Quality control of external conformal radiotherapy treatment planning systems softwares is a crucial issue. The treatment quality depends directly on the quality of treatment planning systems (TPS). Radiotherapists need to be sure that softwares compute accurately each parameter of the treatment. This paper focuses on the quality control of geometrical tools of the treatment planning systems, i.e. the virtual simulation software. These TPS compute the geometrical part of the treatment. They define the targets and shapes of the irradiation beams. Four operations done by these TPS are examined in this work. The quality control of the auto-contouring, auto-margin, isocenter computation and collimator conformation tools is treated with a new method based on Digital Test Objects (DTO). Standard methods for this quality control have been set up from the development of some Physical Test Objects (PTO). These methods are time-consuming, incomplete and inaccurate. Results are biased by the CT-scanner acquisition of PTOs and error evaluation is done with the graphic tools of the TPS. Our method uses DTOs and allows for an automated qualitative error evaluation. DTOs present many advantages for TPS quality control. They lead to a fast, accurate, complete and automatic quality assessment. Special DTOs have been developed to control the TPS tools mentioned previously as well as their automatic result analysis methods. A TPS has been controlled with these test objects. The quality assessment shows some errors and highlights some particularities in the TPS tools functioning. This quality control was then compared with the standard quality control.
Accurate isocentre positioning of the treatment machine is essential for the radiation therapy process, especially in
stereotactic radio surgery and in image guided radiation therapy.
We present in this paper a new method to evaluate a software which is used to perform an automatic analysis of the
Winston-Lutz test used in order to determine position and size of the isocentre. The method consists of developing
digital phantoms that simulate mechanical distortions of the treatment machine as well as misalignments of the
positioning laser targeting the isocentre. These Digital Test Objects (DTOs) offer a detailed and profound evaluation of
the software and allow determining necessary adjustments which lead to high precision and therefore contributes to a
better treatment targeting.
Conformal radiotherapy helps to deliver an accurate and effective cancer treatment by exactly targeting the
tumor. In this purpose, softwares of the treatment planning system (TPS) compute every geometric parameters
of the treatment. It is essential to control the quality of them because the TPS performances are directly
connected with the precision on the treated region. The standard method to control them is to use physical
test objects (PTOs).1, 2 The use of PTOs introduces uncertainties in the quality assessment because of the CT
scan. Another method to assess the quality of these softwares is to use digital test objects (DTOs).3-5 DTOs
are exactly known in a continuous and a discrete way. Thus the assessment of the TPS quality can be more
accurate and faster. The fact that the DTO characteristics are well known allows to calculate a theoretical result.
The comparison of the TPS and this theoretical results leads to a quantitative assessment of the TPS softwares
quality. This work presents the control of major quality criteria of digitally reconstructed radiograph (DRR)
computation: ray divergence, ray incidence and spatial resolution. Fully automated methods to control these
points have been developed. The same criteria have been tested with PTO and the quality assessments by the
two methods have been compared. The DTO methods appeared to be much more accurate because computable.
This paper deals with the CT scanner images quality control, which is an important part of the quality control process of the CT scanner, which consists of making measurement in images of dedicated phantoms.
Standard methods consist of scan explorations of phantoms that contain different specific patterns1, 2. These methods rely on manual measurements with graphics tools in corresponding images (density, position, length...) or automatic measurements developed in softwares3, 4 that use some masks to determine the region of interest (ROI). The problem of these masks is that they may produce wrong results in case of misalignment of the phantom.
We propose a new method that consists, firstly of developing software tools that are capable of performing an automated analysis of CT images of three standard phantoms, LAP5 , GEMS6 and CATPHAN6007, in terms of slice thickness, spatial resolution, low and high level contrast, noise and uniformity. The method we have developed is completely automatic because it uses some protocols and special treatments in the images to automatically detect the position and the size of the ROI. Secondly, to test the performances of our software tools, we develop two digital phantoms which reproduce the exact geometry and composition of the physical phantoms, i.e. some perfect CT images of the real phantoms, and a complete set of distorted digital phantoms which represent the "perfect" phantom distorted by noise and blur calibrated functions to test the performances of our automated analysis software.
Quality Control (QC) procedures are mandatory to achieve accuracy in radiotherapy treatments. For that purpose, classical methods generally use physical phantoms that are acquired by the system in place of the patient. In this paper, the use of digital test objects (DTO) replace the actual acquisition1. A DTO is a 3D scene description composed of simple and complex shapes from which discrete descriptions can be obtained. For QC needs, both the DICOM format (for Treatment Planning System (TPS) inputs) as well as continuous descriptions are required. The aim of this work is to define an equivalence model between a continuous description of the three dimensional (3D) scene used to define the DTO, and the DTO characteristics. The purpose is to have an XML- DTO description in order to compute discrete calculations from a continuous description. The defined structure allows also to obtain the three dimensional matrix of the DTO and then the series of slices stored in the DICOM format. Thus, it is shown how possibly design DTO for quality control in CT simulation and dosimetry.
Nowadays, most of treatments for external radiotherapy are prepared with Treatment Planning Systems (TPS) which uses a virtual patient generated by a set of transverse slices acquired with a CT scanner of the patient in treatment position 1 2 3. In the first step of virtual simulation, the TPS is used to define a ballistic allowing a good target covering and the lowest irradiation for normal tissues. This parameters optimisation of the treatment with the TPS is realised with particular graphic tools allowing to: •Contour the target, •Expand the limit of the target in order to take into account contouring uncertainties, patient set up errors, movements of the target during the treatment (internal movement of the target and external movement of the patient), and beam's penumbra, •Determine beams orientation and define dimensions and forms of the beams, •Visualize beams on the patient's skin and calculate some characteristic points which will be tattooed on the patient to assist the patient set up before treating, •Calculate for each beam a Digital Reconstructed Radiography (DRR) consisting in projecting the 3D CT virtual patient and beam limits with a cone beam geometry onto a plane. These DRR allow one for insuring the patient positioning during the treatment, essentially bone structures alignment by comparison with real radiography realized with the treatment X-ray source in the same geometric conditions (portal imaging).
Then DRR are preponderant to insure the geometric accuracy of the treatment. For this reason quality control of its computation is mandatory4 . Until now, this control is realised with real test objects including some special inclusions4 5 . This paper proposes to use some numerical test objects to control the quality DRR calculation in terms of computation time, beam angle, divergence and magnification precision, spatial and contrast resolutions. The main advantage of this proposed method is to avoid a real test object CT acquisition allowing for a drastic time reduction of the control as well as its automatic control. This method has been used to test a new method to compute DRR6 and is here presented to control a standard DRR calculation algorithm7 .
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