This manuscript presents a comprehensive analysis of the use of PET/CT in RT planning among RadOncs in Germany. The study outlines the current landscape of PET/CT utilization according to clinical indication and addresses issues related to reimbursement, access, and the impact on treatment planning. The survey was sent to all members of the German Association for Radiation Oncology (DEGRO; 1232 members in the mailing list), with 156 participants (13%) answering the survey. Unfortunately, three of Germany’s less densely populated states are only represented by one participant each (Brandenburg, Saarland, and Saxony-Anhalt). Due to the heterogeneity of the collected data, the authors decided to mainly perform a descriptive analysis. Limitations stem from the lack of data on PET/CT use among RadOncs before this survey (no longitudinal comparison over the years) and the fact that there are hardly any comparable surveys from other countries.

During the past decade, impactful trials have been performed on the use of different PET tracers for RT planning, such as the GLIAA trial (amino acid PET in patients with recurrent glioblastoma; NCT01252459; Oehlke et al. [10]). In a pilot prospective trial (GLIAA pilot), the authors found [18F]FET PET together with MRI to be most suitable for contouring recurrent glioblastoma tumor tissue [11]. The prospective randomized multicentric PET-PLAN trial (NSCLC contouring based on FDG PET/CT; NCT00697333; Nestle et al. [3]) demonstrated improved local control after PET-based contouring (target volume reduction) without increased treatment-related toxicity. The German Hodgkin Study Group (GHSG) trials HD16, HD17, and HD18 (PET-guided indication for RT, PET-guided contouring; NCT00736320, NCT01356680, NCT00515554 [12,13,14,15]) investigated involved-site RT and demonstrated that PET-guided treatment decision making even impacts patients’ outcome and quality of life (QoL): further analyses of the HD18 trial reported faster recovery from fatigue and faster return to work in Hodgkin lymphoma patients when treatment decisions (RT, chemotherapy, immunotherapy) are made based on PET [16]. In meningioma, the use of [11C]-methionine (MET-PET) in target volume delineation was superior to conventional imaging (CT, MRI; Grosu et al. [17]).

For PSMA PET there is a 2021 German survey evaluating the acceptance and use of PET/CT in clinical routine for RT as well as its impact on target volume definition and dose prescription (Vogel et al. [18]). The group found an overall accessibility to PSMA PET in 78% of participants, which is higher than the numbers in our survey (“direct access within my practice/clinic/university hospital” [for all tracers, not specifically PSMA]: 59% of surveyed). An explanation for this discrepancy could be that the 2021 trial participants were not explicitly asked whether their access to PET is within their own practice/clinic/institution (which was a criterion in the corresponding question in our survey). In the literature and in clinical practice, the value of PSMA PET/CT in primary high-risk prostate cancer and oligometastatic and recurrent disease (see also the PSMA SRT trial) is high [19,20,21,22,23,24].

There are ongoing trials on PET-guided dose escalation in glioblastoma (PRIDE—PRotective VEGF Inhibition for Isotoxic Dose Escalation in Glioblastoma; NCT05871021; ARO 2022-12; PI: Prof. M. Niyazi), in NSCLC (PACCELIO—FDG-PET based small-volume accelerated immunochemoradiotherapy in locally advanced NSCLC; NCT06102057; ARO 2023-06; PI: Prof. U. Nestle), in HNC (INDIRA-MISO trial, radiation dose prescription in HNC based on F‑MISO-PET hypoxia imaging; NCT03865277; PI: Prof. M. Krause), and in prostate cancer (HypoFocal SBRT: PSMA-PET/MRI-Based Focal Dose Escalation in Patients with Primary Prostate Cancer Treated with Stereotactic Body Radiation Therapy; PI: Prof. A.-L. Grosu) [25]. In recent years, any new developments in injectable tracers have soon found their way into radiooncological use (PSMA, FAPI), strengthening the close link between radiotherapy and nuclear medicine [26,27,28,29,30,31].

In our analysis, the proportion of PET/CTs conducted in the planning position is currently low, despite existing data and recommendations supporting enhanced alignment and reduced radiation exposure through the combination of PET and planning CT [32, 33]. One factor contributing to the limited use of planning PET/CT is likely the requirement for the presence of an MTR in the nuclear medicine department. In our survey, 38% of participants indicated performing planning PET/CT, but only 29% stated actually having an MRT physically present in the nuclear medicine department, also to help with positioning. Thus, one can presume that a significant number of planning PET/CTs are performed without a dedicated MTR, probably reducing the quality of reproducibility and thus the quality of the subsequent radiotherapy. It should be acknowledged that during their education, MTRs are equally trained in radiology, nuclear medicine, and radiotherapy. Thus, there might be expertise of radiotherapy MTRs in PET departments, particularly in the MVZ setting of clinics/practices with various radiation disciplines. However, technicians from specialized units (e.g., nuclear medicine) often lack the confidence to perform tasks such as patient positioning and immobilization, especially if they have been away from the joint training program for a significant length of time. We see potential for improvement through accessible refresher courses at annual congresses and conferences, which would enhance skills and confidence.

In pelvic/urogenital tumors like prostate or cervical cancer [34], a disadvantage in employing planning PET/CT is due to an overshadowing PET tracer accumulation in the full bladder (patients are routinely advised to have a full bladder in the planning CT), compromising the visibility and differentiation of the primary tumor region (in cervical, prostate, rectal, or anal cancer patients). Further logistical challenges arise when patients requiring thermoplastic masks (HNC, brain tumors) need to have these created in a separate appointment before the PET scan (additional work for staff and patients). Interestingly, in our analysis, the overall acceptance rate of diagnostic FDG PET/CT is highest in practices, outpatient clinics, and medical care centers (MVZs) and lower in university hospitals (“strongly agree” and “agree” rate in practices: 47 and 43% vs. 29 and 38% in university hospitals, respectively). Rates for planning PET/CTs are highest in university hospitals; however, we suspect that in our survey, the terms “planning PET-CT” and “diagnostic PET-CT” were misleading, leading to the abovementioned heterogeneity in answers. The term “planning PET” refers to scans conducted in planning position. The corresponding questions in the survey had a note saying “PET/CT in planning position, with immobilization devices and a technician/RadOnc physically present during the scan.” However, we suppose that some participants could have interpreted “planning PET-CT” as referring to examinations done in preparation for radiation therapy but not explicitly performed in planning positions. This may have contributed to the unexpected variations in response patterns observed between private practices and university hospitals.

There is a list of indications approved by the Joint Federal Committee (G-BA) for financial compensation (reimbursement) of PET/CTs within the scope of compulsory health insurance (GKV), private health insurance (PKV), and via internal cost allocation (interne Leistungsverrechnung) between different departments in one hospital association. The catalog of indications and recommendations is continuously expanded, with PET constantly reassessed by the G‑BA. Detached from this, the outpatient specialist care (Ambulante Spezialfachärztliche Versorgung [ASV]) according to Social Code § 116b SGB V offers another option for financial compensation of PET/CT in patients with gynecological (except breast), urological, thoracic, head and neck, skin, brain/neurooncological, and gastrointestinal malignancies as well as sarcoma for practices and hospitals participating in the ASV network.

Possibly, a survey similar to this one directed at nuclear medicine (NucMed) physicians could provide further insights and answer questions regarding referral of patients from RadOnc departments, the availability of tracers within the PET centers or the complexity of reimbursement, which remains a significant barrier to PET availability in Germany. The results collected in this survey may be biased by the exclusive RadOnc perspective. The RadOnc/NucMed working group (AG Nuklearmedizin/Strahlentherapie der DGN und DEGRO) is considering setting up a second survey among NucMeds to answer these questions.

In our survey, NSCLC, lymphoma, and CUP were the most frequent tumor entities for requesting PET/CT in a radiooncology context and among these entities, reimbursement is considered certain. National and international guidelines show good evidence for PET/CT in head and neck tumors and esophageal cancer, for instance, but in Germany, these indications can only be reimbursed in the context of ASV care [35, 36]. To counteract the tendency of establishing the indication for PET/CT depending on the probability of financial reimbursement and not primarily on the basis of current guidelines or treatment recommendations, the German Society of Nuclear Medicine (DGN) and the German Society of Radiation Oncology (DEGRO) need to improve interdisciplinary collaboration and work on transparency in terms of reimbursement.