O. Pradier

Impact of tumor size and tracer uptake heterogeneity in (18)F-FDG PET and CT non-small cell lung cancer tumor delineation.

The objectives of this study were to investigate the relationship between CT- and 18F-FDG PET–based tumor volumes in non–small cell lung cancer (NSCLC) and the impact of tumor size and uptake heterogeneity on various approaches to delineating uptake on PET images. Methods: Twenty-five NSCLC cancer patients with 18F-FDG PET/CT were considered. Seventeen underwent surgical resection of their tumor, and the maximum diameter was measured. Two observers manually delineated the tumors on the CT images and the tumor uptake on the corresponding PET images, using a fixed threshold at 50% of the maximum (T50), an adaptive threshold methodology, and the fuzzy locally adaptive Bayesian (FLAB) algorithm. Maximum diameters of the delineated volumes were compared with the histopathology reference when available. The volumes of the tumors were compared, and correlations between the anatomic volume and PET uptake heterogeneity and the differences between delineations were investigated. Results: All maximum diameters measured on PET and CT images significantly correlated with the histopathology reference (r > 0.89, P < 0.0001). Significant differences were observed among the approaches: CT delineation resulted in large overestimation (+32% ± 37%), whereas all delineations on PET images resulted in underestimation (from −15% ± 17% for T50 to −4% ± 8% for FLAB) except manual delineation (+8% ± 17%). Overall, CT volumes were significantly larger than PET volumes (55 ± 74 cm3 for CT vs. from 18 ± 25 to 47 ± 76 cm3 for PET). A significant correlation was found between anatomic tumor size and heterogeneity (larger lesions were more heterogeneous). Finally, the more heterogeneous the tumor uptake, the larger was the underestimation of PET volumes by threshold-based techniques. Conclusion: Volumes based on CT images were larger than those based on PET images. Tumor size and tracer uptake heterogeneity have an impact on threshold-based methods, which should not be used for the delineation of cases of large heterogeneous NSCLC, as these methods tend to largely underestimate the spatial extent of the functional tumor in such cases. For an accurate delineation of PET volumes in NSCLC, advanced image segmentation algorithms able to deal with tracer uptake heterogeneity should be preferred.

Cervix cancer brachytherapy: high dose rate.

Cervical cancer, although less common in industrialized countries, is the fourth most common cancer affecting women worldwide and the fourth leading cause of cancer death. In developing countries, these cancers are often discovered at a later stage in the form of locally advanced tumour with a poor prognosis. Depending on the stage of the disease, treatment is mainly based on a chemoradiotherapy followed by uterovaginal brachytherapy ending by a potential remaining tumour surgery or in principle for some teams. The role of irradiation is crucial to ensure a better local control. It has been shown that the more the delivered dose is important, the better the local results are. In order to preserve the maximum of organs at risk and to allow this dose escalation, brachytherapy (intracavitary and/or interstitial) has been progressively introduced. Its evolution and its progressive improvement have led to the development of high dose rate brachytherapy, the advantages of which are especially based on the possibility of outpatient treatment while maintaining the effectiveness of other brachytherapy forms (i.e., low dose rate or pulsed dose rate). Numerous innovations have also been completed in the field of imaging, leading to a progress in treatment planning systems by switching from two-dimensional form to a three-dimensional one. Image-guided brachytherapy allows more precise target volume delineation as well as an optimized dosimetry permitting a better coverage of target volumes.

[Benefits of breathing-adapted radiation therapy for breast cancer].

PURPOSE The purpose of this study was to compare free-breathing radiotherapy, end-expiration gating and end-inspiration gating for left breast cancer, with respect to the target volume coverage and dose to organs at risk. PATIENTS AND METHODS Sixteen patients underwent 3D and 4D simulation CT. For each patient, five dosimetric plans were compared: free breathing, end-inspiration gating, end-expiration gating, and two optimised plans with a 3mm reduction of the posterior field edge to create optimised end-inspiration and end-expiration plans. Dose-volume parameters, including planning target volume coverage and dose to lung, heart and left anterior descending coronary artery were analysed. RESULTS Planning target volume coverage was adequate and similar in the five dosimetric plans (P=0.49). Significant advantage was found for end-inspiration gating in sparing the ipsilateral lung, heart and left anterior descending coronary artery compared to free-breathing 3D radiotherapy. Optimised end-inspiration was even more favourable than end-inspiration gating (P<0.05), with less dose delivered to the ipsilateral lung, heart and left anterior descending coronary artery. When compared to end-expiration gating, end-inspiration gating dosimetric outcomes were similar regarding lung and left anterior descending coronary artery doses, but the heart dose was inferior on the end-inspiration gating compared to end-expiration gating. CONCLUSION Breathing-adapted radiation therapy allowed for dose reduction to organs at risk (left lung, heart and left anterior descending coronary artery), while keeping the same planning target volume coverage. Therefore it can be considered as an interesting option for left breast cancer radiation treatment.

SU-E-J-184: Stereo Time-Of-Flight System for Patient Positioning in Radiotherapy

PURPOSE The objective of this work is to test the advantage of using the surface acquired by two stereo Time-of-Flight (ToF) cameras in comparison of the use of one camera only for patient positioning in radiotherapy. METHODS A first step consisted on validating the use of a stereo ToFcamera system for positioning management of a phantom mounted on a linear actuator producing very accurate and repeatable displacements. The displacements between two positions were computed from the surface point cloud acquired by either one or two cameras thanks to an iterative closest point algorithm. A second step consisted on determining the displacements on patient datasets, with two cameras fixed on the ceiling of the radiotherapy room. Measurements were done first on voluntary subject with fixed translations, then on patients during the normal clinical radiotherapy routine. RESULTS The phantom tests showed a major improvement in lateral and depth axis for motions above 10 mm when using the stereo-system instead of a unique camera (Fig1). Patient measurements validate these results with a mean real and measured displacement differences in the depth direction of 1.5 mm when using one camera and 0.9 mm when using two cameras (Fig2). In the lateral direction, a mean difference of 1 mm was obtained by the stereo-system instead of 3.2 mm. Along the longitudinal axis mean differences of 5.4 and 3.4 mm with one and two cameras respectively were noticed but these measurements were still inaccurate and globally underestimated in this direction as in the literature. Similar results were also found for patient subjects with a mean difference reduction of 35%, 7%, and 25% for the lateral, depth, and longitudinal displacement with the stereo-system. CONCLUSION The addition of a second ToF-camera to determine patient displacement strongly improved patient repositioning results and therefore insures better radiation delivery.

Comparaison de la fonction érectile après traitement curatif du cancer de prostate à faible risque par curiethérapie et par prostatectomie radicale : étude prospective chez des patients ayant un score IIEF5 initial > 16

Objectifs Évaluer les résultats fonctionnels à distance d’une chirurgie de la convexité pour maladie de Lapeyronie et courbure congénitale de verge, au moyen d’un nouveau questionnaire. Méthodes Il s’agit d’une étude rétrospective, monocentrique, à partir d’une cohorte de patients atteints de la maladie de Lapeyronie, ou d’une courbure congénitale de verge. Tous les patients ont été opérés par le même chirurgien, de mai 2008 à février 2013. Étaient inclus les patients opérés d’une chirurgie de la convexité par la technique de Nesbit, Yackia ou Diamond shape. Le taux de courbure pré opératoire a été mesuré. Un questionnaire fonctionnel post opératoire a été soumis à tous les patients par téléphone ou par courrier, composé de 19 questions, ainsi que le questionnaire IEF5. Résultats Cinquante huit patients ont été opérés d’une correction de courbure de verge, 46 pour une maladie de Lapeyronie, et 12 pour une courbure congénitale. La courbure initiale moyenne est de 72,4◦. Les patients se déclarent insatisfaits dans 25 % des cas, avec un coefficient de corrélation avec la courbure initiale de 0,2. La courbure résiduelle est de 13,1◦, et le raccourcissement ressort comme une cause fréquente d’insatisfaction dans 47,5 % des cas. Il occasionne une sortie non volontaire du vagin dans 35 % des cas. La vie sexuelle des patients est identique ou améliorée pour 35 % des patients par rapport à avant. Dans 5 % des cas, les patients décrivent une érection insuffisante ou impossible ce qui va dans le sens de l’IEF5 moyen qui est de 19,3/25. Conclusion La déformation résiduelle (13,1◦) et un IIEF5 moyen à 22,5/30 montrent que l’IIEF est un mauvais reflet de l’activité sexuelle post opératoire. Le taux d’insatisfaction globale est élevé (25 %) et l’amélioration de leur vie sexuelle plutôt faible (35 %) liés principalement au raccourcissement de verge responsable de sortie involontaire du vagin dans 35 % des cas. De nouveaux outils d’évaluation deviennent indispensables. Déclaration d’intérêts Les auteurs n’ont pas transmis de déclarations de conflits d’intérêts.

SU-E-J-268: Is It Necessary to Account for Organs at Risk Respiratory Induced Motion Effects in Radiotherapy Planning with Tumor Tracking?

PURPOSE The objective of this study was to evaluate the necessity to account for the organs at risk (OARs) respiratory induced motion in addition to the tumor displacement when planning a radiotherapy treatment that accounts for tumor motion. METHODS For 18 lung cancer patients, conformational radiotherapy treatment plans were generated using 3 different CT volumes: the two extreme respiratory phases corresponding to either the full inspiration (plan 1) or expiration (plan 3), as well as a manually deformed phase consisting in full inspiration combined with the full expiration tumor location (plan 2) simulating a tumor tracking plan without addressing OARs motion. Treatment plans were initially created on plan 1 and then transferred to plan 2 and 3 which represent respectively the tumor displacement only and the whole anatomic variations due to breathing. The dose coverage and the dose delivered to the OARs were compared using conformational indexes and generalized equivalent uniform dose. RESULTS The worst conformational indexes were obtained for plans with all anatomic deformations (Table 1) with an underestimation of the 95% isodose spreading on healthy tissue compared to plans considering the tumor displacement only. Furthermore, mean doses to the OARs when accounting for all the anatomic changes were always higher than those associated with the tumor displacement only: the mean difference between these two plans was 1±1.37 Gy (maximum of 3.8 Gy) for the heart and 1.4±1.42 Gy (maximum of 4.1 Gy) for the lung in which the tumor was located (Figure 1). CONCLUSION OARs deformations due to breathing motion should be included in the treatment planning in order to avoid unnecessary OARs dose and/or allow for a tumor dose escalation. This is even more important for treatments like stereotactic radiation therapy which necessitates a high precision ballistic and dose control.

SU‐E‐J‐97: Predictive and Prognostic Clinical Values of 18F‐FDG PET Based Measurements in Locally Advanced Esophageal Cancer Are Not Improved by Partial Volume Effects Correction

Purpose: We have previously demonstrated that functional tumor volume (TV) and Total Lesion Glycolysis (TLG=TV×SUVmean) measured on pretreatment 18F‐FDG PET scans were significant predictors of response and prognostic factors of survival, whereas SUV measurements were not. The objective of this study was to investigate the impact of partial volume effects (PVE) correction (PVC) on this clinical value. Methods: 50 patients with esophageal cancer treated with concomitant radiochemotherapy were retrospectively analyzed. 18F‐FDG PET baseline scans were corrected for PVE with iterative deconvolution with wavelet‐based denoising. Tumors were subsequently delineated using the Fuzzy Locally Adaptive Bayesian (FLAB) algorithm on both original and corrected images. Maximum and peak SUV, TV, mean SUV, and TLG were extracted and compared. The value of each parameter (with or without PVC) was investigated using Kruskal‐Wallis tests regarding response and Kaplan‐Meier curves regarding survival. Results: Whereas PVC had a significant quantitative impact on the absolute values of each parameter (up to more than 100% for SUVmax), the respective clinical value was not significantly modified whether for overall survival or response to therapy. No significant improvement was observed after PVC for the already established significant predictive and prognostic value of TV and TLG. Similarly, the non significant predictive and prognostic value of the various SUV measurements was not improved by PVC and was even lowered in some cases. Conclusions: PVC did not modify significantly the previously established clinical value of tumor volume or TLG. In addition, the limited value of SUV measurements in this context may therefore not be explained by the lack of PVC since PVC did not improve their clinical value and in most cases it even lowered it.

SU-E-J-113: Impact of 4D PET and Motion Correction in the Delineation of Gross Tumor Volume for Radiotherapy Treatment Planning in Lung Cancer

Purpose: To quantitatively assess the impact of motion correction in 4D‐PET images on the accuracy of automatic lungtumour volume delineation for radiotherapytreatment planning and the resulting dosimetry modifications.Methods: : Simulated 18F‐FDG‐PET data using the NURBS‐based Cardiac‐Torso phantom and Geant4 Application for Tomography Emission were considered. Homogeneous and heterogeneous spherical cases were designed with two tumor‐to‐background (T:B) contrasts (4 and 10) and 3 motion amplitudes (0.5, 1.5 and 2.5cm). Two more realistic cases derived from real clinical PET/CT datasets were also generated. Data were corrected for respiratory motion using two Methods: reconstruction incorporating elastic transformations and super‐resolution. The tumours were segmented with the Fuzzy Locally Adaptive Bayesian algorithm on each respiratory phase with or without correction and on the motion average image. For heterogeneous cases global and boost volumes were delineated. The union of the volumes at each phase with or without motion correction, the average PET volume and the volume with internal margins added to one respiratory phase were compared to the union of the simulated volumes (ground‐truths). For each of these target volumes, IMRT planning was used to compare the different motion management approaches in terms of impact on dosimetry.Results: The smallest and largest volumes were obtained on the average PET and the one with internal margins respectively. The best compromise between sensitivity and positive predictive value were obtained with corrected PET, with similar results for both corrections. The best compromise between ground‐truth volume coverage and organs‐at‐risk sparing was achieved by the volumes with most accurate delineation. The volume with margins always covered the ground‐truth Conclusions: 4D‐PET with motion correction leads to more accurate delineation of lungtumours and boost volumes in the presence of respiratory motion. This also leads to improved margins for treatment planning.

Adapting dose prescription to tumour heterogeneities: The impact of the functional contrast

Tumours are heterogeneous structures. The evolution of functional imaging techniques and the use of new tracers for PET images allow characterizing tumour heterogeneities in terms of clonogenic cell density, partial oxygen pressure or proliferation. Within this context, the basic idea is to prescribe PET-based non uniform dose distributions in order to improve treatment outcome. Two scenarios can be considered to adapt treatment to tumour heterogeneities: namely the dose boosting or the dose redistribution. In the first case a sub-volume within the tumour will receive a higher dose, while in the second scenario the mean dose is kept equal to the clinical uniform dose but is redistributed within the tumour compartments considered. A dose redistribution based on maximisation of the tumour control probability (TCP) under constraint was considered. A number of FDG and FMISO PET simulated datasets considering different tumour shapes and heterogeneities and two clinical cases were used in this study. For each case six contrasts were considered in order to analyse the impact of the functional contrast on dose calculation and treatment outcome calculated with TCP. For all contrasts considered there is only a small benefit using dose redistribution with FDG-PET (TCP increase < 3%) but a high benefit with FMISO-PET images (TCP increase > 5%). For the dose boosting scenario the TCP increase is higher (up to 7% and 55% for a 5Gy boost applied to FDG and FMISO PET resp.).