@inproceedings{li-liu-2026-lotus,
title = "{LOTUS}: Language-Vision Optimal Transport for Unified Report Synthesis",
author = "Li, Xuhui and
Liu, Jiachen",
editor = "Zhang, Yue and
Xu, Ruifeng and
Purwarianti, Ayu and
Rong, Tong and
Suzuki, Jun",
booktitle = "Findings of the {A}ssociation for {C}omputational {L}inguistics: {IJCNLP}-{AACL} 2026",
month = nov,
year = "2026",
address = "Hengqin, China",
publisher = "Association for Computational Linguistics",
url = "https://aclanthology.org/2026.findings-aacl.86/",
pages = "1746--1762",
ISBN = "979-8-89176-444-6",
abstract = "Automated radiology report generation can reduce reporting burden, but existing encoder-decoder systems still rely on soft cross-attention that offers no geometric guarantee that generated tokens consume the correct visual evidence. We present LOTUS, an optimal-transport framework that places alignment supervision directly at the decoder evidence interface. LOTUS introduces Cross-Attention OT (CA-OT) to align decoder token states with visual patches, and extends it with Prototype OT (Proto-OT) for structure-level alignment between visual and textual codebooks. Experiments on IU X-Ray and ROCO, complemented by a scalability study on MIMIC-CXR-RRG, show that decoder-side OT improves macro-level clinical-label agreement while maintaining competitive language quality. In multi-seed IU X-Ray evaluation, LOTUS-Deep improves macro clinical F1 from 0.162 to 0.201 over the CE baseline, and on ROCO it yields micro-F1 gains on a thoracic-label proxy (0.395 to 0.600). We also provide a population-level risk-gap bound that justifies expected OT regularization as a principled cross-modal training signal."
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<abstract>Automated radiology report generation can reduce reporting burden, but existing encoder-decoder systems still rely on soft cross-attention that offers no geometric guarantee that generated tokens consume the correct visual evidence. We present LOTUS, an optimal-transport framework that places alignment supervision directly at the decoder evidence interface. LOTUS introduces Cross-Attention OT (CA-OT) to align decoder token states with visual patches, and extends it with Prototype OT (Proto-OT) for structure-level alignment between visual and textual codebooks. Experiments on IU X-Ray and ROCO, complemented by a scalability study on MIMIC-CXR-RRG, show that decoder-side OT improves macro-level clinical-label agreement while maintaining competitive language quality. In multi-seed IU X-Ray evaluation, LOTUS-Deep improves macro clinical F1 from 0.162 to 0.201 over the CE baseline, and on ROCO it yields micro-F1 gains on a thoracic-label proxy (0.395 to 0.600). We also provide a population-level risk-gap bound that justifies expected OT regularization as a principled cross-modal training signal.</abstract>
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%0 Conference Proceedings
%T LOTUS: Language-Vision Optimal Transport for Unified Report Synthesis
%A Li, Xuhui
%A Liu, Jiachen
%Y Zhang, Yue
%Y Xu, Ruifeng
%Y Purwarianti, Ayu
%Y Rong, Tong
%Y Suzuki, Jun
%S Findings of the Association for Computational Linguistics: IJCNLP-AACL 2026
%D 2026
%8 November
%I Association for Computational Linguistics
%C Hengqin, China
%@ 979-8-89176-444-6
%F li-liu-2026-lotus
%X Automated radiology report generation can reduce reporting burden, but existing encoder-decoder systems still rely on soft cross-attention that offers no geometric guarantee that generated tokens consume the correct visual evidence. We present LOTUS, an optimal-transport framework that places alignment supervision directly at the decoder evidence interface. LOTUS introduces Cross-Attention OT (CA-OT) to align decoder token states with visual patches, and extends it with Prototype OT (Proto-OT) for structure-level alignment between visual and textual codebooks. Experiments on IU X-Ray and ROCO, complemented by a scalability study on MIMIC-CXR-RRG, show that decoder-side OT improves macro-level clinical-label agreement while maintaining competitive language quality. In multi-seed IU X-Ray evaluation, LOTUS-Deep improves macro clinical F1 from 0.162 to 0.201 over the CE baseline, and on ROCO it yields micro-F1 gains on a thoracic-label proxy (0.395 to 0.600). We also provide a population-level risk-gap bound that justifies expected OT regularization as a principled cross-modal training signal.
%U https://aclanthology.org/2026.findings-aacl.86/
%P 1746-1762
Markdown (Informal)
[LOTUS: Language-Vision Optimal Transport for Unified Report Synthesis](https://aclanthology.org/2026.findings-aacl.86/) (Li & Liu, Findings 2026)
ACL