Search

Résumé L’objectif était d’étudier trois plans de traitements dont un en modulation d’intensité lors de l’irradiation cérébrale d’une femme enceinte, afin de délivrer la dose la plus faible au fœtus. Le traitement envisagé était de 60 Gy dans le volume cible prévisionnel. Les mesures ont été réalisées à la partie supérieure et au milieu de l’utérus sur un fantôme RANDO associé à des plaques équivalent eau accolées. Le premier plan comportait quatre faisceaux délivrés selon une méthode conformationelle par un accélérateur Varian équipé d’un collimateur de 120 lames, le deuxième utilisait des faisceaux non coplanaires et le troisième testait une technique avec modulation d’intensité. Les trois plans utilisaient des photons de 6 MV. Avec la technique conformationelle, la dose mesurée à la partie supérieure de l’utérus était de 8,3 mGy et celle au centre de 6,3 mGy. Les doses reçues par le fœtus étaient supérieures avec la technique conformationelle tridimensionnelle et non coplanaire. Avec la modulation d’intensité, la dose à la partie supérieure de l’utérus était de 23,8 mGy et celle à la partie moyenne de 14,3 mGy. En raison de l’utilisation de lames et de faisceaux non coplanaires, la modulation d’intensité ne paraît donc a priori pas une technique adaptée pour le traitement d’une femme enceinte. Cependant, la dose reçue par le fœtus restant faible et inférieure à celle de 100 mGy recommandée par la Commission internationale de protection radiologique, il est possible d’envisager l’utilisation de cette technique pour une meilleure épargne des organes à risque chez la mère. The purpose was to assess three treatments planning techniques including one in intensity-modulated radiation therapy (IMRT) for cerebral irradiation of pregnant woman, in order to limit the dose delivered to the foetus. The treatment provided was 60 Gy to the planning target volume. Estimated foetal dose was measured using an anthropomorphic phantom, on the upper and middle part of the uterus. The first plan consisted in four beams in conformational technique delivered from a Varian accelerator with a 120 leaves collimator, the second one used non-coplanar fields and the third one assessed IMRT. With the conformational technique, the dose at the upper part of the uterus was 8.3 mGy and 6.3 mGy at the middle part. The dose delivered to the foetus was higher with the non-coplanar fields. In IMRT, the dose at the upper part of the uterus was 23.8 mGy and 14.3 mGy at the middle part. The three plans used 6 MV X-rays. Because of the use of leaves and non-coplanar fields, IMRT does not seem to be the optimal technique for the treatment of pregnant woman. However, the dose delivered to the foetus remains low and below the dose of 100 mGy recommended by the International Commission of Radiological Protection. It seems possible to consider the use of this technique for a better sparing of organs at risk for the mother. [ABSTRACT FROM AUTHOR]

Abstract: Multimodality imaging plays a key role in the management of malignant tumours by radiation oncologists. The tumour extension at diagnosis identifies the patients in whom curative-intent radiotherapy is indicated. The target volumes and organs at risk are delineated on the relevant image modality (CT, MRI, PET), co-registered on a CT scan in treatment position for dose calculation purpose. The treatment machines are nowadays able to achieve heterogeneous dose distributions, possibly modulated within the target volume according to variations in the risk of failure. For instance, areas with high initial FDG uptake, low oxygenation, or insufficient response during radiotherapy could become the targets for selective dose increase. The scientific challenge includes registration and iterative segmentation of poorly contrasted images acquired on living bodies (variation in acquisition position, physiological movements and hollow organs filling, signal alteration induced by treatment…). The clinical validation of these innovative approaches and their diffusion in daily routine require a very close collaboration between many disciplines, based on a common language and understanding of radiotherapy target volumes, as illustrated in the present paper with FDG-PET imaging. [Copyright &y& Elsevier]

In PET/CT thoracic imaging, respiratory motion reduces image quality. A solution consists in performing respiratory gated PET acquisitions. The aim of this study was to generate clinically realistic Monte-Carlo respiratory PET data, obtained using the 4D-NCAT numerical phantom and the GATE simulation tool, to assess the impact of respiratory motion and respiratory-motion compensation in PET on lesion detection and volume measurement. To obtain reconstructed images as close as possible to those obtained in clinical conditions, a particular attention was paid to apply to the simulated data the same correction and reconstruction processes as those applied to real clinical data. The simulations required 140,000 h (CPU) generating 1.5 To of data (98 respiratory gated and 49 ungated scans). Calibration phantom and patient reconstructed images from the simulated data were visually and quantitatively very similar to those obtained in clinical studies. The lesion detectability was higher when the better trade-off between lesion movement limitation (compared to ungated acquisitions) and image statistic preservation is considered (respiratory cycle sampling in 3 frames). We then compared the lesion volumes measured on conventional PET acquisitions versus respiratory gated acquisitions, using an automatic segmentation method and a 40%-threshold approach. A time consuming initial manual exclusion of noisy structures needed with the 40%-threshold was not necessary when the automatic method was used. The lesion detectability along with the accuracy of tumor volume estimates was largely improved with the gated compared to ungated PET images. [ABSTRACT FROM AUTHOR]