(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose:
To evaluate the feasibility of implementing fast inverse planning simulated annealing (IPSA) technique for high dose rate brachytherapy plans using Henschke tandem and ovoids (T&O) apparatus.
Methods:
This study is composed of ten T&O cases from nine cervical cancer patients treated 2017-2019. The prescription was 28Gy in 4 fractions. Radiation oncologist contoured the high-risk clinical treatment volume (HR-CTV), bladder, rectum, and sigmoid (MD contours). Standard T&O implants were performed with Foley catheter in bladder (contrasted balloon) and contrasted intravaginal balloons. Three different IPSA techniques were tested: IPSA using MD contours; IPSA using both MD contours and the T&O applicator with ovoids contoured as half spheres; and
IPSA based on both MD contours and the T&O applicator with ovoids contoured as tubes. The contours of T&O implants only extend to include dwell positions in the treatment plan. The dose constraints to bladder, rectum, and sigmoid were calculated based on the equivalent dose in 2Gy fraction.
Results:
D90 doses in this study were identical or within 0.5% difference of the original treatment plans. Seven of ten IPSA test plans using the contours of HR-CTV, bladder, rectum, and sigmoid achieved D2cc doses to bladder, rectum, and sigmoid under the dose constraints. Nine of ten IPSA plans using HR-CTV, bladder, rectum, sigmoid, and the tandem ovoid applicator attained D2cc doses to bladder, rectum, and sigmoid under the dose constraints. Very similar dose distributions were shown in the IPSA plans using the ovoids contoured as half spheres and using the ovoids contoured as tubes.
Conclusion:
Fastest IPSA is based on the contours of HR-CTV, bladder, rectum, and sigmoid. However, IPSA using both MD contours and the T&O applicator will allow more plans to meet the dose constraints.
Keywords
Not Applicable / None Entered.
Taxonomy
TH- Brachytherapy: HDR Brachytherapy
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