Atypical meningioma: patterns of postradiotherapy recurrences.

PURPOSE: There is no consensus on a target definition and optimal dose in radiotherapy for atypical meningioma (AM). Insight into the postradiotherapy recurrence pattern is needed for optimal target definition and local control. The objective was to describe the patterns of recurrence after postoperative or salvage radiotherapy in patients with AM. MATERIALS AND METHODS: A retrospective analysis was conducted of patients treated for intracranial AM with (fractionated) stereotactic radiotherapy (FSRT). The relationships between postradiotherapy recurrences, the dura and irradiated volume were established. Moreover, the dose prescriptions and fractionation schedules were converted to a reference to determine the relationship between dose and local control. RESULTS: The included patients received 57 (F)SRT treatments and 73 surgeries. Recurrent disease was found in 21 of 29 patients (72%) and after 39 of 57 (F)SRTs (68%). The median interval to first recurrence was 39.7 months. Of these recurrences, 25 were in-field, 11 were marginal, and 3 were out of field. In-field recurrence rates after biological equivalent doses < 60 Gy or ≥ 60 Gy were 50% and 21%. All recurrences were connected to the dura. Of the marginal recurrences, 64% were within 2 cm and 91% were within 3 cm of the volume receiving the prescribed dose. CONCLUSIONS: AM frequently recurs after radiotherapy. All postradiotherapy recurrences were connected to the dura. Most marginal recurrences occurred within 3 cm of the irradiated abnormal dura. The lowest rate of in-field recurrences occurred after equivalent doses of least 60 Gy in 2 Gy fractions suggesting a dose-effect relationship.

Improving anatomical mapping of complexly deformed anatomy for external beam radiotherapy and brachytherapy dose accumulation in cervical cancer.

PURPOSE: In the treatment of cervical cancer, large anatomical deformations, caused by, e.g., tumor shrinkage, bladder and rectum filling changes, organ sliding, and the presence of the brachytherapy (BT) applicator, prohibit the accumulation of external beam radiotherapy (EBRT) and BT dose distributions. This work proposes a structure-wise registration with vector field integration (SW+VF) to map the largely deformed anatomies between EBRT and BT, paving the way for 3D dose accumulation between EBRT and BT. METHODS: T2w-MRIs acquired before EBRT and as a part of the MRI-guided BT procedure for 12 cervical cancer patients, along with the manual delineations of the bladder, cervix-uterus, and rectum-sigmoid, were used for this study. A rigid transformation was used to align the bony anatomy in the MRIs. The proposed SW+VF method starts by automatically segmenting features in the area surrounding the delineated organs. Then, each organ and feature pair is registered independently using a feature-based nonrigid registration algorithm developed in-house. Additionally, a background transformation is calculated to account for areas far from all organs and features. In order to obtain one transformation that can be used for dose accumulation, the organ-based, feature-based, and the background transformations are combined into one vector field using a weighted sum, where the contribution of each transformation can be directly controlled by its extent of influence (scope size). The optimal scope sizes for organ-based and feature-based transformations were found by an exhaustive analysis. The anatomical correctness of the mapping was independently validated by measuring the residual distances after transformation for delineated structures inside the cervix-uterus (inner anatomical correctness), and for anatomical landmarks outside the organs in the surrounding region (outer anatomical correctness). The results of the proposed method were compared with the results of the rigid transformation and nonrigid registration of all structures together (AST). RESULTS: The rigid transformation achieved a good global alignment (mean outer anatomical correctness of 4.3 mm) but failed to align the deformed organs (mean inner anatomical correctness of 22.4 mm). Conversely, the AST registration produced a reasonable alignment for the organs (6.3 mm) but not for the surrounding region (16.9 mm). SW+VF registration achieved the best results for both regions (3.5 and 3.4 mm for the inner and outer anatomical correctness, respectively). All differences were significant (p < 0.02, Wilcoxon rank sum test). Additionally, optimization of the scope sizes determined that the method was robust for a large range of scope size values. CONCLUSIONS: The novel SW+VF method improved the mapping of large and complex deformations observed between EBRT and BT for cervical cancer patients. Future studies that quantify the mapping error in terms of dose errors are required to test the clinical applicability of dose accumulation by the SW+VF method.