ESTRO 2024 - Abstract Book

S2150

Clinical - Upper GI

ESTRO 2024

4. Lin, S. H. et al. Randomized Phase IIB Trial of Proton Beam Therapy Versus Intensity-Modulated Radiation Therapy for Locally Advanced Esophageal Cancer. J. Clin. Oncol. 38, 1569 – 1579 (2020).

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Daily online plan adaptation in neoadjuvant chemoradiotherapy for esophageal cancer.

Leigh A.P. Bruijs 1 , Thomas Weststrate 1 , Karin N. Goudschaal 1 , Irma W.E.M. van Dijk 1 , Jorrit Visser 1 , Joost J.C. Verhoeff 1 , Marjan A. Admiraal 1 , Arjan Bel 1 , Peter S.N. van Rossum 1,2 1 Amsterdam UMC, Radiation Oncology, Amsterdam, Netherlands. 2 Amsterdam UMC, Cancer Center Amsterdam, Amsterdam, Netherlands

Purpose/Objective:

A standard of care in patients with locally advanced esophageal cancer is neoadjuvant chemoradiotherapy followed by surgery 1,2 , and adjuvant immunotherapy in case of an incomplete pathologic response 3 . Since there is interfraction variation in patients’ daily anatomy, this is compensated with large margins during radiotherapy treatment. However, with the recent introduction of the Ethos Therapy TM system (version 1.1, Varian), daily online adaptive radiotherapy based on a conebeam CT-scan (CBCT) can be applied, in which a new treatment plan is calculated based on new contours from the patients’ anatomy of that day. Ethos Therapy TM system uses artificial intelligence and deformable image registration which automates large parts of the anatomical contouring and plan optimization process. To assess the potential dosimetric benefits of daily online adaptive radiotherapy compared to the current standard of practice of non-adaptive radiotherapy, a retrospective in silico study was performed in patients with esophageal cancer receiving neoadjuvant chemoradiotherapy. Ten patients treated with neoadjuvant chemoradiotherapy for distal esophageal or gastroesophageal-junction cancer on the Ethos Therapy TM were enrolled. To assess daily plan adaptation, an online adaptive radiotherapy workflow was first simulated on weekly scans and results extrapolated for the other fractions of the week. The clinical treatment plan at baseline and weekly CBCTs (acquired during fraction 1, 6, 11, 16, 21) were obtained for all patients. A treatment template was established based on a 3-arc VMAT plan, and organ-at-risk constraints were determined in accordance with our clinical standards. Planning target volume (PTV) margins were reduced from 10, 7, and 7 mm in cranio-caudal, left-right, and antero-posterior direction to 5, 5, and 3 mm, respectively, which was deemed feasible through the compensation for interfraction variation by the adaptive workflow. Adaptive treatment sessions were simulated within the online Ethos test environment (Varian Emulator). Based on CBCTs, new contours were automatically suggested and manually adjusted under supervision of a radiation oncologist. Subsequently, a new plan was calculated for each studied fraction. To compare with standard clinical practice, the adapted contours on the CBCT were also propagated to the planning CT using rigid bone-match registration on the spine. Dose volume histograms (DVHs) were calculated using the clinically used treatment plan on the daily anatomy, creating the non-adaptive dose distribution, which was compared with the adaptive treatment plan using DVH metrics. Specifically, Internal Clinical Target Volume (ICTV) coverage as defined by the near-minimum dose (i.e. D98%) and the ICTV D0.1 cm 3 were compared. Additionally, the mean heart dose (MHD) and the fraction-equivalent of V30Gy of the heart (i.e. V1.3Gy), as well as the mean lung dose (MLD), fraction-equivalent of V20Gy (i.e. V0.87Gy) and V10Gy Material/Methods: