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A Study of Evaluation of Optimal PTV Margins for Patients Receiving Prostate IGRT based on CBCT Data Dose Calculation

Posted on:2015-05-07Degree:M.SType:Thesis
University:The University of ToledoCandidate:Gill, Sukhdeep KaurFull Text:PDF
GTID:2474390017990731Subject:Health Sciences
Abstract/Summary:
Image-Guided Radiation Therapy (IGRT) is used in the treatment of prostate cancer to assist in precise dose delivery to the tumor and to maximize sparing of normal structures. The prostate, bladder, rectum and femoral heads can be imaged before every treatment and, with the use of Cone beam Computed Tomography (CBCT) imaging, the actual dose delivered to these organs can be monitored based on the patient's daily anatomy. Daily set-up variations during prostate IMRT yields differences in the actual doses vs. expected doses received by the prostate, rectum and bladder. This study evaluates the optimal PTV margins for patients receiving CBCT-guided prostate IMRT based on the daily CBCT dose calculation. To determine the optimal PTV margin for CBCT-guided prostate IMRT, the prostate and organ at risk doses were estimated from daily CBCT and compared to those expected from planning. Four plans were generated with different CTV to PTV margins and these plans were transferred onto the daily CBCT. The actual delivered doses to the prostate, contoured as the CTV, were calculated on daily CBCTs using anatomy specific CT to density curves. Evaluation of the dose-volume histograms showed that a 3-5mm PTV margin was optimal for prostate IMRT, when daily CBCT is used for image guidance.;The second part of this study includes a volumetric dose comparison of the rectum and bladder based on daily CBCT with respect to planned doses. The volume of the bladder and rectum changes during treatment and has an effect on the cumulative dose received by these organs. It was observed that the volumetric dose received by the bladder decreases as the volume of the bladder increases. There was no particular trend observed between volumetric dose and rectal volume.
Keywords/Search Tags:Dose, Prostate, PTV margins, Optimal PTV, CBCT, Bladder
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