Customer
Paul Scherrer Institute
Identical Data Required for Comparison
As part of the radiotherapy project at the Paul Scherrer Institute (PSI) in Villigen, Switzerland, a comparative assessment of radiation therapy techniques is being undertaken. The goal of this work is to be able to present in easily understood but convincing format the improved distributions to both target and normal tissue that will result from the spot-scanning method of proton radiotherapy.
The aim of the work is to identify those clinical indications in which a definitive difference can be shown between the efficacy of proton radiotherapy and the routinely available photon therapy techniques, compare proton dose distributions with state-of-the-art photon planning methods, and assess the relative merits of spot scanning methods of proton beam delivery with the more conventional passive-scattering method of proton delivery.
For accurate comparison of the efficacy of photon and proton treatments, it is imperative that identical data are available to all the planning systems to be used in the comparisons. To facilitate this, a set of common file formats has been developed that allows data to be transferred easily between different planning and computer systems. Formats have been defined to represent both CT and dose distributions as 3D distributions and to store volumes of interest (VOIs) in both vertex and voxel representations. All file types consist entirely of integer values and are read and written as integer stream files with no system- or language-dependent record structure.
Create a Portable and Easily Distributed System
A model for the dual display and analysis of dose distributions from different plans has been developed using PV-WAVE data visualization. The main advantages of PV-WAVE in this application are that it has optimized array manipulation capabilities, allowing for fast processing of two- and three-dimensional data sets, and a command language that can easily be transferred between VMS® and UNIX® with little or no modification.
Together, these features provide a high-level tool with which development times can be significantly reduced. The combination of stream data file formats and the PV-WAVE shell provides a very portable system that can be easily distributed over different hardware platforms in the future.
The analysis software provides a tool for presenting separate dose distributions on the same display for direct visual comparison. Transaxial and coronal slices of the CT and dose data sets can be interactively selected and displayed, with the position of the orthogonal cuts being defined using cross hair cursors controlled by a mouse. The dose distribution can be represented by overlaying the dose on the CT data using color wash and/or by the use of isodose contours. Full interactive control of the CT window, dose banding, and display levels are all provided by the use of widget-type control boxes.
The functionality of the system has been written using PV-WAVE and its associated routines. PV-WAVE is ideally suited to such applications, with the slicing of the 3D volume data into orthogonal planes being achieved with simple, single-line commands. Similarly, the overlaying of dose and VOI information onto the CT data can be efficiently accomplished using look-up tables and the array operations provided by the command language.
Two main analysis tools have been included in the comparison software. The simplest allows users to plot profiles of both distributions along any of the three axes defined by the cross hair cursors. A more three-dimensional analysis of the plan is provided by the dose-volume histogram (DVH) facility. DVHs provide a method of representing 3D dose distributions for selected VOIs in a convenient 2D format.
In brief, the DVH curve shows the volume (ordinate) of the selected VOI irradiated to a level equal to or greater than any given dose value (abscissa). Although spatial information is invariably lost, the DVH provides a succinct summary of the dose in the selected VOI.
All DVH calculations and geometric manipulations are performed using C functions called from the PV-WAVE shell using the LINKNLOAD dynamic linking function. Although many of the calculations necessary to produce the DVH plots could be achieved using PV-WAVE, the use of external C routines gives additional flexibility.
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