ESTRO 2024 - Abstract Book

S1005

Clinical - Gynaecology

ESTRO 2024

treatment planning libraries known as an "evolutive library" (n=1). The ITV approach involved extracting CTV-T contours from pre-treatment CT scans with full and empty bladders, creating motion-based ITVs. LOP-ITV method typically resulted in 2-3 plans. However, one study went a step further by creating 7 plans. Image assessment methods for LOP ART varied among the studies. CBCT was commonly used for plan verification and selection, supported by deformable registration for dose assessment (n=6). Fiducial markers and daily CBCT scans improved plan selection based on target positioning in four studies (n=2). Some studies employed bi-weekly CBCT (n=2), while another added a weekly post-treatment CT scan to monitor changes during treatment (n=1). Two studies relied on a weekly CT for daily plan selection, while a single study used bi-weekly ultrasound to select the daily plan based on bladder filling, in comparison to pre-treatment CT images.

The triggering criteria varied widely between reactive approach studies. The triggering criteria included CTV-T (D98) below 95% (47.5 Gy) and min CTV-T < 40 Gy (applied clinically).

Two studies scheduled offline MRI-based replanning with 3-5 mm CTV-PTV margins; replanning occurred four times in one study and the second study conducted a single scheduled replanning (mid-treatment).

Two studies used ETHOS software for real-time ART. Another approach used automated daily replanning with MR guidance, based on weekly MRIs with 3-5 mm PTV margins.

Dosimetric Benefits

We observed varied margins, plan numbers, and dosimetric metrics reported across the studies. Reporting methods included volume-based assessments, percentage of patients benefiting, and graphical representations, including both target and OAR, preventing straightforward comparison between studies. Common CTV-T dose metrics included D98%, V95%, and V42.75 Gy, while frequently used OAR metrics included V40 Gy and V45 Gy. Results varied depending on margin type. Table 1 uses arrows to illustrate the relative advantages of each approach compared to different treatment arms. Table 1 demonstrates that each ART approach has effectively reduced irradiated volumes without compromising target coverage compared to non-ART.