19 results on '"Thierens, H."'
Search Results
2. Monte Carlo modeling of the ModuLeaf miniature MLC for small field dosimetry and quality assurance of the clinical treatment planning system.
- Author
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Crop F, Reynaert N, Pittomvils G, Paelinck L, De Gersem W, De Wagter C, Vakaet L, De Neve W, and Thierens H
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- Algorithms, Computer Simulation, Dose-Response Relationship, Radiation, Humans, Monte Carlo Method, Particle Accelerators, Phantoms, Imaging, Photons, Quality Control, Radiation Dosage, Radiometry, Radiosurgery instrumentation, Radiotherapy Dosage, X-Ray Film, Radiotherapy Planning, Computer-Assisted methods
- Abstract
The purpose of this investigation was the verification of both the measured data and quality of the implementation of the add-on ModuLeaf miniature multileaf collimator (ML mMLC) into the clinical treatment planning system for conformal stereotactic radiosurgery treatment. To this end the treatment head with ML mMLC was modeled in the BEAMnrc Monte Carlo (MC) code. The 6 MV photon beams used in the setup were first benchmarked with a set of measurements. A total ML mMLC transmission of 1.13% of the 10 x 10 cm2 open field dose was measured and reproduced with the BEAMnrc/DOSXYZnrc code. Correspondence between calculated and measured output factors (OFs) was within 2%. Correspondence between MC and measured profiles was within 2% dose and 2 mm distance, only for the smallest 0.5 x 0.5 cm2 field the results were within 3% dose. In the next step, the MC model was compared with Gafchromic film measurements and Pinnacle(3) 7.4 f (convolution superposition algorithm) calculated dose distributions, using a gamma evaluation comparison, for a multi-beam patient setup delivered to a Lucytrade mark phantom. The gamma evaluation of the MC versus Gafchromic film resulted in 3.4% of points not fulfilling gamma
- Published
- 2007
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- View/download PDF
3. Conversion of CT numbers into tissue parameters for Monte Carlo dose calculations: a multi-centre study.
- Author
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Vanderstraeten B, Chin PW, Fix M, Leal A, Mora G, Reynaert N, Seco J, Soukup M, Spezi E, De Neve W, and Thierens H
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- Biophysical Phenomena, Biophysics, Female, Humans, Male, Monte Carlo Method, Phantoms, Imaging, Radiotherapy, High-Energy, Neoplasms diagnostic imaging, Neoplasms radiotherapy, Radiotherapy Planning, Computer-Assisted statistics & numerical data, Tomography, X-Ray Computed statistics & numerical data
- Abstract
The conversion of computed tomography (CT) numbers into material composition and mass density data influences the accuracy of patient dose calculations in Monte Carlo treatment planning (MCTP). The aim of our work was to develop a CT conversion scheme by performing a stoichiometric CT calibration. Fourteen dosimetrically equivalent tissue subsets (bins), of which ten bone bins, were created. After validating the proposed CT conversion scheme on phantoms, it was compared to a conventional five bin scheme with only one bone bin. This resulted in dose distributions D(14) and D(5) for nine clinical patient cases in a European multi-centre study. The observed local relative differences in dose to medium were mostly smaller than 5%. The dose-volume histograms of both targets and organs at risk were comparable, although within bony structures D(14) was found to be slightly but systematically higher than D(5). Converting dose to medium to dose to water (D(14) to D(14wat) and D(5) to D(5wat)) resulted in larger local differences as D(5wat) became up to 10% higher than D(14wat). In conclusion, multiple bone bins need to be introduced when Monte Carlo (MC) calculations of patient dose distributions are converted to dose to water.
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- 2007
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4. Comparison of 6 MV and 18 MV photons for IMRT treatment of lung cancer.
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Madani I, Vanderstraeten B, Bral S, Coghe M, De Gersem W, De Wagter C, Thierens H, and De Neve W
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- Aged, Dose-Response Relationship, Radiation, Female, Humans, Male, Middle Aged, Monte Carlo Method, Radiotherapy Dosage, Carcinoma, Non-Small-Cell Lung radiotherapy, Lung Neoplasms radiotherapy, Photons, Radiotherapy Planning, Computer-Assisted
- Abstract
Background and Purpose: To compare 6 MV and 18 MV photon intensity modulated radiotherapy (IMRT) for non-small cell lung cancer., Materials and Methods: Doses for a cohort of 10 patients, typical for our department, were computed with a commercially available convolution/superposition (CS) algorithm. Final dose computation was also performed with a dedicated IMRT Monte Carlo dose engine (MCDE)., Results: CS plans showed higher D(95%) (Gy) for the GTV (68.13 vs 67.36, p=0.004) and CTV (67.23 vs 66.87, p=0.028) with 18 than with 6 MV photons. MCDE computations demonstrated higher doses with 6 MV than 18 MV in D(95%) for the PTV (64.62 vs 63.64, p=0.009), PTV(optim) (65.48 vs 64.83, p=0.014) and CTV (66.22 vs 65.64, p=0.027). Dose inhomogeneity was lower with 18 than with 6 MV photons for GTV (0.08 vs 0.09, p=0.007) and CTV (0.10 vs 0.11, p=0.045) in CS but not MCDE plans. 6 MV photons significantly (D(33%); p=0.045) spared the esophagus in MCDE plans. Observed dose differences between lower and higher energy IMRT plans were dependent on the individual patient., Conclusions: Selection of photon energy depends on priority ranking of endpoints and individual patients. In the absence of highly accurate dose computation algorithms such as CS and MCDE, 6 MV photons may be the prudent choice.
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- 2007
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5. Comparison of dose-volume histograms of IMRT treatment plans for ethmoid sinus cancer computed by advanced treatment planning systems including Monte Carlo.
- Author
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Paelinck L, Smedt BD, Reynaert N, Coghe M, Gersem WD, Wagter CD, Vanderstraeten B, Thierens H, and Neve WD
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- Dose-Response Relationship, Radiation, Humans, Ethmoid Sinus radiation effects, Monte Carlo Method, Paranasal Sinus Neoplasms radiotherapy, Radiotherapy Planning, Computer-Assisted, Radiotherapy, Intensity-Modulated
- Abstract
Background and Purpose: To recompute clinical intensity-modulated treatment plans for ethmoid sinus cancer and to compare quantitatively the dose-volume histograms (DVHs) of the planning target volume (PTV) and the optic organs at risk., Material and Methods: Ten step-and-shoot intensity-modulated treatment plans were enrolled in this study. Large natural and surgical air cavities challenged the calculation systems. Each optimized treatment plan was recalculated by two superposition convolution (TMS and Pinnacle) and a Monte Carlo system (MCDE). To compare the resulting DVHs, a one-way ANOVA for repeated measurements was performed and multiple pairwise comparisons were made., Results: The tails of the PTV-DVHs were significantly higher for the Monte Carlo system. The DVHs of the critical organs displayed some statistically but not always clinically significant differences. For the individual patients, the three planning systems sometimes reproduced clinically discrepant DVHs that were not significantly different when averaged over all patients., Conclusions: Dose to air cavities contains computational uncertainty. As this dose is clinically irrelevant and optimizing it is meaningless, we recommended extracting the air from the PTV when constructing the PTV-DVH. The planning systems considered reproduce DVHs that are significantly different, especially in the tail region of PTV-DVHs.
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- 2006
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6. Accuracy of patient dose calculation for lung IMRT: A comparison of Monte Carlo, convolution/superposition, and pencil beam computations.
- Author
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Vanderstraeten B, Reynaert N, Paelinck L, Madani I, De Wagter C, De Gersem W, De Neve W, and Thierens H
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- Body Burden, Carcinoma, Non-Small-Cell Lung physiopathology, Computer Simulation, Humans, Lung Neoplasms physiopathology, Models, Statistical, Monte Carlo Method, Organ Specificity, Radiotherapy Dosage, Relative Biological Effectiveness, Reproducibility of Results, Sensitivity and Specificity, Algorithms, Carcinoma, Non-Small-Cell Lung radiotherapy, Lung Neoplasms radiotherapy, Models, Biological, Radiometry methods, Radiotherapy Planning, Computer-Assisted methods, Radiotherapy, Conformal methods
- Abstract
The accuracy of dose computation within the lungs depends strongly on the performance of the calculation algorithm in regions of electronic disequilibrium that arise near tissue inhomogeneities with large density variations. There is a lack of data evaluating the performance of highly developed analytical dose calculation algorithms compared to Monte Carlo computations in a clinical setting. We compared full Monte Carlo calculations (performed by our Monte Carlo dose engine MCDE) with two different commercial convolution/superposition (CS) implementations (Pinnacle-CS and Helax-TMS's collapsed cone model Helax-CC) and one pencil beam algorithm (Helax-TMS's pencil beam model Helax-PB) for 10 intensity modulated radiation therapy (IMRT) lung cancer patients. Treatment plans were created for two photon beam qualities (6 and 18 MV). For each dose calculation algorithm, patient, and beam quality, the following set of clinically relevant dose-volume values was reported: (i) minimal, median, and maximal dose (Dmin, D50, and Dmax) for the gross tumor and planning target volumes (GTV and PTV); (ii) the volume of the lungs (excluding the GTV) receiving at least 20 and 30 Gy (V20 and V30) and the mean lung dose; (iii) the 33rd percentile dose (D33) and Dmax delivered to the heart and the expanded esophagus; and (iv) Dmax for the expanded spinal cord. Statistical analysis was performed by means of one-way analysis of variance for repeated measurements and Tukey pairwise comparison of means. Pinnacle-CS showed an excellent agreement with MCDE within the target structures, whereas the best correspondence for the organs at risk (OARs) was found between Helax-CC and MCDE. Results from Helax-PB were unsatisfying for both targets and OARs. Additionally, individual patient results were analyzed. Within the target structures, deviations above 5% were found in one patient for the comparison of MCDE and Helax-CC, while all differences between MCDE and Pinnacle-CS were below 5%. For both Pinnacle-CS and Helax-CC, deviations from MCDE above 5% were found within the OARs: within the lungs for two (6 MV) and six (18 MV) patients for Pinnacle-CS, and within other OARs for two patients for Helax-CC (for Dmax of the heart and D33 of the expanded esophagus) but only for 6 MV. For one patient, all four algorithms were used to recompute the dose after replacing all computed tomography voxels within the patient's skin contour by water. This made all differences above 5% between MCDE and the other dose calculation algorithms disappear. Thus, the observed deviations mainly arose from differences in particle transport modeling within the lungs, and the commissioning of the algorithms was adequately performed (or the commissioning was less important for this type of treatment). In conclusion, not one pair of the dose calculation algorithms we investigated could provide results that were consistent within 5% for all 10 patients for the set of clinically relevant dose-volume indices studied. As the results from both CS algorithms differed significantly, care should be taken when evaluating treatment plans as the choice of dose calculation algorithm may influence clinical results. Full Monte Carlo provides a great benchmarking tool for evaluating the performance of other algorithms for patient dose computations.
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- 2006
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7. Implementation of biologically conformal radiation therapy (BCRT) in an algorithmic segmentation-based inverse planning approach.
- Author
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Vanderstraeten B, De Gersem W, Duthoy W, De Neve W, and Thierens H
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- Computer Simulation, Fluorodeoxyglucose F18, Humans, Image Interpretation, Computer-Assisted methods, Radiopharmaceuticals, Radiotherapy Dosage, Models, Biological, Oropharyngeal Neoplasms diagnostic imaging, Oropharyngeal Neoplasms radiotherapy, Positron-Emission Tomography methods, Radiometry methods, Radiotherapy Planning, Computer-Assisted methods, Radiotherapy, Conformal methods
- Abstract
The development of new biological imaging technologies offers the opportunity to further individualize radiotherapy. Biologically conformal radiation therapy (BCRT) implies the use of the spatial distribution of one or more radiobiological parameters to guide the IMRT dose prescription. Our aim was to implement BCRT in an algorithmic segmentation-based planning approach. A biology-based segmentation tool was developed to generate initial beam segments that reflect the biological signal intensity pattern. The weights and shapes of the initial segments are optimized by means of an objective function that minimizes the root mean square deviation between the actual and intended dose values within the PTV. As proof of principle, [(18)F]FDG-PET-guided BCRT plans for two different levels of dose escalation were created for an oropharyngeal cancer patient. Both plans proved to be dosimetrically feasible without violating the planning constraints for the expanded spinal cord and the contralateral parotid gland as organs at risk. The obtained biological conformity was better for the first (2.5 Gy per fraction) than for the second (3 Gy per fraction) dose escalation level.
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- 2006
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8. Denoising of Monte Carlo dose calculations: smoothing capabilities versus introduction of systematic bias.
- Author
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De Smedt B, Fippel M, Reynaert N, and Thierens H
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- Filtration methods, Head and Neck Neoplasms diagnostic imaging, Head and Neck Neoplasms pathology, Humans, Phantoms, Imaging, Radiography, Algorithms, Bias, Head and Neck Neoplasms radiotherapy, Monte Carlo Method, Radiotherapy Planning, Computer-Assisted methods
- Abstract
In order to evaluate the performance of denoising algorithms applied to Monte Carlo calculated dose distributions, conventional evaluation methods (rms difference, 1% and 2% difference) can be used. However, it is illustrated that these evaluation methods sometimes underestimate the introduction of bias, since possible bias effects are averaged out over the complete dose distribution. In the present work, a new evaluation method is introduced based on a sliding window superimposed on a difference dose distribution (reference dose-noisy/denoised dose). To illustrate its importance, a new denoising technique (ANRT) is presented based upon a combination of the principles of bilateral filtering and Savitzky-Golay filters. This technique is very conservative in order to limit the introduction of bias in high dose gradient regions. ANRT is compared with IRON for three challenging cases, namely an electron and photon beam impinging on heterogeneous phantoms and two IMRT treatment plans of head-and-neck cancer patients to determine the clinical relevance of the obtained results. For the electron beam case, IRON outperforms ANRT concerning the smoothing capabilities, while no differences in systematic bias are observed. However, for the photon beam case, although ANRT and IRON perform equally well on the conventional evaluation tests (rms difference, 1% and 2% difference), IRON clearly introduces much more bias in the penumbral regions while ANRT seems to introduce no bias at all. When applied to the IMRT patient cases, both denoising methods perform equally well regarding smoothing and bias introduction. This is probably caused by the summation of a large set of different beam segments, decreasing dose gradients compared to a single beam. A reduction in calculation time without introducing large systematic bias can shorten a Monte Carlo treatment planning process considerably and is therefore very useful for the initial trial and error phase of the treatment planning process.
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- 2006
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9. Investigation of geometrical and scoring grid resolution for Monte Carlo dose calculations for IMRT.
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De Smedt B, Vanderstraeten B, Reynaert N, De Neve W, and Thierens H
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- Body Burden, Computer Simulation, Humans, Models, Statistical, Monte Carlo Method, Radiation Protection methods, Radiotherapy Dosage, Relative Biological Effectiveness, Risk Assessment methods, Risk Factors, Transducers, Algorithms, Head and Neck Neoplasms radiotherapy, Lung Neoplasms radiotherapy, Models, Biological, Radiometry methods, Radiotherapy Planning, Computer-Assisted methods, Radiotherapy, Conformal methods
- Abstract
Monte Carlo based treatment planning of two different patient groups treated with step-and-shoot IMRT (head-and-neck and lung treatments) with different CT resolutions and scoring methods is performed to determine the effect of geometrical and scoring voxel sizes on DVHs and calculation times. Dose scoring is performed in two different ways: directly into geometrical voxels (or in a number of grouped geometrical voxels) or into scoring voxels defined by a separate scoring grid superimposed on the geometrical grid. For the head-and-neck cancer patients, more than 2% difference is noted in the right optical nerve when using voxel dimensions of 4 x 4 x 4 mm3 compared to the reference calculation with 1 x 1 x 2 mm3 voxel dimensions. For the lung cancer patients, 2% difference is noted in the spinal cord when using voxel dimensions of 4 x 4 x 10 mm3 compared to the 1 x 1 x 5 mm3 calculation. An independent scoring grid introduces several advantages. In cases where a relatively high geometrical resolution is required and where the scoring resolution is less important, the number of scoring voxels can be limited while maintaining a high geometrical resolution. This can be achieved either by grouping several geometrical voxels together into scoring voxels or by superimposing a separate scoring grid of spherical voxels with a user-defined radius on the geometrical grid. For the studied lung cancer cases, both methods produce accurate results and introduce a speed increase by a factor of 10-36. In cases where a low geometrical resolution is allowed, but where a high scoring resolution is required, superimposing a separate scoring grid on the geometrical grid allows a reduction in geometrical voxels while maintaining a high scoring resolution. For the studied head-and-neck cancer cases, calculations performed with a geometrical resolution of 2 x 2 x 2 mm3 and a separate scoring grid containing spherical scoring voxels with a radius of 2 mm produce accurate results and introduce a speed increase by a factor of 13. The scoring grid provides an additional degree of freedom for limiting calculation time and memory requirements by selecting optimized scoring and geometrical voxel dimensions in an independent way.
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- 2005
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10. Experimental verification of lung dose with radiochromic film: comparison with Monte Carlo simulations and commercially available treatment planning systems.
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Paelinck L, Reynaert N, Thierens H, De Neve W, and De Wagter C
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- Body Burden, Film Dosimetry methods, Humans, Lung radiation effects, Monte Carlo Method, Organ Specificity, Quality Assurance, Health Care methods, Relative Biological Effectiveness, Reproducibility of Results, Sensitivity and Specificity, Algorithms, Lung physiopathology, Lung Neoplasms radiotherapy, Models, Biological, Radiation Protection methods, Radiometry methods, Radiotherapy Planning, Computer-Assisted methods
- Abstract
The purpose of this study was to assess the absorbed dose in and around lung tissue by performing radiochromic film measurements, Monte Carlo simulations and calculations with superposition convolution algorithms. We considered a layered polystyrene phantom of 12 x 12 x 12 cm3 containing a central cavity of 6 x 6 x 6 cm3 filled with Gammex RMI lung-equivalent material. Two field configurations were investigated, a small 1 x 10 cm2 field and a larger 10 x 10 cm2 field. First, we performed Monte Carlo simulations to investigate the influence of radiochromic film itself on the measured dose distribution when the film intersects a lung-equivalent region and is oriented parallel to the central beam axis. To that end, the film and the lung-equivalent materials were modelled in detail, taking into account their specific composition. Next, measurements were performed with the film oriented both parallel and perpendicular to the central beam axis to verify the results of our Monte Carlo simulations. Finally, we digitized the phantom in two commercially available treatment planning systems, Helax-TMS version 6.1A and Pinnacle version 6.2b, and calculated the absorbed dose in the phantom with their incorporated superposition convolution algorithms to compare with the Monte Carlo simulations. Comparing Monte Carlo simulations with measurements reveals that radiochromic film is a reliable dosimeter in and around lung-equivalent regions when the film is positioned perpendicular to the central beam axis. Radiochromic film is also able to predict the absorbed dose accurately when the film is positioned parallel to the central beam axis through the lung-equivalent region. However, attention must be paid when the film is not positioned along the central beam axis, in which case the film gradually attenuates the beam and decreases the dose measured behind the cavity. This underdosage disappears by offsetting the film a few centimetres. We find deviations of about 3.6% between Monte Carlo and the superposition convolution algorithm of Pinnacle behind the lung region, for both field configurations. Pinnacle is quite accurate in the lung region. Deviations up to 5.6% for the small field are found in the lung region between Monte Carlo and the superposition convolution algorithm of Helax-TMS. Behind the lung region, Helax-TMS is in better agreement with Monte Carlo. Radiochromic film measurements or Monte Carlo simulations are reliable methods to establish the dose in and around lung tissue.
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- 2005
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11. The importance of accurate linear accelerator head modelling for IMRT Monte Carlo calculations.
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Reynaert N, Coghe M, De Smedt B, Paelinck L, Vanderstraeten B, De Gersem W, Van Duyse B, De Wagter C, De Neve W, and Thierens H
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- Dose-Response Relationship, Radiation, Humans, Models, Theoretical, Monte Carlo Method, Phantoms, Imaging, Software, Time Factors, Tomography, X-Ray Computed, Head pathology, Head and Neck Neoplasms radiotherapy, Particle Accelerators instrumentation, Radiotherapy Planning, Computer-Assisted methods, Radiotherapy, Conformal methods
- Abstract
Two Monte Carlo dose engines for radiotherapy treatment planning, namely a beta release of Peregrine and MCDE (Monte Carlo dose engine), were compared with Helax-TMS (collapsed cone superposition convolution) for a head and neck patient for the Elekta SLi plus linear accelerator. Deviations between the beta release of Peregrine and MCDE up to 10% were obtained in the dose volume histogram of the optical chiasm. It was illustrated that the differences are not caused by the particle transport in the patient, but by the modelling of the Elekta SLi plus accelerator head and more specifically the multileaf collimator (MLC). In MCDE two MLC modules (MLCQ and MLCE) were introduced to study the influence of the tongue-and-groove geometry, leaf bank tilt and leakage on the actual dose volume histograms. Differences in integral dose in the optical chiasm up to 3% between the two modules have been obtained. For single small offset beams though the FWHM of lateral profiles obtained with MLCE can differ by more than 1.5 mm from profiles obtained with MLCQ. Therefore, and because the recent version of MLCE is as fast as MLCQ, we advise to use MLCE for modelling the Elekta MLC. Nevertheless there still remains a large difference (up to 10%) between Peregrine and MCDE. By studying small offset beams we have shown that the profiles obtained with Peregrine are shifted, too wide and too flat compared with MCDE and phantom measurements. The overestimated integral doses for small beam segments explain the deviations observed in the dose volume histograms. The Helax-TMS results are in better agreement with MCDE, although deviations exceeding 5% have been observed in the optical chiasm. Monte Carlo dose deviations of more than 10% as found with Peregrine are unacceptable as an influence on the clinical outcome is possible and as the purpose of Monte Carlo treatment planning is to obtain an accuracy of 2%. We would like to emphasize that only the Elekta MLC has been tested in this work, so it is certainly possible that alpha releases of Peregrine provide more accurate results for other accelerators.
- Published
- 2005
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12. DOSSCORE: an accelerated DOSXYZnrc code with an efficient stepping algorithm and scoring grid.
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De Smedt B, Reynaert N, De Neve W, and Thierens H
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- Electrons, Humans, Monte Carlo Method, Neoplasms radiotherapy, Phantoms, Imaging, Photons therapeutic use, Scattering, Radiation, Algorithms, Radiation Dosage, Radiotherapy Planning, Computer-Assisted
- Abstract
DOSSCORE is an accelerated version of DOSXYZnrc that allows photons to cross voxel boundaries of the same medium and utilizes a separate scoring grid superimposed on the geometrical grid. Two different stepping algorithms, the hownear method and the scaling method are implemented in DOSSCORE. The hownear method allows particles to travel larger distances in homogeneous regions where there is no interest in the dose deposition of these particles, whilst the scaling method utilizes a stepping algorithm in which particles are only slowed down by the boundaries of the geometrical voxels and not by the boundaries of the scoring voxels. For CT-based phantoms, only photon ray tracing is applied, which results in a rather modest speed gain of factor 1.2 compared to DOSXYZnrc. The hownear method and scaling method do not increase the speed for CT-based phantoms, but only for homogeneous phantoms and phantoms with a limited number of small heterogeneities. In cases where a small number of scoring voxels are needed, the hownear method performs better than the scaling method, whilst the opposite is true for cases when many scoring voxels are needed. The photon transport is accelerated by almost a factor of 2 for all phantoms (homogeneous, heterogeneous with much homogeneity and CT-based phantoms) compared to DOSXYZnrc. For a small number of scoring voxels, the hownear method is up to a factor of 2.6 and 1.9 faster than DOSXYZnrc for homogeneous and heterogeneous phantoms in the case of photon beams. For an electron beam, a speed gain of factor 2.4 is obtained. For a full scoring grid like the one used in DOSXYZnrc, the scaling method is up to a factor of 2.2 and 1.7 faster than DOSXYZnrc for homogeneous and heterogeneous phantoms in the case of photon beams. For an electron beam, a speed gain of factor 2 is obtained. A speed increase without biasing the results is very relevant. The use of two separate grids, the more efficient stepping algorithms and the accelerated photon transport can be applied to every EGS-based or other Monte Carlo code.
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- 2004
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13. Monte Carlo model of the Elekta SLiplus accelerator: validation of a new MLC component module in BEAM for a 6 MV beam.
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Van de Walle J, Martens C, Reynaert N, Palmans H, Coghe M, De Neve W, De Wagter C, and Thierens H
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- Equipment Design, Equipment Failure Analysis methods, Monte Carlo Method, Quality Control, Radiometry, Radiotherapy Dosage, Scattering, Radiation, Software Validation, Algorithms, Radiotherapy Planning, Computer-Assisted methods, Radiotherapy, Conformal instrumentation, Radiotherapy, Conformal methods
- Abstract
A new component module (CM), called MLCE, has been implemented in the BEAM program. The CM takes into account the particular 'tongue-and-groove' design of the Elekta multi-leaf collimator (MLC) and the air gap between the leaves. The model was validated by two series of measurements and simulations. The first benchmarking series focuses on the interleaf leakage and the intraleaf transmission. The measurement showed a total transmission through the MLC of 1.42% of the open field dose. Two Monte Carlo (MC) simulations were made, the first with the new CM MLCE (inclusive of air gap) and the second with the CM MLCQ (exclusive of air gap), which is available in the BEAM distribution. When the air gap between the leaves was determined by varying the parameters of the leaf geometry within tolerance limits on the technical drawing, the total measured transmission of 1.42% was well reproduced by the CM MLCE. In contrast, MC simulations with MLCQ showed that the transmission through the MLC calculated without the interleaf leakage is only 44% of the total transmitted radiation. The relevance of the detailed MLC modelling was demonstrated also by studying the 'adjacent' tongue-and-groove effect, where two adjacent (not opposing) leaves are complementary, opened or closed. The two complementary leaf settings were simulated both with the CM MLCE and MLCQ. A comparison with measurements was made. In regions covered by two or more leaves, the dose increased by 14% for two leaves and by 40% for more than two leaves when the interleaf leakage was included in the transmission. The tongue-and-groove effect was perfectly reproduced by the MLCE module.
- Published
- 2003
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14. Patient dosimetry for 131I-MIBG therapy for neuroendocrine tumours based on 123I-MIBG scans.
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Monsieurs M, Brans B, Bacher K, Dierckx R, and Thierens H
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- Adolescent, Adult, Aged, Body Burden, Child, Child, Preschool, Feasibility Studies, Female, Follow-Up Studies, Humans, Male, Middle Aged, Radiometry methods, Radionuclide Imaging, Radiopharmaceuticals therapeutic use, Radiotherapy Dosage, 3-Iodobenzylguanidine therapeutic use, Neuroendocrine Tumors diagnostic imaging, Neuroendocrine Tumors radiotherapy, Radiotherapy Planning, Computer-Assisted methods, Whole-Body Counting methods
- Abstract
Pre-therapeutic metaiodobenzylguanidine (MIBG) scans can be performed using labelling with either iodine-123 or iodine-131. (123)I-MIBG scans provide better image quality and count statistics, while (131)I-MIBG allows registration of tracer kinetics over a longer period. The aim of this study was to determine how much information about the (131)I-MIBG therapy total body dose according to the MIRD formalism can be gathered from (123)I-MIBG pre-therapy scans. Thirty-eight (131)I-MIBG therapies administered to a total of 15 patients suffering from neuroblastoma ( n=6), carcinoid tumours ( n=5), phaeochromocytoma ( n=3) and medullary thyroid carcinoma ( n=1) were included. The mean administered activity was 5.3 GBq (SD 2.4 GBq). Three biplanar (123)I-MIBG total body scans were taken only once before a series of therapies while three biplanar (131)I-MIBG scans were taken after each therapy. Attenuation correction was performed taking into account the difference in attenuation between (123)I and (131)I. Using the MIRD formalism, the total body dose to the patient was calculated on the basis of: (1) a single exponential fit drawn through the data from the (123)I-MIBG pre-therapy scans, (2) a bi-exponential fit through the combined data of (123)I-MIBG pre-therapy and (131)I-MIBG post-therapy scans. The mean total body dose calculated in our study was significantly higher for patients suffering from neuroblastoma (mean+/-SD 0.37+/-0.21 mGy/MBq) than for patients suffering from phaeochromocytoma (0.08+/-0.02 mGy/MBq), carcinoid tumours (0.07+/-0.01 mGy/MBq) and medullary thyroid carcinoma (0.09 mGy/MBq). The correlation coefficient between the dose calculated on the basis of the (123)I-MIBG pre-therapy scans and the subsequent (131)I-MIBG therapy was 0.93 when a correction factor of 1.26 was taken into account. When considering all following therapies, the correlation was 0.85 and the correction factor, 1.20. Our results show that it is feasible to use data from pre-therapy (123)I-MIBG scans to calculate the total body dose of the subsequent (131)I-MIBG therapy.
- Published
- 2002
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15. Dosimetry of 192Ir sources used for endovascular brachytherapy.
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Reynaert N, Van Eijkeren M, Taeymans Y, and Thierens H
- Subjects
- Angioplasty, Balloon, Coronary, Biophysical Phenomena, Biophysics, Combined Modality Therapy, Coronary Disease therapy, Humans, Monte Carlo Method, Phantoms, Imaging, Radiometry instrumentation, Radiometry methods, Recurrence, Brachytherapy methods, Coronary Disease radiotherapy, Iridium Radioisotopes therapeutic use, Radiotherapy Planning, Computer-Assisted
- Abstract
An in-phantom calibration technique for 192Ir sources used for endovascular brachytherapy is presented. Three different source lengths were investigated. The calibration was performed in a solid phantom using a Farmer-type ionization chamber at source to detector distances ranging from 1 cm to 5 cm. The dosimetry protocol for medium-energy x-rays extended with a volume-averaging correction factor was used to convert the chamber reading to dose to water. The air kerma strength of the sources was determined as well. EGS4 Monte Carlo calculations were performed to determine the depth dose distribution at distances ranging from 0.6 mm to 10 cm from the source centre. In this way we were able to convert the absolute dose rate at 1 cm distance to the reference point chosen at 2 mm distance. The Monte Carlo results were confirmed by radiochromic film measurements, performed with a double-exposure technique. The dwell times to deliver a dose of 14 Gy at the reference point were determined and compared with results given by the source supplier (CORDIS). They determined the dwell times from a Sievert integration technique based on the source activity. The results from both methods agreed to within 2% for the 12 sources that were evaluated. A Visual Basic routine that superimposes dose distributions, based on the Monte Carlo calculations and the in-phantom calibration, onto intravascular ultrasound images is presented. This routine can be used as an online treatment planning program.
- Published
- 2001
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16. Monte Carlo calculations of dose distributions around 32P and 198Au stents for intravascular brachytherapy.
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Reynaert N, Verhaegen F, Taeymans Y, Van Eijkeren M, and Thierens H
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- Angioplasty, Balloon, Coronary, Biophysical Phenomena, Biophysics, Brachytherapy statistics & numerical data, Constriction, Pathologic, Gold Radioisotopes therapeutic use, Humans, Microscopy, Electron, Scanning, Phosphorus Radioisotopes therapeutic use, Blood Vessels radiation effects, Brachytherapy instrumentation, Monte Carlo Method, Radiotherapy Planning, Computer-Assisted statistics & numerical data, Stents
- Abstract
3D dose distributions are calculated for a 32P impregnated stent and a 198Au stent for intravascular brachytherapy with the EGS4 Monte Carlo simulation code. The stents were modeled as a combination of eight helicoidal struts. This allowed investigation of the effect of the stent geometry and the electron absorption in the strut material on the dose distributions. Absorbed dose to water was calculated at radial distances ranging from 50 microm to 5 mm from the stent surface. The dose distributions around the stents are compared to the dose distribution around an intravascular brachy-therapy 192Ir source, also calculated with the EGS4 Monte Carlo code. The dose profiles near the struts show hot spots. At 50 microm distance a peak to valley ratio of 3 for 32P and 6 for 198Au in the dose distribution is obtained. For both the isotopes the inhomogeneities decrease with distance and at a radial depth of 350 microm the effect becomes negligible. The calculations showed the importance of the effect of the absorption in the stent material as this leads to a dose decrease to 67% for the 198Au stent and to 77% for 32P near the stent at a distance of 2 mm from the stent axis. It is concluded that from the dosimetric point of view, the 198Au stent is inferior to the 32P stent and the 192Ir source. Application of the 198Au stent in clinical practice requires further investigation of the importance of the adventitia in the restenosis process, and the tolerance dose of the intima.
- Published
- 1999
- Full Text
- View/download PDF
17. In-water calibration of PDR 192Ir brachytherapy sources with an NE2571 ionization chamber.
- Author
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Reynaert N, Verhaegen F, and Thierens H
- Subjects
- Brachytherapy instrumentation, Calibration, Monte Carlo Method, Photons, Radiotherapy Dosage, Reproducibility of Results, Water, X-Rays, Brachytherapy methods, Iridium Radioisotopes therapeutic use, Phantoms, Imaging, Radiotherapy Planning, Computer-Assisted instrumentation, Radiotherapy Planning, Computer-Assisted methods
- Abstract
An ionometric calibration procedure for 192Ir PDR brachytherapy sources in terms of dose rate to water is presented. The calibration of the source is performed directly in a water phantom at short distances (1.0, 2.5 and 5.0 cm) using an NE2571 Farmer type ion chamber. To convert the measured air-kerma rate in water to dose rate to water a conversion factor (CF) was calculated by adapting the medium-energy x-ray dosimetry protocol for a point source geometry (diverging beam). The obtained CF was verified using two different methods. Firstly, the CF was calculated by Monte Carlo simulations, where the source-ionization chamber geometry was modelled accurately. In a second method, a combination of Monte Carlo simulations and measurements of the air-kerma rate in water (at 1.0, 2.5 and 5.0 cm distance) and in air (1 m distance) was used to determine the CF. The obtained CFs were also compared with conversion factors calculated with the adapted dosimetry protocol for high-energy photons introduced by Tölli. All calculations were done for a Gammamed PDR 192Ir source-NE2571 chamber geometry. The conversion factors obtained with the four different methods agree to within 1% at the three distances of interest. We obtained the following values (medium-energy x-ray protocol): CF(1 cm) = 1.458; CF(2.5 cm) = 1.162; CF(5.0 cm) = 1.112 (1 sigma = 0.7% for the three distances of interest). The obtained results were checked with TLD measurements. The values of the specific dose rate constant and the radial dose function calculated in this work are in accordance with the literature data.
- Published
- 1998
- Full Text
- View/download PDF
18. Comparison of measured and calculated dose distributions in lung after electron beam treatment of the chest wall.
- Author
-
Seuntjens J, Van der Plaetsen A, Thierens H, and Piessens M
- Subjects
- Biophysical Phenomena, Biophysics, Electrons, Humans, Models, Structural, Monte Carlo Method, Radiotherapy Dosage, Radiotherapy Planning, Computer-Assisted statistics & numerical data, Radiotherapy, High-Energy methods, Radiotherapy, High-Energy statistics & numerical data, Thermoluminescent Dosimetry, Thorax radiation effects, Lung radiation effects, Radiotherapy Planning, Computer-Assisted methods
- Abstract
In this paper a comparison of measured and calculated absorbed dose distributions due to 6 and 8 MeV electron irradiation of a thorax phantom consisting of layers of tissue equivalent materials and infinite cylindrical rib inhomogeneities are presented. Dose measurements, carried out in lung equivalent tissue using thermoluminescent dosimeters for the phantom with and without the rib inhomogeneities, are compared with calculations using a typical two-dimensional (2-D) treatment planning system and EGS4 Monte Carlo calculations. The results show that the used 2-D planning system generally reproduces the dose distribution for the phantom without the cylindrical inhomogeneities. As results from the calculations of ratios of the doses in the phantom with ribs to the doses in the phantom without ribs, the dose perturbations are well reproduced by the EGS4 Monte Carlo calculations, but seriously underestimated by the planning system. The deviations are in the same direction for both energies, but are more pronounced for 6 MeV electrons. The disagreement between the results of the planning system on one hand and the Monte Carlo calculations and experiments on the other hand for the multirib system used is examined further by calculating dose distributions for a phantom containing only one infinite rib. The calculations show that the 2-D treatment planning system generally yields broader and less profound minima in the dose distribution directly beneath the inhomogeneities, with deviations more prominent at lower energies. In addition to the limitation of the central ray approximation, it is suggested that these discrepancies may be due to a too large electron pencil beam spread resulting from the implementation of a range straggling modification function of limited validity at the depths beyond dose maximum for these energies and these tissues.
- Published
- 1994
- Full Text
- View/download PDF
19. Verification of absorbed doses determined with thimble and parallel-plate ionization chambers in clinical electron beams using ferrous sulphate dosimetry.
- Author
-
Van der Plaetsen A, Seuntjens J, Thierens H, and Vynckier S
- Subjects
- Biophysical Phenomena, Biophysics, Electrons, Ferrous Compounds, Humans, Models, Structural, Models, Theoretical, Particle Accelerators, Radiotherapy, High-Energy, Radiometry instrumentation, Radiotherapy Planning, Computer-Assisted
- Abstract
Absorbed dose values determined with the commonly applied NACP and PTW/Markus parallel-plate chambers and the cylindrical NE2571 Farmer chamber were compared to values obtained with ferrous sulphate dosimetry in a number of electron beams. For the ionometry with the parallel-plate chambers the dose-to-air chamber factor ND (or Ngas) was derived from a 60Co beam calibration free in air with an additional buildup layer of 0.54 g cm-2 graphite as proposed by the protocol for electron dosimetry published by the Netherlands Commission on Radiation Dosimetry. For the product kattkm in this calibration geometry values of 0.980 +/- 0.003 [1 standard deviation (s.d.)] and 0.993 +/- 0.004 (1 s.d.) were obtained for the parallel-plate NACP and PTW/Markus chambers, respectively. The behavior of the fluence perturbation correction factor pf versus the mean electron energy at depth was deduced for the flat PTW/Markus and cylindrical NE2571 chamber by comparison with the NACP chamber, for which pf was assumed unity. Our results show a small but significant energy dependence of pf for the PTW/Markus chamber. The absorbed dose values, determined ionometrically with the different chambers considered in the study using the experimentally determined kattkm and pf values, are systematically 0.5% higher than those obtained with ferrous sulphate dosimetry adopting 352 x 10(-6) m-2 kg-1 Gy-1 for epsilon mG. The performed comparative study confirms also that for the NACP chamber pf is unity independent of the electron energy down to a mean energy at depth of 2 MeV.
- Published
- 1994
- Full Text
- View/download PDF
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