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- Morén, Björn, 1987-, et al.
(författare)
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Dosimetric impact of a robust optimization approach to mitigate effects from rotational uncertainty in prostate intensity‐modulated brachytherapy
- 2023
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Ingår i: Medical physics (Lancaster). - : WILEY. - 0094-2405 .- 2473-4209. ; 50:2, s. 1029-1043
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundIntensity-modulated brachytherapy (IMBT) is an emerging technology for cancer treatment, in which radiation sources are shielded to shape the dose distribution. The rotatable shields provide an additional degree of freedom, but also introduce an additional, directional, type of uncertainty, compared to conventional high-dose-rate brachytherapy (HDR BT). PurposeWe propose and evaluate a robust optimization approach to mitigate the effects of rotational uncertainty in the shields with respect to planning criteria. MethodsA previously suggested prototype for platinum-shielded prostate Yb-169-based dynamic IMBT is considered. We study a retrospective patient data set (anatomical contours and catheter placement) from two clinics, consisting of six patients that had previously undergone conventional Ir-192 HDR BT treatment. The Monte Carlo-based treatment planning software RapidBrachyMCTPS is used for dose calculations. In our computational experiments, we investigate systematic rotational shield errors of +/- 10 degrees and +/- 20 degrees, and the same systematic error is applied to all dwell positions in each scenario. This gives us three scenarios, one nominal and two with errors. The robust optimization approach finds a compromise between the average and worst-case scenario outcomes. ResultsWe compare dose plans obtained from standard models and their robust counterparts. With dwell times obtained from a linear penalty model (LPM), for 10 degrees errors, the dose to urethra (D0.1cc) and rectum (D0.1cc and D1cc) increase with up to 5% and 7%, respectively, in the worst-case scenario, while with the robust counterpart, the corresponding increases were 3% and 3%. For all patients and all evaluated criteria, the worst-case scenario outcome with the robust approach had lower deviation compared to the standard model, without compromising target coverage. We also evaluated shield errors up to 20 degrees and while the deviations increased to a large extent with the standard models, the robust models were capable of handling even such large errors. ConclusionsWe conclude that robust optimization can be used to mitigate the effects from rotational uncertainty and to ensure the treatment plan quality of IMBT.
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| 2. |
- Morén, Björn, 1987-, et al.
(författare)
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Optimization in treatment planning of high dose‐rate brachytherapy : Review and analysis of mathematical models
- 2021
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Ingår i: Medical Physics. - : Wiley-Blackwell Publishing Inc.. - 2473-4209 .- 0094-2405. ; 48:5, s. 2057-2082
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Forskningsöversikt (refereegranskat)abstract
- Treatment planning in high dose‐rate brachytherapy has traditionally been conducted with manual forward planning, but inverse planning is today increasingly used in clinical practice. There is a large variety of proposed optimization models and algorithms to model and solve the treatment planning problem. Two major parts of inverse treatment planning for which mathematical optimization can be used are the decisions about catheter placement and dwell time distributions. Both these problems as well as integrated approaches are included in this review. The proposed models include linear penalty models, dose–volume models, mean‐tail dose models, quadratic penalty models, radiobiological models, and multiobjective models. The aim of this survey is twofold: (i) to give a broad overview over mathematical optimization models used for treatment planning of brachytherapy and (ii) to provide mathematical analyses and comparisons between models. New technologies for brachytherapy treatments and methods for treatment planning are also discussed. Of particular interest for future research is a thorough comparison between optimization models and algorithms on the same dataset, and clinical validation of proposed optimization approaches with respect to patient outcome.
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| 3. |
- Morén, Björn, 1987-, et al.
(författare)
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Technical note: evaluation of a spatial optimization model for prostate high dose‐rate brachytherapy in a clinical treatment planning system
- 2023
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Ingår i: Medical physics (Lancaster). - : WILEY. - 0094-2405 .- 2473-4209. ; 50:2, s. 688-693
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundSpatial properties of a dose distribution, such as volumes of contiguous hot spots, are of clinical importance in treatment planning for high dose-rate brachytherapy (HDR BT). We have in an earlier study developed an optimization model that reduces the prevalence of contiguous hot spots by modifying a tentative treatment plan. PurposeThe aim of this study is to incorporate the correction of hot spots in a standard inverse planning workflow and to validate the integrated model in a clinical treatment planning system. The spatial function is included in the objective function for the inverse planning, as opposed to in the previous study where it was applied as a separate post-processing step. Our aim is to demonstrate that fine-adjustments of dose distributions, which are often performed manually in todays clinical practice, can be automated. MethodsA spatial optimization function was introduced in the treatment planning system RayStation (RaySearch Laboratories AB, Stockholm, Sweden) via a research interface. A series of 10 consecutive prostate patients treated with HDR BT was retrospectively replanned with and without the spatial function. ResultsOptimization with the spatial function decreased the volume of the largest contiguous hot spot by on average 31%, compared to if the function was not included. The volume receiving at least 200% of the prescription dose decreased by on average 11%. Target coverage, measured as the fractions of the clinical target volume (CTV) and the planning target volume (PTV) receiving at least the prescription dose, was virtually unchanged (less than a percent change for both metrics). Organs-at-risk received comparable or slightly decreased doses if the spatial function was included in the optimization model. ConclusionsOptimization of spatial properties such as the volume of contiguous hot spots can be integrated in a standard inverse planning workflow for brachytherapy, and need not be conducted as a separate post-processing step.
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| 4. |
- Rodhe, P., et al.
(författare)
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Modelling of peripheral fluid accumulation after a crystalloid bolus in female volunteers - a mathematical study
- 2010
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Ingår i: Computational and Mathematical Methods in Medicine. - : Taylor and Francis. - 1748-670X .- 1748-6718. ; 11:4, s. 341-351
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Tidskriftsartikel (refereegranskat)abstract
- Objective. To simultaneously model plasma dilution and urinary output in female volunteers. Methods. Ten healthy female non-pregnant volunteers, aged 21-39 years (mean 29), with a bodyweight of 58-67kg (mean 62.5kg) participated. No oral fluid or food was allowed between midnight and completion of the experiment. The protocol included an infusion of acetated Ringer's solution, 25ml/kg over 30min. Blood samples (4ml) were taken every 5min during the first 120min, and thereafter the sampling rate was every 10min until the end of the experiment at 240min. A standard bladder catheter connected to a drip counter to monitor urine excretion continuously was used. The data were analysed by empirical calculations as well as by a mathematical model. Results. Maximum urinary output rate was found to be 19 (13-31) ml/min. The subjects were likely to accumulate three times as much of the infused fluid peripherally as centrally; 1/=2.7 (2.0-5.7). Elimination efficacy, Eeff, was 24 (5-35), and the basal elimination kb was 1.11 (0.28-2.90). The total time delay Ttot of urinary output was estimated as 17 (11-31) min. Conclusion. The experimental results showed a large variability in spite of a homogenous volunteer group. It was possible to compute the infusion amount, plasma dilution and simultaneous urinary output for each consecutive time point and thereby the empirical peripheral fluid accumulation. The variability between individuals may be explained by differences in tissue and hormonal responses to fluid boluses, which needs to be further explored.
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