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Retrospective analysis of adaptation frequencies and factors in offline in offline adaptive proton therapy
Journal article   Open access   Peer reviewed

Retrospective analysis of adaptation frequencies and factors in offline in offline adaptive proton therapy

Farideh Pak, Hailei Zhang, Yao Hao, Matthew Schmidt, Weiren Liu, Joshua Schiff, Eric Laugeman, Michael Watts, Stephanie Perkins and Tianyu Zhao
Journal of applied clinical medical physics, Vol.27(5), pp.e70604-n/a
05/2026
DOI: 10.1002/acm2.70604
PMCID: PMC13239404
PMID: 42204770
url
https://doi.org/10.1002/acm2.70604View
Published (Version of record) Open Access

Abstract

Purpose/objective Offline adaptation is a standard practice in radiation therapy to adjust treatment plans for various reasons. Although offline adaptation in proton therapy has been addressed in prior studies, further research is still needed to clarify the underlying reasons. Because of the unique dosimetric properties of protons, it is essential to know why and when offline adaptation is needed. In this retrospective study, in‐room CT‐on‐Rails (CToR) scans were used to characterize the reasons and frequency of offline adaptive proton therapy for head and neck (HN), breast or chest wall (breast/CW), and prostate cases. Materials/methods A cohort of 166 cases receiving proton therapy from 2020 to 2023 were reviewed retrospectively, including 76 HN cases, 50 breast/CW, and 40 prostate cases. The imaging frequency and incidence of replanning were recorded, and the rationales for replanning were investigated through anatomic review, dose volume histogram (DVH) comparison, and dose evaluations. Results Overall, replanning occurred in 11% of all the cases, with 13% of HN and 16% of breast/CW cases needing replanning. No prostate cases required replanning. HN cases were planned in 20 to 33 fractions, and no timing pattern of replanning emerged. Breast/CW were planned in 16 to 25 fractions, with replanning peaking at fractions 3–6 and 14 and again at 17. Anatomy changes most frequently triggered offline adaptation for HN cases, while more offline adaptation in breast/CW cases were due to displacement of tissue expander magnets. Conclusion This study uncovered different trends in the rationale for offline adaptation in proton therapy. HN cancer patients were more likely to need adaptation due to anatomy changes whereas breast/CW patients more often needed adaptation due to tissue expander magnet migration. Prostate cases showed stable treatment plans and dose distribution through the treatment course.
 adaptive breast and chest wall head and neck prostate proton therapy

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