| 1. |
- Götstedt, Julia, et al.
(författare)
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Edge area metric complexity scoring of volumetric modulated arc therapy plans
- 2021
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Ingår i: Physics & Imaging in Radiation Oncology. - : Elsevier BV. - 2405-6316. ; 17, s. 124-129
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose: Aperture-based complexity metrics have been suggested as a method to score complexity of volumetric modulated arc therapy (VMAT) plans. The purpose of this study was to evaluate the edge area metric (EAM) for clinical VMAT plans on a control point and treatment plan level. Materials and methods: EAM on a control point level was evaluated based on film measurements of 18 static beam openings originating from VMAT plans. EAM on a treatment plan level (arithmetic mean value of EAM scores for control points) was evaluated based on measurements with the Delta(4)(R) for 200 VMAT plans for four different treatment sites: pelvic, thorax, head and neck, and prostate. Measurements were compared to calculations and dose difference and gamma pass rates were evaluated. Results: EAM scores on a control point level correlated with Pearson's r-values of -0.96 and -0.77 to dose difference and gamma pass rates, respectively. The prostate plans had the highest average EAM score. A connection between smaller PTVs and higher EAM scores was found. No correlation between the evaluation result and EAM on a plan level was found. Conclusions: EAM on a control point level was shown to correlate to the difference between measured and calculated 2D dose distributions of clinical VMAT beam openings. No correlation was found for EAM on a plan level for clinical treatment plans.
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| 2. |
- Götstedt, Julia
(författare)
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Evaluation of absorbed dose uncertainty in modulated radiotherapy plans
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of this work was to develop and evaluate methods to meet the challenges of quality control (QC) for modulated radiotherapy plans. It was shown that nine of 15 intensity modulated radiotherapy (IMRT) plans, with deliberately introduced dose errors larger than 5% in at least one evaluated dose volume histogram (DVH) metric, were not detected with a QC method which combined Delta4 (ScandiDos) measurements and internationally recommended criteria for evaluation (Paper I). The dose difference between calculation and high spatial resolution measurements, using EBT3 film and electronic portal imaging device (EPID), for 30 static beam apertures of varying size and shape was used as a measure of beam aperture complexity (Paper II). The linear correlation to the beam aperture complexity was evaluated for three aperture-based complexity metrics developed in this study and five other metrics suggested in the literature. The strongest correlation, with a Pearson’s r-value of -0.94, was found for the developed edge area metric (EAM). EAM was further evaluated for 18 static beam openings originating from control points of clinically used volumetric modulated arc therapy (VMAT) plans and for 200 full VMAT plans planned for different treatment sites (Paper III). The results indicated that the EAM must be interpreted differently for different diagnoses. Evaluation of beam aperture shape, modulation variations, measurements, and delivery simulations, as methods for assessment of the dosimetric uncertainty for VMAT plans, showed that the dosimetric uncertainty could differ even though the plans appeared to be equal based solely on dosimetric comparisons of the dose distributions, e.g., DVH metric evaluations (Paper IV). In conclusion, it is possible to decrease dosimetric uncertainties in modulated radiotherapy plans to enable a higher treatment quality. The dosimetric uncertainties can be assessed by different methods but it is important to define the purpose of the method, and to validate that the method fulfils the defined purpose.
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| 3. |
- Götstedt, Julia, et al.
(författare)
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Evaluation of measures related to dosimetric uncertainty of VMAT plans
- 2022
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914.
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Tidskriftsartikel (refereegranskat)abstract
- Dosimetric uncertainty is most often not included in the process of creating and selecting plans for treatment. Treatment planning and the physician's choice of treatment plan is instead often based only on evaluation of clinical goals of the calculated absorbed dose distribution. Estimation of the dosimetric uncertainty could potentially have impact in the process of comparing and selecting volumetric modulated arc therapy (VMAT) plans. In this study, different measures for estimation of dosimetric uncertainty based on treatment plan parameters for plans with similar dose distributions were evaluated. VMAT plans with similar dose distributions but with different treatment plan designs were created using three different optimization methods for each of ten patient cases (tonsil and prostate cancer). Two plans were optimized in Eclipse, one with and one without the use of aperture shape controller, and one plan was optimized in RayStation. The studied measures related to dosimetric uncertainty of treatment plans were aperture-based complexity metric analysis, investigation of modulation level of multi leaf collimator leaves, gantry speed and dose rate, quasi-3D measurements and evaluation of simulations of realistic delivery variations. The results showed that there can be variations in dosimetric uncertainty for treatment plans with similar dose distributions. Dosimetric uncertainty assessment could therefore have impact on the choice of plan to be used for treatment and lead to a decrease in the uncertainty level of the delivered absorbed dose distribution. This study showed that aperture shape complexity had a larger impact on dosimetric uncertainty compared to modulation level of MLC, gantry speed and dose rate.
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| 4. |
- Hernandez, Victor, et al.
(författare)
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What is plan quality in radiotherapy? The importance of evaluating dose metrics, complexity, and robustness of treatment plans.
- 2020
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Ingår i: Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology. - : Elsevier BV. - 1879-0887. ; 153, s. 26-33
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Tidskriftsartikel (refereegranskat)abstract
- Plan evaluation is a key step in the radiotherapy treatment workflow. Central to this step is the assessment of treatment plan quality. Hence, it is important to agree on what we mean by plan quality and to be fully aware of which parameters it depends on. We understand plan quality in radiotherapy as the clinical suitability of the delivered dose distribution that can be realistically expected from a treatment plan. Plan quality is commonly assessed by evaluating the dose distribution calculated by the treatment planning system (TPS). Evaluating the 3D dose distribution is not easy, however; it is hard to fully evaluate its spatial characteristics and we still lack the knowledge for personalising the prediction of the clinical outcome based on individual patient characteristics. This advocates for standardisation and systematic collection of clinical data and outcomes after radiotherapy. Additionally, the calculated dose distribution is not exactly the dose delivered to the patient due to uncertainties in the dose calculation and the treatment delivery, including variations in the patient set-up and anatomy. Consequently, plan quality also depends on the robustness and complexity of the treatment plan. We believe that future work and consensus on the best metrics for quality indices are required. Better tools are needed in TPSs for the evaluation of dose distributions, for the robust evaluation and optimisation of treatment plans, and for controlling and reporting plan complexity. Implementation of such tools and a better understanding of these concepts will facilitate the handling of these characteristics in clinical practice and be helpful to increase the overall quality of treatment plans in radiotherapy.
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| 5. |
- Terzidis, Emmanouil, 1994, et al.
(författare)
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Assessing the fraction of dose originating from the penumbra region for plans of varied complexity
- 2024
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Ingår i: European Congress of Radiation Oncology (2024.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Purpose: The absorbed dose delivered to the patient that originates from a penumbra region have larger uncertainties compared to the dose delivered from the center of the treatment field. 1,2 The magnitude of these uncertainties could be important input when evaluating absorbed dose to organs at risk (OARs) and target volumes. The aim of this work was to examine the fraction of penumbra dose in three-dimensions (3D) for volumetric modulated arc therapy (VMAT) plans of different complexities. Methods and Materials: A C# software was developed in our department, able to calculate the fraction of penumbra dose in relation to the total dose in each voxel and visualize it as a 3D distribution (penumbra map). Twelve treatment plans of previously treated patients have been selected to represent different types of treatment geometry and different treatment sites (prostate, head & neck, lung and gynecological cancer). The clinical plan used for the actual treatment of the patient was reoptimized in Eclipse TPS (Varian Medical Systems, Palo Alto, CA), to create one plan with reduced complexity (“simple plan”) and one of higher complexity (“complex plan”). These additional plans were generated by altering the monitor unit constraint and the aperture shape controller level, while retaining a similar dose distribution. The fraction of penumbra dose was calculated for both the clinical and the newly generated plans creating in total 36 penumbra maps. Results: The generated penumbra maps were able to highlight anatomical regions with high fraction of penumbra dose (e.g., above 50%). These regions were mostly observed outside the planning target volume (PTV), regardless of treatment site and complexity level. Generally, the fraction of penumbra dose, both inside and outside the PTV, was increased with increased plan complexity. The average fraction of penumbra dose for the body, PTV and an example OAR are shown in Table 1 across all analyzed plans. For certain cases, the absorbed dose in parts of OARs originated from penumbra regions to a considerable degree, even for the least complex version of the plan. Examples are shown in Figure 1 featuring the rectum in a prostate plan and the parotid glands in a head & neck plan. Conclusion: The proposed method functions as a tool for assessing the extent to which the dose to certain voxels is influenced by the penumbra. A link was established between increased complexity and increased mean fraction of penumbra dose. Therefore, this approach could be used to quantify the complexity of the treatment plan in 3D
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| 6. |
- Terzidis, Emmanouil, 1994, et al.
(författare)
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Different aspects of plan complexity in prostate VMAT plans
- 2023
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596.
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Konferensbidrag (refereegranskat)abstract
- In this work we evaluated VMAT plan complexity by using different methods and approaches: complexity related to the aperture shape, the nature of the dynamic delivery, the impact of delivery variations as well as complexity analyses based on measurements. Prostate cancer treatment plans with different levels of complexity were created for three different patient cases. The plans intended to be most complex were also scored to be the most complex according to the evaluation methods used. The results for the other plans were more diverse. The methods that included 3D spatial information on complexity gave additional information important for the analysis of clinical relevance. In order to use specific complexity estimation methods for taking clinical decisions it is essential to understand how different aspects of complexity are incorporated in each method.
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| 7. |
- Terzidis, Emmanouil, 1994, et al.
(författare)
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Uppskattning av dosimetriska osäkerheter baserat på andel dos från penumbraregionen för VMAT-planer av olika komplexitet
- 2023
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Ingår i: Nationellt möte om sjukhusfysik 2023.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Absorbed dose delivered to the patient from a penumbra region have higher uncertainties compared to the dose delivered from the center of the treatment field. The magnitude of these uncertainties could be important input when evaluating absorbed dose to organs at risk (OARs) and target volumes, especially for plans of increased complexity. The aim of this work was to examine the fraction of penumbra dose in 3D for VMAT plans of different complexities. Methods and Materials: A C# software was developed in our department, able to estimate the fraction of penumbral dose in relation to the total dose, in each voxel and visualize it as a 3D distribution (uncertainty map). Twelve treatment plans of previously treated patients have been selected to represent different types of treatment geometry and different types of diagnose (prostate, head & neck, lung and gynecological cancer). The clinical plan used for the actual treatment of the patient was reoptimized in Eclipse TPS (Varian Medical Systems, Palo Alto, CA), to create one plan with reduced complexity (“simple plan”) and one of higher complexity (“complex plan”). These additional plans were generated by altering the MU constraint and the aperture shape controller (ASC) level, while retaining a similar dose distribution. The fraction of penumbra dose was calculated for both the clinical and the newly generated plans creating in total 36 uncertainty maps. Results: The generated uncertainty maps were able to highlight anatomical regions with high fraction of penumbra dose (e.g., above 50%). These regions were mostly observed outside the planning target volume (PTV). Generally, the fraction of penumbra dose, both inside and outside the PTV, was increased with increased plan complexity. For certain cases, the absorbed dose in OARs originated from penumbra regions to a considerable degree, even for the least complex version of the plan. An example is shown for the rectum in Figure 1. This observation proves the importance of evaluating dosimetric uncertainty in 3D. Conclusion: A connection was established between dose uncertainty due to fraction of penumbra dose and plan complexity. Furthermore, it is important to evaluate this uncertainty on a 3D-voxel-level.
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