[en] Advances in technology have initiated a process of redefinition of planning and evaluation of brachytherapy. The new approach involves conformal positioning of a source configuration for which the treatment isodose contour is adapted to the shape of the target volume which is defined by 3D dimensional imaging. A good implant aims for a balance between good coverage of the target volume, a high dose uniformity inside the target volume and a steep dose fall-off outside the target volume. Computer hardware and software is now available to obtain a high level of sophistication, for instance in treatment planning. In addition, new after loading equipment became available allowing a large variety in source placement in the catheters. To facilitate optimisation procedures, new parameters for the judgement of the quality of the implant have been suggested. (author)

No abstract available

[en] The objective of new treatment techniques by high energy photon beams is to improve the dose distribution and to decrease the radiation dose to healthy tissues around the tumour. The treatment volume must have the nearest possible form and dimensions of the target volume. In this article, the author recalls the principle of conventional treatment techniques in fixed and dynamic fields, and explains the principle of conformation radiotherapy in giving its advantages. A best adjustment of the treatment volume to the target volume form is permitted and the local control probability increase is possible in increasing radiation doses without enlarging frequency and severity of secondary effects

[en] A multi-leaf collimator (MLC) has been designed to replace directly the standard collimator of a SATURNE IV Series linac. It consists of 2 x 32 tungsten leaves and one set of upper block jaws. Isodose curves and dose profiles were measured for symmetric fields at the depth of the maximum and the reference depths for 6 MV, 10 MV, 18 MV photon beams. The penumbra (80%-20%) corresponding to the face and the side of the leaves have been compared with the standard collimators. Along with the X direction, the field delimitation is performed primarily with the leaves which are continuously variable in position. Along the Y direction, the field is initially approximated by the closure of opposite leaf pairs; then the Y upper jaws produce the exact size of the required field. As the leaves move linearly the penumbra (80%-20%) corresponding to the leaf ends is minimized and held constant at all positions by curvature of their faces. Penumbra obtained with the superposition of leaves and Y jaws depend on their relative position. The penumbra is minimum when the leaf side and the Y jaw edge coincide and the comparison of the measurement values with the conventional collimator shows that the differences are within 1 mm. When the leaves delineating the field are not entirely covered by the Y block upper jaws, the penumbra increases, and the junction of the opposing leaves, a width increase up to 3.5 mm has been measured

[en] The collimator multi lamina studied here, in current use conditions, shows dosimetric characteristics equivalent to classical collimator's ones. An experimental study of dose distribution in the case of complex fields, and the modeling for the calculation of doses distribution will allow clinical evaluation of this prototype. 4 refs., 6 figs

[en] Inappropriate positioning of interstitial iridium 192 implants, used as booster dose in the breast conserving treatment of mammary cancer, may cause disturbing teleangiectasia of the breast skin, when high radiation doses are delivered on the dermal blood vessels. Based on the localization of the vascular plexuses in human breast skin, and on the dose distribution around different types of interstitial implants, a method is described to avoid overlap between the high dose area of the implant and the blood vessels in the skin. The latter are demonstrated to run within the first 5 mm under the epiderm. For source lengths varying from 5 to 8 cm, simple mathematical relations exist between the maximal security margin (MSM) and intersource distance (E) for single plane implants (MSM = 0.4 (E + 1)), double plane square implants (MSM = 0.4 E) and double plane triangular implants (MSM = 0.4 (E - 1)). We developed a device to measure precisely the distance between the radioactive wires and the overlying skin, along the whole source trajectory. Using this method, the occurrence of teleangiectasia in the breast skin after interstitial implants with Ir 192 may be significantly reduced

[en] The development of new irradiation techniques such as conformal radiotherapy increasingly implies the use of a multileaf collimator. The measurement of dose gradients in the penumbra region, and of dose distributions at the edge of complex shaped fields defined by multileaf collimators requires a high definition dosimetric method. Nowadays film digitizers have been notably improved and allow the film dosimetry to be faster, more accurate, presenting a sensitivity and high spatial resolution. To be able to perform the study of physical and dosimetric specifications of a multileaf collimator, we have evaluated the performances of the Vidar VCR-12 digitizer, with respect to its sensitivity, linearity, optical density range and the resolution. These performances were compared with the performances of different systems already in use in our department, either manual or automatic, using specific patterns. The main limitation for dosimetric use is the detection threshold that can introduce errors in isodose calculation, especially for the lowest values. The result of the intercomparisons have allowed corrections to be added, taking into account this Vidar problem. The results obtained after correction for the dose profiles of squared fields are in good agreement with ionization chamber measurements in a water phantom. It is concluded that Vidar digitizer is suitable for the use of film dosimetry for the dose distributions in fields defined by multileaf collimator

No abstract available

[en] Low dose rate interstitial brachytherapy is the treatment of choice in non advanced tongue carcinoma at Institut Gustave Roussy. A group of 16 patients treated between 1982 and 1989 was retrospectively analyzed. Thirteen patients were treated by exclusive brachytherapy and three patients by a combination of external radiotherapy and brachytherapy. All tumors were implanted using a plastic tube technique loaded with Ir-192 sources. The Paris system of dosimetry was used, in which all radioactive lines must be equidistant, parallel and of the same activity. A mean basal dose rate was calculated as being the average of the sum of all the basal doses in the system. The reference isodose chosen for treatment prescription was by convention the 85% isodose. A heterogeneity index (HI) was defined as the ratio of the difference between the maximal and minimal basal dose rates and the mean basal dose rate in the central plane of the application. The value of this HI varies between 0 (perfect implant) and 1, increasing with the inhomogeneity of the dose rate of the application. HI=(BD max - BD min)/BD mean In the group of 13 patients, treated with brachytherapy alone, the prescribed dose varied between 70 and 75 Gy. The mean activity of the Ir-192 wires was 4.94 μGyhm/cm (range: 3.42 - 7.52 μGyhm/cm). The mean value of the HI in this group was 0.2543 (range: 0.0572 - 0.5767). In the group of 3 patients, treated with brachytherapy as a boost, the prescribed dose varied between 30 and 45 Gy. The mean activity of the Ir-192 wires was 3.36 μGyhm/cm (range: 2.65 - 4.32 μGyhm/cm). The mean value of the HI for this group was 0.2633 (range: 0.0845 - 0.4739). These preliminary results show large variations in the HI between implants, with a 10 fold increase of difference in the exclusive brachytherapy group. This could correlate with treatment outcome and morbidity. Data on 40 patients with more than 5 years follow-up will be presented. The prescribed total treatment time and dose will be compared to the real treatment time and delivered dose. All these factors will be correlated to clinical data, such as local control and complication rate

[en] The Moving Strip Technique for irradiation of the abdomen perfected by Fletcher and Delclos represents considerable progress in terms of radiotherapy for carcinomas of the ovary by virtue of its simplicity, good tolerance, the homogeneous dose delivered to the entire abdominal cavity and the absence of sequelae. It is possible to deliver a dose of the order of 2,500 rads in 10 days to each abdominal segment, this being equivalent to 3,500 rads in 3,5 weeks. This moderate dose is aimed only at dealing with micromodular invasion and the superimposition of added local doses is required for residual tumour, marked using clips. From a histological standpoint, the worst group seems to be adenocarcinomas. Systematic sequential surgery for excision or reduction, chemotherapy to dry out ascites, moving strip irradiation with superimposed doses locally and long term chemotherapy should make it possible to improve the prognostic results of this tumour, for which the outlook remains poor