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  • 1.
    Andisheh, Bahram
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Brahme, Anders
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Bitaraf, Mohammad Ali
    Mavroidis, Panayiotis
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Lind, Bengt K
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Clinical and radiobiological advantages of single-dose stereotactic light-ion radiation therapy for large intracranial arteriovenous malformations. Technical note2009In: Journal of Neurosurgery, ISSN 0022-3085, E-ISSN 1933-0693, Vol. 111, no 5, p. 919-926Article in journal (Refereed)
    Abstract [en]

    OBJECT:

    Radiation treatment of large arteriovenous malformations (AVMs) remains difficult and not very effective, even though seemingly promising methods such as staged volume treatments have been proposed by some radiation treatment centers. In symptomatic patients harboring large intracranial AVMs not amenable to embolization or resection, single-session high-dose stereotactic radiation therapy is a viable option, and the special characteristics of high-ionization-density light-ion beams offer several treatment advantages over photon and proton beams. These advantages include a more favorable depth-dose distribution in tissue, an almost negligible lateral scatter of the beam, a sharper penumbra, a steep dose falloff beyond the Bragg peak, and a higher probability of vascular response due to high ionization density and associated induction of endothelial cell proliferation and/or apoptosis. Carbon ions were recently shown to be an effective treatment for skull-base tumors. Bearing that in mind, the authors postulate that the unique physical and biological characteristics of light-ion beams should convey considerable clinical advantages in the treatment of large AVMs. In the present meta-analysis the authors present a comparison between light-ion beam therapy and more conventional modalities of radiation treatment with respect to these lesions.

    METHODS:

    Dose-volume histograms and data on peripheral radiation doses for treatment of large AVMs were collected from various radiation treatment centers. Dose-response parameters were then derived by applying a maximum likelihood fitting of a binomial model to these data. The present binomial model was needed because the effective number of crucial blood vessels in AVMs (the number of vessels that must be obliterated to effect a cure, such as large fistulous nidus vessels) is low, making the Poisson model less suitable. In this study the authors also focused on radiobiological differences between various radiation treatments.

    RESULTS:

    Light-ion Bragg-peak dose delivery has the precision required for treating very large AVMs as well as for delivering extremely sharp, focused beams to irregular lesions. Stereotactic light-ion radiosurgery resulted in better angiographically defined obliteration rates, less white-matter necrosis, lower complication rates, and more favorable clinical outcomes. In addition, in patients treated by He ion beams, a sharper dose-response gradient was observed, probably due to a more homogeneous radiosensitivity of the AVM nidus to light-ion beam radiation than that seen when low-ionization-density radiation modalities, such as photons and protons, are used.

    CONCLUSIONS:

    Bragg-peak radiosurgery can be recommended for most large and irregular AVMs and for the treatment of lesions located in front of or adjacent to sensitive and functionally important brain structures. The unique physical and biological characteristics of light-ion beams are of considerable advantage for the treatment of AVMs: the densely ionizing beams of light ions create a better dose and biological effect distribution than conventional radiation modalities such as photons and protons. Using light ions, greater flexibility can be achieved while avoiding healthy critical structures such as diencephalic and brainstem nuclei and tracts. Treatment with the light ion He or Li is more suitable for AVMs <or= 10 cm(3), whereas treatment with the light ion Li, Be, or C may be more appropriate for larger AVMs. A binomial model based on the effective number of crucial vessels in the AVM may be used quite well to predict AVM obliteration probabilities for both small and large AVMs when therapies involving either photons or light ions are used.

  • 2.
    Toma-Dasu, Iuliana
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet, Sweden.
    Sandström, Helena
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet, Sweden.
    Barsoum, Pierre
    Karolinska University Hospital, Sweden.
    Dasu, Alexandru
    Linköping University, Sweden.
    To fractionate or not to fractionate? That is the question for the radiosurgery of hypoxic tumors2014In: Journal of Neurosurgery, ISSN 0022-3085, E-ISSN 1933-0693, Vol. 121, no Suppl. 2, p. 110-115Article in journal (Refereed)
    Abstract [en]

    Purpose: This study aimed to investigate the impact of tumour hypoxia on treatment outcome for metastases commonly treated with radiosurgery using one fraction of radiation. It also aimed to investigate the gain that could be expected from reoxygenation if the treatment is delivered in few radiation fractions.

    Methods: In silico metastases-like radiosurgery targets were modelled with respect to size, density of clonogenic cells and oxygenation. Treatment plans were produced for the targets using Leksell GammaPlan delivering clinically relevant doses and evaluating the tumour control probability (TCP) that could be expected in each case. Fractionated schedules with 3, 4 and 5 fractions resulting in similar biological effective doses were also considered for the larger target and TCP was determined under the assumption that local reoxygenation takes place between fractions.

    Results: The results showed that well-oxygenated small and medium-size metastases are well controlled by radiosurgery treatments delivering 20 or 22 Gy at the periphery, the TCP ranging from 90% to 100%. If they are moderately hypoxic the TCP could decrease to 60%. For large metastases, the TCP ranges from 0 to 19% depending on tumour oxygenation. However, for fractionated treatments, the TCP for hypoxic tumours could significantly increase up to 51%, if reoxygenation occurs between fractions.

    Conclusion: This study shows that hypoxia worsens the response to single-fraction radiosurgery, especially for large tumours. However, fractionated therapy for large hypoxic tumours might considerably improve the TCP and might constitute a simple way to improve the outcome of radiosurgery for patients with hypoxic tumours.

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