TSG ASHA 3D XRT ASHA Radiotherapy Treatment Planning System (RTPS) is computer software based electronic system that is used to simulate the application of radiation to a patient for a proposed radiotherapy treatment in order to pre-evaluate the total curative and harmful effects. It provides estimates of absorbed dose distribution in the patient using mathematical algorithms. A qualified person uses the information of absorbed dose distributions in planning a course of radiotherapy.

Safety concerns of the patient are due to inaccuracies in the input data, limitations of algorithms, errors in treatment planning process, and improper use of output data should the resulting data be used for treatment purposes. For protection against occurrence of such safety hazards, the ASHA RTPS has been tested for compliance with International Electrotechnical Commission Standard IEC 62083 on requirement for the safety of RTPS.

ASHA RTPS employs many types of input data, calculation algorithms and provides outputs in many forms. It follows ICRU recommendations on terminology and presentation of information to the user. Accompanying documents created by the system provide information for the user to make informed choices during the treatment planning process.

External Beam Planning Functions
External beam planning supports Image guided planning functions. Radiation dose is visualized on patient images in 2D/3D. Functions and features implemented in the software are guided by ICRU recommendations. Patient data required is a set of transverse images of the volume of interest of the patient. This data is acquired from DICOM compliant CT/MRI in a network. External skin, target volume and structures of interest are segmented with auto-contouring function or manual outlining.

Many options for defining beam configurations are available. Beams of any cross section may be positioned on the patient at any distance from the source normally feasible for clinical work. Beam modifiers such as wedges, blocks, compensators and bolus may be placed in the path of the beam for modifying the dose pattern to the patient.

Dose may be calculated for a selected or all beams, for a selected or central or all slices. A 3D dose matrix of Relative Dose Factors (RDF) is created. Dose is computed for a grid of 10,000 points per section, and then interpolated for any finer grid resolution. Choice of dose calculation methods is provided. Analytical models, interpolation from measured beam data, Pencil Beam algorithm, Clarkson scatter dose calculation by integration of contribution from sectors, or user provided algorithms are supported. Equivalent path length technique for inhomogeniety and surface correction is used. Incident and Exit dose on the central axis of each beam (after modification) is computed. Dose statistics such as maximum, minimum, mean, median and model dose to each structure is computed. Radiobiological evaluation of dose using LQ model with user specified parameters for acute and late reactions. TDF model of radiobiological dose evaluation is also supported. Choice of normalization methods is supported including normalization at ICRU point. “Beam ON” time in monitor units or minutes is calculated for the prescribed dose with a given fractionation schedule. Automatic decay correction for isotope (cobalt-60) is applied.

Dose Display Dose is displayed on CT/MRI images as isodose lines with annotations and color wash (single or rainbow colors) as relative dose percentage or absolute dose. Point dose, point coordinates, name of structure containing the point, density at the point, and distance from an arbitrary fixed point is automatically displayed at the mouse cursor position. Graphical dose display along a line drawn interactively with a mouse is provided. Graphical dose display on a slice plane as a dynamic “elevation grid” with movable view point. DVH graphs for each structure, both integral and differential, is displayed / printed. DVH data is also available in MS Excel worksheet. Dose component in the DVH analysis may be absolute dose or radiobiological effective dose based on LQ model. Planning for upto five phases of treatment is allowed. Each phase has an independent beam plan and prescription.

3D Visualization
Software is based on a concept of “Scene Graphics” using a set of 3D objects positioned in space and viewed from a “View Point”. Patient images, segmented structures, beams, dose envelopes, treatment couch, applicators etc., are converted into 3D objects using X3D technology. As “view Point” is moved, the rendered scene changes accordingly. Software changes the “View Point” interactively with a mouse or keyboard. 3D objects are assigned color, texture and transparency level.

Software allows color and transparency to be changed interactively, thus allowing objects to disappear in order to reveal other objects behind. View Point can be taken close to the objects to render expanded detailed view. The patient can be virtually examined by changing the view, transparency, color and orientation of objects. 3D data may be compressed for communication through internet for visualization by a web browser at another site. Please note that “View Point” “sees” the objects with one eye only. So the perception of depth of object is feasible with slight movement of the “View Point”. Dose envelope is created by using a dose matrix. Dose matrix may be for External Beam, Brachytherapy, or combined dose. Dose may be as simple absorbed dose in Gys or converted to radiobiological equivalent dose based on dose delivery schedule. Beam Eye View(BEV), Observer’s Eye View(OEV) and Z-View are rendered by taking the “View Point” to specific positions. Software provides functions to render the scene for these specific views. Viewing is available in any orientation with Zoom-In, Zoom-Out and rotate operations. Coronal, sagital and transverse views are created dynamically by clicking a point in the volume of the patient. Dose may be evaluated on these cut views by movement of cursor. Point dose, coordinates, slice number, structure name and its density is displayed with each movement of mouse cursor.

Interface with Water Phantom System
Dosimetry data from any one computerized water phantom system from may be used for beam library creation and maintenance by file transfer in a LAN or media exchange. Proprietary formats of Welhofer and Scanditronics units are supported. Support for any other format shall be provided on request.

DICOM Network Interface
The system has network communication interface with DICOM compliant CT, MRI, Simulator, ultrasound, and TPS equipment for image data acquisition. DICOM image data is received from the image source equipment through “push” model of Composite objects store. SOP Classes supported are: Computed Radiography Image Storage 1.2.840.10008.5.1.4.1.1.1, CT Image Storage 1.2.840.10008.5.1.4.1.1.2, MR Image Storage 1.2.840.10008.5.1.4.1.1.4, X-Ray Radiofluoroscopic Image Storage 1.2.840.10008.5.1.4.1.1.12.2, Ultrasound Image Storage 1.2.840.10008.5.1.4.1.1.6.1, RT Dose Storage 1.2.840.10008.5.1.4.1.1.481.2, RT Image Storage 1.2.840.10008.5.1.4.1.1.481.1, RT Plan Storage 1.2.840.10008.5.1.4.1.1.481.5, RT Structure Set Storage 1.2.840.10008.5.1.4.1.1.481.3 and Secondary Capture Image Storage 1.2.840.10008.5.1.4.1.1.7. Network and cabling is customized to the installation requirement. Physical network supporting Transmission Control Program / Internet Protocol shall be provided by the hospital. CT Image data is converted from Hounsfield Units into density values for reconstruction of image for display and dose calculations. Hounsfield values are computed from Modality Look Up Table or by using Rescale Slope / Rescale Intercept data available in the image. Density values of pixels are used to reconstruct images for display and CT based planning. Voxel Densities are displayed for each voxel position traversed by mouse cursor, along with other information like dose, coordinates in mm, distance from a fixed point, and the name of the structure containing the voxel. Dose calculation algorithm uses voxel densities instead of average density of segmented structures for computation of attenuation of the beam ray through the voxel. Segmentation of structures is used for calculating dose profiles, dose-volume analysis, 3D visualization and simulation of beam setup by viewing the patient through the beam eye view. The scale of pixels, slice thickness, slice offset, and other image characteristics are acquired automatically from the DICOM data set. Data for image data set transferred from imaging source equipment is stored in a Relational Data Base, with each series in a separate directory. All images from a series are converted to the proprietary format for radiation treatment planning, and stored with RTP data. RTP images are based on density profile of the transverse slice. DICOM data set may be deleted from the data base after the patient planning is completed. DICOM data set is not used for RTP again.