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Liquid ionization chamber calibrated gel dosimetry in conformal stereotactic radiotherapy of brain lesions
Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience, Neurosurgery.
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2008 (English)In: Acta Oncologica, ISSN 0284-186X, E-ISSN 1651-226X, Vol. 47, no 6, 1099-1109 p.Article in journal (Refereed) Published
Abstract [en]

Hypofractionated conformal stereotactic radiotherapy (HCSRT) is an established method of treating brain lesions such as arteriovenous malformations (AVMs) and brain metastases. The aim of this study was to investigate the reliability of treatment plans in the terms of dose distribution and absorbed dose for HCSRT.

Methods and materials. Treatment plans for three different clinical intracerebral targets, AVMs, were transferred to a CT study of a spherical water filled phantom simulating the human head and recalculated for the phantom geometry using a standard treatment planning system utilizing a pencil beam algorithm for dose calculation. The calculated absorbed dose, relative three dimensional (3D) dose distribution and dose conformity were investigated using gel dosimetry normalized to liquid ionization chamber (LIC) measurements.

Results. The measured absorbed dose to the dose reference point was found to be within 2% of the calculated dose for all three targets. The measured dose distribution was found to be within 3% and 2 mm of the calculated dose for more than 93% of all points in the target volume for all three targets.

Conclusions. The results show that the investigated standard treatment planning system can correctly predict the absorbed dose and dose distribution in different types of intracerebral targets and that the treatment can be delivered according to the plan.

Place, publisher, year, edition, pages
2008. Vol. 47, no 6, 1099-1109 p.
Identifiers
URN: urn:nbn:se:umu:diva-10573DOI: 10.1080/02841860801888781PubMedID: 18607837OAI: oai:DiVA.org:umu-10573DiVA: diva2:150244
Available from: 2008-10-01 Created: 2008-10-01 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Hypofractionated conformal stereotactic radiotherapy in the treatment of AVMs and cerebral metastases
Open this publication in new window or tab >>Hypofractionated conformal stereotactic radiotherapy in the treatment of AVMs and cerebral metastases
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hypofractionated conformal stereotactic radiotherapy (HCSRT) has been used for the treatment of AVMs at the Umeå University Hospital since 1986. From this year and onwards an increasing number of patients with single or oligo brain metastases have also been treated using this technique.

In paper I we have retrospectively evaluated our treatment results of AVMs in terms of obliteration and complications. The rates of obliteration and complications seem to be comparable with SRS even if the AVM volumes in our series were larger than in most series with SRS. In paper II we have retrospectively evaluated the results in terms of local control, survival and complications in two groups of patients with single or oligo brain metastases. One group was treated with HCSRT alone and the other group was treated with whole brain radiotherapy in combination with a stereotactic boost. Controversy still exists concerning the benefit of additional use of WBRT in combination with stereotactic irradiation. The survival times were equal in the two groups and no significant difference in local control was observed. The omission of WBRT seems to carry a higher risk for development new brain metastases distant from the irradiated area. In paper III we report the treatment results in a subgroup of AVMs treated with a combination of embolisation and HCSRT. We also focus on the reduction of vascular density within the nidus of an AVM and propose a method to digitally compare images and more objectively assess a reduction in vascular density following embolisation. Obliteration rates seem comparable with other series using a combination of SRS and embolisation even if our rate of complications was higher than what is usually reported. Using luminescence as measure of vascular density all AVMs seemed to be less dense after embolisation.

Treatment accuracy in terms of reproducibility of the isocenter in consecutive treatment sessions is crucial in fractionated radiotherapy. In paper IV we have radiologically evaluated the reproducibility of the isocenter in successive treatment sessions using the non invasive relocatable Fixster frame. There was a high degree of reproducibility and only small errors that most likely is of no clinical importance.

A reliable dose plan is equally important as a tool to predict the dose delivered inside and outside the target volume. In paper V we have evaluated the reliability of treatment plans in HCSRT for targets of different geometry and size. A liquid ion chamber and gel dosimeter was used for assessment of dose distribution and absorbed dose. The doseplanning system proved to be accurate in predicting the absorbed dose and dose distribution for the different targets.

Publisher
91 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1042
Keyword
arteriovenous malformations, brain metastases, hypofractionation, stereotactic radiotherapy, LINAC, embolisation
Research subject
Clinical Neurophysiology
Identifiers
urn:nbn:se:umu:diva-864 (URN)91-7264-135-5 (ISBN)
Public defence
2006-10-13, Sal B, plan 9, 1D, Tandläkarhögskolan, Umeå, 09:00 (English)
Opponent
Available from: 2006-09-18 Created: 2006-09-18 Last updated: 2009-10-09Bibliographically approved

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