Search

External beam radiotherapy is extensively used to treat cervical carcinomas. A single planning CT scan enables the calculation of the dose distribution. The treatment is delivered over five weeks. Large per-treatment anatomical variations may hamper the dose delivery, with the potential of an organ-at-risk (OAR) overdose and a tumor underdose. To anticipate these deformations, a recent approach proposed three planning CTs with variable bladder volumes, which had the limitation of not covering all per-treatment anatomical variations. An original patient-specific population-based library has been proposed. It consisted of generating two representative anatomies, in addition to the standard planning CT anatomy. First, the cervix and bladder meshes of a population of 20 patients (314 images) were registered to an anatomical template, using a deformable mesh registration. An iterative point-matching algorithm was developed based on local shape context (histogram of polar or cylindrical coordinates and geodesic distance to the base) and on a topology constraint filter. Second, a standard principal component analysis (PCA) model of the cervix and bladder was generated to extract the dominant deformation modes. Finally, specific deformations were obtained using posterior PCA models, with a constraint representing the top of the uterus deformation. For a new patient, the cervix-uterus and bladder were registered to the template, and the patient’s modeled planning library was built according to the model deformations. This method was applied following a leave-one-patient-out cross-validation. The performances of the modeled library were compared to those of the three-CT-based library, showing an improvement in both target coverage and OAR sparing. [ABSTRACT FROM AUTHOR]

Purpose: In the context of adaptive radiation therapy (ART) for locally advanced cervical carcinoma (LACC), this study proposed an original cone‐beam computed tomography (CBCT)‐guided “Evolutive library” and evaluated it against four other known radiotherapy (RT) strategies. Material and methods: For 20 patients who underwent intensity‐modulated radiation therapy (IMRT) for LACC, three planning CTs [with empty (EB), intermediate (IB), and full (FB) bladder volumes], a CT scan at 20 Gy and bi‐weekly CBCTs for 5 weeks were performed. Five RT strategies were simulated for each patient: “Standard RT” was based on one IB planning CT; “internal target volume (ITV)‐based RT” was an ITV built from the three planning CTs; “RT with one mid‐treatment replanning (MidTtReplan)” corresponded to the standard RT with a replanning at 20 Gy; “Pretreatment library ART” using a planning library based on the three planning CTs; and the “Evolutive library ART”, which was the “Pretreatment library ART” strategy enriched by including some CBCT anatomies into the library when the daily clinical target volume (CTV) shape differed from the ones in the library. Two planning target volume (PTV) margins of 7 and 10 mm were evaluated. All the strategies were geometrically compared in terms of the percentage of coverage by the PTV, for the CTV and the organs at risk (OAR) delineated on the CBCT. Inadequate coverage of the CTV and OARs by the PTV was also assessed using deformable image registration. The cumulated dose distributions of each strategy were likewise estimated and compared for one patient. Results: The “Evolutive library ART” strategy involved a number of added CBCTs: 0 for 55%; 1 for 30%; 2 for 5%; and 3 for 10% of patients. Compared with the other four, this strategy provided the highest CTV geometric coverage by the PTV, with a mean (min–max) coverage of 98.5% (96.4–100) for 10 mm margins and 96.2% (93.0–99.7) for 7 mm margins (P < 0.05). Moreover, this strategy significantly decreased the geometric coverage of the bowel. CTV undercoverage by PTV occurred in the anterior and superior uterine regions for all strategies. The dosimetric analysis at 7 mm similarly demonstrated that the “Evolutive library ART” increased the V42.75Gy of the CTV by 27%, 20%, 13%, and 28% compared with “Standard RT”, “ITV‐based RT”, “MidTtReplan”, and “Pretreatment library ART”, respectively. The dose to the bowel was also decreased by the “Evolutive library ART” compared with that by the other strategies. Conclusion: The “Evolutive library ART” is a personalized ART strategy that comprises a pretreatment planning library of three CT scans, enriched for half of the patients by one to three per‐treatment CBCTs. This original strategy increased both the CTV coverage and bowel sparing compared with all the other tested strategies and enables us to consider a PTV margin reduction. [ABSTRACT FROM AUTHOR]

Purpose To describe the evolution and to assess the predictive value of metabolic parameters with different SUV threshold segmentations calculated from two 18F-FDG-PET/CT, one prior to and the other one during concomitant chemoradiation therapy (CCRT), for locally-advanced cervical cancer (LACC). Material and methods 53 patients treated for LACC by CCRT underwent FDG-PET/CT before treatment (PET1) and another one at 40 Gy (PET2). The PET analyzed parameters were: maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolysis (TLG). MTVs were automatically segmented using various percentage SUVmax thresholds (30–70%) and fixed SUV thresholds (all voxels with SUV >1–20). The parameters’ predictive capabilities for disease-free (DFS) and overall survival (OS) were assessed using the Harrell’s C-index ( c ) and Cox regression model. Results Depending on the SUVmax threshold, the relative decreases in MTV and TLG from PET1 to PET2 were, on average, 65% (range: 63–70%) and 85% (range: 83–86%), respectively. The strongest predictive threshold segmentations were 55% SUVmax in PET1 and 32% in PET2. Significant predictors of DFS in multivariate analysis ( c = 0.82) were MTV1 (55% SUVmax) in PET1 and TLG2 (32% SUVmax) in PET2. MTV1 (55%) was the most significant OS predictor. Conclusions MTV and TLG calculated with a threshold of 55% SUVmax and 32% SUVmax from pre- and per-treatment PET scans respectively, can be used to predict patient outcome after CCRT for LACC. [ABSTRACT FROM AUTHOR]