Main Session
Sep 29
PQA 06 - Genitourinary Cancer, Gynecological Cancer, and Health Care Access and Engagement

3760 - CT-guided and MR-guided Adaptive Radiotherapy for Gynecological SBRT Treatments: A Dosimetry and Workflow Analysis

02:15pm - 03:30pm ET
Poster Hall - Exhibit Hall A
Screen: 25
POSTER

Presenter(s)

Dishane Luximon, PhD Headshot
Dishane Luximon, PhD - University of California Los Angeles, Los Angeles, CA

D. C. Luximon1, R. Ariani2, J. Charters1, D. O'Connell1, and P. S. Venkat1; 1UCLA, Department of Radiation Oncology, Los Angeles, CA, 2Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA

Purpose/Objective(s): To evaluate the dosimetric benefit of online adaptive radiotherapy (oART) for adjuvant gynecological SBRT and to compare plan quality and workflow efficiency between CT-guided (CTgART) and MR-guided (MRgART) adaptive platforms within the phase I HERA trial (NCT06538337).

Materials/Methods: Ten patients (50 fractions) treated between September 2024 and October 2025 were analyzed (CTgART: 35 fractions; MRgART: 15 fractions). For CTgART, each adapted plan was compared with its corresponding non-adapted plan recalculated on the anatomy of the day. Student’s paired t-tests were used to determine statistical significance (p<0.05). Adapted plans between CTgART and MRgART were compared dosimetrically, using Welch’s t-tests for statistical significance (p<0.05). For each comparison, the dose constraints defined by the trial protocol were used as baseline. Timestamps from each adaptive system were extracted from the system logs and compared for each fraction.

Results: Daily adaptation substantially improved paravaginal PTV coverage (V28.5Gy: 98.2% vs 86.1%, p<0.01) and CTV coverage (V30Gy: 98.3% vs 77.3%, p<0.01), with 71% of non-adaptive fractions failing the target goals. Adaptive planning also substantially improved bowel sparing (V25Gy: 27.3cc vs 54.2cc, p<0.01). Between CTgART and MRgART platforms, paravaginal target coverage was comparable. CTgART achieved higher nodal PTV coverage (V28.5Gy: 95.4% vs 90.7%, p<0.01), while MRgART demonstrated improved bladder sparing (V20Gy: 23.4% vs 43.4%, p<0.01). The CTgART workflow was more efficient (average 49.4 vs 91.9 minutes) and had fewer treatment interruptions (5.7% vs 33.3%).

Conclusion: Online adaptation is essential to consistently meet protocol targets in gynecological SBRT, enhancing both target coverage and OAR sparing. While CTgART and MRgART achieve similar overall plan quality, the CTgART workflow currently demonstrates superior workflow efficiency.

Table 1: Dosimetry comparison between the CTgART (N=35) and the non-adaptive fractions (i.e. original plan applied to the anatomy of the day, N=35). The bold text shows the best performing regimen, and the text in italics indicates failure to meet HERA dosimetric goals.

Trial Protocol

(Coverage/fx)

 Adaptive

(Average Coverage/fx)

 Non-Adaptive

(Average Coverage/fx)

 Statistical Significance

Paravaginal PTV (V28.5Gy)

 =95%

 98.2%

 86.1%

P < 0.01

Paravaginal CTV

(V30Gy)

 =95%

 98.3%

 77.3%

P < 0.01

Nodal PTV (V28.5Gy)

 =95%

 95.4%

 95.9%

 P = 0.12

Rectum (V20Gy)

 <60%

 24.8%

 31.5%

 P = 0.03

Rectum (V27.5Gy)

 <45%

 6.7%

 13.6%

 P < 0.01

Rectum (V29Gy)

 <20%

 3.2%

 10.2%

 P < 0.01

Rectum (D0.035cc)

 <6.4Gy

 6.1Gy

 6.1Gy

 P = 0.89

Bowel Loop (V25Gy)

 <40cc

 27.3cc

 54.2cc

P < 0.01

Bowel Loop

(D0.035cc)

 <6.4Gy

 6.0Gy

 6.5Gy

P < 0.01

Bladder (V20Gy)

 <60%

 43.4%

 44.1%

 P = 0.69

Bladder (V25Gy)

 <55%

 15.7%

 14.1%

 P = 0.26

Bladder (V30Gy)

 <20%

 1.4%

 2.6%

 P = 0.09

Bladder (D0.035cc)

 <6.4Gy

 6.1Gy

 6.2Gy

 P = 0.24