A hybrid approach for fusing 4D-MRI temporal information with 3D-CT for the study of lung and lung tumor motion.

PURPOSE: Accurate visualization of lung motion is important in many clinical applications, such as radiotherapy of lung cancer. Advancement in imaging modalities [e.g., computed tomography (CT) and MRI] has allowed dynamic imaging of lung and lung tumor motion. However, each imaging modality has its advantages and disadvantages. The study presented in this paper aims at generating synthetic 4D-CT dataset for lung cancer patients by combining both continuous three-dimensional (3D) motion captured by 4D-MRI and the high spatial resolution captured by CT using the authors' proposed approach. METHODS: A novel hybrid approach based on deformable image registration (DIR) and finite element method simulation was developed to fuse a static 3D-CT volume (acquired under breath-hold) and the 3D motion information extracted from 4D-MRI dataset, creating a synthetic 4D-CT dataset. RESULTS: The study focuses on imaging of lung and lung tumor. Comparing the synthetic 4D-CT dataset with the acquired 4D-CT dataset of six lung cancer patients based on 420 landmarks, accurate results (average error <2 mm) were achieved using the authors' proposed approach. Their hybrid approach achieved a 40% error reduction (based on landmarks assessment) over using only DIR techniques. CONCLUSIONS: The synthetic 4D-CT dataset generated has high spatial resolution, has excellent lung details, and is able to show movement of lung and lung tumor over multiple breathing cycles.

A spatiotemporal-based scheme for efficient registration-based segmentation of thoracic 4-D MRI.

Dynamic three-dimensional (3-D) (four-dimensional, 4-D) magnetic resonance (MR) imaging is gaining importance in the study of pulmonary motion for respiratory diseases and pulmonary tumor motion for radiotherapy. To perform quantitative analysis using 4-D MR images, segmentation of anatomical structures such as the lung and pulmonary tumor is required. Manual segmentation of entire thoracic 4-D MRI data that typically contains many 3-D volumes acquired over several breathing cycles is extremely tedious, time consuming, and suffers high user variability. This requires the development of new automated segmentation schemes for 4-D MRI data segmentation. Registration-based segmentation technique that uses automatic registration methods for segmentation has been shown to be an accurate method to segment structures for 4-D data series. However, directly applying registration-based segmentation to segment 4-D MRI series lacks efficiency. Here we propose an automated 4-D registration-based segmentation scheme that is based on spatiotemporal information for the segmentation of thoracic 4-D MR lung images. The proposed scheme saved up to 95% of computation amount while achieving comparable accurate segmentations compared to directly applying registration-based segmentation to 4-D dataset. The scheme facilitates rapid 3-D/4-D visualization of the lung and tumor motion and potentially the tracking of tumor during radiation delivery.

Radical radiotherapy with high-dose-rate brachytherapy for uterine cervix cancer long-term results.

The aim of this is to report the results of radical radiotherapy in carcinoma of the cervix treated by high-dose rate (HDR) intracavitary brachytherapy and external beam radiotherapy (XRT) at a single centre in Singapore. This is a retrospective analysis of 106 consecutive cases with histologically proven cervical cancer, treated by HDR brachytherapy and XRT at the Mount Elizabeth Hospital from 1990 to 1993. External beam radiotherapy to the pelvis was delivered with 6 MV photons, to 45-50.4 Gy in 1.8 Gy fractions. High-dose-rate brachytherapy comprised two to three applications of an intrauterine tandem with paired ovoids, to a median dose of 18 Gy to point 'A', carried out during XRT. All 106 patients completed treatment. Their ages ranged from 32 to 80 years (median 57 years). Most patients presented with stage II or III disease (44 and 37%, respectively) and with squamous cell carcinoma (91%). Median follow-up time was 59 months (range 2-169 months). The 5-year relapse-free survival rate across all stages was 71%. The corresponding overall survival rate was 69%. Local control was achieved in 86 patients (81%); six patients had residual disease (6%), and 14 patients had local recurrence (13%). Fourteen patients developed metastatic disease (13%). On univariate analysis, tumour stage, haemoglobin level, number of brachytherapy treatments and overall treatment time were found to be prognostic factors for overall survival. Late complications were mild (Radiation Therapy Oncology Group score 1-2), except for one patient with grade 4 rectal toxicity. The complication rates were 8, 14 and 45%, respectively, for the rectum, bladder and vagina (stenosis). The use of two to three fractions of HDR intracavitary brachytherapy in addition to pelvic XRT achieves good outcomes.