%0 Journal Article
%T Optimization of extracranial stereotactic radiation therapy of small lung lesions using accurate dose calculation algorithms
%A Barbara Dobler
%A Cornelia Walter
%A Antje Knopf
%A Daniella Fabri
%A Rainer Loeschel
%A Martin Polednik
%A Frank Schneider
%A Frederik Wenz
%A Frank Lohr
%J Radiation Oncology
%D 2006
%I BioMed Central
%R 10.1186/1748-717x-1-45
%X A 9-field conformal treatment plan was generated on an inhomogeneous phantom with lung mimics and a soft tissue equivalent insert, mimicking a lung tumor. The dose distribution was calculated with the Pencil Beam and Collapsed Cone algorithms implemented in Masterplan (Nucletron) and the Monte Carlo system XVMC and validated using Gafchromic EBT films. Differences in dose distribution were evaluated. The plans were then optimized by adding segments to the outer shell of the target in order to increase the dose near the interface to the lung.The Pencil Beam algorithm overestimated the dose by up to 15% compared to the measurements. Collapsed Cone and Monte Carlo predicted the dose more accurately with a maximum difference of -8% and -3% respectively compared to the film. Plan optimization by adding small segments to the peripheral parts of the target, creating a 2-step fluence modulation, allowed to increase target coverage and homogeneity as compared to the uncorrected 9 field plan.The use of forward 2-step fluence modulation in radiotherapy of small lung lesions allows the improvement of tumor coverage and dose homogeneity as compared to non-modulated treatment plans and may thus help to increase the local tumor control probability. While the Collapsed Cone algorithm is closer to measurements than the Pencil Beam algorithm, both algorithms are limited at tissue/lung interfaces, leaving Monte-Carlo the most accurate algorithm for dose prediction.In external beam radiation therapy of lung tumors, even in extracranial stereotactic high dose ablative treatments, in-field relapses are observed even at high doses [1-3].It is well known that the Pencil Beam dose calculation algorithm (PB), which is most commonly implemented in commercial treatment planning systems, has limited accuracy especially at the interface of tissues with large differences in electron density, as it is the case at the interface lung/tumor [4]. Collapsed Cone convolution methods (CC) and Monte Carlo
%U http://www.ro-journal.com/content/1/1/45