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Ludwig Bogner

Publications and source records attributed to Ludwig Bogner.

4 recordsLinked to original sources
PubMed2006

Application of the inverse Monte Carlo treatment planning system IKO for an inhomogeneous dose prescription in the sense of dose painting.

Biological imaging (PET SPECTJfMRI, MRS, etc.) is able to provide tri-dimensional biological information, i.e. proliferation, cell density, hypoxia or choline/citrate ratio. The implementation of this information in a treatment plan can be utilised to escalate the dose in target subvolumes. For this purpose, a treatment planning system has to be able to realise an inhomogeneous dose prescription with sufficient spatial resolution. The present study investigated to which extent the inverse Monte Carlo treatment planning system IKO (inverse kernel optimization), developed at our department, can modulate an inhomogeneous dose prescription. As a qualifier to describe this ability, we defined in analogy to imaging a modulation transfer function for treatment planning systems. In addition two clinical cases, a prostate case and a head-and-neck case, were set up with different dose prescriptions in different subtargets. The modulation transfer function revealed that IKO is able to modulate structures larger than 1.3 cm with sharp dose gradients. Also, IKO is able to modulate several subtargets inside a prostate with different escalated doses. The dose-volume histograms of the head-and-neck case showed a good dose coverage of the target volumes, as well as a good protection of the organs at risk according to the dose constraints. As a result, IKO is able to realise a heterogeneous dose prescription in the sense of "dose painting".

Algorithms↗
PubMed2004

Verification of IMRT: techniques and problems.

PURPOSE: IMRT (intensity-modulated radiotherapy) verification techniques are reviewed together with investigations demonstrating the intrinsic verification problems. MATERIAL AND METHODS: Different IMRT verification procedures for either class solutions or individual patients are demonstrated. Among the latter are techniques like fluence or three-dimensional (3-D) dose distribution verification within a transfer phantom. Different radiographic films and absolute dose probes are investigated for their suitability. Finally, Monte Carlo techniques (XVMC/VEF) are used for error detection and IMRT verification. RESULTS: During introduction of clinical IMRT for head and neck (H and N) tumors, we concurrently applied fluence, relative, and absolute dose measurement. While fluence and relative dose are in rather good agreement with calculations, absolute dose is always low when compared to the TPS (TMS 6.1A, Nucletron B.V.) by 5-7%. This deviation seems to depend not on the number of segments, but can strongly depend on MLC misalignment. Further investigations have revealed the importance of a detailed commissioning of the TPS down to the small-field range using diamond or diode probes and its detailed verification. In addition, simple tests have shown that dose calculation approximations in the IMRT option of TMS are one major source of the dose deviation. XVMC/VEF does not use such approximations. CONCLUSION: The procedure starts with a detailed TPS commissioning and verification process. Different verification methods are recommended during clinical IMRT implementation phase, in order to locate sources of error. Later on, a minimal program could consist of a fluence or relative dose verification procedure with few films and absolute dose measurement, followed by an intensive MLC quality assurance (QA). Inverse Monte Carlo systems, like IMCO(++)/IKO or Hyperion, seem to be able to reduce the effort.

Head and Neck Neoplasms↗
PubMed2002

[IMCO(++)--a Monte Carlo based IMRT system].

The application of intensity modulated radiotherapy (IMRT) to dose escalation in the target volume sets particular demands in terms of accuracy of dose calculation. Dose calculation errors due to approximations are compensated by the optimization algorithm, a procedure that ultimately leads to incorrect fluence modulation. Such inaccuracies affect particularly the dose distribution in areas with secondary electron disequilibrium. In case tissues heterogeneity predominates, conventional dose calculation methods (such as Pencil Beam) can produce relative errors up to more than 10%. The accuracy can be significantly improved by the application of a Monte-Carlo (MC) algorithm. This paper describes a MC-based inverse treatment planning algorithm (IMCO++), based on a non-iterative approach with a feedback-controlling process. The convergence behavior of IMCO++ was investigated and the used MC dose-calculation codes MMms and XVMC were compared by means of a heterogeneous phantom. IMCO++ plans were optimized in various phantoms. All plans showed conformity in terms of dose distribution of the target volume and dose reduction in risk organs (according to the requirements of the target parameter), as well as a very fast convergence of the algorithm (in less than 10 optimization steps).

Humans↗