| 1. |
- Ferreira, Brigida Costa, et al.
(författare)
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Effective beam directions using radiobiologically optimized IMRT of node positive breast cancer
- 2006
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Ingår i: Physica medica (Testo stampato). - 1120-1797 .- 1724-191X. ; 22:1, s. 3-15
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study was to investigate the optimal coplanar beam directions when treating an early breast cancer with locoregional lymphatic spread with a few radiobiologically optimized intensity modulated beams. Also to determine the increase in the probability of complication-free cure with the number of beam portals and the smallest number required to perform a close to optimal treatment for this tumour site. Four test patients with stage II left-sided breast cancer were studied with heart, lung and contralateral breast as principal organs at risk. The clinical target volume consisted of the breast tissue remaining after surgery, the axillary, the internal mammary as well as the supraclavicular lymph nodes. Through an exhaustive search of all possible beam directions the most effective coplanar beams with one to four intensity modulated photon beam portals were investigated. Comparisons with uniform beam treatment techniques and up to 12 intensity modulated beams were also made. The different plans were optimized using the probability of complication-free tumour cure, P+, as biological objective function. When using two intensity modulated beam directions three major sets of suitable directions were identified denoted by A, P and T A corresponds to an anterior oblique pair of beams around 25 degrees and 325 degrees, P is a perpendicular lateral pair at around 50 and 130 whereas T is a more conventional tangential pair at around 155 degrees and 300 degrees. Interestingly, these configurations identify simply three major effective beam directions namely at 30 degrees +/- 20 degrees, 145 degrees +/- 20 degrees and 310 degrees +/- 15 degrees. For the three intensity modulated beam technique a combination of these three effective beam directions generally covered the global maximum of the probability of complication-free tumour control. The improvement in complication-free cure probability with two optimally selected intensity modulated beams is around 10% when compared to a uniform beam technique with three to four beam portals. This increase is mainly due to a reduction by almost 1% in the probability of injury to the heart and an increase of 6% in the probability of local tumour control. When three or four biologically optimized beam portals are used a further increase in the probability of complication-free cure of about 6% can often be obtained. This improvement is caused by a small decrease in the probability of injury to the heart, left lung and other surrounding normal tissue, as well as a slight further increase in the probability of tumour control. The increase in the treatment outcome is minimal when more than four intensity modulated beams are employed. A small increase in dose homogeneity in the target volume and a slight decrease in the normal tissue volume receiving high dose may be seen, but without appreciably improving the complication-free cure probability. For a stage II breast cancer, three and in more complex cases four optimally oriented beams are sufficient to reach close to the maximum probability of complication-free tumour control when biologically optimized intensity modulated dose delivery is used. Angle of incidence optimization may then be advantageous starting from the given most effective three beam directions.
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| 2. |
- de Las Heras Gala, Hugo, et al.
(författare)
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Quality control in cone-beam computed tomography (CBCT) EFOMP-ESTRO-IAEA protocol (summary report)
- 2017
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 39, s. 67-72
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the guideline presented in this article is to unify the test parameters for image quality evaluation and radiation output in all types of cone-beam computed tomography (CBCT) systems. The applications of CBCT spread over dental and interventional radiology, guided surgery and radiotherapy. The chosen tests provide the means to objectively evaluate the performance and monitor the constancy of the imaging chain. Experience from all involved associations has been collected to achieve a consensus that is rigorous and helpful for the practice. The guideline recommends to assess image quality in terms of uniformity, geometrical precision, voxel density values (or Hounsfield units where available), noise, low contrast resolution and spatial resolution measurements. These tests usually require the use of a phantom and evaluation software. Radiation output can be determined with a kerma-area product meter attached to the tube case. Alternatively, a solid state dosimeter attached to the flat panel and a simple geometric relationship can be used to calculate the dose to the isocentre. Summary tables including action levels and recommended frequencies for each test, as well as relevant references, are provided. If the radiation output or image quality deviates from expected values, or exceeds documented action levels for a given system, a more in depth system analysis (using conventional tests) and corrective maintenance work may be required.
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| 3. |
- Almhagen, Erik, et al.
(författare)
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A beam model for focused proton pencil beams
- 2018
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Ingår i: Physica medica (Testo stampato). - : Elsevier. - 1120-1797 .- 1724-191X. ; 52, s. 27-32
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: We present a beam model for Monte Carlo simulations of the IBA pencil beam scanning dedicated nozzle installed at the Skandion Clinic. Within the nozzle, apart from entrance and exit windows and the two ion chambers, the beam traverses vacuum, allowing for a beam that is convergent downstream of the nozzle exit. Materials and methods: We model the angular, spatial and energy distributions of the beam phase space at the nozzle exit with single Gaussians, controlled by seven energy dependent parameters. The parameters were determined from measured profiles and depth dose distributions. Verification of the beam model was done by comparing measured and GATE acquired relative dose distributions, using plan specific log files from the machine to specify beam spot positions and energy. Results: GATE-based simulations with the acquired beam model could accurately reproduce the measured data. The gamma index analysis comparing simulated and measured dose distributions resulted in > 95% global gamma index pass rates (3%/2 mm) for all depths. Conclusion: The developed beam model was found to be sufficiently accurate for use with GATE e.g. for applications in quality assurance (QA) or patient motion studies with the IBA pencil beam scanning dedicated nozzles.
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| 4. |
- Almhagen, Erik, et al.
(författare)
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Plan robustness and RBE influence for proton dose painting by numbers for head and neck cancers
- 2023
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Ingår i: Physica medica (Testo stampato). - : Elsevier. - 1120-1797 .- 1724-191X. ; 115, s. 103157-
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Tidskriftsartikel (refereegranskat)abstract
- PurposeTo investigate the feasibility of dose painting by numbers (DPBN) with respect to robustness for proton therapy for head and neck cancers (HNC), and to study the influence of variable RBE on the TCP and OAR dose burden.Methods and materialsData for 19 patients who have been scanned pretreatment with PET-FDG and subsequently treated with photon therapy were used in the study. A dose response model developed for photon therapy was implemented in a TPS, allowing DPBN plans to be created. Conventional homogeneous dose and DPBN plans were created for each patient, optimized with either fixed RBE = 1.1 or a variable RBE model. Robust optimization was used to create clinically acceptable plans. To estimate the maximum potential loss in TCP due to actual SUV variations from the pre-treatment imaging, we applied a test case with randomized SUV distribution.ResultsRegardless of the use of variable RBE for optimization or evaluation, a statistically significant increase (p < 0.001) in TCP was found for DPBN plans as compared to homogeneous dose plans. Randomizing the SUV distribution decreased the TCP for all plans. A correlation between TCP increase and variance of the SUV distribution and target volume was also found.ConclusionDPBN for protons and HNC is feasible and could lead to a TCP gain. Risks associated with the temporal variation of SUV distributions could be mitigated by imposing minimum doses to targets. The correlation found between TCP increase and SUV variance and target volume may be used for patient selection.
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| 5. |
- Andersson, Jonas, 1975-, et al.
(författare)
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Artificial intelligence and the medical physics profession-A Swedish perspective
- 2021
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Ingår i: Physica Medica-European Journal of Medical Physics. - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 88, s. 218-225
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Tidskriftsartikel (refereegranskat)abstract
- Background: There is a continuous and dynamic discussion on artificial intelligence (AI) in present-day society. AI is expected to impact on healthcare processes and could contribute to a more sustainable use of resources allocated to healthcare in the future. The aim for this work was to establish a foundation for a Swedish perspective on the potential effect of AI on the medical physics profession. Materials and methods: We designed a survey to gauge viewpoints regarding AI in the Swedish medical physics community. Based on the survey results and present-day situation in Sweden, a SWOT analysis was performed on the implications of AI for the medical physics profession. Results: Out of 411 survey recipients, 163 responded (40%). The Swedish medical physicists with a professional license believed (90%) that AI would change the practice of medical physics but did not foresee (81%) that AI would pose a risk to their practice and career. The respondents were largely positive to the inclusion of AI in educational programmes. According to self-assessment, the respondents' knowledge of and workplace preparedness for AI was generally low. Conclusions: From the survey and SWOT analysis we conclude that AI will change the medical physics profession and that there are opportunities for the profession associated with the adoption of AI in healthcare. To overcome the weakness of limited AI knowledge, potentially threatening the role of medical physicists, and build upon the strong position in Swedish healthcare, medical physics education and training should include learning objectives on AI.
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| 6. |
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| 7. |
- 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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| 8. |
- Ardenfors, Oscar, et al.
(författare)
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Organ doses from a proton gantry-mounted cone-beam computed tomography system characterized with MCNP6 and GATE
- 2018
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 53, s. 56-61
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Tidskriftsartikel (refereegranskat)abstract
- PurposeTo determine organ doses from a proton gantry-mounted cone-beam computed tomography (CBCT) system using two Monte Carlo codes and to study the influence on organ doses from different acquisition modes and repeated imaging.MethodsThe CBCT system was characterized with MCNP6 and GATE using measurements of depth doses in water and spatial profiles in air. The beam models were validated against absolute dose measurements and used to simulate organ doses from CBCT imaging with head, thorax and pelvis protocols. Anterior and posterior 190° scans were simulated and the resulting organ doses per mAs were compared to those from 360° scans. The influence on organ doses from repeated imaging with different imaging schedules was also investigated.ResultsThe agreement between MCNP6, GATE and measurements with regard to depth doses and beam profiles was within 4% for all protocols and the corresponding average agreement in absolute dose validation was 4%. Absorbed doses for in-field organs from 360° scans ranged between 6 and 8 mGy, 15–17 mGy and 24–54 mGy for the head, thorax and pelvis protocols, respectively. Cumulative organ doses from repeated CBCT imaging ranged between 0.04 and 0.32 Gy for weekly imaging and 0.2–1.6 Gy for daily imaging. The anterior scans resulted in an average increase in dose per mAs of 24% to the organs of interest relative to the 360° scan, while the posterior scan showed a 37% decrease.ConclusionsA proton gantry-mounted CBCT system was accurately characterized with MCNP6 and GATE. Organ doses varied greatly depending on acquisition mode, favoring posterior scans.
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| 9. |
- Ardenfors, Oscar, et al.
(författare)
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Out-of-field doses from secondary radiation produced in proton therapy and the associated risk of radiation-induced cancer from a brain tumor treatment
- 2018
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 53, s. 129-136
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Tidskriftsartikel (refereegranskat)abstract
- PurposeTo determine out-of-field doses produced in proton pencil beam scanning (PBS) therapy using Monte Carlo simulations and to estimate the associated risk of radiation-induced second cancer from a brain tumor treatment.MethodsSimulations of out-of-field absorbed doses were performed with MCNP6 and benchmarked against measurements with tissue-equivalent proportional counters (TEPC) for three irradiation setups: two irradiations of a water phantom using proton energies of 78-147 MeV and 177-223 MeV, and one brain tumor irradiation of a whole-body phantom. Out-of-field absorbed and equivalent doses to organs in a whole-body phantom following a brain tumor treatment were subsequently simulated and used to estimate the risk of radiation-induced cancer. Additionally, the contribution of absorbed dose originating from radiation produced in the nozzle was calculated from simulations.ResultsOut-of-field absorbed doses to the TEPC ranged from 0.4 to 135 mu Gy/Gy. The average deviation between simulations and measurements of the water phantom irradiations was about 17%. The absorbed dose contribution from radiation produced in the nozzle ranged between 0 and 70% of the total dose; the contribution was however small in absolute terms. The absorbed and equivalent doses to the organs ranged between 0.2 and 60 mu Gy/Gy and 0.5-151 mu Sv/Gy. The estimated lifetime risk of radiation-induced second cancer was approximately 0.01%.ConclusionsThe agreement of out-of-field absorbed doses between measurements and simulations was good given the sources of uncertainties. Calculations of out-of-field organ doses following a brain tumor treatment indicated that proton PBS therapy of brain tumors is associated with a low risk of radiation-induced cancer.
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| 10. |
- Astaraki, Mehdi, PhD Student, 1984-, et al.
(författare)
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Benign-malignant pulmonary nodule classification in low-dose CT with convolutional features
- 2021
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 83, s. 146-153
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Low-Dose Computed Tomography (LDCT) is the most common imaging modality for lung cancer diagnosis. The presence of nodules in the scans does not necessarily portend lung cancer, as there is an intricate relationship between nodule characteristics and lung cancer. Therefore, benign-malignant pulmonary nodule classification at early detection is a crucial step to improve diagnosis and prolong patient survival. The aim of this study is to propose a method for predicting nodule malignancy based on deep abstract features.Methods: To efficiently capture both intra-nodule heterogeneities and contextual information of the pulmonary nodules, a dual pathway model was developed to integrate the intra-nodule characteristics with contextual attributes. The proposed approach was implemented with both supervised and unsupervised learning schemes. A random forest model was added as a second component on top of the networks to generate the classification results. The discrimination power of the model was evaluated by calculating the Area Under the Receiver Operating Characteristic Curve (AUROC) metric. Results: Experiments on 1297 manually segmented nodules show that the integration of context and target supervised deep features have a great potential for accurate prediction, resulting in a discrimination power of 0.936 in terms of AUROC, which outperformed the classification performance of the Kaggle 2017 challenge winner.Conclusion: Empirical results demonstrate that integrating nodule target and context images into a unified network improves the discrimination power, outperforming the conventional single pathway convolutional neural networks.
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| 11. |
- Astaraki, Mehdi, PhD Student, 1984-, et al.
(författare)
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Early survival prediction in non-small cell lung cancer from PET/CT images using an intra-tumor partitioning method
- 2019
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 60, s. 58-65
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Tidskriftsartikel (refereegranskat)abstract
- PurposeTo explore prognostic and predictive values of a novel quantitative feature set describing intra-tumor heterogeneity in patients with lung cancer treated with concurrent and sequential chemoradiotherapy.MethodsLongitudinal PET-CT images of 30 patients with non-small cell lung cancer were analysed. To describe tumor cell heterogeneity, the tumors were partitioned into one to ten concentric regions depending on their sizes, and, for each region, the change in average intensity between the two scans was calculated for PET and CT images separately to form the proposed feature set. To validate the prognostic value of the proposed method, radiomics analysis was performed and a combination of the proposed novel feature set and the classic radiomic features was evaluated. A feature selection algorithm was utilized to identify the optimal features, and a linear support vector machine was trained for the task of overall survival prediction in terms of area under the receiver operating characteristic curve (AUROC).ResultsThe proposed novel feature set was found to be prognostic and even outperformed the radiomics approach with a significant difference (AUROCSALoP = 0.90 vs. AUROCradiomic = 0.71) when feature selection was not employed, whereas with feature selection, a combination of the novel feature set and radiomics led to the highest prognostic values.ConclusionA novel feature set designed for capturing intra-tumor heterogeneity was introduced. Judging by their prognostic power, the proposed features have a promising potential for early survival prediction.
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| 12. |
- Berthon, Beatrice, et al.
(författare)
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PETSTEP : generation of synthetic PET lesions for fast evaluation of segmentation methods
- 2015
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 31:8, s. 969-980
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: This work describes PETSTEP (PET Simulator of Tracers via Emission Projection): a faster and more accessible alternative to Monte Carlo (MC) simulation generating realistic PET images, for studies assessing image features and segmentation techniques.Methods: PETSTEP was implemented within Matlab as open source software. It allows generating threedimensional PET images from PET/CT data or synthetic CT and PET maps, with user-drawn lesions and user-set acquisition and reconstruction parameters. PETSTEP was used to reproduce images of the NEMA body phantom acquired on a GE Discovery 690 PET/CT scanner, and simulated with MC for the GE Discovery LS scanner, and to generate realistic Head and Neck scans. Finally the sensitivity (S) and Positive Predictive Value (PPV) of three automatic segmentation methods were compared when applied to the scanner-acquired and PETSTEP-simulated NEMA images.Results: PETSTEP produced 3D phantom and clinical images within 4 and 6 min respectively on a single core 2.7 GHz computer. PETSTEP images of the NEMA phantom had mean intensities within 2% of the scanner-acquired image for both background and largest insert, and 16% larger background Full Width at Half Maximum. Similar results were obtained when comparing PETSTEP images to MC simulated data. The S and PPV obtained with simulated phantom images were statistically significantly lower than for the original images, but led to the same conclusions with respect to the evaluated segmentation methods.Conclusions: PETSTEP allows fast simulation of synthetic images reproducing scanner-acquired PET data and shows great promise for the evaluation of PET segmentation methods.
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| 13. |
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| 14. |
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| 15. |
- Buizza, Giulia, et al.
(författare)
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Early tumor response prediction for lung cancer patients using novel longitudinal pattern features from sequential PET/CT image scans
- 2018
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Ingår i: Physica medica (Testo stampato). - : ELSEVIER SCI LTD. - 1120-1797 .- 1724-191X. ; 54, s. 21-29
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: A new set of quantitative features that capture intensity changes in PET/CT images over time and space is proposed for assessing the tumor response early during chemoradiotherapy. The hypothesis whether the new features, combined with machine learning, improve outcome prediction is tested. Methods: The proposed method is based on dividing the tumor volume into successive zones depending on the distance to the tumor border. Mean intensity changes are computed within each zone, for CT and PET scans separately, and used as image features for tumor response assessment. Doing so, tumors are described by accounting for temporal and spatial changes at the same time. Using linear support vector machines, the new features were tested on 30 non-small cell lung cancer patients who underwent sequential or concurrent chemoradiotherapy. Prediction of 2-years overall survival was based on two PET-CT scans, acquired before the start and during the first 3 weeks of treatment. The predictive power of the newly proposed longitudinal pattern features was compared to that of previously proposed radiomics features and radiobiological parameters. Results: The highest areas under the receiver operating characteristic curves were 0.98 and 0.93 for patients treated with sequential and concurrent chemoradiotherapy, respectively. Results showed an overall comparable performance with respect to radiomics features and radiobiological parameters. Conclusions: A novel set of quantitative image features, based on underlying tumor physiology, was computed from PET/CT scans and successfully employed to distinguish between early responders and non-responders to chemoradiotherapy.
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| 16. |
- Bujila, Robert, et al.
(författare)
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A validation of SpekPy: A software toolkit for modelling X-ray tube spectra
- 2020
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 75, s. 44-54
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To validate the SpekPy software toolkit that has been developed to estimate the spectra emitted fromtungsten anode X-ray tubes. The model underlying the toolkit introduces improvements upon a well-knownsemi-empirical model of X-ray emission.Materials and methods: Using the same theoretical framework as the widely-used SpekCalc software, new electronpenetration data was simulated using the Monte Carlo (MC) method, alternative bremsstrahlung crosssectionswere applied, L-line characteristic emissions were included, and improvements to numerical methodsimplemented. The SpekPy toolkit was developed with the Python programming language. The toolkit was validatedagainst other popular X-ray spectrum models (50 to 120 kVp), X-ray spectra estimated with MC (30 to150 kVp) as well as reference half value layers (HVL) associated with numerous radiation qualities from standardlaboratories (20 to 300 kVp).Results: The toolkit can be used to estimate X-ray spectra that agree with other popular X-ray spectrum modelsfor typical configurations in diagnostic radiology as well as with MC spectra over a wider range of conditions.The improvements over SpekCalc are most evident at lower incident electron energies for lightly and moderatelyfiltered radiation qualities. Using the toolkit, estimations of the HVL over a large range of standard radiationqualities closely match reference values.Conclusions: A toolkit to estimate X-ray spectra has been developed and extensively validated for central-axisspectra. This toolkit can provide those working in Medical Physics and beyond with a powerful and user-friendlyway of estimating spectra from X-ray tubes.
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| 17. |
- Bujila, Robert, et al.
(författare)
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Practical approaches to approximating MTF and NPS in CT with an example application to task-based observer studies
- 2017
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 33, s. 16-25
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To investigate two methods of approximating the Modulation Transfer Function (MTF) and Noise Power Spectrum (NPS) in computed tomography (CT) for a range of scan parameters, from limited image acquisitions. Methods: The two methods consist of 1) using a linear systems approach to approximate the NPS for different filtered backprojection (FBP) kernels with a filter function derived from the kernel ratio of determined MTFs and 2) using an empirical fitted model to approximate the MTF and NPS. In both cases a scaling function accounts for variations in mAs and kV. The two methods of approximating the MTF/ NPS are further investigated by comparing image quality figure of merits (FOM) d' and AUC calculated using approximations of the MTF/NPS and MTF/NPS that have been determined for different mAs/kV levels and reconstruction kernels. Results: The greatest RMSE for NPS approximated for a range of mAs/kVp/convolution kernels using both methods and compared to determined NPS was 0.05 of the peak value. The RMSE for FOM with the kernel ratio method were at most 0.1 for d' and 0.01 for the AUC. Using the empirical model method, the RMSE for FOM were at most 0.02 for d' and 0.001 for the AUC. Conclusions: The two methods proposed in this paper can provide a convenient way of approximating the MTF and NPS for use in, among other things, mathematical observer studies. Both methods require a relatively small number of direct determinations of NPS from scan acquisitions to model the NPS/MTF for arbitrary mAs and kV.
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| 18. |
- Crafoord, Joakim, et al.
(författare)
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Comparison of two landmark based image registration methods for use with a body atlas
- 2000
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Ingår i: Physica medica (Testo stampato). - 1120-1797 .- 1724-191X. ; 16:2, s. 75-82
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Tidskriftsartikel (refereegranskat)abstract
- We describe preliminary work registering abdominal MRI images from three healthy male volunteers. Anatomically selected 3D homologous point pairs (landmarks), from which eigenvalues were generated to form the basis for a 3D non-affine polynomial transformation, were placed on axial slices alone and on axial, coronal and sagittal slices. Registration accuracy was judged visually by comparing superimposed 3D isosurfaces from the reference, untransformed, and transformed volume data and by comparing merged 2D slices projected fi om the transformed and reference volume data superimposed with 2D isolines. The squared sum of intensity differences between the transformed/untransformed and the reference volume was significant at the 0.05 (p >0.05) confidence level. The correlation coefficient improved by an average of 38% and the cross correlation between pixel values improved by an average of 22%. In each trial, the standard deviation of the landmarks after transformation was within one voxel and the standard error of the mean was not significantly different from zero at the 0.05 confidence level. Abdominal isosurface volume differences (between individuals) changed from an average of 14.5% before registration to 2.9% after registration. This experiment shows that it is possible to choose landmarks such that abdominal data from different subject volumes can be mapped to a common reference, and thus that it is possible to use this combined volume both to form an atlas and to warp abdominal data from an atlas to a patient volume.
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| 19. |
- Dasu, Alexandru, et al.
(författare)
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Models for the risk of secondary cancers from radiation therapy
- 2017
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Ingår i: Physica medica (Testo stampato). - London : Elsevier BV. - 1120-1797 .- 1724-191X. ; 42, s. 232-238
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Tidskriftsartikel (refereegranskat)abstract
- The interest in the induction of secondary tumours following radiotherapy has greatly increased as developments in detecting and treating the primary tumours have improved the life expectancy of cancer patients. However, most of the knowledge on the current levels of risk comes from patients treated many decades ago. As developments of irradiation techniques take place at a much faster pace than the progression of the carcinogenesis process, the earlier results could not be easily extrapolated to modern treatments. Indeed, the patterns of irradiation from historically-used orthovoltage radiotherapy and from contemporary techniques like conformal radiotherapy with megavoltage radiation, intensity modulated radiation therapy with photons or with particles are quite different. Furthermore, the increased interest in individualised treatment options raises the question of evaluating and ranking the different treatment plan options from the point of view of the risk for cancer induction, in parallel with the quantification of other long-term effects. It is therefore inevitable that models for risk assessment will have to be used to complement the knowledge from epidemiological studies and to make predictions for newer forms of treatment for which clinical evidence is not yet available. This work reviews the mathematical models that could be used to predict the risk of secondary cancers from radiotherapy-relevant dose levels, as well as the approaches and factors that have to be taken into account when including these models in the clinical evaluation process. These include the effects of heterogeneous irradiation, secondary particles production, imaging techniques, interpatient variability and other confounding factors.
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| 20. |
- Dasu, Alexandru, et al.
(författare)
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Normal tissue sparing potential of scanned proton beams with and without respiratory gating for the treatment of internal mammary nodes in breast cancer radiotherapy
- 2018
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 52, s. 81-85
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Tidskriftsartikel (refereegranskat)abstract
- Proton therapy has shown potential for reducing doses to normal tissues in breast cancer radiotherapy. However data on the impact of protons when including internal mammary nodes (IMN) in the target for breast radiotherapy is comparatively scarce. This study aimed to evaluate normal tissue doses when including the IMN in regional RT with scanned proton beams, with and without respiratory gating. The study cohort was composed of ten left-sided breast patients CT-scanned during enhanced inspiration gating (EIG) and free-breathing (FB). Proton plans were designed for the target including or excluding the IMN. Targets and organs-at-risk were delineated according to RTOG guidelines. Comparison was performed between dosimetric parameters characterizing target coverage and OAR radiation burden. Statistical significance of differences was tested using a paired, two-tailed Student's t-test. Inclusion of the IMN in the target volume led to a small increase of the cardiopulmonary burden. The largest differences were seen for the ipsilateral lung where the mean dose increased from 6.1 to 6.6 Gy (RBE) (P < 0.0001) in FB plans and from 6.9 to 7.4 Gy (RBE) (P = 0.003) in EIG plans. Target coverage parameters were very little affected by the inclusion of IMN into the treatment target. Radiotherapy with scanned proton beams has the potential of maintaining low cardiovascular burden when including the IMN into the target, irrespective of whether respiratory gating is used or not.
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| 21. |
- Dzintars, Erik, et al.
(författare)
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Application of an independent dose calculation software for estimating the impact of inter-fractional setup shifts in Helical Tomotherapy treatments
- 2013
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 29:6, s. 615-623
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to validate the capability of in-house independent point dose calculation software to be used as a second check for Helical Tomotherapy treatment plans. The software performed its calculations in homogenous conditions (using the Cheese phantom, which is a cylindrical phantom with radius 15 cm and length 18 cm) using a factor-based algorithm. Fifty patients, who were treated for pelvic (10), prostate (14), lung (10), head 82 neck (12) and brain (4) cancers, were used. Based on the individual patient kVCT images and the pretreatment MVCT images for each treatment fraction, the corresponding daily patient setup shifts in the IEC-X, IEC-Y, and IEC-Z directions were registered. For each patient, the registered fractional setup shifts were grouped into systematic and random shifts. The average systematic dosimetric variations showed small dose deviation for the different cancer types (1.0%-3.0%) compared to the planned dose. Of the fifty patients, only three had percent differences larger than 5%. The average random dosimetric variations showed relatively small dose deviations (0.2%-1.1%) compared to the planned dose. None of the patients had percent differences larger than 5%. By examining the individual fractions of each patient, it is observed that only in 31 out of 1358 fractions the percent differences exceeded the border of 5%. These results indicate that the overall dosimetric impact from systematic and random variations is small and that the software is a capable platform for independent point dose validation for the Helical Tomotherapy modality.
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| 22. |
- Esposito, M, et al.
(författare)
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PRaVDA: The first solid-state system for proton computed tomography
- 2018
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Ingår i: Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB). - : Elsevier BV. - 1724-191X. ; 55, s. 149-154
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 23. |
- Flejmer, Anna M., 1971-, et al.
(författare)
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Impact of physiological breathing motion for breast cancer radiotherapy with proton beam scanning - An in silico study
- 2017
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 39, s. 88-94
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the impact of breathing motion on proton breast treatment plans. Twelve patients with CT datasets acquired during breath-hold-at-inhalation (BHI), breath-hold-at-exhalation (BHE) and in free-breathing (FB) were included in the study. Proton plans were designed for the left breast for BHI and subsequently recalculated for BHE or designed for FB and recalculated for the extreme breath-hold phases. The plans were compared from the point of view of their target coverage and doses to organs-at-risk. The median amplitude of breathing motion determined from the positions of the sternum was 4.7 mm (range 0.5-14.6 mm). Breathing motion led to a degradation of the dose coverage of the target (heterogeneity index increased from 4-7% to 8-11%), but the degraded values of the dosimetric parameters of interest fulfilled the clinical criteria for plan acceptance. Exhalation decreased the lung burden [average dose 3.1-4.5 Gy (RBE)], while inhalation increased it [average dose 5.8-6.8 Gy (RBE)]. The individual values depended on the field arrangement. Smaller differences were seen for the heart [average dose 0.1-0.2 Gy (RBE)] and the LAD [1.9-4.6 Gy (RBE)]. Weak correlations were generally found between changes in dosimetric parameters and respiratory motion. The differences between dosimetric parameters for various breathing phases were small and their expected clinical impact is consequently quite small. The results indicated that the dosimetric parameters of the plans corresponding to the extreme breathing phases are little affected by breathing motion, thus suggesting that this motion might have little impact for the chosen beam orientations with scanned proton beams.
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| 24. |
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| 25. |
- Henry, Thomas, et al.
(författare)
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Interlaced proton grid therapy - Linear energy transfer and relative biological effectiveness distributions
- 2019
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 56, s. 81-89
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Interlaced beams have previously been proposed for delivering proton grid therapy. This study aims to assess dose-averaged LET (LETd ) and RBE-weighted dose (D-RBE ) distributions of such beam geometries, and compare them with conventional intensity modulated proton therapy (IMPT). Methods: IMPT plans and four different interlaced proton grid therapy plans were generated for five patient cases (esophagus, lung, liver, prostate, anus). The constant RBE = 1.1 was assumed for optimization. The LETd was subsequently Monte Carlo calculated for each plan and used as input for two LET-dependent variable RBE models. The fulfilment of clinical goals, along with DVH and spatial distribution evaluations, were then assessed and compared. Results: All plans fulfilled the clinical target goals assuming RBE = 1.1. The target coverage was slightly compromised for some grid plans when assuming the variable RBE models. All IMPT plans, and 18 of 20 grid plans, fulfilled all clinical goals for the organs at risk when assuming RBE = 1.1, whereas most plans failed at least one goal when assuming the variable RBE models. Compared with the IMPT plans, the grid plans demonstrated substantially different LETd distributions due to the fundamentally different beam geometries. However, D-RBE distributions in the target were similar. Conclusions: Despite the unconventional beam geometries of interlaced proton grid plans, with resulting alternating dose and LETd patterns, the fulfillment of realistic clinical goals seems to be comparable to regular IMPT plans, both assuming RBE = 1.1 and variable RBE models. In addition, the alternating grid patterns do not seem to give rise to unexpected D-RBE hot-spots.
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| 26. |
- Hindorf, Cecilia, et al.
(författare)
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Traceable calibration with 177Lu and comparison of activity meters at hospitals in Norway and Sweden
- 2023
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Ingår i: Physica medica (Testo stampato). - : Elsevier. - 1120-1797 .- 1724-191X. ; 116
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: The activity meter is used to determine the activity of delivered radiopharmaceuticals, administered activity to patients and reference activity when gamma-cameras are calibrated prior to imaged-based dosimetry. The aim is to describe a procedure for cross-calibration of activity meters at different clinical sites, and report on 177Lu activity results when using factory-set calibration factors compared to when calibration is performed with traceability to a primary standard.Methods: Thirty activity meters placed at seven hospitals in Norway and Sweden from four manufacturers: Capintec, Commecer, NuviaTech and Veenstra were included. A stock solution with 177Lu was prepared at the local sites and measured in each activity meter with factory settings. The solution was shipped to the reference site at Lund University for measurements in a secondary standard activity meter. Deviations between local and reference activity measurements were determined for three geometries: 25-mL vial, 10-mL syringe and 1-mL syringe.Results: The median of the deviations was 6.4 % for the 25 mL vial, 5.9 % for the 10 mL syringe and 6.8 % for the 1 mL syringe. The median of the deviations for the 25 mL vial, was 1.5 % for activity meters from Capintec, 7.0 % for Comecer, 11.0 % for NuviaTech and 2.4 % for Veenstra. The majority of the deviations were positive and the maximum deviation was 14.5 %.Conclusion: The activity of 177Lu measured in an activity meter with factory-set dial settings may yield deviations up to 14.5%, compared to activities measured with traceability to a primary standard. This would imply an undertreatment of patients.
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| 27. |
- Häger, Wille, et al.
(författare)
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Overall survival prediction for high-grade glioma patients using mathematical modeling of tumor cell infiltration
- 2023
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 113
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: This study aimed at applying a mathematical framework for the prediction of high-grade gliomas (HGGs) cell invasion into normal tissues for guiding the clinical target delineation, and at investigating the possibility of using tumor infiltration maps for patient overall survival (OS) prediction. Material & methods: A model describing tumor infiltration into normal tissue was applied to 93 HGG cases. Tumor infiltration maps and corresponding isocontours with different cell densities were produced. ROC curves were used to seek correlations between the patient OS and the volume encompassed by a particular isocontour. Area-Under-the-Curve (AUC) values were used to determine the isocontour having the highest predictive ability. The optimal cut-off volume, having the highest sensitivity and specificity, for each isocontour was used to divide the patients in two groups for a Kaplan-Meier survival analysis. Results: The highest AUC value was obtained for the isocontour of cell densities 1000 cells/mm3 and 2000 cells/mm3, equal to 0.77 (p < 0.05). Correlation with the GTV yielded an AUC of 0.73 (p < 0.05). The Kaplan-Meier survival analysis using the 1000 cells/mm3 isocontour and the ROC optimal cut-off volume for patient group selection rendered a hazard ratio (HR) of 2.7 (p < 0.05), while the GTV rendered a HR = 1.6 (p < 0.05). Conclusion: The simulated tumor cell invasion is a stronger predictor of overall survival than the segmented GTV, indicating the importance of using mathematical models for cell invasion to assist in the definition of the target for HGG patients.
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| 28. |
- Häger, Wille, 1990-
(författare)
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Overall survival prediction for high-grade glioma patients using mathematical modelling of tumor cell infiltration
-
Ingår i: Physica medica (Testo stampato). - 1120-1797 .- 1724-191X.
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Forskningsöversikt (refereegranskat)abstract
- Purpose: This study aimed at applying a mathematical framework for the prediction of high-grade gliomas (HGGs) cell invasion into normal tissues for guiding the clinical target delineation, and at investigating the possibility of using tumor infiltration maps for patient overall survival (OS) prediction.Material & Methods: A model describing tumor infiltration into normal tissue was applied to 93 HGG cases. Tumor infiltration maps and corresponding isocontours with different cell densities were produced. ROC curves were used to seek correlations between the patient OS and the volume encompassed by a particular isocontour. Area-Under-the-Curve (AUC) values were used to determine the isocontour having the highest predictive ability. The optimal cut-off volume, having the highest sensitivity and specificity, for each isocontour was used to divide the patients in two groups for a Kaplan-Meier survival analysis.Results: The highest AUC value was obtained for the isocontour of cell densities 1000 cells/mm³ and 2000 cells/mm³, equal to 0.77 (p < 0.05). Correlation with the GTV yielded an AUC of 0.73 (p < 0.05). The Kaplan-Meier survival analysis using the 1000 cells/mm³ isocontour and the ROC optimal cut-off volume for patient group selection rendered a hazard ratio (HR) of 2.7 (p < 0.05), while the GTV rendered a HR = 1.6 (p < 0.05).Conclusion: The simulated tumor cell invasion is a stronger predictor of overall survival than the segmented GTV, indicating the importance of using mathematical models for cell invasion to assist in the definition of the target for HGG patients.
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| 29. |
- Ivashchenko, Oleksandra V., et al.
(författare)
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Time-Activity data fitting in molecular Radiotherapy : Methodology and pitfalls
- 2024
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Ingår i: Physica medica (Testo stampato). - : Elsevier. - 1120-1797 .- 1724-191X. ; 117
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Tidskriftsartikel (refereegranskat)abstract
- Absorbed radiation doses are essential in assessing the effects, e.g. safety and efficacy, of radiopharmaceutical therapy (RPT). Patient-specific absorbed dose calculations in the target or the organ at risk require multiple inputs. These include the number of disintegrations in the organ, i.e. the time-integrated activities (TIAs) of the organs, as well as other parameters describing the process of radiation energy deposition in the target tissue (i.e. mean energy per disintegration, radiation dose constants, etc). TIAs are then estimated by incorporating the area under the radiopharmaceutical's time-activity curve (TAC), which can be obtained by quantitative measurements of the biokinetics in the patient (typically based on imaging data such as planar scintigraphy, SPECT/CT, PET/CT, or blood and urine samples). The process of TAC determination/calculation for RPT generally depends on the user, e.g., the chosen number and schedule of measured time points, the selection of the fit function, the error model for the data and the fit algorithm. These decisions can strongly affect the final TIA values and thus the accuracy of calculated absorbed doses. Despite the high clinical importance of the TIA values, there is currently no consensus on processing time-activity data or even a clear understanding of the influence of uncertainties and variations in personalised RPT dosimetry related to user-dependent TAC calculation. As a first step towards minimising site-dependent variability in RPT dosimetry, this work provides an overview of quality assurance and uncertainty management considerations of the TIA estimation.
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| 30. |
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| 31. |
- Jiménez-Ortega, E., et al.
(författare)
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Dose painting by means of Monte Carlo treatment planning at the voxel level
- 2017
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 42, s. 339-344
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To develop a new optimization algorithm to carry out true dose painting by numbers (DPBN) planning based on full Monte Carlo (MC) calculation.Methods: Four configurations with different clustering of the voxel values from PET data were proposed. An optimization method at the voxel level under Lineal Programming (LP) formulation was used for an inverse planning and implemented in CARMEN, an in-house Monte Carlo treatment planning system.Results: Beamlet solutions fulfilled the objectives and did not show significant differences between the different configurations. More differences were observed between the segment solutions. The plan for the dose prescription map without clustering was the better solution.Conclusions: LP optimization at voxel level without dose-volume restrictions can carry out true DPBN planning with the MC accuracy.
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| 32. |
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| 33. |
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| 34. |
- Kempe, Johanna, et al.
(författare)
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Analytical theory for the fluence, planar fluence, energy fluence, planar energy fluence and absorbed dose of primary particles and their fragments in broad therapeutic light ion beams
- 2010
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 26:1, s. 6-16
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the present work is to develop analytical expressions for the depth variation of the fluence, planar fluence, the energy fluence, planar energy fluence, the mean energy and absorbed dose of primary ions and their associated fragments in tissue-like media with ranges of clinical interest. The analytical expressions of the primary ions and associated fragments take into account nuclear interactions, energy losses, range straggling and multiple scattering. The analytical models of the radiation field quantities were compared with the results of the modified Monte Carlo (MC) code SHIELD-HIT+. The results show that the shape of the depth absorbed dose distribution of the primary particles is characterized by an increasingly steep exponential fluence decrease with depth as the charge and atomic weight increase. This is accompanied by a compensating increased energy loss towards the Bragg peak as the charge of the ion increases. These largely compensating mechanisms are the main reason that the depth absorbed dose curve of all light ions is surprisingly similar. In addition, a rather uniform dose in the plateau region is obtained since the increasing fragment production almost precisely compensates the loss of primaries. The dominating light fragments such as protons and alpha particles are characterized by longer ranges than the primaries and their depth dose curves to some extent coincide well with the depth fluence curves due to a rather slow variation of mean stopping powers. In contrast, the heavier fragments are characterized by the build up of a slowing down spectrum similar to that of the primaries but with initially slightly shorter or longer ranges depending on their mass to atomic number ratio. The presented analytical theory for the light ion penetration in matter agree quite well with the MC and experimental data and may be very useful for fast analytical calculations of quantities like mean energy, fluence, energy fluence, absorbed dose, and LET.
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| 35. |
- Lazzeroni, M., et al.
(författare)
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Evaluating the impact of a rigid and a deformable registration method of pre-treatment images for hypoxia-based dose painting
- 2024
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 122
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: To assess the impact of rigid and deformable image registration methods (RIR, DIR) on the outcome of a hypoxia-based dose painting strategy. Materials and methods: Thirty head and neck cancer patients were imaged with [18F]FMISO-PET/CT before radiotherapy. [18F]FMISO-PET/CT images were registered to the planning-CT by RIR or DIR. The [18F]FMISO uptake was converted into oxygen partial pressure (pO2) maps. Hypoxic Target Volumes were contoured on pO2 maps for the deformed (HTVdef) and non-deformed (HTV) cases. A dose escalation strategy by contours, aiming at 95 % tumour control probability (TCP), was applied. HTVs were characterised based on geometry-related metrics, the underlying pO2 distribution, and the dose boost level. A dosimetric and radiobiological evaluation of selected treatment plans made considering RIR and DIR was performed. Moreover, the TCP of the RIR dose distribution was evaluated when considering the deformed [18F]FMISO-PET image as an indicator of the actual target radiosensitivity to determine the potential impact of an unalignment. Results: Statistically significant differences were found between HTV and HTVdef for volume-based metrics and underlying pO2 distribution. Eight out of nine treatment plans for HTV and HTVdef showed differences on the level 10 %/3 mm on a gamma analysis. The TCP difference, however, between RIR and the case when the RIR dose distribution was used with the deformed radiosensitivity map was below 2 pp. Conclusions: Although the choice of the CTplan-to-PET registration method pre-treatment impacts the HTV localisation and morphology and the corresponding dose distribution, it negligibly affects the TCP in the proposed dose escalation strategy by contours.
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| 36. |
- Lazzeroni, Marta, et al.
(författare)
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Evaluation of third treatment week as temporal window for assessing responsiveness on repeated FDG-PET scans in Non-Small Cell Lung Cancer patients
- 2018
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 46, s. 45-51
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Early assessment of tumour response to treatment with repeated FDG-PET-CT imaging has potential for treatment adaptation but it is unclear what the optimal time window for this evaluation is. Previous studies indicate that changes in SUVmean and the effective radiosensitivity (alpha(eff), accounting for uptake variations and accumulated dose until the second FDG-PET-CT scan) are predictive of 2-year overall survival (OS) when imaging is performed before radiotherapy and during the second week. This study aims to investigate if multiple FDG-PET-derived quantities determined during the third treatment week have stronger predictive power.Methods: Twenty-eight lung cancer patients were imaged with FDG-PET-CT before radiotherapy (PET1) and during the third week (PET2). SUVmean, SUVmax, SUVpeak, MTV41%-50% (Metabolic Tumour Volume), TLG41%-50% (Total Lesion Glycolysis) in PET1 and PET2 and their change (), as well as average alpha(eff) (<(alpha)over bar >(eff)) and the negative fraction of alpha(eff) values (f(alpha eff) (< 0)) were determined. Correlations were sought between FDG-PET-derived quantities and OS with ROC analysis.Results: Neither SUVmean, SUVmax, SUVpeak in PET1 and PET2 (AUC = 0.5-0.6), nor their changes (AUC = 0.5-0.6) were significant for outcome prediction purposes. Lack of correlation with OS was also found for (alpha) over bar (eff) (AUC = 0.5) and f(alpha eff) (<) 0 (AUC = 0.5). Threshold-based quantities (MTV41%-50%, TLG41%-50%) and their changes had AUC= 0.5-0.7. P-values were in all cases >> 0.05.Conclusions: The poor OS predictive power of the quantities determined from repeated FDG-PET-CT images indicates that the third week of treatment might not be suitable for treatment response assessment. Comparatively, the second week during the treatment appears to be a better time window.
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| 37. |
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| 38. |
- Lindstrom, Jan, et al.
(författare)
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Experimental assessment of a phosphor model for estimating the relative extrinsic efficiency in radioluminescent detectors
- 2020
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Ingår i: Physica medica (Testo stampato). - : Elsevier. - 1120-1797 .- 1724-191X. ; 76, s. 117-124
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Tidskriftsartikel (refereegranskat)abstract
- Optimising phosphor screens in dose detectors or imaging sensor designs is a cumbersome and time- consuming work normally involving specialised measuring equipment and advanced modelling. It is known that crucial optical parameters of the same phosphor may vary within a wide range of values. The aim of this work was to experimentally assess a simple previously published model where the case specific optical parameters (scattering and absorption) are instead represented by a fixed, single parameter, the light extinction factor, xi. The term extrinsic efficiency, N, of a phosphor is also introduced, differing from the common denotation "absolute efficiency", after noting that unknown factors (such as temperature dependence) can have an influence during efficiency estimations and hence difficult to claim absoluteness. N is expressed as the ratio of light energy emitted per unit area at the phosphor surface to incident x-ray energy fluence. By focusing on ratios and relative changes in this study, readily available instruments in a Medical Physics Department (i.e. a photometer) could be used. The varying relative extrinsic efficiency for an extended range of particle sizes (7.5 and 25 mu m) and layer thicknesses (220 to 830 mu m) were calculated in the model from the input parameters: the mean particle size of the phosphor, the layer thickness, the light extinction factor and the calculated energy imparted to the layer. In-house manufactured screens (Gd2O2S:Tb) were used for better control of design parameters. The model provided good qualitative agreement to experiment with quantitative deviations in relative extrinsic efficiency within approximately 2%.
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| 39. |
- Lorentsson, Robert, 1969, et al.
(författare)
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Evaluation of an automatic method for detection of defects in linear and curvilinear ultrasound transducers
- 2021
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Ingår i: Physica Medica-European Journal of Medical Physics. - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 84, s. 33-40
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The high incidence of defective ultrasound transducers in clinical practice has been shown in several studies. Recently, a novel method using only stored images for automatic detection of defective transducers was presented. The method makes it possible to remotely monitor many transducers at the same time and send a notification when a defective transducer is found. The purpose of the present study was to evaluate the novel method and assess how well it performs when compared to an established method as reference. Methods: To evaluate the novel method, in-air images were collected from 81 transducers in radiologic departments in nine hospitals. Two observers assessed the in-air images and marked the defects. Receiver operating characteristic (ROC)- and alternative free response receiver operating characteristic (AFROC)-curves and their figures of merit (FOM) were calculated for the novel method, using marked defects in the in-air images as reference truth. Results: The area under the ROC curve was 0.88 (SD 0.06), and the AFROC FOM was 0.71 (SE 0.07). Conclusion: The result shows that the novel method has a good agreement with the in-air method for detecting defects in ultrasound systems. This indicates that the novel method could be a complement to the normal quality control for early, and automatic detection of defects.
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| 40. |
- Lundman, Josef A., et al.
(författare)
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Effect of gradient field nonlinearity distortions in MRI-based attenuation maps for PET reconstruction
- 2017
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Ingår i: Physica medica (Testo stampato). - : Elsevier Sci Ltd. - 1120-1797 .- 1724-191X. ; 35, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Attenuation correction is a requirement for quantification of the activity distribution in PET. The need to base attenuation correction on MRI instead of CT has arisen with the introduction of integrated PET/MRI systems. The aim was to describe the effect of residual gradient field nonlinearity distortions on PET attenuation correction. Methods: MRI distortions caused by gradient field nonlinearity were simulated in CT images used for attenuation correction in PET reconstructions. The simulations yielded radial distortion of up to +/- 2: 3 mm at 15 cm from the scanner isocentre for distortion corrected images. The mean radial distortion of uncorrected images were 6.3 mm at the same distance. Reconstructions of PET data were performed using the distortion corrected images as well as the images where no correction had been applied. Results: The mean relative difference in reconstructed PET uptake intensity due to incomplete distortion correction was less than +/- 5%. The magnitude of this difference varied between patients and the size of the distortions remaining after distortion correction. Conclusions: Radial distortions of 2 mm at 15 cm radius from the scanner isocentre lead to PET attenuation correction errors smaller than 5%. Keeping the gradient field nonlinearity distortions below this limit can be a reasonable goal for MRI systems used for attenuation correction in PET for quantification purposes. A higher geometrical accuracy may, however, be warranted for quantification of peripheral lesions. These distortions can, e.g., be controlled at acceptance testing and subsequent quality assurance intervals.
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| 41. |
- Mavroidis, Panayiotis, et al.
(författare)
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Radiobiological evaluation of prostate cancer IMRT and conformal-RT plans using different treatment protocols
- 2017
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 40, s. 33-41
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to evaluate the clinical efficacy of both step-and-shoot IMRT and 3D-Conformal Radiation Therapy modalities (CRT) in treating prostate cancer using radiobiological measures. Another aim was to estimate the risks for developing secondary malignancies in bladder and rectum due to radiotherapy from the corresponding modalities. The treatment plans of ten prostate cancer patients were developed using IMRT and CRT. For the IMRT plans, two beam energies and two treatment protocols were used (the RTOG 0415 and a most restrictive one proposed by Fox Chase Cancer Center (FCCC)). For the evaluation of these plans, the complication-free tumor control probability, the total probability of injury, the total probability of control/benefit, and the biologically effective uniform dose were employed. Furthermore, based on the dosimetric data of IMRT and CRT, the risk for secondary malignancies was calculated for bladder and rectum. The average risk for secondary malignancy was lower for the bladder (0.37%) compared to the rectum (0.81%) based on all the treatment plans of the ten prostate cancer patients. The highest average risk for secondary malignancy for bladder and rectum was for the CRT-6X modality (0.46% and 1.12%, respectively) and the lowest was for the IMRT RTOG-18X modality (0.33% and 0.56%, respectively). The > Grade 2 LENT/SOMA response probability was lower for the bladder than for the rectum in all the plans. For the bladder the highest average value was for the IMRT RTOG-18X (0.9%) and the lowest was for the CRT-18X modality (0.1%). For the rectum, the highest average value was for the IMRT RTOG-6X (11.9%) and the lowest was for the IMRT FCCC-18X modality (2.2%). By using radiobiological measures it is shown that the IMRT FCCC plans had the lowest risks for normal tissue complications, whereas the IMRT RTOG had the highest. Regarding the risk for secondary malignancies, the CRT plans showed the highest values for both bladder and rectum.
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| 42. |
- Mondlane, Gracinda, 1987-, et al.
(författare)
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Comparative study of the calculated risk of radiation-induced cancer after photon- and proton-beam based radiosurgery of liver metastases
- 2017
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 42, s. 263-270
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Tidskriftsartikel (refereegranskat)abstract
- IntroductionThe potential of proton therapy to improve the sparing of the healthy tissue has been demonstrated in several studies. However, even small doses delivered to the organs at risk (OAR) may induce long-term detriments after radiotherapy. In this study, we investigated the possibility to reduce the risk of radiation-induced secondary cancers with intensity modulated proton therapy (IMPT), when used for radiosurgery of liver metastases.Material and methodsTen patients, previously treated for liver metastases with photon-beam based stereotactic body radiation therapy (SBRT) were retrospectively planned for radiosurgery with IMPT. A treatment plan comparison was then performed in terms of calculated risk of radiation-induced secondary cancer. The risks were estimated using two distinct models (Dasu et al., 2005; Schneider et al., 2005, 2009). The plans were compared pairwise with a two-sided Wilcoxon signed-rank test with a significance level of 0.05.ResultsReduced risks for induction of fatal and other types of cancers were estimated for the IMPT plans (p < 0.05) with the Dasu et al. model. Using the Schneider et al. model, lower risks for carcinomainduction with IMPT were estimated for the skin, lungs, healthy part of the liver, esophagus and the remaining part of the body (p < 0.05). The risk of observing sarcomas in the bone was also reduced with IMPT (p < 0.05).ConclusionThe findings of this study indicate that the risks of radiation-induced secondary cancers after radiosurgery of liver metastases may be reduced, if IMPT is used instead of photon-beam based SBRT.
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| 43. |
- Nieminen, Miika T., et al.
(författare)
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If you can make it, you can share it – Perspectives on the first DIY-fair at the European congress of medical physics (ECMP, DUBLIN 2022)
- 2024
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Ingår i: Physica medica (Testo stampato). - : Elsevier. - 1120-1797 .- 1724-191X. ; 118
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Tidskriftsartikel (refereegranskat)abstract
- The medical physics and engineering community is known for being active in conjuring do-it-yourself (DIY) -solutions to support their clinical and research work. To facilitate the exchange of solutions and ideas, a DIY-fair was held for the first time at the European Congress of Medical Physics (ECMP) in August 2022 in Dublin, Ireland. Altogether 32 contributions were presented, consisting of software, scripts, 3D-printed customized solutions, devices, gadgets and phantoms. All contributions were published in video format on a dedicated YouTube channel, and most were also presented in person at the conference. The fair demonstrated that there is an unmet need for sharing and distributing information on self-created solutions in the medical physics community. The authors propose the creation of a dedicated platform for sharing such content within our community, as well as a continuity of DIY-fairs at future ECMP meetings.
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| 44. |
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| 45. |
- Nowik, P., et al.
(författare)
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The synthetic localizer radiograph – A new CT scan planning method
- 2019
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 61, s. 58-63
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Tidskriftsartikel (refereegranskat)abstract
- Objective: To investigate if the conventional localizer radiograph (LR)can be replaced by a synthetic LR (SLR), generated from a low-dose spiral CT scan, for CT scan planning with minimal changes to current clinical workflows. Methods: A dosimetric comparison of SLRs and LRs was made using Monte Carlo methods. Water equivalent diameters (WEDs)of a centered and mis-centered phantom were estimated from low-dose spiral CT scans and LRs acquired at different angles. Body sizes, in the form of two lengths and two diameters obtained from SLRs and LRs, were compared for 10 patients (4 men and 6 women with a mean age of 74.8 and 76.2 years respectively)undergoing CT of thorax and abdomen. The image quality of SLRs for CT scan planning relative to LRs was rated using a 5-grade scale by four radiologists and two CT radiographers. Results: An SLR can be obtained at a comparable effective dose to that of traditionally acquired LRs: 0.14 mSv. WEDs from LRs were more affected by mis-centering than WEDs calculated from low-dose spiral scans. One significant discrepancy of estimated body sizes was observed, the broadest part of the patient that on lateral localizers showed a mean deviation of 17.7 mm (range: 7.3–28.7 mm, p < 0.001). The anteroposterior/posteroanterior SLR image quality was assessed as better compared to an LR while the same could not be shown for lateral localizers. Conclusions: SLRs based on low-dose spiral scans can replace LRs for CT planning.
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| 46. |
- Olofsson, Nils, et al.
(författare)
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Dosimetric robustness of lung tumor photon radiotherapy evaluated from multiple event CT imaging
- 2022
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Ingår i: Physica medica (Testo stampato). - : Elsevier. - 1120-1797 .- 1724-191X. ; 103, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Intrafractional respiratory motion is a concern for lung tumor radiotherapy but full evaluation of its impact is hampered by the lack of images representing the true motion. This study presents a novel evaluation using free-breathing images acquired over realistic treatment times to study the dosimetric impact of respiratory motion in photon radiotherapy.Methods: Cine-CT images of 14 patients with lung cancer acquired during eight minutes of free-breathing at three occasions were used to simulate dose tracking of four different planning methods. These methods aimed to deliver 54 Gy in three fractions to D50% of the target and were denoted as robust 4D (RB4), homogeneous fluence to the ITV (FLU) and an isodose prescription to the ITV with a high central dose (ISD), concurrently renormalized (IRN). Differences in dose coverage probability and homogeneity between the methods were quantified. Correlations between underdosage and attributes regarding the tumor and its motion were investigated.Results: Despite tumor motion amplitudes being larger than in the 4DCT all but FLU achieved the intended CTV D50% for the cohort average. For all methods but IRN at least 93% of the patients would have received 95% of the intended dose. No differences in D50% were found between RB4 and ISD nor IRN. However, RB4 led to better homogeneity.Conclusions: Tumor motion in free-breathing not covered by the 4DCT had a small impact on dose. The RB4 is recommended for planning of free-breathing treatments. No factor was found that consistently correlated dose degradation with patient or motion attributes.
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| 47. |
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| 48. |
- Palm, Stig, 1964
(författare)
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Clinical alpha-particle dosimetry.
- 2018
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Ingår i: Physica medica. - 1120-1797 .- 1724-191X.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 49. |
- Quast, Ulrich, et al.
(författare)
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A brachytherapy photon radiation quality index Q(BT) for probe-type dosimetry
- 2016
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Ingår i: Physica medica (Testo stampato). - : ELSEVIER SCI LTD. - 1120-1797 .- 1724-191X. ; 32:6, s. 741-748
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: In photon brachytherapy (BT), experimental dosimetry is needed to verify treatment plans if planning algorithms neglect varying attenuation, absorption or scattering conditions. The detectors response is energy dependent, including the detector material to water dose ratio and the intrinsic mechanisms. The local mean photon energy E(r) must be known or another equivalent energy quality parameter used. We propose the brachytherapy photon radiation quality index Q(BT) ((E) over bar), to characterize the photon radiation quality in view of measurements of distributions of the absorbed dose to water, D-w, around BT sources. Materials and methods: While the external photon beam radiotherapy (EBRT) radiation quality index Q(EBRT) ((E) over bar) = TPR1020((E) over bar) is not applicable to BT, the authors have applied a novel energy dependent parameter, called brachytherapy photon radiation quality index, defined as Q(BT) ((E) over bar) = D-prim(r = 2 cm; theta(0) = 90 degrees)/D-prim(r(0) = 1 cm; theta(0) = 90 degrees), utilizing precise primary absorbed dose data, D-prim, from source reference databases, without additional MC-calculations. Results and discussion: For BT photon sources used clinically, Q(BT) ((E) over bar) enables to determine the effective mean linear attenuation coefficient (mu) over bar (E) and thus the effective energy of the primary photons E-prim(eff)(r(0), theta(0)) at the TG-43 reference position P-ref (r(0) = 1 cm; theta(0) = 90 degrees) being close to the mean total photon energy (E) over bar (tot)(r(0), theta(0)). If one has calibrated detectors, published (E) over bar (tot)(r) and the BT radiation quality correction factor k(Q, Q0)(BT) ((E) over bar, r, theta) for different BT radiation qualities Q and Q(0), the detectors response can be determined and D-w(r, theta) measured in the vicinity of BT photon sources. Conclusions: This novel brachytherapy photon radiation quality index Q(BT) characterizes sufficiently accurate and precise the primary photon` s penetration probability and scattering potential. (C) 2016 Published by Elsevier Ltd on behalf of Associazione Italiana di Fisica Medica.
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| 50. |
- Raptis, Apostolos, et al.
(författare)
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Cancer risk after breast proton therapy considering physiological and radiobiological uncertainties
- 2020
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 76, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- Background: The reduced normal tissue dose burden from protons can reduce the risk of second cancer for breast cancer patients. Breathing motion and the impact of variable relative biological effectiveness (RBE) are however concerns for proton dose distributions. This study aimed to quantify the impact of these factors on risk predictions from proton and photon therapy.Materials and methods: Twelve patients were planned in free breathing with protons and photons to deliver 50 Gy (RBE) in 25 fractions (assuming RBE = 1.1 for protons) to the left breast. Second cancer risk was evaluated with several models for the lungs, contralateral breast, heart and esophagus as organs at risk (OARs). Plans were recalculated on CT-datasets acquired in extreme phases to account for breathing motion. Proton plans were also recalculated assuming variable RBE for a range of radiobiological parameters.Results: The OARs received substantially lower doses from protons compared to photons. The highest risks were for the lungs (average second cancer risks of 0.31% and 0.12% from photon and proton plans, respectively). The reduced risk with protons was maintained, even when breathing and/or RBE variation were taken into account. Furthermore, while the total risks from the photon plans were seen to increase with the integral dose, no such correlation was observed for the proton plans.Conclusions: Protons have an advantage over the photons with respect to the induction of cancer. Uncertainties in physiological movements and radiobiological parameters affected the absolute risk estimates, but not the general trend of lower risk associated with proton therapy.
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