Organs-at-risk contouring on head CT for RT planning using 3D slicer-A preliminary study

International audienceIn radiotherapy, computed tomography (CT) images are typically used for radiation treatment planning. Accurate segmentation of radiation sensitive healthy tissues, organs-atrisk (OARs), is important for radiation treatment planning for brain tumor. 3D Slicer has been applied in many medical applications including tumor segmentation on head MR images. However, to the best of our knowledge, there have been no studies using 3D Slicer for segmenting OARs on head CT images. This preliminary study evaluates the segmentation of seven OARs on head CTs using 3D Slicer. Results are comparable to state-ofthe- art approaches but a larger dataset is required to verify the results. © 2019 IEEE

Planification selon la position moyenne du cycle respiratoire : modèle de planification optimale pour une distribution de dose dans les tumeurs pulmonaires. [Mid-ventilation position planning: optimal model for dose distribution in lung tumour].

International audiencePURPOSE: The dose distribution for lung tumour is estimated using a 3D-CT scan, and since a person breathes while the images are captured, the dose distribution doesn't reflect the reality. A 4D-CT scan integrates the motion of the tumour during breathing and, therefore, provides us with important information regarding tumour's motion in all directions, the motion volume (ITV) and the time-weighted average position (MVP). PATIENT AND METHODS: Based on these two concepts, we have estimated, for a lung carcinoma case a 3D dose distribution from a 3D-CT scan, and a 4D dose distribution from a 4-D CT scan. To this, we have applied a non-rigid registration to estimate the cumulative dose. RESULTS: Our study shows that the 4D dose estimation of the GTV is almost the same when made using MVP and ITV concepts, but sparring of the healthy lung is better done using the MPV model (MVP), as compared to the ITV model. This improvement of the therapeutic index allows, from a projection on the theoretical maximal dose to PTV (strictly restricted to doses for the lungs and the spinal cord), for an increase of about 11% on the total dose (maximal dose of 86 Gy for the ITV and 96 Gy for the MVP). CONCLUSION: Further studies with more patients are needed to confirm our data

Dosimetric Benefit of Adaptive Radiation Therapy With Reduced Planning Target Volume Margins in Cervix Carcinoma

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Radiothérapie guidée par l'image : pourquoi, comment et résultats. [Image-guided radiotherapy: rational, modalities and results].

International audienceThe objective of Image-Guided Radiotherapy (IGRT) is to take in account the inter- or/and intrafraction anatomic variations (organ motion and deformations) in order to improve treatment accuracy. The IGRT should therefore translate in a clinical benefit the recent advances in both tumor definition thanks to functional imaging, and dose distribution thanks to intensity modulated radiotherapy. The IGRT enables direct or indirect tumor visualization during radiation delivery. If the tumor position does not correspond with the theoretical location of target derived from planning system, the table is moved. In case of important uncertainties related to target deformation, a new planning can be discussed. IGRT is realized by different types of devices which can vary in principle and as well as in their implementation: from LINAC-integrated-kV (or MV)-Cone Beam CTs to helicoidal tomotherapy, Cyberknife and Novalis low-energy stereoscopic imaging system. These techniques led to a more rational choice of Planning Target Volume. Being recently introduced in practice, the clinical results of this technique are still limited. Nevertheless, until so far, IGRT has showed promising results with reports of minimal acute toxicity. This review describes IGRT for various tumor localizations. The dose delivered by on board imaging should be taken in account. A strong quality control is required for safety and proper prospective evaluation of the clinical benefit of IGRT

Planning Library Based on Population Shape Analysis for Cervical Adaptive Radiotherapy

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12 - Dosimetric benefit of adaptive radiotherapy with reduced PTV margins in cervix carcinoma

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Bénéfice de la radiothérapie adaptative par bibliothèque de plans de traitement pour les cancers du col utérin ?

National audiencePurpose - In case of intensity-modulated radiotherapy (IMRT) for locally advanced cervix carcinoma, the objectives were to quantify the difference between the planned and the delivered doses by a standard irradiation, and to estimate the dosimetric benefit of a pretreatment planning library-based adaptive radiotherapy. Material and methods - Ten patients with locally advanced cervix carcinoma had three planning CTs corresponding to three bladder volumes: empty, intermediate (vi) and full. On each CT, two IMRT plans were generated to deliver 45 Gy to the planning target volume (PTV), with two different margins: clinical target volume (CTV)+10mm and CTV+15 mm. Using bi-weekly CBCTs, three scenarios of treatment have been simulated and compared: standard IMRT (one vi planning) with 10 and 15 mm margins and adaptive radiotherapy with 10mm margin. The cumulated dose in the organs at risk was estimated by elastic registration. Result - In case of standard IMRT, the cumulated dose was significantly different than the planning dose, with an under-dose of the CTV and the bladder, and an over-dose of the rectum and the peritoneal cavity. For 54% of the fractions, the adaptive radiotherapy planning was not based on vi. Considering the cumulated dose and compared to IMRT with 10-mm margin, adaptive radiotherapy increased the dose to the CTV (1.4 Gy for D98%) and decreased slightly the dose to the rectum and the peritoneal cavity. Compared to a standard IMRT with 15 mm margin, adaptive radiotherapy decreased significantly the dose to the rectum (20% for V40), the bladder (13% for V40) and the peritoneal cavity (2% for V35). Conclusion - A pretreatment planning library-based adaptive radiotherapy in cervix carcinoma decreases the dose to the organs at risk and increases the dose to the CTV