Master of Science (MS)
Physics and Astronomy
Purpose: To determine the dosimetric accuracy of TomoTherapy’s database technique for delivery verification and dose reconstruction in post-mastectomy radiation therapy (PMRT) treatments. Methods and Materials: Archived treatment data for 5 patients treated at MBPCC were restored to the TomoTherapy research computer system. Pretreatment MVCT images and exit detector dosimetry data collected during treatment of these patients were used to calculate the DV sinogram for each treatment fraction. The DV sinogram and MVCT image for each fraction were used to reconstruct the delivered dose for that fraction using a convolution/superposition algorithm. The reconstructed doses were compared to previously acquired TLD doses for each patient. To supplement the results from the retrospective patient data comparison, and to reduce the variables involved in a patient treatment, a PMRT treatment was created for the RANDO phantom. Measured TLD doses were compared to reconstructed doses computed from the DV sinogram and MVCT images as well as reconstructed doses from the DV sinogram and kVCT images. Results: The mean difference for all the patient data was -3.2 ± 4.7%. Approximately 66% of the data points agreed within 5%. The largest difference between measured and calculated doses was -17.3%. The mean difference for the phantom data for DV doses calculated from MVCT was 3.9 ± 2.6%. The largest difference between measured and calculated doses was 9.0%. Approximately 63% of the data points agreed within 5%. The mean difference for the phantom data for DV doses calculated from kVCT was 0.6 ± 2.9%. The largest difference between measured and calculated doses was 5.4%. Approximately 88% of the data points agreed within 5%. Conclusion: Patient motion was removed in the phantom study and there was still a large number of data points outside 5% for the DV doses calculated with MVCT. The DV doses calculated with kVCT had better agreement which indicates an inaccurate IVDT was used in the MVCT dose calculations. Discrepancies between TLD and reconstructed doses may be a result of the several problems including the inherent relatively large uncertainty of TLD, IVDT inaccuracies, and limitations of the database technique calculations near the surface.
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Roberts, Matthew, "Comparison of TLD dose and reconstructed dose for post-mastectomy radiation therapy with TomoTherapy" (2011). LSU Master's Theses. 1491.
Parker, Brent C