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Session: Brachytherapy - III [Return to Session]

Evaluation of Dose Accumulation with Deformable Image Registration of External-Beam Radiotherapy and Brachytherapy for Cervical Cancer

M Tariq, N Lavini*, S Souri, G Gill, NewYork-Presbyterian, Queens, NY

Presentations

SU-H400-IePD-F7-5 (Sunday, 7/10/2022) 4:00 PM - 4:30 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 7

Purpose: The standard approach to evaluate cumulative dose to OARs and target coverage is DVH summation between EBRT and BT for cervical cancer. To consider anatomical and target volume changes of the cervical target, we compare with dose accumulation based on deformable image registration (DIR).

Methods: Five patients were studied who received 5040cGy (180cGyx28) of EBRT followed by three fractions (2100cGy total) of HDR using the Henschke applicator. Using Velocity (Varian Medical Systems, Palo Alto, CA), dose summation was applied with rigid registration of all three BT fractions onto the third BT fraction CT-SIM scan. The EBRT dose was deformed onto the third fraction BT scan and summed with the total BT dose. Total EBRT and BT dose was converted into EQD2 (Gy). Cumulative BT+EBRT DVH parameters based on DIR were compared with linear DVH summation and percent and absolute dose differences reported. The mean Jacobian determinant was reported for each patient to quantitatively assess DIR uncertainty.

Results: Average percent differences of DVH summation and DIR-based dose accumulation were 0.77%, 1.26% and 1.90% for bladder, rectum and HR-CTV respectively. Average absolute dose differences were 1.26Gy, 1.52Gy and 2.16Gy for bladder, rectum and HR-CTV respectively. DVH summation overestimated D90% for HR-CTV for four out of five patients, five patients for rectum D2cc and four patients for bladder D2cc. For DIR uncertainty, the average Jacobian determinant was 0.71, 0.99 and 1.22 for the bladder, rectum and HR-CTV respectively.

Conclusion: With DIR, absolute differences of OARs were up to 1Gy and 2Gy for HR-CTV. DVH summation is an accurate method of evaluating cumulative dose to OARs and target. We demonstrate the use of DIR-based dose accumulation from EBRT and BT. The importance of this method can be clinically utilized to modify fractional BT dose to account for anatomical and target volume changes.

Keywords

Not Applicable / None Entered.

Taxonomy

TH- Brachytherapy: GYN Intracavity Brachytherapy

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