Elinore Wieslander

Publications (9)30.89 Total impact

• Article: Influence of dose calculation algorithms on the predicted dose distribution and NTCP values for NSCLC patients.

  Tine B Nielsen, Elinore Wieslander, Antonella Fogliata, Morten Nielsen, Olfred Hansen, Carsten Brink
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  ABSTRACT: To investigate differences in calculated doses and normal tissue complication probability (NTCP) values between different dose algorithms. Six dose algorithms from four different treatment planning systems were investigated: Eclipse AAA, Oncentra MasterPlan Collapsed Cone and Pencil Beam, Pinnacle Collapsed Cone and XiO Multigrid Superposition, and Fast Fourier Transform Convolution. Twenty NSCLC patients treated in the period 2001-2006 at the same accelerator were included and the accelerator used for treatments were modeled in the different systems. The treatment plans were recalculated with the same number of monitor units and beam arrangements across the dose algorithms. Dose volume histograms of the GTV, PTV, combined lungs (excluding the GTV), and heart were exported and evaluated. NTCP values for heart and lungs were calculated using the relative seriality model and the LKB model, respectively. Furthermore, NTCP for the lungs were calculated from two different model parameter sets. Calculations and evaluations were performed both including and excluding density corrections. There are found statistical significant differences between the calculated dose to heart, lung, and targets across the algorithms. Mean lung dose and V20 are not very sensitive to change between the investigated dose calculation algorithms. However, the different dose levels for the PTV averaged over the patient population are varying up to 11%. The predicted NTCP values for pneumonitis vary between 0.20 and 0.24 or 0.35 and 0.48 across the investigated dose algorithms depending on the chosen model parameter set. The influence of the use of density correction in the dose calculation on the predicted NTCP values depends on the specific dose calculation algorithm and the model parameter set. For fixed values of these, the changes in NTCP can be up to 45%. Calculated NTCP values for pneumonitis are more sensitive to the choice of algorithm than mean lung dose and V20 which are also commonly used for plan evaluation. The NTCP values for heart complication are, in this study, not very sensitive to the choice of algorithm. Dose calculations based on density corrections result in quite different NTCP values than calculations without density corrections. It is therefore important when working with NTCP planning to use NTCP parameter values based on calculations and treatments similar to those for which the NTCP is of interest.
  Medical Physics 05/2011; 38(5):2412-8. · 2.83 Impact Factor
• Article: A Monte Carlo study of a flattening filter-free linear accelerator verified with measurements.

  Mårten Dalaryd, Gabriele Kragl, Crister Ceberg, Dietmar Georg, Brendan McClean, Sacha af Wetterstedt, Elinore Wieslander, Tommy Knöös
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  ABSTRACT: A Monte Carlo model of an Elekta Precise linear accelerator has been built and verified by measured data for a 6 and 10 MV photon beam running with and without a flattening filter in the beam line. In this study the flattening filter was replaced with a 6 mm thick copper plate, provided by the linac vendor, in order to stabilize the beam. Several studies have shown that removal of the filter improves some properties of the photon beam, which could be beneficial for radiotherapy treatments. The investigated characteristics of this new beam included output, spectra, mean energy, half value layer and the origin of scattered photons. The results showed an increased dose output per initial electron at the central axis of 1.76 and 2.66 for the 6 and 10 MV beams, respectively. The number of scattered photons from the accelerator head was reduced by (31.7 ± 0.03)% (1 SD) for the 6 MV beam and (47.6 ± 0.02)% for the 10 MV beam. The photon energy spectrum of the unflattened beam was softer compared to a conventional beam and did not vary significantly with the off-axis distance, even for the largest field size (0-20 cm off-axis).
  Physics in Medicine and Biology 12/2010; 55(23):7333-44. · 2.83 Impact Factor
• Article: The effect of different lung densities on the accuracy of various radiotherapy dose calculation methods: implications for tumour coverage.

  Lasse Rye Aarup, Alan E Nahum, Christina Zacharatou, Trine Juhler-Nøttrup, Tommy Knöös, Håkan Nyström, Lena Specht, Elinore Wieslander, Stine S Korreman
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  ABSTRACT: To evaluate against Monte-Carlo the performance of various dose calculations algorithms regarding lung tumour coverage in stereotactic body radiotherapy (SBRT) conditions. Dose distributions in virtual lung phantoms have been calculated using four commercial Treatment Planning System (TPS) algorithms and one Monte Carlo (MC) system (EGSnrc). We compared the performance of the algorithms in calculating the target dose for different degrees of lung inflation. The phantoms had a cubic 'body' and 'lung' and a central 2-cm diameter spherical 'tumour' (the body and tumour have unit density). The lung tissue was assigned five densities (rho(lung)): 0.01, 0.1, 0.2, 0.4 and 1g/cm(3). Four-field treatment plans were calculated with 6- and 18 MV narrow beams for each value of rho(lung). We considered the Pencil Beam Convolution (PBC(Ecl)) and the Analytical Anisotropic Algorithm (AAA(Ecl)) from Varian Eclipse and the Pencil Beam Convolution (PBC(OMP)) and the Collapsed Cone Convolution (CCC(OMP)) algorithms from Oncentra MasterPlan. When changing rho(lung) from 0.4 to 0.1g/cm(3), the MC median target dose decreased from 89.2% to 74.9% for 6 MV and from 83.3% to 61.6% for 18 MV (of dose maximum in the homogenous case at both energies), while for both PB algorithms the median target dose was virtually independent of lung density. Both PB algorithms overestimated the target dose, the overestimation increasing as rho(lung) decreased. Concerning target dose, the AAA(Ecl) and CCC(OMP) algorithms appear to be adequate alternatives to MC.
  Radiotherapy and Oncology 04/2009; 91(3):405-14. · 5.58 Impact Factor
• Article: Experience from long-term monitoring of RAKR ratios in (192)Ir brachytherapy.

  Asa Carlsson Tedgren, Emil Bengtsson, Håkan Hedtjärn, Asa Johansson, Leif Karlsson, Inger-Lena Lamm, Marie Lundell, Younes Mejaddem, Per Munck Af Rosenschöld, Josef Nilsson, Elinore Wieslander, Jeanette Wolke
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  ABSTRACT: Ratios of values of brachytherapy source strengths, as measured by hospitals and vendors, comprise constant differences as, e.g., systematic errors in ion chamber calibration factors and measurement setup. Such ratios therefore have the potential to reveal the systematic changes in routines or calibration services at either the hospital or the vendor laboratory, which could otherwise be hidden by the uncertainty in the source strength values. The RAKR of each new source in 13 afterloading units at five hospitals were measured by well-type ion chambers and compared to values for the same source stated on vendor certificates. Differences from unity in the ratios of RAKR values determined by hospitals and vendors are most often small and stable around their mean values to within +/- 1.5%. Larger deviations are rare but occur. A decreasing ratio, seen at two hospitals for the same source, was useful in detecting an erroneous pressure gauge at the vendor's site. Establishing a mean ratio of RAKR values, as measured at the hospital and supplied on the vendor certificate, and monitoring this as a function of time are an easy way for the early detection of problems with equipment or routines at either the hospital or the vendor site.
  Radiotherapy and Oncology 10/2008; 89(2):217-21. · 5.58 Impact Factor
• Article: Modelling of an Orthovoltage X-ray Therapy Unit with the EGSnrc Monte Carlo Package

  Tommy Knöös, Per Munck af Rosenschöld, Elinore Wieslander
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  ABSTRACT: Simulations with the EGSnrc code package of an orthovoltage x-ray machine have been performed. The BEAMnrc code was used to transport electrons, produce x-ray photons in the target and transport of these through the treatment machine down to the exit level of the applicator. Further transport in water or CT based phantoms was facilitated by the DOSXYZnrc code. Phase space files were scored with BEAMnrc and analysed regarding the energy spectra at the end of the applicator. Tuning of simulation parameters was based on the half-value layer quantity for the beams in either Al or Cu. Calculated depth dose and profile curves have been compared against measurements and show good agreement except at shallow depths. The MC model tested in this study can be used for various dosimetric studies as well as generating a library of typical treatment cases that can serve as both educational material and guidance in the clinical practice
  Journal of Physics Conference Series 07/2007; 74(1):021009.
• Article: A virtual-accelerator-based verification of a Monte Carlo dose calculation algorithm for electron beam treatment planning in clinical situations.

  Elinore Wieslander, Tommy Knöös
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  ABSTRACT: The introduction of Monte Carlo (MC) techniques for treatment planning and also for verification purposes will have considerable impact on the radiation therapy planning process. The aim of this work was to use a virtual accelerator to study the performance of a MC-based electron dose calculation algorithm, implemented in a commercial treatment planning system. The performance in phantoms containing air and bone as well as in patient-specific geometries (thorax wall, nose, parotid gland and spinal cord) has been studied. The agreement between the virtual accelerator and the MC dose calculation algorithm is generally very good. A gamma-evaluation with criteria of 0.03 Gy/3 mm (per Gy at the depth of maximum dose) shows that, even for the worst cases, only a small volume of about 1.5% has gamma>1.0. In the worst case, with the 0.02 Gy/2 mm criteria, about 92% of the volume receiving more than 0.85 Gy per 100 monitor units (MU) has gamma-values <1.0. The corresponding value for the volume receiving more than 0.10 Gy/100 MU is about 98%. For the 18 MeV spinal-cord case, where a 6 x 20 cm2 insert is used, the TPS underestimates the dose outside the primary field due to inadequate modelling of the insert. The possibility of dose calculations in typical patient cases makes the virtual accelerator a powerful tool for validation and evaluation of dose calculation algorithms present in treatment planning systems.
  Radiotherapy and Oncology 03/2007; 82(2):208-17. · 5.58 Impact Factor
• Article: Comparison of dose calculation algorithms for treatment planning in external photon beam therapy for clinical situations.

  Tommy Knöös, Elinore Wieslander, Luca Cozzi, Carsten Brink, Antonella Fogliata, Dirk Albers, Håkan Nyström, Søren Lassen
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  ABSTRACT: A study of the performance of five commercial radiotherapy treatment planning systems (TPSs) for common treatment sites regarding their ability to model heterogeneities and scattered photons has been performed. The comparison was based on CT information for prostate, head and neck, breast and lung cancer cases. The TPSs were installed locally at different institutions and commissioned for clinical use based on local procedures. For the evaluation, beam qualities as identical as possible were used: low energy (6 MV) and high energy (15 or 18 MV) x-rays. All relevant anatomical structures were outlined and simple treatment plans were set up. Images, structures and plans were exported, anonymized and distributed to the participating institutions using the DICOM protocol. The plans were then re-calculated locally and exported back for evaluation. The TPSs cover dose calculation techniques from correction-based equivalent path length algorithms to model-based algorithms. These were divided into two groups based on how changes in electron transport are accounted for ((a) not considered and (b) considered). Increasing the complexity from the relatively homogeneous pelvic region to the very inhomogeneous lung region resulted in less accurate dose distributions. Improvements in the calculated dose have been shown when models consider volume scatter and changes in electron transport, especially when the extension of the irradiated volume was limited and when low densities were present in or adjacent to the fields. A Monte Carlo calculated algorithm input data set and a benchmark set for a virtual linear accelerator have been produced which have facilitated the analysis and interpretation of the results. The more sophisticated models in the type b group exhibit changes in both absorbed dose and its distribution which are congruent with the simulations performed by Monte Carlo-based virtual accelerator.
  Physics in Medicine and Biology 12/2006; 51(22):5785-807. · 2.83 Impact Factor
• Article: A virtual-accelerator-based verification of a Monte Carlo dose calculation algorithm for electron beam treatment planning in homogeneous phantoms.

  Elinore Wieslander, Tommy Knöös
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  ABSTRACT: By introducing Monte Carlo (MC) techniques to the verification procedure of dose calculation algorithms in treatment planning systems (TPSs), problems associated with conventional measurements can be avoided and properties that are considered unmeasurable can be studied. The aim of the study is to implement a virtual accelerator, based on MC simulations, to evaluate the performance of a dose calculation algorithm for electron beams in a commercial TPS. The TPS algorithm is MC based and the virtual accelerator is used to study the accuracy of the algorithm in water phantoms. The basic test of the implementation of the virtual accelerator is successful for 6 and 12 MeV (gamma < 1.0, 0.02 Gy/2 mm). For 18 MeV, there are problems in the profile data for some of the applicators, where the TPS underestimates the dose. For fields equipped with patient-specific inserts, the agreement is generally good. The exception is 6 MeV where there are slightly larger deviations. The concept of the virtual accelerator is shown to be feasible and has the potential to be a powerful tool for vendors and users.
  Physics in Medicine and Biology 04/2006; 51(6):1533-44. · 2.83 Impact Factor
• Article: Dose perturbation in the presence of metallic implants: treatment planning system versus Monte Carlo simulations.

  Elinore Wieslander, Tommy Knöös
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  ABSTRACT: An increasing number of patients receiving radiation therapy have metallic implants such as hip prostheses. Therefore, beams are normally set up to avoid irradiation through the implant; however, this cannot always be accomplished. In such situations, knowledge of the accuracy of the used treatment planning system (TPS) is required. Two algorithms, the pencil beam (PB) and the collapsed cone (CC), are implemented in the studied TPS. Comparisons are made with Monte Carlo simulations for 6 and 18 MV. The studied materials are steel, CoCrMo, Orthinox, TiAlV and Ti. Monte Carlo simulated depth dose curves and dose profiles are compared to CC and PB calculated data. The CC algorithm shows overall a better agreement with Monte Carlo than the PB algorithm. Thus, it is recommended to use the CC algorithm to get the most accurate dose calculation both for the planning target volume and for tissues adjacent to the implants when beams are set up to pass through implants.
  Physics in Medicine and Biology 11/2003; 48(20):3295-305. · 2.83 Impact Factor