Browsing by Author "Barclay, Jennifer"
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Item Masking Enhances Accuracy of Bladder Deformation in Multi-Fraction Adaptive Brachytherapy as a First Step Toward Composite Dose Estimation(2014-02-04) Barclay, Jennifer; Albuquerque, Kevin; Pompos, Arnold; Gu, XuejunBACKGROUND: GEC-ESTRO guidelines for cervix HDR brachytherapy advocate measurement of the minimum dose to the 2cc volume of organs at risk (OAR) receiving the highest amount of radiation and summation across multiple treatment fractions to give a worst-case-scenario cumulative dose estimate. If the OAR from different fractions could be accurately co-registered using deformation, then a more accurate composite dose could be obtained. OBJECTIVE: As a first step toward composite dose estimation, we sought to assess and improve the quality of bladder deformation using a technique called masking, which involves resetting the pixel values within a contour. METHODS: CT scans from nine cervical cancer patients with bladders contoured by radiation oncologists were obtained, and the urethra near the bladder was contoured using the catheter as a fixed reference point. Three copies of each CT were made: the first was unaltered, the second had the bladder masked, and the third had the bladder masked at one pixel value and the rest of the body masked at a different pixel value. Using VelocityAI 2.8.1, the bladder was deformed onto the target (Fraction 1) planning CT from subsequent planning CTs in an attempt to match up the tissue from different fractions. To assess the accuracy of the deformation, several indices were used: the percent error of the deformed bladder volume from the expected volume, the conformality index, the Hausdorff distance, and the distance between the centers of the deformed urethra and the target urethra. RESULTS: Deformation quality improved with masking. The standard deviation of the percent error was reduced from 18.1% with no masking to 4.3% with masking. Mean conformality increased from 0.83 with no masking, to 0.91 with the bladder masked, to 0.93 with body and bladder masked (P<0.001). The mean Hausdorff distance decreased from 13.8mm without masking, to 9.1mm with the bladder masked, to 5.7mm with body and bladder masked (P<0.001). The mean error in the urethra deformation increased from 4.3mm without masking, to 5.2mm with the bladder masked, to 6.6mm with body and bladder masked (P=0.08). CONCLUSION: The accuracy of bladder deformation can be significantly improved by masking. With masking, the volume and location of the deformed bladder more closely approached that of the target bladder than without masking. Thus masking has the potential to improve the accuracy of dose deformation and composite dose calculation in adaptive brachytherapy.Item A Ready Reference for Estimating Dose to Pelvic Node Metastases from High Dose Rate Brachytherapy (HDR-BT) in Cervical Cancer(2014-02-04) McKeever, Matthew R.; Hwang, Lindsay; Barclay, Jennifer; Dubas, Jeffrey; Xi, Yin; Bailey, April; Albuquerque, KevinINTRODUCTION: Metastasis to lymph nodes is one of the best predictive indicators of recurrence and death for cervical cancer patients. A dose of greater than 55 Gy is recommended for nodes 2 cm or less for durable control. It is expected that nodes closer to the radiation source will receive a higher dose. In this study we explored the relationship between lymph node location and the Point A dose as a means of assisting the radiation oncologist to determine the required boost dose. METHODS: This retrospective study from 2009 through 2013 included 29 cervical cancer patients receiving high dose rate brachytherapy and had a total of 60 metastases to pelvic lymph nodes. The lymph nodes were mapped and contoured in the treatment planning system.. The external beam and brachytherapy doses and percentage of brachytherapy point A dose received by each lymph node were calculated. RESULTS: The median doses from brachytherapy and external beam radiation to the lymph nodes were 5.5 Gy (range, 1.4-12.4 Gy) and 49.6 Gy (range, 42.5-62.9 Gy), respectively. The median total dose for all lymph nodes was 56.5 Gy (range, 46.5-66.3 Gy). The dose from brachytherapy accounted for 9.97% of the total dose to the lymph node. The location of the lymph node affected the dose received. The common iliac nodes, which were furthest from the uterus, received 3.18 Gy (11.09 % of point A); the internal iliac nodes received 4.29 Gy (16.43% of point A); and the external iliac nodes, which were closest to the uterus, received 6.05 Gy (21.75% of point A). As expected, nodes closer to the uterus received higher doses of brachytherapy radiation. DISCUSSION AND CONCLUSION: The common iliac nodes received the smallest fraction of the brachytherapy dose and thus need the greatest external boost dose. Also the internal iliac lymph nodes above the sacroiliac joint, the external iliac lymph nodes anterior to the acetabular line, and the external iliac nodes lateral to the external iliac artery received a smaller amount of the brachytherapy dose than the rest of the nodes in their group. This will require them to have a higher boost dose from external beam compared to other nodes in their group. The results of this study provide radiation oncologists a reference for determining which nodes require an external beam boost dose and the optimal boost dose for those nodes. Improved optimization of the boost dose should lead to better local control and outcomes for patients.