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. 2023 Nov 23;15(23):5545. doi: 10.3390/cancers15235545

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© 2023 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

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(a) Keywords co-occurrence network. Each vertex represents a keyword, and its size is proportional to the occurrence. Each cluster (colors) can be considered as a topic macro-area. The proximity among keywords in the network indicates a large proportion of articles addressing them together. “Radiotherapy” was excluded from the figure because it would have covered the other keywords. List of abbreviations: SBRT (stereotactic body radiation therapy). (b) Thematic evolution of keywords (2002–2022); blue dots: top three proton therapy-associated keywords for each year; the line-span indicates the interquartile range of the keyword distribution over years.