[en] The computer-based learning methods in medicine have been well established as stand-alone learning systems. Recently, these systems were enriched with the use of telematics technology to provide distance learning capabilities. Stereotactic radiotherapy is more of the most representative advanced radiotherapy techniques. Due to the multidisciplinary character of the technique and the rapid evolution of technology implemented, the demands in training have increased. The potential of interactive multimedia and Internet technologies for the achievement of distance learning capabilities in this domain are investigated. The realization of a computer-based educational program in stereotactic radiotherapy in a multimedia format is a new application in the computer-aided distance learning field. The system is built according to a client and server architecture, based on the Internet infrastructure, and composed of server nodes. The impact of the system may be described in terms of: time and transportation costs saving, flexibility in training (scheduling, rate and subject selection), online communication and interaction with experts, cost effective access to material (delivery or access by a large number of users and revision of the material by avoiding and database development. (authors)

[en] Introduction: The most used imaging modality for diagnosis and localisation of arteriovenous malformations (AVMs) treated with stereotactic radiotherapy is angiography. The fact that the angiographic images are projected images imposes the need of the 3D reconstruction of the lesion. This, together with the 3D head anatomy from CT images could provide all the necessary information for stereotactic treatment planning. We have developed a method to combine the complementary information provided by angiography and 2D computerized tomography, matching the reconstructed AVM structure with the reconstructed head of the patient. Materials and methods: The ISIS treatment planning system, developed at Institute Curie, has been used for image acquisition, stereotactic localisation and 3D visualisation. A series of CT slices are introduced in the system as well as two orthogonal angiographic projected images of the lesion. A simple computer program has been developed for the 3D reconstruction of the lesion and for the superposition of the target contour on the CT slices of the head. Results and conclusions: In our approach we consider that the reconstruction can be made if the AVM is approximated with a number of adjacent ellipses. We assessed the method comparing the values of the reconstructed and the actual volumes of the target using linear regression analysis. For treatment planning purposes we overlapped the reconstructed AVM on the CT slices of the head. The above feature is to our knowledge a feature that the majority of the commercial stereotactic radiotherapy treatment planning system could not provide. The implementation of the method into ISIS TPS shows that we can reliably approximate and visualize the target volume

[en] The dose distributional advantages of the heavy charged-particles can be fully exploited by using very efficient and accurate dose calculation algorithms, which can generate optimal three-dimensional scanning patterns. An inverse therapy planning algorithm for dynamically scanned, narrow heavy charged-particle beams is presented in this paper. The irradiation 'start point' is defined at the distal end of the target volume, right-down, in a beam's eye view. The peak-dose of the first elementary beam is set to be equal to the prescribed dose in the target volume, and is defined as the reference dose. The weighting factor of any Bragg-peak is determined by the residual dose at the point of irradiation, calculated as the difference between the reference dose and the cumulative dose delivered at that point of irradiation by all the previous Bragg-peaks. The final pattern consists of the weighted Bragg-peaks irradiation density. Dose distributions were computed using two different scanning steps equal to 0.5 mm, and 1 mm respectively. Very accurate and precise localized dose distributions, conform to the target volume, were obtained. (authors)

[en] Several stereotactic irradiation techniques, using Linacs with the patient in lying and sitting position and a Gamma Knife Unit, were compared with regard to mono-isocentric three-dimensional dose distributions. Three types of target volumes, a sphere and two ellipsoids, were used for the comparisons. All three targets were centered on a real head, reconstructed from transversal CT scans. The ARTEMIS 3D Treatment Planning System, developed by the Tenon Hospital, Paris, was used for the dosimetry and the dose-volume histogram (DVH) calculation. For the comparative study, several quantitative parameters were used, derived from the dose-volume histogram calculation. Differential DVHs were plotted for each target volume and beam arrangement. Irradiation techniques were compared by deriving quantitative parameters from the DVHs such as mean and integral dose delivered to the target and normal tissue irradiated, as well as by the relative volume of the examined areas. All techniques used in this study produced very similar dose distributions. The small differences confirm the capability of the studied techniques to produce the same irradiation effects. By changing from the spherical target shape to a more elliptical shape, more of the normal tissue was irradiated with higher doses. For elliptical cases we therefore identified a need for more conformal stereotactic planning

[en] A dose-volume histogram (Dh) computation program was developed for brachytherapy treatment planning in an attempt to benefit from the DVS's ability to present graphically information on 3D dose distributions. The program is incorporated into a planning system that utilizes a pair of orthogonal radiographs to localize the radiation sources. DVHs are calculated for the volume of tissue enclosed by an isodose surface (e.g. half the value of the reference isodose). The calculation algorithm is based on a non-uniform random sampling that gives a denser point distribution at the centre of the implants. Our program was tested and proved to be fast enough for clinical use and sufficiently accurate (i.e. computation time of 20 s and less than 2% relative error for one point source, for 100 000 calculation points). The accuracy improves when a larger calculation point number is used, but the computation time also increases proportionally. The DVH is presented in the form of a simple graph or table, or as Anderson's 'natural' DVH graph. The cumulative DVH tables can be used to extract a series of indexes characterizing the homogeneity and the dose levels of the distribution in the treatment volume and the surrounding tissues. If a reference plan is available, the DVH results can be assessed relative to the reference plan's DVH. (author)

[en] Detailed quality control (QC) protocols are a necessity for modern radiotherapy departments. The established QC protocols for treatment planning systems (TPS) do not include recommendations on the advanced features of three-dimensional (3D) treatment planning, like the dose volume histograms (DVH). In this study, a test protocol for DVH characteristics was developed. The protocol assesses the consistency of the DVH computation to the dose distribution calculated by the same TPS by comparing DVH parameters with values obtained by the isodose distributions. The computation parameters (such as the dimension of the computation grid) that are applied to the TPS during the tests are not fixed but set by the user as if the test represents a typical clinical case. Six commercial TPS were examined with this protocol within the frame of the EC project Dynarad (Biomed I). The results of the intercomparison prove the consistency of the DVH results to the isodose values for most of the examined TPS. However, special attention should be paid when working with cases of adverse conditions such as high dose gradient regions. In these cases, higher errors are derived, especially when an insufficient number of dose calculation points are used for the DVH computation. (author)

[en] During the past decade, tumor and normal tissue reactions after radiotherapy have been increasingly quantified in radiobiological terms. For this purpose, response models describing the dependence of tumor and normal tissue reactions on the irradiated volume, heterogeneity of the delivered dose distribution and cell sensitivity variations can be taken into account. The probability of achieving a good treatment outcome can be increased by using an objective function such as P₊, the probability of complication-free tumor control. A new procedure is presented, which quantifies P₊ from the dose delivery on 2D surfaces and 3D volumes and helps the user of any treatment planning system (TPS) to select the best beam orientations, the best beam modalities and the most suitable beam energies. The final step of selecting the prescribed dose level is made by a renormalization of the entire dose plan until the value of P₊ is maximized. The index P₊ makes use of clinically established dose-response parameters, for tumors and normal tissues of interest, in order to improve its clinical relevance. The results, using P₊, are compared against the assessments of experienced medical physicists and radiation oncologists for two clinical cases. It is observed that when the absorbed dose level for a given treatment plan is increased, the treatment outcome first improves rapidly. As the dose approaches the tolerance of normal tissues the complication-free curve begins to drop. The optimal dose level is often just below this point and it depends on the geometry of each patient and target volume. Furthermore, a more conformal dose delivery to the target results in a higher control rate for the same complication level. This effect can be quantified by the increased value of the P₊ parameter. (orig.)

[en] Full text: In this study we sought to evaluate and accent the importance of radiobiological parameter selection and implementation to the normal tissue complication proba bility (NTCP) models. The relative seriality (RS) and the Lyman-Kutcher-Burman (LKB) models were studied. For each model, a minimum and maximum set of radiobio logical parameter sets was selected from the overall pub lished sets applied in literature and a theoretical mean parameter set was computed. In order to investigate the potential model weaknesses in NTCP estimation and to point out the correct use of model parameters, these sets were used as input to the RS and the LKB model, esti mating radiation induced complications for a group of 36 breast cancer patients treated with radiotherapy. The clin ical endpoint examined was Radiation Pneumonitis. Each model was represented by a certain dose-response range when the selected parameter sets were applied. Comparing the models with their ranges, a large area of coincidence was revealed. If the parameter uncertainties (standard deviation) are included in the models, their area of

[en] The various components of the accelerator treatment head act as sources of contaminating electrons. The presence of contamination electrons increases the surface dose, which deteriorates the skin-sparing effect. The present study examines the sources of this 'contamination', the influence on the surface dose and the shape of the build-up curve. The Monte Carlo simulation of two linear accelerators, Saturne-25 and -41, allowed us to study the influence of electron contamination in various therapeutic energies and in different geometries. The Saturne-25 and -41 cover a wide range of therapeutic energies with nominal energies 12/23 MV and 6/15 MV, respectively. The analysis of the results shows that at a source-to-surface distance of 100 cm and a wide opening of the collimators, the main sources of contaminating electrons are the flattening filter and the air below it. The contribution of the secondary contamination electrons on the surface dose is 16% for 6 MV and 12 MV, 6% for 15 MV and 17% for 23 MV. The energy spectra of electrons coming from the flattening filter and the air below it are completely different. The air produces electrons of low energies. The mean energies of these spectra vary from 1 MeV to 2 MeV depending on the nominal energy of the photon beam. The secondary electrons generated by the flattening filter produce a wide energy spectrum with mean energies of the same order of the bremsstrahlung spectrum. The flattening filter absorbs the secondary electrons generated in the target, the primary collimator and the air inside the head. (author)

[en] Purpose: A newly developed non-invasive immobilization frame for stereotactic radiotherapy is presented, which is intended to be used for both imaging (computed tomography (CT) and angiography) and radiotherapeutic procedures. Materials and methods: The frame is made of duraluminium so as to be stable and light and it has an elliptical shape. The immobilization is achieved using three stable locations on the patient's head, i.e. the upper dentition, the nose and the back of the neck. The fixation on the three locations ensures complete immobilization in all directions. Results: The immobilization frame can be fitted as many times as is needed to most heads. In order to assess the accuracy of relocation, repeated fittings on two volunteers and on 22 patients undergoing stereotactic treatment were performed (more than 200 mountings in total), which showed maximum anterior-posterior, inferior-superior and lateral reproducibility in positioning of less than 1 mm in all cases. Conclusions and discussion: The in-house-constructed stereotactic frame is simple to use, easily made, non-invasive, relocatable and well tolerated by the patients, providing the possibility of multiple fractions. The major advantage of using such a non-invasive stereotactic frame is the flexibility in timing the different diagnostic procedures (CT and angiography) as well as providing the possibility to extend the use to large brain lesions (treatment without an additional collimator) where a high precision is also required. It also offers significant labour and cost saving over the invasive frames and the majority of the non-invasive frames. To date, 22 patients with ages varying between 12 and 70 years have been treated using this method. (Copyright (c) 1998 Elsevier Science B.V., Amsterdam. All rights reserved.)