S2929
RTT- RTT operational practice and workflow innovations
ESTRO 2026
Digital Poster 3075
grouped by workflow into consecutive cohorts: RO-led (September 2019 – November 2021) and RTT-led (April 2022 – October 2023), with a break during training and handover. All patients were treated with 25 – 42.7 Gy in 5 – 7 alternate day fractions, 9-field IMRT using adapt to shape (ATS) workflow. Patients with 30Gy or less also received brachytherapy prior to EBRT. The clinical target volume (CTV) included the prostate and any extracapsular or seminal vesicle extension. PTV margins were 5mm (all RO-led), 5mm (RT-led 25-30Gy) or 4mm (3mm left-right) (RTT-led 42.7Gy). Clinical outcomes were assessed using the Phoenix definition of BRFS at 12-months. Toxicity was quantified prospectively using CTCAE v3.0. Mean doses for each cohort PTV, bladder, urethra and rectum were summarized from summation of the adapted plan doses and normalized to prescription Results: 166 prostate ART patients were reviewed: 78 RO-led and 88 RTT-led. Median (min,max) PSA at 12-months was 0.5 (0.01-10.20) in RO-led and 0.22 (0.01-6.60) RTT- led cohorts (p = 0.092), with no biochemical recurrence in either group at 12-months. G2+ urinary toxicity is summarized in Table 1, with increased incidence in the RT-led cohort only during RT (9% vs. 26%; p = 0.007). G2+ rectal toxicity was not significantly different between the cohorts during RT (0.6%), nor at 1-month (0.6%), 6-months (0.6%) or 12-months (1.2%). Mean PTV D95 coverage, Bladder 1cc and mean Urethra dose were all statistically significantly (p < 0.007) higher in the RO-cohort, but the magnitude of the differences was not clinically significant (0.99% vs 0.98%, 1.05% vs 1.02% and 1.06% vs 1.02%). Mean Rectum 1cc and D50 were similar in both cohorts. Conclusion: Acute G2+ GU toxicity was higher in the RTT-cohort, however the incidence at 12 months was comparable to the RO-cohort. GI toxicity remained low for both cohorts and neither group experienced a biochemical relapse. Although longer follow-up is necessary, this work suggests that there was little clinical difference in dosimetry, toxicity and outcomes as a result of adopting RTT-led MRL adaptive workflows for prostate ART Keywords: adaptive radiation therapy, RTT-led, prostate RT
Daily MRI-guided radiotherapy for borderline resectable pancreatic tumors: feasibility and efficiency of a RTT-only workflow Sonja Verheijen, Nienke W. Weitkamp, Miguel A. Palacios, Omar Bohoudi, Anna M.E. Bruynzeel, Eva Versteijne Department of Radiation Oncology, Amsterdam UMC, Amsterdam, Netherlands Purpose/Objective: Radiotherapy for borderline resectable pancreatic cancer remains technically challenging. On conventional CBCT-linacs, poor soft-tissue visibility requires fiducials (figure 1), large target margins and expiration gating, resulting in long, complex treatments with side effects. To overcome these limitations, a MRI-guided protocol on the MRIdian MR- linac (ViewRay Systems) was implemented at Amsterdam UMC, aiming for a fully RTT-only workflow—without daily physician presence during treatment. Material/Methods: A protocol was developed and RTTs were trained to perform all steps of daily MRI-guided non-adaptive treatment. The improved soft-tissue visualization on MRI enabled reduction of the CTV–PTV margin from 10 mm to 5 mm compared to the CBCT-linac protocol, and due to real-time gating and target tracking, no ITV was required. Patients received 15 fractions of 2.4 Gy (5 fractions per week), combined with weekly gemcitabine (1000mg/m2). Treatment times, workflow irregularities and physician support were recorded.
Figure 1: Visibility pancreas lesions on CBCT versus MRI-images (MRIdian). Results: Since May 2024, 28 patients with a borderline resectable pancreatic tumor have been treated. For two patients, suspicious locoregional lymph nodes were included in the gross tumor volume (GTV). After the first three patients, RTTs independently performed the complete workflow. In four fractions, physician support was requested due to image matching challenges. For two patients with large day-to-day anatomical variation, the team (RTTs, physician, and
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