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Session: Therapy General ePoster Viewing [Return to Session]

Retrospective Evaluation of Per-Fraction Vs. Per-Implant HDR Brachytherapy Planning of Locally Advanced Cervical Cancer Patients Delivered with a Combined Intracavitary/interstitial Technique

M Maynard*, G Owen, J Peng, A Rapchak, W Godwin, D McDonald, S Roles, J Winiecki, S Cooper, H Eldredge-Hindy, Medical University of South Carolina, Charleston, SC

Presentations

PO-GePV-T-61 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: To investigate the dosimetric effect of reducing the number of planned HDR fractions in select locally advanced cervical cancer (LACC) patients being treated with combined intracavitary/interstitial HDR brachytherapy.

Methods: Ten patients were originally treated with combined intracavitary/interstitial HDR brachytherapy (BT) following external beam radiation therapy (EBRT). Each patient received 7Gy x 4 fractions divided equally among two applicator implants. (i.e. two fractions per implant delivered on consecutive days). Each patient had consistent bladder filling through each implant and no interstitial needles were adjusted after initial placement. Each fraction was delivered with a new HDR plan based on daily CT imaging. Per-implant dosimetry (i.e. two planned fractions) was simulated by recreating plans from implant days on the following day’s imaging and structure set (i.e. fraction 1 to 2 and fraction 3 to 4). High-risk CTV (HR-CTV) and organ-at-risk (OAR) EQD2 (BT+EBRT) were evaluated and compared for both data sets.

Results: Optimal and acceptable OAR D2cc EQD2 criteria were adopted from the EMBRACE II protocol. Optimal and acceptable HR-CTV D90 EQD2 criteria were set at >85Gy and >80Gy, respectively. Per-implant HR-CTV and OAR EQD2 all remained within the same acceptability band (e.g. optimal or acceptable) observed in the per-fraction data set, with one exception where the rectum D2cc was acceptable in the per-fraction data set and optimal in the per-implant dataset (65.1Gy vs. 63.5Gy). The mean absolute differences (range) between per-implant and per-fraction EQD2 [Gy] parameters were: HR-CTV: -0.16 (-3.51—1.66), bladder: +0.77 (-1.93—6.42), rectum: +0.20 (-1.57—2.47), bowel: -0.93 (-8.30—0.35), sigmoid: -0.08 (-4.87—2.30).

Conclusion: Reducing the number of planned HDR fractions in a 7Gy x 4, two-implant regimen yielded low dosimetric impact for LACC patients where sufficient HR-CTV coverage and OAR sparing were achieved on implant days.

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