase the therapeutic gain in prostate radiotherapy.
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| 3. |
- Dasu, Alexandru, et al.
(författare)
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The risk for secondary cancers in patients treated for prostate carcinoma – An analysis with the competition dose response model
- 2009
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Ingår i: IFMBE Proceedings. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1680-0737 .- 1433-9277. ; 25/III, s. 237-240
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Tidskriftsartikel (refereegranskat)abstract
- The risk for radiation-induced cancers has become increasingly important as patient survival following radiotherapy has increased due to the advent of new methods for early detection and advanced treatment. Attempts have been made to quantify the risk of cancer that may be associated with various treatment approaches, but the accuracy of predictions is rather low due to the influence of many confounding factors. It is the aim of this paper to investigate the impact of dose heterogeneity and inter-patient anatomical heterogeneity that may be encountered in a population of patients undergoing radiotherapy and are thought to influence risk predictions. Dose volume histograms from patients treated with radiation for the carcinoma of the prostate have been used to calculate the risk for secondary malignancies using a competition dose-response model previously developed. Biologically-relevant parameters derived from clinical and experimental data have been used for the model. The results suggested that dose heterogeneity plays an important role in predicting the risk for secondary cancer and that it should be taken into account through the use of dose volume histograms. Consequently, dose-response relationships derived for uniform relationships should be used with care to predict the risk for secondary malignancies in heterogeneously irradiated tissues. Inter-patient differences could lead to considerable uncertainties in the shape of the relationship between predicted risk and average tissue dose, as seen in epidemiological studies. They also lead to rather weak correlations between the risk for secondary malignancies and target volumes. The results stress the importance of taking into account the details of the clinical delivery of dose in radiotherapy for treatment plan evaluation or for retrospective analyses of the induction of secondary cancers. Nevertheless, the levels of risks are generally low and they could be regarded as the price of success for the advances in the radiotherapy of the prostate.
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| 4. |
- Dukov, Nikolay, et al.
(författare)
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Experimental Evaluation of Physical Breast Phantoms for 2D and 3D Breast X-Ray Imaging Techniques
- 2021
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Ingår i: 8th European Medical and Biological Engineering Conference - Proceedings of the EMBEC 2020. - Cham : Springer International Publishing. - 1680-0737 .- 1433-9277. - 9783030646097 ; 80, s. 544-552
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Konferensbidrag (refereegranskat)abstract
- Anthropomorphic phantoms are models of real or virtual parts of the body, organ or tissue, represented by tissue-equivalent materials that aim to provide a realistic and accurate representation of their anatomy and properties. The aim of this study is to evaluate experimentally the suitability of 3D printed materials in the production of both, physical breast phantoms and abnormalities, to be used in optimization tasks in breast imaging. For this purpose, we designed three computational breast models, composed of skin, duct tree, adipose compartments and lesions. Subsequently, they were printed by using two 3D printing technologies and different printing materials, which were previously studied in details. The physical phantoms were scanned at a mammography machine, which allows 2D and 3D mammography (tomosynthesis) modes. The images were evaluated from an experienced radiologist. The results showed that tomosynthesis images are characterized with better realism compared to 2D mammography images. Next step is improvement in the printing quality of tumour formations as well as quantitative evaluation of the obtained results.
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| 5. |
- Toma-Dasu, Iuliana, et al.
(författare)
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Biologically-optimised IMRT based on molecular imaging of tumour hypoxia : the impact of the tracer used
- 2013
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Ingår i: IFMBE Proceedings. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 1680-0737 .- 1433-9277. ; 39, s. 1742-1745, s. 1742-1745
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Tidskriftsartikel (refereegranskat)abstract
- One of the most challenging tasks of current radiation therapy is the individualisation of the treatment plans through biological optimisation and adaptation to functional aspects. This study aims to explore the robustness of a newly proposed method of treatment planning optimisation based on patient-specific radiation sensitivity determined by tumour hypoxia. Theoretical three-dimensional tumours with heterogeneous oxygenations were used to investigate the efficiency of various approaches for calculating the optimal dose distribution and the effects of reoxygenation during the treatment duration. The impact of the spatial averaging implied by the imaging method in combination with the binding properties of the tracer used has also been investigated. It has been shown that a newly proposed method for dose prescription based on functional imaging of hypoxia could lead to improved local control for several tracers that could be practically used. The approach for dose prescription appears to have a significant impact for tumours with dynamic hypoxia. Furthermore, the average implied by the imaging method could reduce the effectiveness of the method, but it still has the potential to provide significantly better results than methods employing highly heterogeneous dose distributions. The results showed that planning and optimisation of treatments based on hypoxia information from PET images is feasible and could provide the tool for individualising the planning on biological and molecular bases.
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| 6. |
- Toma-Dasu, Iuliana, et al.
(författare)
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The value of individual measurements for tumor control probability predictions in head and neck patients
- 2015
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Ingår i: World Congress on Medical Physics and Biomedical Engineering, June 7-12, 2015, Toronto, Canada. - Cham : Springer. - 9783319193861 - 9783319193878 ; 51, s. 1675-1678
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Konferensbidrag (refereegranskat)abstract
- In the age of personalized cancer medicine, individual measurements of in vitro radiosensitivity and proliferation parameters have great potential for predicting treatment outcome. However, cellular radiosensitivity is quite heterogeneous and therefore concerns exist towards its impact on treatment predictions. It was therefore the purpose of this study to investigate this aspect. Individually-determined radiosensitivities and potential doubling times, as well as tumor volumes from 46 head-and-neck carcinomas treated with radiotherapy, were used to predict tumor control probabilities (TCP) under various biologically-relevant assumptions for heterogeneity in radiosensitivity. TCP predictions were then compared to clinical local control using a ROC curve analysis. The analysis showed that TCP calculated under the assumption of heterogeneous radiosensitivity have the same power of distinguishing between patients with or without local control as from single values for the radiobiological parameters (a sensitivity of 66% and a specificity of 80% for an area under the curve of 0.69). The only difference was in the discrimination criterion (TCP>93% for single parameters and TCP>65% for heterogeneous parameters), illustrating the difference in appearance of the TCP curve under the assumption of heterogeneity. Nevertheless, the results showed that individually determined radiobiological parameters could be quite effective towards predicting treatment outcome for individual patients.
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| 7. |
- Toma-Dasu, Iuliana, et al.
(författare)
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Therapy optimization based on non-linear uptake of PET tracers versus “linear dose painting”
- 2009
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Ingår i: IFMBE Proceedings. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1680-0737 .- 1433-9277. ; 25/I, s. 221-224
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Tidskriftsartikel (refereegranskat)abstract
- Treatment optimization based on positron emission tomography (PET) images of tumor hypoxia has been proposed as a method to improve the cure rates in radiotherapy through the increased dose delivery to tumor regions with increased radioresistance. One of the major advantages of PET imaging of hypoxia is that it can provide information on both the extent and the spatial distribution of the resistant regions. One of the key issues for the practical implementation of this approach is the accurate conversion of the intensities in the recorded images into radiosensitivity maps that could then be used for dose escalation. The present paper explores the influence of the conversion from uptake to prescribed doses. Transformation functions derived from the uptake properties of the PET tracers were taken into consideration. The results have shown that the available tracers have different uptake properties and therefore they could interpret differently the gradients in the images which in turn would lead to different dose predictions. Best results in terms of dose prescription would therefore be achieved by carefully taking into account the uptake characteristics of the imaged tracers. Linear approximations could lead to unnecessary overestimations of the doses for cases of partial hypoxia in tumors. This highlights the need for more experimental studies of the uptake properties of PET tracers proposed to image tissue hypoxia. These would eventually provide more reliable methods for dose prescription that could be used with optimization algorithms for the successful individualization of radiation therapy.
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| 8. |
- Albinsson, John, et al.
(författare)
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Tracking Performance of Several Combinations of Common Evaluation Metrics and Sub-pixel Methods
- 2015
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Ingår i: 16th Nordic-Baltic Conference on Biomedical Engineering. - Cham : Springer International Publishing. - 1680-0737. ; 48, s. 13-16, s. 13-16
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Konferensbidrag (refereegranskat)abstract
- Motion estimation in a series of consecutive images is used in a variety of areas, e.g. video compression and investigation of tissue characteristics and organ function in medical images. Several methods exist both for estimating motions on a pixel level, e.g. block-matching in which two blocks in consecutive images are compared by an evaluation metric, and on a sub-pixel level. In this paper, we have evaluated the tracking performance of all combinations between three evaluation metrics and eight sub-pixel estimation methods. The tracking performance of a sub-pixel method varies depending on the evaluation metric used. This indicates that a reported tracking performance for a sub-pixel estimation method can be significantly different when combined with another evaluation metric. Also there is a large variation in the time needed for the motion estimations depending primarily on the sub-pixel method used but also on the evaluation metric.
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| 9. |
- Arvidsson, Jonathan, 1986, et al.
(författare)
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Automated estimation of in-plane nodule shape in chest tomosynthesis images
- 2015
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Ingår i: International Federation for Medical and Biological Engineering Proceedings. - Cham : Springer International Publishing. - 1680-0737. - 9783319129679 ; 48, s. 20-23
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Konferensbidrag (refereegranskat)abstract
- The purpose of this study was to develop an automated segmentation method for lung nodules in chest tomo-synthesis images. A number of simulated nodules of different sizes and shapes were created and inserted in two different locations into clinical chest tomosynthesis projections. The tomosynthesis volumes were then reconstructed using standard cone beam filtered back projection, with 1 mm slice interval. For the in-plane segmentation, the central plane of each nodule was selected. The segmentation method was formulated as an optimization problem where the nodule boundary corresponds to the minimum of the cost function, which is found by dynamic programming. The cost function was composed of terms related to pixel intensities, edge strength, edge direction and a smoothness constraint. The segmentation results were evaluated using an overlap measure (Dice index) of nodule regions and a distance measure (Hausdorff distance) between true and segmented nodule. On clinical images, the nodule segmentation method achieved a mean Dice index of 0.96 ± 0.01, and a mean Hausdorff distance of 0.5 ± 0.2 mm for isolated nodules and for nodules close to other lung structures a mean Dice index of 0.95 ± 0.02 and a mean Hausdorff distance of 0.5 ± 0.2 mm. The method achieved an acceptable accuracy and may be useful for area estimation of lung nodules.
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| 10. |
- Ask, Per, et al.
(författare)
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Certification of Clinical Engineers in Sweden
- 2009
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Ingår i: WORLD CONGRESS ON MEDICAL PHYSICS AND BIOMEDICAL ENGINEERING, VOL 25, PT 12. - Berlin, Heidelberg : Springer Science Business Media. - 1680-0737. ; 25:12, s. 430-431
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Tidskriftsartikel (refereegranskat)abstract
- The Swedish Society for Biomedical Engineering and Physics have certified clinical engineers since 1994. The certification is done on tow levels: Master of science and Bachelor of science. We have in total had 614 applications and certified 341 engineers We have certified a total of 341 persons of which 75 are at the master level and 266 at the bachelor level. We are pleased to note that through the years so many engineers have applied and have get a certification. The interest for applying was very large in the beginning but decreased after some years.
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