Purpose: We conducted a cost-effectiveness analysis in which we compared a preoperative [¹⁸F]Fluorocholine PET/CT-based one-stop-shop imaging strategy with current best practice in which [¹⁸F]Fluorocholine PET/CT is only recommended after negative or inconclusive [^99mTc]Tc-methoxy isobutyl isonitrile SPECT/CT for patients suffering from primary hyperparathyroidism. We investigated whether the one-stop-shop strategy performs as well as current best practice but at lower costs. Methods: We developed a cohort-level state transition model to evaluate both imaging strategies respecting an intraoperative parathyroid hormone monitored treatment setting as well as a traditional treatment setting. The model reflects patients’ hospital journeys after biochemically diagnosed primary hyperparathyroidism. A cycle length of twelve months and a lifetime horizon were used. We conducted probabilistic analyses simulating 50,000 cohorts to assess joint parameter uncertainty. The incremental net monetary benefit and cost for each quality-adjusted life year were estimated. Furthermore, threshold analyses regarding the tariff of [¹⁸F]Fluorocholine PET/CT and the sensitivity of [^99mTc]Tc-methoxy isobutyl isonitrile SPECT/CT were performed. Results: The simulated long-term health effects and costs were similar for both imaging strategies. Accordingly, there was no incremental net monetary benefit and the one-stop-shop strategy did not result in lower costs. These results applied to both treatment settings. The threshold analysis indicated that a tariff of €885 for [¹⁸F]Fluorocholine PET/CT was required to be cost-effective compared to current best practice. Conclusion: Both preoperative imaging strategies can be used interchangeably. Daily clinical practice grounds such as available local resources and patient preferences should inform policy-making on whether a hospital should implement the one-stop-shop imaging strategy.

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Background and Objective
This systematic literature review addresses model-based cost-effectiveness studies for therapy response monitoring with positron emission tomography (PET) generally combined with low-dose computed tomography (CT) for various cancer types. Given the known heterogeneity in therapy response events, studies should consider patient-level modelling rather than cohort-based modelling because of its flexibility in handling these events and the time to events. This review aims to identify the modelling methods used and includes a systematic assessment of the assumptions made in the current literature.

Methods
This study was conducted and reported following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 statement. Information sources included electronic bibliographic databases, reference lists of review articles and contact with experts in the fields of nuclear medicine, health technology assessment and health economics. Eligibility criteria included peer-reviewed scientific publications and published grey literature. Literature searches, screening and critical appraisal were conducted by two reviewers independently. The Consolidated Health Economic Evaluation Reporting Standards (CHEERS) were used to assess the methodological quality. The Bias in Economic Evaluation (ECOBIAS) checklist was used to determine the risk of bias in the included publications.

Results
The search results included 2959 publications. The number of publications included for data extraction and synthesis was ten, representing eight unique studies. These studies addressed patients with lymphoma, advanced head and neck cancers, brain tumours, non-small cell lung cancer and cervical cancer. All studies addressed response to chemotherapy. No study evaluated response to immunotherapy. Most studies positioned PET/CT as an add-on modality and one study positioned PET/CT as a replacement for conventional imaging (X-ray and contrast-enhanced CT). Three studies reported decision-tree structures, four studies reported cohort-level state-transition models and one study reported a partitioned survival model. No patient-level models were reported. The simulation horizons adopted ranged from 1 year to lifetime. Most studies reported a probabilistic analysis, whereas two studies reported a deterministic analysis only. Two studies conducted a value of information analysis. Multiple studies did not adequately discuss model-specific aspects of bias. Most importantly and regularly observed were a high risk of structural assumptions bias, limited simulation horizon bias and wrong model bias.

Conclusions
Model-based cost-effectiveness analysis for therapy response monitoring with PET/CT was based on cohorts of patients instead of individual patients in the current literature. Therefore, the heterogeneity in therapy response events was commonly not addressed appropriately. Further research should include more advanced and patient-level modelling approaches to accurately represent the complex context of clinical practice and, therefore, to be meaningful to support decision making.

Registration
This review is registered in PROSPERO, the international prospective register of systematic reviews funded by the National Institute for Health Research, with CRD42023402581.@en