Propagation of registration uncertainty during multi-fraction cervical cancer brachytherapy.

Multi-fraction cervical cancer brachytherapy is a form of image-guided radiotherapy that heavily relies on 3D imaging during treatment planning, delivery, and quality control. In this context, deformable image registration can increase the accuracy of dosimetric evaluations, provided that one can account for the uncertainties associated with the registration process. To enable such capability, we propose a mathematical framework that first estimates the registration uncertainty and subsequently propagates the effects of the computed uncertainties from the registration stage through to the visualizations, organ segmentations, and dosimetric evaluations. To ensure the practicality of our proposed framework in real world image-guided radiotherapy contexts, we implemented our technique via a computationally efficient and generalizable algorithm that is compatible with existing deformable image registration software. In our clinical context of fractionated cervical cancer brachytherapy, we perform a retrospective analysis on 37 patients and present evidence that our proposed methodology for computing and propagating registration uncertainties may be beneficial during therapy planning and quality control. Specifically, we quantify and visualize the influence of registration uncertainty on dosimetric analysis during the computation of the total accumulated radiation dose on the bladder wall. We further show how registration uncertainty may be leveraged into enhanced visualizations that depict the quality of the registration and highlight potential deviations from the treatment plan prior to the delivery of radiation treatment. Finally, we show that we can improve the transfer of delineated volumetric organ segmentation labels from one fraction to the next by encoding the computed registration uncertainties into the segmentation labels.

Prostate brachytherapy postimplant dosimetry: automatic plan reconstruction of stranded implants.

PURPOSE: Plan reconstruction for permanent implant prostate brachytherapy is the process of determining the correspondence between planned and implanted seeds in postimplant analysis. Plan reconstruction informs many areas of brachytherapy quality assurance, including the verification of seed segmentation, misplacement and migration assessment, implant simulations, and the dosimetry of mixed-activity or mixed-species implants. METHODS: An algorithm has been developed for stranded implants which uses the interseed spacing constraints imposed by the suture to improve the accuracy of reconstruction. Seventy randomly selected clinical cases with a mean of 23.6 (range 18-30) needles and mean density of 2.0 (range 1.6-2.6) 2.0 (range 1.6-2.6) seeds/cm3 were automatically reconstructed and the accuracy compared to manual reconstructions performed using a custom 3D graphical interface. RESULTS: Using the automatic algorithm, the mean accuracy of the assignment relative to manual reconstruction was found to be 97.7 +/- 0.5%. Fifty-two of the 70 cases (74%) were error-free; of seeds in the remaining cases, 96.7 +/- 0.3% were found to be attributed to the correct strand and 97.0 +/-0.3% were correctly connected to their neighbors. Any necessary manual correction using the interface is usually straightforward. For the clinical data set tested, neither the number of seeds or needles, average density, nor the presence of clusters was found to have an effect on reconstruction accuracy using this method. CONCLUSIONS: Routine plan reconstruction of stranded implants can be performed with a high degree of accuracy to support postimplant dosimetry and quality analyses.

Population-based study of biochemical and survival outcomes after permanent 125I brachytherapy for low- and intermediate-risk prostate cancer.

OBJECTIVES: To analyze the biochemical and survival outcomes after permanent low-dose-rate prostate brachytherapy in a large, consecutive, population-based cohort of patients. METHODS: A total of 1006 consecutive implants were performed from July 20, 1998 to October 23, 2003 for men with low-risk and "low-tier" intermediate-risk prostate cancer. The prescribed minimal peripheral dose was 144 Gy, using 0.33 mCi (125)I sources and a preplan technique with a strong posterior-peripheral dose bias. Most patients (65%) had received 6 months of androgen deprivation therapy. Supplemental external beam radiotherapy was not used. The prognostic features, dose metrics, and follow-up data were prospectively collected. Kaplan-Meier and Cox regression analyses were used to assess the factors associated with freedom from biochemical recurrence and survival. RESULTS: The median patient age at treatment was 66 years. The median follow-up was 54 months for biochemical outcomes and 66 months for survival. The actuarial freedom from biochemical recurrence rate was 95.6% +/- 1.6% at 5 years and 94.0% +/- 2.2% at 7 years. On multivariate analysis, the pretreatment prostate-specific antigen level (P = .03) and androgen deprivation therapy use (P = .04) were predictive of the freedom from biochemical recurrence. The actuarial rates of distant metastasis and disease-specific death at 5 years were both <1%. The overall survival rate at 5 years was 95.2% +/- 1.4% and was 93.4% +/- 1.8% at 7 years. On multivariate analysis, only age was predictive of overall survival (P = .011). CONCLUSIONS: When consistently planned and delivered, low-dose-rate brachytherapy, without supplemental external beam radiotherapy or intraoperative planning, can produce cancer-specific outcomes for men with low- and "low-tier" intermediate-risk prostate cancer at least equal to that produced by dose-escalated external beam radiotherapy or surgical prostatectomy.