ABSTRACT
Respiratory motion during intensity modulated radiation therapy (IMRT) causes two types of problems. First, the clinical target volume (CTV) to planning target volume (PTV) margin needed to account for respiratory motion means that the lung and heart dose is higher than would occur in the absence of such motion. Second, because respiratory motion is not synchronized with multileaf collimator (MLC) motion, the delivered dose is not the same as the planned dose. The aims of this work were to evaluate these problems to determine (a) the effects of respiratory motion and setup error during breast IMRT treatment planning, (b) the effects of the interplay between respiratory motion and multileaf collimator (MLC) motion during breast IMRT delivery, and (c) the potential benefits of breast IMRT using breath-hold, respiratory gated, and 4D techniques. Seven early stage breast cancer patient data sets were planned for IMRT delivered with a dynamic MLC (DMLC). For each patient case, eight IMRT plans with varying respiratory motion magnitudes and setup errors (and hence CTV to PTV margins) were created. The effects of respiratory motion and setup error on the treatment plan were determined by comparing the eight dose distributions. For each fraction of these plans, the effect of the interplay between respiratory motion and MLC motion during IMRT delivery was simulated by superimposing the respiratory trace on the planned DMLC leaf motion, facilitating comparisons between the planned and expected dose distributions. When considering respiratory motion in the CTV-PTV expansion during breast IMRT planning, our results show that PTV dose heterogeneity increases with respiratory motion. Lung and heart doses also increase with respiratory motion. Due to the interplay between respiratory motion and MLC motion during IMRT delivery, the planned and expected dose distributions differ. This difference increases with respiratory motion. The expected dose varies from fraction to fraction. However, for the seven patients studied and respiratory trace used, for no breathing, shallow breathing, and normal breathing, there were no statistically significant differences between the planned and expected dose distributions. Thus, for breast IMRT, intrafraction motion degrades treatment plans predominantly by the necessary addition of a larger CTV to PTV margin than would be required in the absence of such motion. This motion can be limited by breath-hold, respiratory gated, or 4D techniques.
Subject(s)
Algorithms , Breast Neoplasms/radiotherapy , Movement , Radiometry/methods , Radiotherapy Planning, Computer-Assisted/methods , Radiotherapy, Conformal/methods , Respiratory Mechanics , Artifacts , Breast Neoplasms/diagnostic imaging , Breast Neoplasms/physiopathology , Heart/physiopathology , Humans , Lung/physiopathology , Models, Biological , Models, Statistical , Motion , Quality Control , Radiation Protection/methods , Radiography , Radiotherapy Dosage , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
The DOSRZ user code, which is part of the EGS4 standard distribution, is widely used in medical physics for the calculation of dose deposition in cylindrical geometries. The code provides the use of advanced Monte-Carlo techniques (PRESTA) and variance reduction methods. In the case of complex cylinder geometries the input of coordinates and radii is not only tedious but also prone to a high error rate. Coordinates are to be stated in absolute numbers. A change of one number, e.g., the slab thickness, requires the change of all subsequent numbers. Furthermore, parameters are only stated as numbers with no indication of their meaning. Obviously, there is a need for a user interface to facilitate the input for DOSRZ and to largely reduce the possibility for errors. We, therefore, wrote a graphical user interface (GUI) consisting of an input mask, a coordinate input interpreter, and a two-dimensional and/or pseudo-three-dimensional display section. The GUI is based on the scripting language Tcl/Tk, which runs under various platforms such as UNIX (LINUX), w95, and WIN NT. It consists of a main window which provides common-style menus and buttons to navigate through the edit dialog boxes. The most important tools are the region input, which enables the user to create the simulation geometry, and the graphics section where the scaled output can be displayed. Different media are shown in different colors which are user defined. Furthermore, the program contains some tools to reduce the probability of an erroneous input in the EGS4 input file. Since Tcl/Tk is a modern scripting language, it offers advanced tools to create the GUI and to "glue" different applications to it. XINPUT may also be considered as a model program for the development of a more general interface to other input areas of the EGS4 simulation code.
