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PURPOSE: To study the image effects of the time-wise dynamic aspect of intravenous contrast agents to enable contrast-enhanced cone-beam CT (CE- CBCT) localization of liver lesions for stereotactic body radiation therapy (SBRT). METHODS: A model was developed to study dynamic IV contrast agents using static phantoms and to derive optimum parameters for CE- CBCT imaging. Ten samples containing iodine at 0-5 mg/mL were prepared in cylindrical tubes, corresponding roughly to 0-100 HU as measured by 120 kV helical CT imaging. Each sample was imaged separately in a tissue- equivalent phantom, yielding ten datasets (roughly 650 projections each) corresponding to these static CBCT images. To reconstruct images of dynamic contrast concentrations, the CBCT 2D projections were re- assembled to match the expected amount of contrast at different points in time. This model was applied to published hepatic contrast enhancement curves, and optimum imaging and contrast injection parameters were derived. RESULTS: A signal-to-noise ratio (SNR) decrease of 25%-75% in dynamic CE-CBCT images from ideal CT of samples with a 20-100 HU difference from water was observed in the un-optimized scans. This demonstrates the difficulty of CE-CBCT, and was noticed even in geometries that minimize or eliminate x-ray scatter, detector glare, and motion. Using our model, we found parameters for iodine injection, CBCT scanning, and injection/scanning timing which optimize contrast enhancement, and a 100% SNR increase with respect to the un-optimized scans was achieved. CONCLUSIONS: The effect of IV contrast is severely degraded in CBCT, and optimization of image and timing parameters is crucial for improved CE-CBCT imaging for target localization. CBCT has very low temporal resolution, and the pharmacokinetics of IV contrast must be carefully considered in order to apply this technique to localize liver lesions for SBRT. This model will be used to establish the feasibility of CE- CBCT for routine localization of liver lesions.
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PURPOSE: We have clinically observed that larger rotational setup errors are more prominent in pediatric patients who received radiation therapy for brain tumors. In this work, we quantitatively evaluated the daily setup corrections in pitch, roll, and yaw axes for children who received intracranial radiation therapy under x-ray image guidance. METHODS: Daily localization data of 43 patients between the ages of 10 months and 21.9 years were analyzed in this study. Patients were immobilized with thermoplastic mask during treatments, and 2D orthogonal x-ray images wereacquired for setup corrections before each treatment. Rotational setup corrections in pitch, roll, and yaw axes were extracted from 873 treatment fractions, and were analyzed for the whole group of patients and for two age groups: < 5 and = 5 years old. RESULTS: The mean values for the pitch corrections were 1.91° and 1.65° (p:0.02), roll corrections were 1.37° and 1° (p<0.001), and yaw corrections were 1.93° and 1.47° (p<0.001), respectively. For patients < 5 years, 21.7% of treatments had pitch corrections more than 3°, versus 15.6% of treatments required pitch corrections more than 3° for patients >= 5 years. Similarly, 10.6% of roll corrections and 20.9% of yaw corrections were more than 3° for patients < 5 years. On the other hand, 2.1% of roll and 13.8% of yaw corrections were more than 3° for patients = 5 years old. CONCLUSIONS: Data indicate that children less than 5 years old are more prone to rotational setup errors during intracranial radiation therapy. This can be attributed to reduced efficacy of immobilization devices due to smaller and rounder anatomicalfeatures of pediatric patients, and challenges in setup while the patient is under anesthesia. The role of daily image guidance and rotational setup corrections becomes important to ensure target coverage, especially for children < 5 years old.
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PURPOSE: Plan report documentation contains numerous details about the treatment plan, but critical information for patient safety is often presented without special emphasis. This can make it difficult to detect errors from treatment planning and data transfer during the initial chart review. The objective of this work is to improve safety measures in radiation therapy practice by customizing the treatment plan report to emphasize safety-critical information. METHODS: Commands within the template file from a commercial planning system (Eclipse, Varian Medical Systems) that automatically generates the treatment plan report were reviewed and modified. Safety-critical plan parameters were identified from published risks known to be inherent in the treatment planning process. Risks having medium to high potential impact on patient safety included incorrect patient identifiers, erroneous use of the treatment prescription, and incorrect transfer of beam parameters or consideration of accessories. Specific examples of critical information in the treatment plan report that can be overlooked during a chart review included prescribed dose per fraction and number of fractions, wedge and open field monitor units, presence of beam accessories, and table shifts for patient setup. RESULTS: Critical information was streamlined and concentrated. Patient and plan identification, dose prescription details, and patient positioning couch shift instructions were placed on the first page. Plan information to verify the correct data transfer to the record and verify system was re-organized in an easy to review tabular format and placed in the second page of the customized printout. Placeholders were introduced to indicate both the presence and absence of beam modifiers. Font sizes and spacing were adjusted for clarity, and departmental standards and terminology were introduced to streamline data communication among staff members. CONCLUSIONS: Plan reporting documentation has been customized to concentrate and emphasize safety-critical information, which should allow for a more efficient, robust chart review process.
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Intensity modulated radiation therapy (IMRT) is a technology intensive treatment modality involving the delivery of highly conformal dose distributions to patients. IMRT is becoming a standard of care for many disease sites and approximately 30%-60% of cancer patients in the United States receive IMRT treatments. Given the complexity of the IMRT treatment planning and delivery processes, a number of AAPM reports and guidance documents addressed the technical aspects of IMRT, including the need for comprehensive acceptance testing, commissioning, and QA programs for IMRT planning and delivery equipment. The implementation of these verification programs is essential to ensure the accuracy of IMRT delivery. Despite the critical role of patient-specific IMRT verification QA to ensure the safe delivery of IMRT treatments to patients as planned, there is little systematic guidance on the type of methodologies, tools, and acceptable tolerance levels that are needed in clinical practice. Furthermore, there are limited discussion on the pros and cons of the different delivery methods for QA measurements, and no recommendations on how to assess the clinical relevance of failed IMRT plans. LEARNING OBJECTIVES: 1. To discuss commonly employed IMRT measurement methods and discuss the pros and cons of each method. 2. To review methodologies for absolute dose verification (single small-volume, 1D, 2D methods), and review dose-difference, DTA, and Gamma analysis techniques including the variability of vendors implementation 3. To review IMRT QA passing rates for given tolerances and action levels, and discuss the clinical relevance of failed IMRT QA.