| 1. |
- Andersson, Peter, 1975, et al.
(författare)
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Cylindrical ionization chamber response in static and dynamic 6 and 15 MV photon beams
- 2023
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Ingår i: Biomedical Engineering & Physics Express. - : Institute of Physics. - 2057-1976. ; 9:2
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Tidskriftsartikel (refereegranskat)abstract
- Purpose. To investigate the response of the CC13 ionization chamber under non-reference photon beam conditions, focusing on penumbra and build-up regions of static fields and on dynamic intensity-modulated beams. Methods. Measurements were performed in 6 MV 100 × 100, 20 × 100, and 20 × 20 mm2 static fields. Monte Carlo calculations were performed for the static fields and for 6 and 15 MV dynamic beam sequences using a Varian multi-leaf collimator. The chamber was modelled using EGSnrc egs_chamber software. Conversion factors were calculated by relating the absorbed dose to air in the chamber air cavity to the absorbed dose to water. Correction and point-dose correction factors were calculated to quantify the conversion factor variations. Results. The correction factors for positions on the beam central axis and at the penumbra centre were 0.98-1.02 for all static fields and depths investigated. The largest corrections were obtained for chamber positions beyond penumbra centre in the off-axis direction. Point-dose correction factors were 0.54-0.71 at 100 mm depth and their magnitude increased with decreasing field size and measurement depth. Factors of 0.99-1.03 were obtained inside and near the integrated penumbra of the dynamic field at 100 mm depth, and of 0.92-0.94 beyond the integrated penumbra centre. The variations in the ionization chamber response across the integrated dynamic penumbra qualitatively followed the behaviour across penumbra of static fields. Conclusions. Without corrections, the CC13 chamber was of limited usefulness for profile measurements in 20-mm-wide fields. However, measurements in dynamic small irregular beam openings resembling the conditions of pre-treatment patient quality assurance were feasible. Uncorrected ionization chamber response could be applied for dose verification at 100 mm depth inside and close to large gradients of dynamically accumulating high- and low-dose regions assuming 3% tolerance between measured and calculated doses. © 2023 The Author(s).
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| 2. |
- Andersson, Patrik, et al.
(författare)
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Effects of lung tissue characterization in radiotherapy of breast cancer under deep inspiration breath hold when using Monte Carlo dosimetry
- 2021
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Ingår i: Physica medica (Testo stampato). - : Associazione Italiana di Fisica Medica. - 1120-1797 .- 1724-191X. ; 90, s. 83-90
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To investigate the sensitivity of Monte Carlo (MC) calculated lung dose distributions to lung tissue characterization in external beam radiotherapy of breast cancer under Deep Inspiration Breath Hold (DIBH). Methods: EGSnrc based MC software was employed. Mean lung densities for one hundred patients were analysed. CT number frequency and clinical dose distributions were calculated for 15 patients with mean lung density below 0.14 g/cm3. Lung volume with a pre-defined CT numbers was also considered. Lung tissue was characterized by applying different CT calibrations in the low-density region and air-lung tissue thresholds. Dose impact was estimated by Dose Volume Histogram (DVH) parameters. Results: Mean lung densities below 0.14 g/cm3 were found in 10% of the patients. CT numbers below −960 HU dominated the CT frequency distributions with a high rate of CT numbers at −990 HU. Mass density conversion approach influenced the DVH shape. V4Gy and V8Gy varied by 7% and 5% for the selected patients and by 9% and 3.5% for the pre-defined lung volume. V16Gy and V20Gy, were within 2.5%. Regions above 20 Gy were affected. Variations in air- lung tissue differentiation resulted in DVH parameters within 1%. Threshold at −990 HU was confirmed by the CT number frequency distributions. Conclusions: Lung dose distributions were more sensitive to variations in the CT calibration curve below lung (inhale) density than to air-lung tissue differentiation. Low dose regions were mostly affected. The dosimetry effects were found to be potentially important to 10% of the patients treated under DIBH.
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| 3. |
- Chakarova, Roumiana, et al.
(författare)
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A Monte Carlo evaluation of beam characteristics for total body irradiation at extended treatment distances
- 2014
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Ingår i: Journal of Applied Clinical Medical Physics. - 1526-9914. ; 15:3, s. 182-189
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Tidskriftsartikel (refereegranskat)abstract
- The aim is to study beam characteristics at large distances when focusing on the electron component. In particular, to investigate the utility of spoilers with various thicknesses as an electron source, as well as the effect of different spoiler-to-surface distances (STSD) on the beam characteristics and, consequently, on the dose in the superficial region. A MC model of a 15 MV Varian accelerator, validated earlier by experimental data at isocenter and extended distances used in large-field total body irradiation, is applied to evaluate beam characteristics at distances larger than 400 cm. Calculations are carried out using BEAMnrc/DOSXYZnrc code packages and phase space data are analyzed by the beam data processor BEAMdp. The electron component of the beam is analyzed at isocenter and extended distances, with and without spoilers as beam modifiers, assuming vacuum or air surrounding the accelerator head. Spoiler thickness of 1.6 cm is found to be optimal compared to thicknesses of 0.8 cm and 2.4 cm. The STSD variations should be taken into account when treating patients, in particular when the treatment protocols are based on a fixed distance to the patient central sagittal plane, and also, in order to maintain high dose in the superficial region.
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| 4. |
- Chakarova, Roumiana, et al.
(författare)
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An automated Monte Carlo QC system for volumetric modulated arc therapy: Possibilities and challenges
- 2018
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Ingår i: Physica Medica-European Journal of Medical Physics. - : Elsevier BV. - 1120-1797. ; 51, s. 32-37
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To develop and implement an automated Monte Carlo (MC) system for patient specific VMAT quality control in a patient geometry that generates treatment planning system (TPS) compliant DICOM objects and includes a module for 3D analysis of dose deviations. Also, the aims were to recommend diagnose specific tolerance criteria and an evaluation procedure. Methods: The EGSnrc code package formed the basis for development of the MC system. The workflow consists of a number of modules connected to a TPS by means of manual DICOM exports and imports which were executed sequentially without user interaction. DVH comparison was performed in the TPS. In addition, MC-and TPS dose distributions were analysed by applying the normalized dose difference (NDD) formalism. NDD failure maps and a pass rate for a certain threshold were obtained. 170 clinical plans (prostate, thorax, head-and-neck and gynecological) were selected for analysis. Results: Agreement within 1.5% was found between clinical-and MC data for the mean dose to the target volumes and within 3% for parameters more sensitive to the shape of the DVH e.g. D-98% PTV. Regarding the NDD analysis, tolerance criteria 2%/3 mm were established for prostate plans and 3%/3 mm for the rest of the cases. Conclusions: An automated MC system was developed and implemented. Evaluation procedure is recommended with NDD-analysis as a first step. For pass rate < 95%, the evaluation continues with comparison of DVH parameters. For deviations larger than 2%, a visual inspection of the clinical-and MC dose distributions is performed.
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| 5. |
- Chakarova, Roumiana, et al.
(författare)
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Monte Carlo optimization of total body irradiation in a phantom and patient geometry.
- 2013
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Ingår i: Physics in medicine and biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 58:8, s. 2461-9
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this work is to apply a Monte Carlo (MC) accelerator model, validated by experimental data at isocentre distances, to a large-field total body irradiation (TBI) technique and to develop a strategy for individual patient treatment on the basis of MC dose distributions. Calculations are carried out using BEAMnrc/DOSXYZnrc code packages for a 15 MV Varian accelerator. Acceptable agreement is obtained between MC data and measurements in a large water phantom behind a spoiler at source-skin distances (SSD) = 460cm as well as in a CIRS® thorax phantom. Dose distributions in patients are studied when simulating bilateral beam delivery at a distance of 480cm to the patient central sagittal plane. A procedure for individual improvement of the dose uniformity is suggested including the design of compensators in a conventional treatment planning system (TPS) and a subsequent update of the dose distribution. It is demonstrated that the dose uniformity for the simple TBI technique can be considerably improved. The optimization strategy developed is straightforward and suitable for clinics where the TPS available is deficient to calculate 3D dose distributions at extended SSD.
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| 6. |
- Chakarova, Roumiana, et al.
(författare)
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Superficial dose distribution in breast for tangential radiation treatment, Monte Carlo evaluation of Eclipse algorithms in case of phantom and patient geometries.
- 2011
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Ingår i: Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology. - : Elsevier BV. - 1879-0887.
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The aim of this study is to examine experimentally and by the Monte Carlo method the accuracy of the Eclipse Pencil Beam Convolution (PBC) and Analytical Anisotropic Algorithm (AAA) algorithms in the superficial region (0-2cm) of the breast for tangential photon beams in a phantom case as well as in a number of patient geometries. The aim is also to identify differences in how the patient computer tomography data are handled by the treatment planning system and in the Monte Carlo simulations in order to reduce influences of these effects on the evaluation. MATERIALS AND METHODS: Measurements by thermoluminescent dosimeters and gafchromic film are performed for six MV tangential irradiation of the cylindrical solid water phantom. Tangential treatment of seven patients is investigated considering open beams. Dose distributions are obtained by the Eclipse PBC and AAA algorithms. Monte Carlo calculations are carried out by BEAMnrc/DOSXYZnrc code package. Calculations are performed with a calculation grid of 1.25×1.25×5mm(3) for PBC and 2×2×5mm(3) for AAA and Monte Carlo, respectively. Dose comparison is performed in both dose and spatial domains by the normalized dose difference method. RESULTS: Experimental profiles from the surface toward the geometrical center of the cylindrical phantom are obtained at the beam entrance and exit as well as laterally. Full dose is received beyond 2mm in the lateral superficial region and beyond 7mm at the beam entrance. Good agreement between experimental, Monte Carlo and AAA data is obtained, whereas PBC is seen to underestimate the entrance dose the first 3-4mm and the lateral dose by more than 5% up to 8mm depth. In the patient cases considered, AAA and Monte Carlo show agreement within 3% dose and 4mm spatial tolerance. PBC systematically underestimates the dose at the breast apex. The dimensions of region out of tolerance vary with the local breast shape. Different interpretations of patient boundaries in Monte Carlo and the Eclipse are found to influence the evaluation. Computer tomography marker wire may introduce local disturbance effects on the comparison as well. These factors are not related to the accuracy of the calculation algorithms and their effect is taken into account in the evaluation. CONCLUSIONS: The accuracy of AAA in the case of the solid water phantom is comparable with that of the Monte Carlo method. The AAA-Monte Carlo differences in the patient cases considered are within 3%, 4mm tolerance. The PBC algorithm does not give equivalent results. In the phantom case, PBC underestimates the lateral dose by more than 5% up to 8mm depth. The PBC-Monte Carlo differences in the patient cases are outside the tolerance at the breast apex. The dimension of region varies with the breast shape being typically 8-10mm long and 6-8mm deep.
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| 7. |
- Hedin, Emma, 1985, et al.
(författare)
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Impact of lung density on the lung dose estimation for radiotherapy of breast cancer
- 2017
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Ingår i: Physics and Imaging in Radiation Oncology. - : Elsevier BV. - 2405-6316. ; 3, s. 5-10
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose: To investigate the impact of the clinical implementation particle transport method on the lung dose evaluation for radiotherapy of breast cancer focusing on dosimetric effects of the lung density. Material and methods: Fourteen patients with left sided breast cancer having both deep inspiration breath hold (DIBH) and free breathing CT scans were studied. Lung density variations for 157 patients treated under DIBH were quantified and the cases with the lowest lung densities for breast and for loco regional treatment added to the study. Dose calculations were performed with the class-b type algorithm AAA and the deterministic algorithm Acuros XB. Monte Carlo method was utilized as reference. Differences in the dose distributions were evaluated by comparing DVH parameters. Results: Lung density variations between 0.08 and 0.3 g/cm3 and between 0.02 and 0.25 g/cm3 were found for loco-regional and tangential breast treatments under DIBH, respectively. Lung DVH parameters for patients with medium and high lung density obtained by the different algorithms agreed within 3%. Larger differences were observed for low lung density cases where the correction based algorithm underestimated V10Gy and overestimated V40Gy by up to 5%. The least affected parameter, V20Gy, deviated by less than 2% for all cases and densities. Conclusions: Dosimetric constrains for lung based on V20Gy required minimum changes due to implementation of the new algorithm regardless of breathing technique or type of treatment. Evaluation criteria utilizing V10Gy or V40Gy needed reconsideration, especially for treatments under DIBH involving low lung density.
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| 8. |
- Hedin, Emma, 1985, et al.
(författare)
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Implementation of Acuros XB in Treatment Planning of SBRT of Lung Cancer
- 2017
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Ingår i: Annals of Radiation Therapy and Oncology. - 2577-8757. ; 1:2
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Tidskriftsartikel (refereegranskat)abstract
- Goal: The overall goal of this study is to present data assisting the implementation of the principle based dose calculation algorithm Acuros XB for Stereotactic Body Radiation Treatments (SBRT) of lung tumors. In particular, the goal is to investigate differences in target dose distributions calculated by the clinical algorithms AAA and Acuros XB as well as by the Monte Carlo method. Materials and Methods: Twenty conventional 3D conformal plans for SBRT of lung cancer were investigated. The prescribed dose was 3 Gy × 22 Gy at the center and 3 Gy × 15 Gy at the periphery of PTV. The plans were originally designed with AAA based on the requirement PTV-V100% (percentage of PTV receiving a dose larger than 100%=45 Gy), to be 100%. Recalculations were performed by utilizing Acuros XB as well as by full Monte Carlo method. Dose variations were evaluated in terms of DVH parameters D5%, D50%, D98% for GTV and PTV as well as PTV-V100%. Five plans showing large algorithm sensitivity in terms of PTV-V100% were re-planned by Acuros XB using the same treatment planning criteria. Results: AAA systematically overestimated the PTV dose compared to Acuros XB and Monte Carlo. Differences between AAA and Acuros XB of up to 8%, 10% and 5% were observed for PTV-D50%, PTV-D98% and PTV-V100%, correspondingly. The values obtained by the Monte Carlo method were up to 7% lower than these for Acuros XB. The variations in the PTV dose estimation could not be related to patient/plan characteristics like target volume, lung tissue volume included in the target or tumor proximity to the lung wall. The variations in the GTV parameters were smaller and the agreement between AAA and AXB as well as between Acuros XB and Monte Carlo was within 3%. Planning with Acuros XB increased the volume of the lung tissue close to the tumor receiving full dose by more than 20%. Conclusion: PTV dose coverage was overestimated in plans calculated by AAA. Transition to Acuros XB without changing the treatment planning criteria increased the dose to the lung tissue close to the tumor. The GTV dose coverage was more robust with respect to the algorithm changes.
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| 9. |
- Hedin, Emma, 1985, et al.
(författare)
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Jaw position uncertainty and adjacent fields in breast cancer radiotherapy.
- 2015
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Ingår i: Journal of applied clinical medical physics / American College of Medical Physics. - : Wiley. - 1526-9914. ; 16:6
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Tidskriftsartikel (refereegranskat)abstract
- Locoregional treatment of breast cancer involves adjacent, half blocked fields matched at isocenter. The objective of this work is to study the dosimetric effects of the uncertainties in jaw positioning for such a case, and how a treatment planning protocol including adjacent field overlap of 1 mm affects the dose distribution. A representative treatment plan, involving 6 and 15 photon beams, for a patient treated at our hospital is chosen. Monte Carlo method (EGSnrc/BEAMnrc) is used to simulate the treatment. Uncertainties in jaw positioning of ± 1 mm are addressed, which implies extremes in reality of 2 mm field gap/overlap when planning adjacent fields without overlap and 1 mm gap or 3 mm overlap for a planning protocol with 1 mm overlap. Dosimetric parameters for PTV, lung and body are analyzed. Treatment planning protocol with 1 mm overlap of the adjacent fields does not considerably counteract possible underdosage of the target in the case studied. PTV-V95% is for example reduced from 95% for perfectly aligned fields to 90% and 91% for 2 mm and 1 mm gap, respectively. However, the risk of overdosage in PTV and in healthy soft tissue is increased when following the protocol with 1 mm overlap. A 3 mm overlap compared to 2 mm overlap results in an increase in maximum dose to PTV, PTV-D2%, from 113% to 121%. V120% for 'Body-PTV' is also increased from 5 cm3 to 14 cm3. A treatment planning protocol with 1 mm overlap does not considerably improve the coverage of PTV in the case of erroneous jaw positions causing gap between fields, but increases the overdosage in PTV and doses to healthy tissue, in the case of overlapping fields, for the case investigated.
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| 10. |
- Lundstedt, Dan, 1970, et al.
(författare)
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Adjuvant Radiation Treatment of Breast Cancer After Mastectomy: Advanced Algorithms and Partial Bolus Improve the Dose Calculation Accuracy in the Case of Thin-Chest-Wall Irradiation
- 2023
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Ingår i: Advances in Radiation Oncology. - : Elsevier BV. - 2452-1094. ; 8:5
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The aim of this study was to examine measured and calculated dose distributions in a thin-chest-wall phantom and estimate the variations in the dose-volume histogram (DVH) parameters used in plan evaluation for patient geometries with chest-wall thicknesses <15 mm with and without bolus implementation. Methods and Materials: Measurements were made using thermoluminescent dosimeters in a chest-wall phantom. The Monte Carlo method, anisotropic analytical algorithm, and Acuros XB Eclipse algorithms were used to calculate dose distributions for clinical plans. DVH parameters for clinical target volume tumor (CTVT) and planning target volume (PTV) and mean doses were evaluated for 15 patients with a chest-wall thickness of 8 to 15 mm with and without partial bolus and for 10 patients with a chest-wall thickness of 20 to 25 mm without bolus. Results: Measurements showed that the dose at a depth of 2 to 12 mm at the beam entrance and laterally was within 90% of the dose at 8 mm depth. Monte Carlo and Acuros XB calculations were well aligned with the experimental data, whereas the anisotropic analytical algorithm underestimated the beam entrance and lateral doses. The DVH parameters for the patients with a thin chest wall were sensitive to calculation algorithm, resolution, body structure definition, and patient geometry. The parameters CTVTV95%, CTVTD98%, and PTVD98% were much lower than the tolerance criteria. Partial bolus improved the values for all algorithms and decreased the variations due to patient geometry. Dose calculations for patients with a chest-wall thickness of 20 to 25 mm resulted in sufficient target coverage and low dependence on patient geometry and calculation algorithm without the use of bolus. Conclusions: Dose calculations using advanced algorithms and resolution <2 mm are recommended for patients with a thin chest wall. Specific DVH criteria or the implementation of partial bolus was needed to facilitate plan development and evaluation for this patient group.
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