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Clinical Significance of Using Simulation Day CT Plan Versus Treatment Day CT Plan for HDR Capri Applicators

A Shiwakoti*, B Patel , E Quan , J Syh , A Farach , R Pino , The Houston Methodist Hospital, Houston, TX


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To investigate the accuracy of using the treatment plan based on initial simulation/first fraction CT to estimate doses to target and organs-at-risk (OAR) for the entire course of high dose rate (HDR) brachytherapy utilizing the Capri applicator.

Methods: In this retrospective study, we evaluated the target and OAR doses for four patients who were treated in our facility with a Capri applicator. For each patient, a treatment plan was generated on the first fraction CT to evaluate total HDR dose. On each following treatment day, a day-of-treatment CT was obtained after the Capri applicator was placed to line up with patient setup marks. For our study, day-of-treatment CT scans were registered with first-fraction CT scans and the HR-CTV was transferred to the new scan. The OARs were then drawn on each CT set to account for anatomical changes. Dwell times and dwell positions were kept identical to the initial plan through all fractions for each patient. D2cc information for bladder, rectum, sigmoid, and bowel along with D90 for HR-CTV were obtained.

Results: The total dose obtained for D2cc of bladder, rectum, sigmoid, and colon along with the D90 for HR-CTV structure for the re-plans when compared with the total dose to the D2cc of the OARs and D90 of the HR-CTV structure for all four patients had an average dose difference of 1.5 Gy for bladder, 1.8 Gy for rectum, 2 Gy for sigmoid, 4.1 Gy for bowel, and 0.7 Gy for HR-CTV.

Conclusion: There are no clinically significant differences in the OARs dose and tumor volume coverage for using a single plan for all treatment fractions versus re-planning for each fractions when anatomical changes are taken into account. This suggests that the initial plan is accurate in estimating the overall doses for HDR Capri treatments.


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