Program Information
Evaluate the Feasibility to Implement a Modified Inverse Planning Simulated Annealing for High Dose Rate Brachytherapy Tandem and Ovoid Plans
Y Jia*, Z Huang , S PRAMANIK , L Rinker , N Dubal , T Stockstill , Methodist University Hospital, Memphis, Tennessee
Presentations
TU-C1-GePD-T-2 (Tuesday, August 1, 2017) 9:30 AM - 10:00 AM Room: Therapy ePoster Lounge
Purpose: To evaluate the feasibility to implement a modified inverse planning simulated annealing (IPSA) for high dose rate brachytherapy (HDR) tandem and ovoid plans.
Methods: This study is based in five tandem and ovoid HDR cases, where a modified IPSA technique based on defining an auxiliary volume surrounding point A is compared with original graphically optimized treatment plan following the ICRU 38 guideline. Foley catheter was inserted into patient’s bladder. Two balloons with contrast were inserted into patient’s vagina; the anterior and posterior balloons were used to push the bladder and rectum away, respectively. The dose was prescribed to point A. In this study, the volume-based IPSA plans were developed: the point A was used to create a three-dimensional auxiliary volume of 0.05 cubic centimeters, and tandem, ovoids, Foley catheter, and rectum were contoured. The surfaces of 5mm from the ovoid surfaces were created and all the contoured structures were used in IPSA optimization. All points defined in the original plans were consistent with the volumes contoured in the study.
Results: The prescription dose to point A in the study was within 1.0% from original plan (except one plan 2.8% closer to prescription and one plan 2.3% higher than original plan). The average dose to the ovoid surface in the IPSA plans was ≤150.3% of the prescription dose. With the same prescription dose to point A, the modified IPSA technique can reduce dose to bladder and rectum points up to 9.3% when the bladder and rectum are near the disease.
Conclusion: Although planning with IPSA is more time-consuming, the modified IPSA technique shows improvements in the dose to organs at risk when compared to graphical optimization. Even though no disease is contoured in treatment plans, the physician reviews the CT to ensure equivalent malignancy anatomy coverage in the original plans.
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