| 1. |
- Andersson, Karin M., 1989-, et al.
(författare)
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Evaluation of a metal artifact reduction algorithm in CT studies used for proton radiotherapy treatment planning
- 2014
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Ingår i: Journal of Applied Clinical Medical Physics. - : John Wiley & Sons. - 1526-9914. ; 15:5, s. 112-119
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Tidskriftsartikel (refereegranskat)abstract
- Metal objects in the body such as hip prostheses cause artifacts in CT images. When CT images degraded by artifacts are used for treatment planning of radiotherapy, the artifacts can yield inaccurate dose calculations and, for particle beams, erroneous penetration depths. A metal artifact reduction software (O-MAR) installed on a Philips Brilliance Big Bore CT has been tested for applications in treatment planning of proton radiotherapy. Hip prostheses mounted in a water phantom were used as test objects. Images without metal objects were acquired and used as reference data for the analysis of artifact-affected regions outside of the metal objects in both the O-MAR corrected and the uncorrected images. Water equivalent thicknesses (WET) based on proton stopping power data were calculated to quantify differences in the calculated proton beam penetration for the different image sets. The WET to a selected point of interest between the hip prostheses was calculated for several beam directions of clinical relevance. The results show that the calculated differences in WET relative to the reference case were decreased when the O-MAR algorithm was applied. WET differences up to 2.0 cm were seen in the uncorrected case while, for the O-MAR corrected case, the maximum difference was decreased to 0.4 cm. The O-MAR algorithm can significantly improve the accuracy in proton range calculations. However, there are some residual effects, and the use of proton beam directions along artifact streaks should only be used with caution and appropriate margins.
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| 2. |
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| 3. |
- Baubeta, Erik, et al.
(författare)
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No gadolinium K‐edge detected on the first clinical photon‐counting computed tomography scanner
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Ingår i: Journal of Applied Clinical Medical Physics. - 1526-9914. ; , s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- PurposeThis study aimed to elucidate whether gadolinium contrast in clinically relevant doses can be used with photon-counting computed tomography (PCCT) as an alternative contrast agent in clinical applications.Material/methodsA CTDI phantom with 3D printed rods filled with different concentrations of gadolinium and iodine contrast was scanned in a PCCT and an energy-integrated computed tomography (EICT). Attenuation values at different monoenergetic steps were extracted for each contrast concentration.ResultsFor PCCT, gadolinium reached an attenuation >100 HU (103 HU) at 40 keV with a concentration 5 mmol/L whereas the same level was reached at 50 keV (118 HU) for 10 mmol/L and 90 keV (114 HU) for 25 mmol/L. For iodine, the same level of attenuation was reached at 100 keV (106 HU) with a concentration 8.75 mg I/mL.For EICT the lowest gadolinium contrast concentration needed to reach >100 HU (108 HU) was 10 mmol/L at 50 keV. For 25 mmol/L 100 HU was reached at 100 keV. For iodine contrast 108 HU was reached at 110 keV for 8.75 mg I/mL.ConclusionNo K-edge potential or difference in attenuation curves between iodine and gadolinium contrast is detected on the first clinical available PCCT. Clinically relevant attenuation levels were barely achieved in this setting with gadolinium concentrations approved for human use. The results of this study suggest that, given current scanning technology, gadolinium is not a clinically useful contrast agent for computed tomography because no K-edge was detected.
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| 4. |
- Bujila, Robert, et al.
(författare)
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Applying three different methods of measuring CTDIfree air to the extended CTDI formalism for wide-beam scanners (IEC 60601-2-44) : a comparative study
- 2018
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Ingår i: Journal of Applied Clinical Medical Physics. - : John Wiley & Sons. - 1526-9914. ; 19:4, s. 281-289
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The weighted CT dose index (CTDIw) has been extended for a nominal total collimation width (nT) greater than 40 mm and relies on measurements of CTDfree air. The purpose of this work was to compare three methods of measuring CTDIfree air and subsequent calculations of CTDIw to investigate their clinical appropriateness.Methods: The CTDIfree air, for multiple nTs up to 160 mm, was calculated from (1) high-resolution air kerma profiles from a step-and-shoot translation of a liquid ionization chamber (LIC) (considered to be a dosimetric reference), (2) pencil ionization chamber (PIC) measurements at multiple contiguous positions, and (3) air kerma profiles obtained through the continuous translation of a solid-state detector. The resulting CTDIfree air was used to calculate the CTDIw, per the extended formalism, and compared.Results: The LIC indicated that a 40 mm nT should not be excluded from the extension of the CTDIw formalism. The solid-state detector differed by as much as 8% compared to the LIC. The PIC was the most straightforward method and gave equivalent results to the LIC.Conclusions: The CTDIw calculated with the latest CTDI formalism will differ most for 160 mm nTs (e.g., whole-organ perfusion or coronary CT angiography) compared to the previous CTDI formalism. Inaccuracies in the measurement of CTDIfree air will subsequently manifest themselves as erroneous calculations of the CTDIw, for nTs greater than 40 mm, with the latest CTDI formalism. The PIC was found to be the most clinically feasible method and was validated against the LIC.
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| 5. |
- 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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| 6. |
- Engström, Andreas, 1983, et al.
(författare)
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A case study of cost-benefit analysis in occupational radiological protection within the healthcare system ofSweden
- 2021
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 22, s. 295-304
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study was to demonstrate cases of cost-benefit analysis within healthcare, of how economic factors can be considered in occupational radiological protection, in agreement with the as low as reasonably achievable principle and present Swedish legislations. In the first part of the present study, a comparison of examples within health economics used by authorities and institutes in Sweden was made. The comparison focused on value of a statistical life, quality-adjusted life year, and monetary cost assigned to a unit of collective dose for radiation protection purposes (α-value). By this comparison, an α-value was determined as an interval between $45 and $450 per man-mSv, for the Swedish society in 2021. The α-value interval can be interpreted as following:. Less than $45 per man-mSv is a good investment. From $45 to $450 per man-mSv, other factors than costs and collective dose are important to consider. More than $450 per man-mSv is too expensive. In the second part of the present study, seven cases of cost-benefit analyses in occupational radiological protection were provided. The present study focused specifically on cases where the relevant factors were costs and collective dose. The present case study shows a large variation in costs per collective dose from different types of occupational radiological protection, used at Skaraborg Hospital in Sweden.
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| 7. |
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| 8. |
- Guo, H. H., et al.
(författare)
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A calibration CT mini-lung-phantom created by 3-D printing and subtractive manufacturing
- 2021
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 22:6, s. 183-190
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Tidskriftsartikel (refereegranskat)abstract
- We describe the creation and characterization of a calibration CT mini-lung-phantom incorporating simulated airways and ground-glass densities. Ten duplicate mini-lung-phantoms with Three-Dimensional (3-D) printed tubes simulating airways and gradated density polyurethane foam blocks were designed and built. Dimensional accuracy and CT numbers were measured using micro-CT and clinical CT scanners. Micro-CT images of airway tubes demonstrated an average dimensional variation of 0.038 mm from nominal values. The five different densities of incorporated foam blocks, simulating ground-glass, showed mean CT numbers (±standard deviation) of −897.0 ± 1.5, −844.1 ± 1.5, −774.1 ± 2.6, −695.3 ± 1.6, and −351.0 ± 3.7 HU, respectively. Three-Dimensional printing and subtractive manufacturing enabled rapid, cost-effective production of ground-truth calibration mini-lung-phantoms with low inter-sample variation that can be scanned simultaneously with the patient undergoing lung quantitative CT.
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| 9. |
- Gustafsson, Christian, et al.
(författare)
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Using C-Arm X-ray images from marker insertion to confirm the gold fiducial marker identification in an MRI-only prostate radiotherapy workflow
- 2018
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 19:6, s. 185-192
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Tidskriftsartikel (refereegranskat)abstract
- Prostate cancer radiotherapy workflows, solely based on magnetic resonance imaging (MRI), are now in clinical use. In these workflows, intraprostatic gold fiducial markers (GFM) show similar signal behavior as calcifications and bleeding in T2-weighted MRI-images. Accurate GFM identification in MRI-only radiotherapy workflows is therefore a major challenge. C-arm X-ray images (CkV-images), acquired at GFM implantation, could provide GFM position information and be used to confirm correct identification in T2-weighted MRI-images. This would require negligible GFM migration between implantation and MRI-imaging. Marker migration was therefore investigated. The aim of this study was to show the feasibility of using CkV-images to confirm GFM identification in an MRI-only prostate radiotherapy workflow. An anterior-posterior digitally reconstructed radiograph (DRR)-image and a mirrored posterior-anterior CkV-image were acquired two weeks apart for 16 patients in an MRI-only radiotherapy workflow. The DRR-image originated from synthetic CT-images (created from MRI-images). A common image geometry was defined between the DRR- and CkV-image for each patient. A rigid registration between the GFM center of mass (CoM) coordinates was performed and the distance between each of the GFM in the DRR- and registered CkV-image was calculated. The same methodology was used to assess GFM migration for 31 patients in a CT-based radiotherapy workflow. The distance calculated was considered a measure of GFM migration. A statistical test was performed to assess any difference between the cohorts. The mean absolute distance difference for the GFM CoM between the DRR- and CkV-image in the MRI-only cohort was 1.7 ± 1.4 mm. The mean GFM migration was 1.2 ± 0.7 mm. No significant difference between the measured total distances of the two cohorts could be detected (P = 0.37). This demonstrated that, a C-Arm X-ray image acquired from the GFM implantation procedure could be used to confirm GFM identification from MRI-images. GFM migration was present but did not constitute a problem.
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| 10. |
- 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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| 11. |
- Haraldsson, André, et al.
(författare)
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A Helical tomotherapy as a robust low-dose treatment alternative for total skin irradiation
- 2019
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 20:5, s. 44-54
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Tidskriftsartikel (refereegranskat)abstract
- Mycosis fungoides is a disease with manifestation of the skin that has traditionally been treated with electron therapy. In this paper, we present a method of treating the entire skin with megavoltage photons using helical tomotherapy (HT), verified through a phantom study and clinical dosimetric data from our first two treated patients. A whole body phantom was fitted with a wetsuit as bolus, and scanned with computer tomography. We accounted for variations in daily setup using virtual bolus in the treatment plan optimization. Positioning robustness was tested by moving the phantom, and recalculating the dose at different positions. Patient treatments were verified with in vivo film dosimetry and dose reconstruction from daily imaging. Reconstruction of the actual delivered dose to the patients showed similar target dose as the robustness test of the phantom shifted 10 mm in all directions, indicating an appropriate approximation of the anticipated setup variation. In vivo film measurements agreed well with the calculated dose confirming the choice of both virtual and physical bolus parameters. Despite the complexity of the treatment, HT was shown to be a robust and feasible technique for total skin irradiation. We believe that this technique can provide a viable option for Tomotherapy centers without electron beam capability.
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| 12. |
- Haraldsson, André, et al.
(författare)
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Surface-guided tomotherapy improves positioning and reduces treatment time : A retrospective analysis of 16 835 treatment fractions
- 2020
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 21:8, s. 139-148
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: In this study, we have quantified the setup deviation and time gain when using fast surface scanning for daily setup/positioning with weekly megavoltage computed tomography (MVCT) and compared it to daily MVCT. Methods: A total of 16 835 treatment fractions were analyzed, treated, and positioned using our TomoTherapy HD (Accuray Inc., Madison, USA) installed with a Sentinel optical surface scanning system (C-RAD Positioning AB, Uppsala, Sweden). Patients were positioned using in-room lasers, surface scanning and MVCT for the first three fractions. For the remaining fractions, in-room laser was used for setup followed by daily surface scanning with MVCT once weekly. The three-dimensional (3D) setup correction for surface scanning was evaluated from the registration between MVCT and the planning CT. The setup correction vector for the in-room lasers was assessed from the surface scanning and the MVCT to planning CT registration. The imaging time was evaluated as the time from imaging start to beam-on. Results: We analyzed 894 TomoTherapy treatment plans from 2012 to 2018. Of all the treatment fractions performed with surface scanning, 90 % of the residual errors were within 2.3 mm for CNS (N = 284), 2.9 mm for H&N (N = 254), 8.7 mm for thorax (N = 144) and 10.9 for abdomen (N = 134) patients. The difference in residual error between surface scanning and positioning with in-room lasers was significant (P < 0.005) for all sites. The imaging time was assessed as total imaging time per treatment plan, modality, and treatment site and found that surface scanning significantly reduced patient on-couch time compared to MVCT for all treatment sites (P < 0.005). Conclusions: The results indicate that daily surface scanning with weekly MVCT can be used with the current target margins for H&N, CNS, and thorax, with reduced imaging time.
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| 13. |
- Hedin, Emma, 1985, et al.
(författare)
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Influence of different dose calculation algorithms on the estimate of NTCP for lung complications.
- 2013
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Ingår i: Journal of applied clinical medical physics / American College of Medical Physics. - : Wiley. - 1526-9914. ; 14:5, s. 127-39
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Tidskriftsartikel (refereegranskat)abstract
- Due to limitations and uncertainties in dose calculation algorithms, different algorithms can predict different dose distributions and dose-volume histograms for the same treatment. This can be a problem when estimating the normal tissue complication probability (NTCP) for patient-specific dose distributions. Published NTCP model parameters are often derived for a different dose calculation algorithm than the one used to calculate the actual dose distribution. The use of algorithm-specific NTCP model parameters can prevent errors caused by differences in dose calculation algorithms. The objective of this work was to determine how to change the NTCP model parameters for lung complications derived for a simple correction-based pencil beam dose calculation algorithm, in order to make them valid for three other common dose calculation algorithms. NTCP was calculated with the relative seriality (RS) and Lyman-Kutcher-Burman (LKB) models. The four dose calculation algorithms used were the pencil beam (PB) and collapsed cone (CC) algorithms employed by Oncentra, and the pencil beam convolution (PBC) and anisotropic analytical algorithm (AAA) employed by Eclipse. Original model parameters for lung complications were taken from four published studies on different grades of pneumonitis, and new algorithm-specific NTCP model parameters were determined. The difference between original and new model parameters was presented in relation to the reported model parameter uncertainties. Three different types of treatments were considered in the study: tangential and locoregional breast cancer treatment and lung cancer treatment. Changing the algorithm without the derivation of new model parameters caused changes in the NTCP value of up to 10 percentage points for the cases studied. Furthermore, the error introduced could be of the same magnitude as the confidence intervals of the calculated NTCP values. The new NTCP model parameters were tabulated as the algorithm was varied from PB to PBC, AAA, or CC. Moving from the PB to the PBC algorithm did not require new model parameters; however, moving from PB to AAA or CC did require a change in the NTCP model parameters, with CC requiring the largest change. It was shown that the new model parameters for a given algorithm are different for the different treatment types.
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| 14. |
- 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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| 15. |
- Huss, Marie, et al.
(författare)
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Fractionated SRT using VMAT and Gamma Knife for brain metastases and gliomas - a planning study
- 2015
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 16:6, s. 3-16
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Tidskriftsartikel (refereegranskat)abstract
- Stereotactic radiosurgery using Gamma Knife (GK) or linear accelerators has been used for decades to treat brain tumors in one fraction. A new positioning system, Extend™, was introduced by Elekta AB for fractionated stereotactic radiotherapy (SRT) with GK. Another option for fractionated SRT is advanced planning and delivery using linacs and volumetric modulated arc therapy (VMAT). This project aims to assess the performance of GK Extend™ for delivering fractionated SRT by comparing GK treatments plans for brain targets performed using Leksell GammaPlan (LGP) with VMAT treatment plans. Several targets were considered for the planning: simulated metastasis- and glioma-like targets surrounding an organ at risk (OAR), as well as three clinical cases of metastases. Physical parameters such as conformity, gradient index, dose to OARs, and brain volume receiving doses above the threshold associated with risk of damaging healthy tissue, were determined and compared for the treatment plans. The results showed that GK produced better dose distributions for target volumes below 15 cm3, while VMAT results in better dose conformity to the target and lower doses to the OARs in case of fractionated treatments for large or irregular volumes. The volume receiving doses above a threshold associated with increased risk of damage to normal brain tissue was also smaller for VMAT. The GK consistently performed better than VMAT in producing a lower dose-bath to the brain. The above is subjected only to margin-dependent fractionated radiotherapy (CTV/PTV). The results of this study could lead to clinically significant decisions regarding the choice of the radiotherapy technique for brain targets.
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| 16. |
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| 17. |
- Jamtheim Gustafsson, Christian, et al.
(författare)
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Deep learning-based classification and structure name standardization for organ at risk and target delineations in prostate cancer radiotherapy
- 2021
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Ingår i: Journal of Applied Clinical Medical Physics. - : John Wiley & Sons. - 1526-9914. ; 22:12, s. 51-63
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Tidskriftsartikel (refereegranskat)abstract
- Radiotherapy (RT) datasets can suffer from variations in annotation of organ at risk (OAR) and target structures. Annotation standards exist, but their description for prostate targets is limited. This restricts the use of such data for supervised machine learning purposes as it requires properly annotated data. The aim of this work was to develop a modality independent deep learning (DL) model for automatic classification and annotation of prostate RT DICOM structures.Delineated prostate organs at risk (OAR), support- and target structures (gross tumor volume [GTV]/clinical target volume [CTV]/planning target volume [PTV]), along with or without separate vesicles and/or lymph nodes, were extracted as binary masks from 1854 patients. An image modality independent 2D InceptionResNetV2 classification network was trained with varying amounts of training data using four image input channels. Channel 1–3 consisted of orthogonal 2D projections from each individual binary structure. The fourth channel contained a summation of the other available binary structure masks. Structure classification performance was assessed in independent CT (n = 200 pat) and magnetic resonance imaging (MRI) (n = 40 pat) test datasets and an external CT (n = 99 pat) dataset from another clinic.A weighted classification accuracy of 99.4% was achieved during training. The unweighted classification accuracy and the weighted average F1 score among different structures in the CT test dataset were 98.8% and 98.4% and 98.6% and 98.5% for the MRI test dataset, respectively. The external CT dataset yielded the corresponding results 98.4% and 98.7% when analyzed for trained structures only, and results from the full dataset yielded 79.6% and 75.2%. Most misclassifications in the external CT dataset occurred due to multiple CTVs and PTVs being fused together, which was not included in the training data.Our proposed DL-based method for automated renaming and standardization of prostate radiotherapy annotations shows great potential. Clinic specific contouring standards however need to be represented in the training data for successful use. Source code is available at https://github.com/jamtheim/DicomRTStructRenamerPublic
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| 18. |
- Konst, B., et al.
(författare)
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Image quality and radiation dose in planar imaging — Image quality figure of merits from the CDRAD phantom
- 2019
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 20:7, s. 151-159
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: A contrast-detail phantom such as CDRAD is frequently used for quality assurance, optimization of image quality, and several other purposes. However, it is often used without considering the uncertainty of the results. The aim of this study was to assess two figure of merits (FOM) originating from CDRAD regarding the variations of the FOMs by dose utilized to create the x-ray image. The probability of overlapping (assessing an image acquired at a lower dose as better than an image acquired at a higher dose) was determined. Methods: The CDRAD phantom located underneath 12, 20, and 26cm PMMA was imaged 16 times at five dose levels using an x-ray system with a flat-panel detector. All images were analyzed by CDRAD Analyser, version 1.1, which calculated the FOM inverse image quality figure (IQFinv) and gave contrast detail curves for each image. Inherent properties of the CDRAD phantom were used to derive a new FOM h, which describes the size of the hole with the same diameter and depth that is just visible. Data were analyzed using heteroscedastic regression of mean and variance by dose. To ease interpretation, probabilities for overlaps were calculated assuming normal distribution, with associated bootstrap confidence intervals. Results: The proportion of total variability in IQFinv, explained by the dose (R2), was 91%, 85%, and 93% for 12, 20, and 26cm PMMA. Corresponding results for h were 91%, 89%, and 95%. The overlap probability for different mAs levels was 1% for 0.8 vs 1.2mAs, 5% for 1.2 vs 1.6mAs, 10% for 1.6 vs 2.0mAs, and 10% for 2.0mAs vs 2.5mAs for 12cm PMMA. For 20cm PMMA, it was 0.5% for 10 vs 16mAs, 13% for 16 vs 20mAs, 14% for 20 vs 25mAs, and 14% for 25 vs 32mAs. For 26cm PMMA, the probability varied from 0% to 6% for various mAs levels. Even though the estimated probability for overlap was small, the 95% confidence interval (CI) showed relatively large uncertainties. For 12cm PMMA, the associated CI for 0.8 vs 1.2mAs was 0.1–3.2%, and the CI for 1.2 vs 1.6mAs was 2.1–7.8%. Conclusions: Inverse image quality figure and h are about equally related to dose level. The FOM h, which describes the size of a hole that should be seen in the image, may be a more intuitive FOM than IQFinv. However, considering the probabilities for overlap and their confidence intervals, the FOMs deduced from the CDRAD phantom are not sensitive to dose. Hence, CDRAD may not be an optimal phantom to differentiate between images acquired at different dose levels. © 2019 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.
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| 19. |
- Konst, Bente, et al.
(författare)
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Novel method to determine recursive filtration and noise reduction in fluoroscopic imaging - a comparison of four different vendors.
- 2021
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Ingår i: Journal of applied clinical medical physics. - : Wiley. - 1526-9914. ; 22:1, s. 281-292
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Tidskriftsartikel (refereegranskat)abstract
- This study attempted to develop a method to measure the applied recursive filtration and to determine the noise reduction of four different fluoroscopic systems. The study also attempted to elucidate the importance of considering the recursive filter for quality control tests concerning signal-to-noise ratio (SNR) or image quality. The vendor's settings for recursive filtration factor (β) are, unfortunately, often not available. Hence, a method to determine the recursive filtration and associated noise reduction would be useful.The recursive filter was determined by using a single fluoroscopic series and the method presented in this study. The theoretical noise reduction based on the choice of β was presented. In addition, the corresponding noise reduction, evaluated as the ratio of the standard deviation of the pixel value between a series with β equal to zero (recursive filtration off) and β>0, was determined for different pulse rates given by pulses per second (pps), doses (mAs) and recursive filter. The images were acquired using clinically relevant radiation quality and quantity.The presented method to measure the recursive filter exhibited high accuracy (1.08%) and precision (1.48%). The recursive filtration and noise reduction were measured for several settings for each vendor. The recursive filtration settings and associated recursive filtration factors for four different vendors were presented.This study presented an accurate method to determine applied recursive filtration, which was easy to determine. Hence, for all quality control purposes, including noise evaluation, it was possible to consider the essential noise reduction given by the settings for recursive filtration. It was also possible to compare the recursive filtration settings and associated recursive filtration within and between vendors.
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| 20. |
- Konst, Bente, et al.
(författare)
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Optimization of photon counting CT for cardiac imaging in patients with left ventricular assist devices: An in-depth assessment of metal artifacts
- 2024
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Ingår i: Journal of Applied Clinical Medical Physics. - : WILEY. - 1526-9914.
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Tidskriftsartikel (refereegranskat)abstract
- PurposePhoton counting CT (PCCT) holds promise for mitigating metal artifacts and can produce virtual mono-energetic images (VMI), while maintaining temporal resolution, making it a valuable tool for characterizing the heart. This study aimed to evaluate and optimize PCCT for cardiac imaging in patients during left ventricular assistance device (LVAD) therapy by conducting an in-depth objective assessment of metal artifacts and visual grading.MethodsVarious scan and reconstruction settings were tested on a phantom and further evaluated on a patient acquisition to identify the optimal protocol settings. The phantom comprised an empty thoracic cavity, supplemented with heart and lungs from a cadaveric lamb. The heart was implanted with an LVAD (HeartMate 3) and iodine contrast. Scans were performed on a PCCT (NAEOTOM Alpha, Siemens Healthcare). Metal artifacts were assessed by three objective methods: Hounsfield units (HU)/SD measurements (DiffHU and SDARTIFACT), Fourier analysis (AmplitudeLowFreq), and depicted LVAD volume in the images (BloomVol). Radiologists graded metal artifacts and the diagnostic interpretability in the LVAD lumen, cardiac tissue, lung tissue, and spinal cord using a 5-point rating scale. Regression and correlation analysis were conducted to determine the assessment method most closely associated with acquisition and reconstruction parameters, as well as the objective method demonstrating the highest correlation with visual grading.ResultsDue to blooming artifacts, the LVAD volume fluctuated between 27.0 and 92.7 cm3. This variance was primarily influenced by kVp, kernel, keV, and iMAR (R2 = 0.989). Radiologists favored pacemaker iMAR, 3 mm slice thickness, and T3D keV and kernel Bv56f for minimal metal artifacts in cardiac tissue assessment, and 110 keV and Qr40f for lung tissue interpretation. The model adequacy for DiffHU SDARTIFACT, AmplitueLowFreq, and BloomVol was 0.28, 0.76, 0.29, and 0.99 respectively for phantom data, and 0.95, 0.98, 1.00, and 0.99 for in-vivo data. For in-vivo data, the correlation between visual grading (VGSUM) and DiffHU SDARTIFACT, AmplitueLowFreq, and BloomVol was -0.16, -0.01, -0.48, and -0.40 respectively.ConclusionWe found that optimal scan settings for LVAD imaging involved using 120 kVp and IQ level 80. Employing T3D with pacemaker iMAR, the sharpest allowed vascular kernel (Bv56f), and VMI at 110 keV with kernel Qr40 yields images suitable for cardiac imaging during LVAD-therapy. Volumetric measurements of the LVAD for determination of the extent of blooming artifacts was shown to be the best objective method to assess metal artifacts.
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| 21. |
- Konst, B., et al.
(författare)
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Radiographic and fluoroscopic X-ray systems: Quality control of the X-ray tube and automatic exposure control using theoretical spectra to determine air kerma and dose to a homogenous phantom
- 2021
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 22:8, s. 204-218
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Tidskriftsartikel (refereegranskat)abstract
- Purpose To develop a method to perform quality control (QC) of X-ray tubes and automatic exposure control (AEC) as a part of the QC of the radiographic and fluoroscopic X-ray system. Our aim is to verify the output from the X-ray tube by comparing the measured radiation output, or air kerma, to the theoretical output given the applied exposure settings and geometry, in addition to comparing the measured kV to the nominal kV. The AEC system for fluoroscopic and conventional X-ray systems is assessed by determining the absorbed dose to a homogenous phantom with different thicknesses. Method This study presents a model to verify the X-ray tube measurement results and a method to determine the dose to a homogenous phantom (D-phantom). The following input is needed: a parameterized model of the X-ray spectrum, the X-ray tube measurements using a multifunctional X-ray meter, the exposure parameters recorded via imaging of polymethyl methacrylate (PMMA) slabs of different thickness that simulate the patient using AEC, and a parameterized model for calculating the dose to water from Monte Carlo simulations. The output is the entrance surface dose (ESD) and absorbed dose in the phantom, D-phantom (mu Gy). In addition, the parameterized X-ray spectrum is used to compare theoretical and measured air kerma as a part of the QC of the X-ray tube. To verify the proposed method, the X-ray spectrum provided in this study, SPECTRUM, was compared to two commercially available spectra, SpekCalc and Institute of Physics and Engineering in Medicine (IPEM) 78. The fraction of energy imparted to the homogenous phantom was compared to the imparted fraction calculated by PCXMC. Results The spectrum provided in this study was in good agreement with two previously published X-ray spectra. The absolute percentage differences of the spectra varied from 0.05% to 3.9%, with an average of 1.4%, compared to SpekCalc. Similarly, the deviation from IPEM report 78 varied from 0.02% to 2.3%, with an average of 0.74%. The SPECTRUM was parameterized for calculation of the imparted fraction for target angles of 10 degrees, 12 degrees, and 15 degrees, kV (50-150 kV) with the materials Al (2.2-8 mm), Cu (0-1 mm), and any combination of the filters, PMMA and water. The deviation of energy imparted from the results by PCXMC was less than 8% for all measurements across different kV, filtration, and vendors, obtained by using PMMA to record the exposure parameters, while the dose was calculated based on water with same thicknesses as the PMMA. Conclusion This study presents an accurate and suitable method to perform a part of the QC of fluoroscopic and conventional X-ray systems with respect to the X-ray tube and the associated AEC system. The method is suitable for comparing protocols within and between systems via the absorbed dose.
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| 22. |
- Kügele, Malin, et al.
(författare)
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Dosimetric effects of intrafractional isocenter variation during deep inspiration breath-hold for breast cancer patients using surface-guided radiotherapy
- 2018
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 19:1, s. 25-38
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to investigate potential dose reductions to the heart, left anterior descending coronary artery (LAD), and ipsilateral lung for left-sided breast cancer using visually guided deep inspiration breath-hold (DIBH) with the optical surface scanning system Catalyst™, and how these potential dosimetric benefits are affected by intrafractional motion in between breath holds. For both DIBH and free breathing (FB), treatment plans were created for 20 tangential and 20 locoregional left-sided breast cancer patients. During DIBH treatment, beam-on was triggered by a region of interest on the xiphoid process using a 3 mm gating window. Using a novel nonrigid algorithm, the Catalyst™ system allows for simultaneous real-time tracking of the isocenter position, which was used to calculate the intrafractional DIBH isocenter reproducibility. The 50% and 90% cumulative probabilities and maximum values of the intrafractional DIBH isocenter reproducibility were calculated and to obtain the dosimetric effect isocenter shifts corresponding to these values were performed in the treatment planning system. For both tangential and locoregional treatment, the dose to the heart, LAD and ipsilateral lung was significantly reduced for DIBH compared to FB. The intrafractional DIBH isocenter reproducibility was very good for the majority of the treatment sessions, with median values of approximately 1 mm in all three translational directions. However, for a few treatment sessions, intrafractional DIBH isocenter reproducibility of up to 5 mm was observed, which resulted in large dosimetric effects on the target volume and organs at risk. Hence, it is of importance to set tolerance levels on the intrafractional isocenter motion and not only perform DIBH based on the xiphoid process.
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| 23. |
- Kügele, Malin, et al.
(författare)
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Surface guided radiotherapy (SGRT) improves breast cancer patient setup accuracy
- 2019
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; , s. 61-68
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The purpose of the study was to investigate if surface guided radiotherapy (SGRT) can decrease setup deviations for tangential and locoregional breast cancer patients compared to conventional laser-based setup (LBS). Materials and Methods: Both tangential (63 patients) and locoregional (76 patients) breast cancer patients were enrolled in this study. For LBS, the patients were positioned by aligning skin markers to the room lasers. For the surface based setup (SBS), an optical surface scanning system was used for daily setup using both single and three camera systems. To compare the two setup methods, the patient position was evaluated using verification imaging (field images or orthogonal images). Results: For both tangential and locoregional treatments, SBS decreased the setup deviation significantly compared to LBS (P < 0.01). For patients receiving tangential treatment, 95% of the treatment sessions were within the clinical tolerance of ≤ 4 mm in any direction (lateral, longitudinal or vertical) using SBS, compared to 84% for LBS. Corresponding values for patients receiving locoregional treatment were 70% and 54% for SBS and LBS, respectively. No significant difference was observed comparing the setup result using a single camera system or a three camera system. Conclusions: Conventional laser-based setup can with advantage be replaced by surface based setup. Daily SGRT improves patient setup without additional imaging dose to breast cancer patients regardless if a single or three camera system was used.
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| 24. |
- Lempart, Michael, et al.
(författare)
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Deep learning-based classification of organs at risk and delineation guideline in pelvic cancer radiation therapy
- 2023
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Ingår i: Journal of Applied Clinical Medical Physics. - 1526-9914. ; 24:9
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Tidskriftsartikel (refereegranskat)abstract
- Deep learning (DL) models for radiation therapy (RT) image segmentation require accurately annotated training data. Multiple organ delineation guidelines exist; however, information on the used guideline is not provided with the delineation. Extraction of training data with coherent guidelines can therefore be challenging. We present a supervised classification method for pelvis structure delineations where bowel cavity, femoral heads, bladder, and rectum data, with two guidelines, were classified. The impact on DL-based segmentation quality using mixed guideline training data was also demonstrated. Bowel cavity was manually delineated on CT images for anal cancer patients (n = 170) according to guidelines Devisetty and RTOG. The DL segmentation quality from using training data with coherent or mixed guidelines was investigated. A supervised 3D squeeze-and-excite SENet-154 model was trained to classify two bowel cavity delineation guidelines. In addition, a pelvis CT dataset with manual delineations from prostate cancer patients (n = 1854) was used where data with an alternative guideline for femoral heads, rectum, and bladder were generated using commercial software. The model was evaluated on internal (n = 200) and external test data (n = 99). By using mixed, compared to coherent, delineation guideline training data mean DICE score decreased 3% units, mean Hausdorff distance (95%) increased 5 mm and mean surface distance (MSD) increased 1 mm. The classification of bowel cavity test data achieved 99.8% unweighted classification accuracy, 99.9% macro average precision, 97.2% macro average recall, and 98.5% macro average F1. Corresponding metrics for the pelvis internal test data were all 99% or above and for the external pelvis test data they were 96.3%, 96.6%, 93.3%, and 94.6%. Impaired segmentation performance was observed for training data with mixed guidelines. The DL delineation classification models achieved excellent results on internal and external test data. This can facilitate automated guideline-specific data extraction while avoiding the need for consistent and correct structure labels.
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| 25. |
- Lorentsson, Robert, 1969, et al.
(författare)
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Comparison of the low-contrast detectability of two ultrasound systems using a grayscale phantom
- 2016
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 17:6, s. 366-378
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the present study was to use a commercially available grayscale phantom to compare two ultrasound systems regarding their ability to reproduce clinically relevant low-contrast objects at different sizes and depths, taking into account human observer variability and other methodological issues related to observer performance studies. One high-end and one general ultrasound scanner from the same manufacturer using the same probe were included. The study was intended to simulate the clinical situation where small low-contrast objects are embedded in relatively homogeneous organs. Images containing 4 and 6.4 mm objects of four different contrasts were acquired from the grayscale phantom at different depths. Six observers participated in a 4-alternative forced-choice study based on 960 images. Case sample and human observer variabilities were taken into account using bootstrapping. At four of sixteen depth/size/contrast combinations, the visual performance of the high-end scanner was significantly higher. Thus, it was possible to use a grayscale phantom to discriminate between the two evaluated ultrasound systems in terms of their ability to reproduce clinically relevant low-contrast objects. However, the number of images and number of observers were larger than those usually used for constancy control.
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| 26. |
- Lorentsson, Robert, 1969, et al.
(författare)
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Method for automatic detection of defective ultrasound linear array transducers based on uniformity assessment of clinical images - A case study
- 2018
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 19:2, s. 265-274
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the present study was to test an idea of and describe a concept of a novel method of detecting defects related to horizontal nonuniformities in ultrasound equipment. The method is based on the analysis of ultrasound images collected directly from the clinical workflow. In total over 31000 images from three ultrasound scanners from two vendors were collected retrospectively from a database. An algorithm was developed and applied to the images, 150 at a time, for detection of systematic dark regions in the superficial part of the images. The result was compared with electrical measurements (FirstCall) of the transducers, performed at times when the transducers were known to be defective. The algorithm made similar detection of horizontal nonuniformities for images acquired at different time points over long periods of time. The results showed good subjective visual agreement with the available electrical measurements of the defective transducers, indicating a potential use of clinical images for early and automatic detection of defective transducers, as a complement to quality control.
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| 27. |
- Mavroidis, Panayiotis, et al.
(författare)
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Expected clinical impact of the differences between planned and delivered dose distributions in helical tomotherapy for treating head and neck cancer using helical megavoltage CT images.
- 2009
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 10:3, s. 2969-
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Tidskriftsartikel (refereegranskat)abstract
- Helical Tomotherapy (HT) has become increasingly popular over the past few years. However, its clinical efficacy and effectiveness continues to be investigated. Pre-treatment patient repositioning in highly conformal image-guided radiation therapy modalities is a prerequisite for reducing setup uncertainties. A MVCT image set has to be acquired to account for daily changes in the patient's internal anatomy and setup position. Furthermore, a comparison should be performed to the kVCT study used for dosimetric planning, by a registration process which results in repositioning the patient according to specific transitional and rotational shifts. Different image registration techniques may lead to different repositioning of the patient and, as a result, to varying delivered doses. This study aims to investigate the expected effect of patient setup correction using the Hi-Art tomotherapy system by employing radiobiological measures such as the biologically effective uniform dose (BEUD) and the complication-free tumor control probability (P+). In this study, a typical case of lung cancer with metastatic head & neck disease was investigated by developing a Helical Tomotherapy plan. For the Tomotherapy HiArt plan, the dedicated Tomotherapy treatment planning station was used. Three dose distributions (planned and delivered with and without patient setup correction) were compared based on radiobiological measures by using the P+ index and the BEUD concept as the common prescription point of the plans and plotting the tissue response probabilities against the mean target dose for a range of prescription doses. The applied plan evaluation method shows that in this cancer case the planned and delivered dose distributions with and without patient setup correction give a P+ of 81.6%, 80.9% and 72.2%, for a BEUD to the planning target volume (PTV) of 78.0Gy, 77.7Gy and 75.4Gy, respectively. The corresponding tumor control probabilities are 86.3%, 85.1% and 75.1%, whereas the total complication probabilities are 4.64%, 4.20% and 2.89%, respectively. HT can encompass the often large PTV required while minimizing the volume of the organs at risk receiving high dose. However, the effectiveness of a HT treatment plan can be considerably deteriorated if an accurate patient setup system is not available. Taking into account the dose-response relations of the irradiated tumors and normal tissues, a radiobiological treatment plan evaluation can be performed, which may provide a closer association of the delivered treatment with the clinical outcome. In such situations, for effective evaluation and comparison of different treatment plans, traditional dose based evaluation tools can be complemented by the use of P+,BEUD diagrams.
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| 28. |
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| 29. |
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| 30. |
- Palmér, Emilia, et al.
(författare)
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Cone beam CT for QA of synthetic CT in MRI only for prostate patients
- 2018
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 19:6, s. 44-52
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Magnetic resonance imaging (MRI)-only radiotherapy is performed without computed tomography (CT). A synthetic CT (sCT) is used for treatment planning. The aim of this study was to develop a clinically feasible quality assurance (QA) procedure for sCT using the kV-cone beam CT (CBCT), in an MRI-only workflow for prostate cancer patients. Material and method: Three criteria were addressed; stability in Hounsfield Units (HUs), deviations in HUs between the CT and CBCT, and validation of the QA procedure. For the two first criteria, weekly phantom measurements were performed. For the third criteria, sCT, CT, and CBCT for ten patients were used. Treatment plans were created based on the sCT (MriPlannerTM). CT and CBCT images were registered to the sCT. The treatment plan was copied to the CT and CBCT and recalculated. Dose–volume histogram (DVH) metrics were used to evaluate dosimetric differences between the sCT plan and the recalculated CT and CBCT plans. HU distributions in sCT, CT, and CBCT were compared. Well-defined errors were introduced in the sCT for one patient to evaluate efficacy of the QA procedure. Results: The kV-CBCT system was stable in HU over time (standard deviation <40 HU). Variation in HUs between CT and CBCT was <60 HU. The differences between sCT–CT and sCT–CBCT dose distributions were below or equal to 1.0%. The highest mean dose difference for the CT and CBCT dose distribution was 0.6%. No statistically significant difference was found between total mean dose deviations from recalculated CT and CBCT plans, except for femoral head. Comparing HU distributions, the CBCT appeared to be similar to the CT. All introduced errors were identified by the proposed QA procedure, except all tissue compartments assigned as water. Conclusion: The results in this study shows that CBCT can be used as a clinically feasible QA procedure for MRI-only radiotherapy of prostate cancer patients.
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| 31. |
- Palmér, Emilia, 1993, et al.
(författare)
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Head and neck cancer patient positioning using synthetic CT data in MRI-only radiation therapy.
- 2022
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Ingår i: Journal of applied clinical medical physics. - : Wiley. - 1526-9914. ; 23:4
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Tidskriftsartikel (refereegranskat)abstract
- The accuracy and precision of patient positioning is crucial in radiotherapy; however, there are no publications available using synthetic computed tomography (sCT) that evaluate rotations in head and neck (H&N) patients positioning or the effect of translation and rotation combined. The aim of this work was to evaluate the differences between using sCT with the CT for 2D- and 3D-patient positioning in a magnetic resonance imaging (MRI)-only workflow.This study included 14 H&N cancer patients, with generated sCT data (MRI Planner v2.2) and the CT deformably registered to the MRI. Patient positioning was evaluated by comparing sCT against CT data: 3D cone beam CT (CBCT) was registered to the deformed CT (dCT) and sCT in six degrees of freedom (DoF) with a rigid auto-registration algorithm and bone threshold, and 2D deformed digital reconstructed radiographs (dDRR) and synthetic DRRs (sDRR) were manually registered to orthogonal projections in five DoF by six blinded observers. The difference in displacement in all DoF were calculated for dCT and sCT, as well as for dDRR and sDRR. The interobserver variation was evaluated by separate application of the paired dDRR and sDRR registration matrices to the original coordinates of the planning target volume (PTV) structures and calculation of the Euclidean distance between the corresponding points. The Dice similarity coefficient (DSC) was calculated between dDRR/sDRR-registered PTVs.The mean difference in patient positioning using CBCT was<0.7mm and<0.3° and using orthogonal projections<0.4mm and<0.2° in all directions. The maximum Euclidean distance was 5.1mm, the corresponding mean (1SD) Euclidean distance and mean DSC were 3.5 ± 0.7mm and 0.93, respectively.This study shows that the sCT-based patient positioning gives a comparable result with that based on CT images, allowing sCT to replace CT as reference for patient treatment positioning.
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| 32. |
- Pettersson, Niclas, 1974, et al.
(författare)
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Intrafractional relationship changes between an external breathing signal and fiducial marker positions in pancreatic cancer patients
- 2020
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 21:3, s. 153-161
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose The purpose of this study of pancreatic cancer patients treated with respiratory-guided stereotactic body radiotherapy (SBRT) on a standard linac was to investigate (a) the intrafractional relationship change (IRC) between a breathing signal and the tumor position, (b) the impact of IRC on the delivered dose, and (c) potential IRC predictors. Materials and methods We retrospectively investigated 10 pancreatic cancer patients with 2-4 implanted fiducial markers in the tumor treated with SBRT. Fluoroscopic images were acquired before and after treatment delivery simultaneously with the abdominal breathing motion. We quantified the IRC as the change in fiducial location for a given breathing amplitude in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions from before to after treatment delivery. The treatment plans were re-calculated after changing the isocenter coordinates according to the IRCs. Four treatment- or patient-related factors were investigated as potential predictors for IRC using linear models. Results The average (+/- 1 SD) absolute IRCs in the LR, AP, and SI directions were 1.2 +/- 1.2 mm, 0.7 +/- 0.7 mm, and 1.1 +/- 0.8 mm, respectively. The average 3D IRC was 2.0 +/- 1.3 mm (range: 0.4-5.3 mm) for a median treatment delivery time of 8.5 min (range: 5.7-19.9 min; n = 31 fractions). The dose coverage of the internal target volume (ITV) decreased by more than 3% points in three of 31 fractions. In those cases, the 3D IRC had been larger than 4.3 mm. The 3D IRC was found to correlate with changes in the minimum breathing amplitude during treatment delivery. Conclusion On average, 2 mm of treatment delivery accuracy was lost due to IRC. Periodical intrafractional imaging is needed to safely deliver respiratory-guided SBRT.
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| 33. |
- Sarudis, Sebastian, 1981, et al.
(författare)
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Surface guided frameless positioning for lung stereotactic body radiation therapy
- 2021
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 22:9, s. 215-226
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose: When treating lung tumors with stereotactic body radiation therapy (SBRT), patient immobilization is of outmost importance. In this study, the intra-fractional shifts of the patient (based on bony anatomy) and the tumor (based on the visible target volume) are quantified, and the associated impact on the delivered dose is estimated for a frameless immobilization approach in combination with surface guided radiation therapy (SGRT) monitoring. Methods: Cone beam computed tomographies (CBCT) were collected in free breathing prior and after each treatment for 25 patients with lung tumors, in total 137 fractions. The CBCT collected after each treatment was registered to the CBCT collected before each treatment with focus on bony anatomy to determine the shift of the patient, and with focus on the visible target volume to determine the shift of the tumor. Rigid registrations with 6 degrees of freedom were used. The patients were positioned in frameless immobilizations with their position and respiration continuously monitored by a commercial SGRT system. The patients were breathing freely within a preset gating window during treatment delivery. The beam was automatically interrupted if isocenter shifts >4 mm or breathing amplitudes outside the gating window were detected by the SGRT system. The time between the acquisition of the CBCTs was registered for each fraction to examine correlations between treatment time and patient shift. The impact of the observed shifts on the dose to organs at risk (OAR) and the gross tumor volume (GTV) was assessed. Results: The shift of the patient in the CBCTs was <= 2 mm for 132/137 fractions in the vertical (vrt) and lateral (lat) directions, and 134/137 fractions in the longitudinal (lng) direction and <= 4 mm in 134/137 (vrt) and 137/137 (lat, lng) of the fractions. The shift of the tumor was <= 2 mm in 116/137 (vrt), 123/137 (lat) and 115/137 (lng) fractions and <= 4 mm in 136/137 (vrt), 137/137 (lat), and 135/137 (lng) fractions. The maximal observed shift in the evaluated CBCT data was 4.6 mm for the patient and 7.2 mm for the tumor. Rotations were <= 3.3 degrees for all fractions and the mean/standard deviation were 0.2/1.0 degrees (roll), 0.1/0.8 degrees; (yaw), and 0.3/1.0 degrees (pitch). The SGRT system interrupted the beam due to intra-fractional isocenter shifts >4 mm for 21% of the fractions, but the patients always returned within tolerance without the need of repositioning. The maximal observed isocenter shift by the SGRT system during the beam holds was 8 mm. For the respiration monitoring, the beam was interrupted at least one time for 54% of the fractions. The visual tumor was within the planned internal target volume (ITV) for 136/137 fractions in the evaluated CBCT data collected at the end of each fraction. For the fraction where the tumor was outside the ITV, the D-98% for the GTV decreased with 0.4 Gy. For the OARs, the difference between planned and estimated dose from the CBCT data (D-2% or D-mean) was <= 2.6% of the prescribed PTV dose. No correlation was found between treatment time and the magnitude of the patient shift. Conclusions: Using SGRT for motion management and respiration monitoring in combination with a frameless immobilization is a feasible approach for lung SBRT.
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| 34. |
- Svalkvist, Angelica, et al.
(författare)
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Evaluation of deep-learning image reconstruction for chest CT examinations at two different dose levels.
- 2023
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Ingår i: Journal of applied clinical medical physics. - : Wiley. - 1526-9914. ; 24:3
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Tidskriftsartikel (refereegranskat)abstract
- The aims of the present study were to, for both a full-dose protocol and an ultra-low dose (ULD) protocol, compare the image quality of chest CT examinations reconstructed using TrueFidelity (Standard kernel) with corresponding examinations reconstructed using ASIR-V (Lung kernel) and to evaluate if post-processing using an edge-enhancement filter affects the noise level, spatial resolution and subjective image quality of clinical images reconstructed using TrueFidelity.A total of 25 patients were examined with both a full-dose protocol and an ULD protocol using a GE Revolution APEX CT system (GE Healthcare, Milwaukee, USA). Three different reconstructions were included in the study: ASIR-V 40%, DLIR-H, and DLIR-H with additional post-processing using an edge-enhancement filter (DLIR-H + E2). Five observers assessed image quality in two separate visual grading characteristics (VGC) studies. The results from the studies were statistically analyzed using VGC Analyzer. Quantitative evaluations were based on determination of two-dimensional power spectrum (PS), contrast-to-noise ratio (CNR), and spatial resolution in the reconstructed patient images.For both protocols, examinations reconstructed using TrueFidelity were statistically rated equal to or significantly higher than examinations reconstructed using ASIR-V 40%, but the ULD protocol benefitted more from TrueFidelity. In general, no differences in observer ratings were found between DLIR-H and DLIR-H + E2. For the three investigated image reconstruction methods, ASIR-V 40% showed highest noise and spatial resolution and DLIR-H the lowest, while the CNR was highest in DLIR-H and lowest in ASIR-V 40%.The use of TrueFidelity for image reconstruction resulted in higher ratings on subjective image quality than ASIR-V 40%. The benefit of using TrueFidelity was larger for the ULD protocol than for the full-dose protocol. Post-processing of the TrueFidelity images using an edge-enhancement filter resulted in higher image noise and spatial resolution but did not affect the subjective image quality.
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| 35. |
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| 36. |
- Weber, Lars, et al.
(författare)
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Verification of dose calculations with a clinical treatment planning system based on a point kernel dose engine
- 2002
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 3:2, s. 73-73
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Tidskriftsartikel (refereegranskat)abstract
- Dose calculations with a collapsed cone algorithm implemented in a clinical treatment planning system have been studied. The algorithm has been evaluated in homogeneous as well as in heterogeneous media, and the results have been compared to measurements and Monte Carlo simulations. Commonly encountered clinical beam configurations as well as more complex geometries have been pursued to test the limitations of the model. The results show that the accuracy level reached allows for clinical use. Some situations, e.g., large wedge beams and dose calculations in the build up region, not specific to the collapsed cone model, show deviations (outside +/- 3%) compared to measurements.
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| 37. |
- Wikström, Kenneth, et al.
(författare)
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Evaluation of four surface surrogates for modeling lung tumor positions over several fractions in radiotherapy
- 2021
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 22:9, s. 103-112
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Patient breathing during lung cancer radiotherapy reduces the ability to keep a sharp dose gradient between tumor and normal tissues. To mitigate detrimental effects, accurate information about the tumor position is required. In this work, we evaluate the errors in modeled tumor positions over several fractions of a simple tumor motion model driven by a surface surrogate measure and its time derivative. The model is tested with respect to four different surface surrogates and a varying number of surrogate and image acquisitions used for model training. Fourteen patients were imaged 100 times with cine CT, at three sessions mimicking a planning session followed by two treatment fractions. Patient body contours were concurrently detected by a body surface laser scanning system BSLS from which four surface surrogates were extracted; thoracic point TP, abdominal point AP, the radial distance mean RDM, and a surface derived volume SDV. The motion model was trained on session 1 and evaluated on sessions 2 and 3 by comparing modeled tumor positions with measured positions from the cine images. The number of concurrent surrogate and image acquisitions used in the training set was varied, and its impact on the final result was evaluated. The use of AP as a surface surrogate yielded the smallest error in modeled tumor positions. The mean deviation between modeled and measured tumor positions was 1.9 mm. The corresponding deviations for using the other surrogates were 2.0 mm (RDM), 2.8 mm (SDV), and 3.0 mm (TP). To produce a motion model that accurately models the tumor position over several fractions requires at least 10 simultaneous surrogate and image acquisitions over 1–2 minutes.
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