21 research outputs found

    Practical robustness evaluation in radiotherapy - A photon and proton-proof alternative to PTV-based plan evaluation

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    Background and purpose: A planning target volume (PTV) in photon treatments aims to ensure that the clinical target volume (CTV) receives adequate dose despite treatment uncertainties. The underlying static dose cloud approximation (the assumption that the dose distribution is invariant to errors) is problematic in intensity modulated proton treatments where range errors should be taken into account as well. The purpose of this work is to introduce a robustness evaluation method that is applicable to photon and proton treatments and is consistent with (historic) PTV-base

    Practical robustness evaluation in radiotherapy - A photon and proton-proof alternative to PTV-based plan evaluation

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    Background and purpose: A planning target volume (PTV) in photon treatments aims to ensure that the clinical target volume (CTV) receives adequate dose despite treatment uncertainties. The underlying static dose cloud approximation (the assumption that the dose distribution is invariant to errors) is problematic in intensity modulated proton treatments where range errors should be taken into account as well. The purpose of this work is to introduce a robustness evaluation method that is applicable to photon and proton treatments and is consistent with (historic) PTV-based treatment plan evaluations. Materials and methods: The limitation of the static dose cloud approximation was solved in a multi-scenario simulation by explicitly calculating doses for various treatment scenarios that describe possible errors in the treatment course. Setup errors were the same as the CTV-PTV margin and the underlying theory of 3D probability density distributions was extended to 4D to include range errors, maintaining a 90% confidence level. Scenario dose distributions were reduced to voxel-wise minimum and maximum dose distributions; the first to evaluate CTV coverage and the second for hot spots. Acceptance criteria for CTV D98 and D2 were calibrated against PTV-based criteria from historic photon treatment plans. Results: CTV D98 in worst case scenario dose and voxel-wise minimum dose showed a very strong correlation with scenario average D98 (R-2 > 0.99). The voxel-wise minimum dose visualised CTV dose conformity and coverage in 3D in agreement with PTV-based evaluation in photon therapy. Criteria for CTV D98 and D2 of the voxel-wise minimum and maximum dose showed very strong correlations to PTV D98 and D2 (R-2 > 0.99) and on average needed corrections of -0.9% and +2.3%, respectively. Conclusions: A practical approach to robustness evaluation was provided and clinically implemented for PTV-less photon and proton treatment planning, consistent with PTV evaluations but without its static dose cloud approximation. (C) 2019 The Authors. Published by Elsevier B.V

    The existence of cranial bone flap displacement during brain radiotherapy

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    This retrospective study examined bone flap displacement during radiotherapy in 25 post-operative brain tumour patients. Though never exceeding 2.5 mm, the sheer frequency of displacement highlights the need for future research on larger populations to validate its presence and assess the potential clinical impact on planning tumour volume margins.</p

    Proton and photon radiotherapy in stage III NSCLC:Effects on hematological toxicity and adjuvant immune therapy

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    Background and purpose: Concurrent chemo-radiotherapy (CCRT) followed by adjuvant durvalumab is standard-of-care for fit patients with unresectable stage III NSCLC. Intensity modulated proton therapy (IMPT) results in different doses to organs than intensity modulated photon therapy (IMRT). We investigated whether IMPT compared to IMRT reduce hematological toxicity and whether it affects durvalumab treatment. Materials and methods: Prospectively collected series of consecutive patients with stage III NSCLC receiving CCRT between 06.16 and 12.22 (staged with FDG-PET-CT and brain imaging) were retrospectively analyzed. The primary endpoint was the incidence of lymphopenia grade ≥ 3 in IMPT vs IMRT treated patients. Results: 271 patients were enrolled (IMPT: n = 71, IMRT: n = 200) in four centers. All patients received platinum-based chemotherapy. Median age: 66 years, 58 % were male, 36 % had squamous NSCLC. The incidence of lymphopenia grade ≥ 3 during CCRT was 67 % and 47 % in the IMRT and IMPT group, respectively (OR 2.2, 95 % CI: 1.0–4.9, P = 0.03). The incidence of anemia grade ≥ 3 during CCRT was 26 % and 9 % in the IMRT and IMPT group respectively (OR = 4.9, 95 % CI: 1.9–12.6, P = 0.001). IMPT was associated with a lower rate of Performance Status (PS) ≥ 2 at day 21 and 42 after CCRT (13 % vs. 26 %, P = 0.04, and 24 % vs. 39 %, P = 0.02). Patients treated with IMPT had a higher probability of receiving adjuvant durvalumab (74 % vs. 52 %, OR 0.35, 95 % CI: 0.16–0.79, P = 0.01). Conclusion: IMPT was associated with a lower incidence of severe lymphopenia and anemia, better PS after CCRT and a higher probability of receiving adjuvant durvalumab.</p

    Local spin polarization at surfaces probed by hollow atoms

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    The relaxation of hollow atoms produced by slow multiply charged ions impinging on surfaces produces characteristic Auger electron spectra. These spectra, which serve as fingerprints of the interaction, can be used to probe local spin ordering at surfaces by relating changes in the intensities of different spin states to local spin polarization at the surface. The area from which the electrons are captured is of the order of a few A(2), only. The potential of the method is illustrated by He2+ and N6+ ions interacting with a ferromagnetic Ni(110) crystal. From the Auger spectra we determine a spin polarization of approximate to-90% at room temperature

    Investigation of spin-polarized surfaces with multiple electron capture spectroscopy

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    Slow, multiply charged ions incident on solid surfaces interact only with a few atomic sites from the top-most surface layer. A novel technique for probing local spin polarization at surfaces was developed, namely multiple electron capture spectroscopy (MECS). This technique is based on the Auger electron emission from doubly excited He atoms formed in front of ferromagnetic surfaces. The temperature dependence of the spin polarization of Fe(110) was obtained and the results are compared with those from the highly polarized Ni(110) surface. (c) 2007 Elsevier B.V. All rights reserved

    Probing local spin ordering at surfaces by He2+ ions

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    The evolution of the vibrational intensity distribution of the singly ionized A (2)Pi state in CO is experimentally examined for photon energy detunings below the adiabatic 0-0 transition of the O 1s -> 2 pi resonance. We have found a strong suppression of the entire vibrational fine structure of this state, leading to its almost complete quenching for certain excitation energies, followed by a partial restoring for larger values of negative photon energy detuning. Our observation, that cannot be rationalized by the known model of a vibrational collapse for energy detuning, may be explained in terms of a Fano interference between the direct and resonant photoionization channels in the presence of strong lifetime vibrational interference
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