Results from more than 13,000 Weight-Bearing CT scans over 6.8 years. Impact on costs, radiation exposure and time spent

International Weight-Bearing CT Society Department for Foot and Ankle Surgery Rummelsberg and Nuremberg, Germany Clinique de l’Union, Foot and Ankle Surgery Centre, Toulouse, France Department of Orthopedics and Rehabilitation, Carver College of Medicine, University of Iowa, Iowa City, USA University of Utah Orthopaedic Center, Salt Lake City, UT, USA Department of Orthopaedics and Traumatology, University Hospital of Ghent, Gent, Belgium Orthopaedic Surgery, The Hospital for Special Surgery, New York, NY, USA

based on measured values from previous studies. For analysis cost effectiveness, device cost, reimbursement and working time cost of radiology technicians were taken into consideration within the local circumstances. Results: 13,156 WBCT scans were obtained in 5,798 patients (5,798 (44%) before treatment; 7,358 (56%) follow-up; mean age, 52.2; 46% male). Primary pathologies were forefoot deformities (n = 1,189 (21%) and ankle instability/cartilage defect (n = 832 (14%)), and hindfoot deformity (n = 765 (13%)). 1,935 WBCT scans were obtained on average yearly, and 10.2 CTs (WBCT group). In 2012, 1,850 R and 254 CTs were obtained (R(+CT) group). Yearly RD was 4.3 uSv for WBCT group and 4.8 uSv for R(+CT) group (difference 0.5 uSv decrease with WBCT 10%, p < 0.01). Yearly T was 113 hours in total (3.5 minutes per patient) for WBCT group and 493 hours in total (16.0 minutes per patient) for R(+CT) group (difference, 380 hours, decrease with WBCT, 77%, p < 0.01). Yearly profit was 53,543 Euro for WBCT group, -723 Euro for R(+CT) group. Conclusions: 13,156 WBCT scans in 5,798 patients as substitution of R(+CT) over a 6.8 year period at a foot and ankle center resulted in 10% decreased RD (minus 0.5 uSV on average per patient). Yearly T decreased 380 hours (77%) in total (12.0 minutes per patient). Yearly financial income increased more than 54,000 Euro in total (58 Euro per patient). RD decreased despite higher radiation dose for WBCT than for R alone, based on substitution of a high number of CTs by WBCT. Other centers with low usage of CT might not decrease RD by substituting R alone by WBCT.

Introduction
Weightbearing CT (WBCT) has been proven to more precisely measure bone position than conventional sequencing including systematic weightbearing radiograph series (R) and optional conventional CT without weightbearing (CT) [4,13,36,43,44,46,47,59]. These improvements are attributed to the absence of superimposition and the possibility to account for rotational errors after the image process [2,44,46]. Time spent on image acquisition (T) has shown to be lower for WBCT than for R and CT [46]. Radiation dose (RD) for WBCT has also shown to be lower than for CT [44,46]. The cost-effectiveness of using WBCT clinical settings is questionable. As far as we know, T, RD and especially cost-effectiveness have not been investigated in a high number of patients so far. The purpose of this study was to assess the potential benefits of using WBCT instead of R and/or CT in a foot and ankle department, regarding RD, T, and cost-effectiveness.

Methods Study design
A WBCT device (PedCAT, Curvebeam, Warrington, PA, USA) was put into operation from July 1, 2013 in the first authorś foot and ankle department. All patients who obtained WBCT (bilateral scan) and/or CT from July 1, 2013 until March 15, 2020 were included in the study (WBCT group).

Control group
All patients who obtained radiographs and/or CT from January 1 to December 31, 2012 were included in the control group (RCT group).
No exclusion criteria for patients were defined (both groups). Initial radiographs in trauma patients and early postoperative (one to four days) radiographs were excluded from the study (both groups)

Data acquisition
Age, gender, primary pathology location, and additional CT (bilateral feet and ankles) were registered. Pathology location was differentiated in ankle, hindfoot, midfoot, forefoot, and multiple other locations based on anatomy as follows: hindfoot between ankle and Chopart joint, midfoot between Chopart and Lisfranc joints, and forefoot distal to Lisfranc joint. Involvement of the joints were defined relative to the main neighbouring location or, when unclear, as multiple location.

Imaging time (T)
T was calculated based on an analysis of previous studies as follows: R (bilateral feet dorsoplantar and lateral, metatarsal head skyline view), 902 seconds; CT (bilateral feet and ankle), 415 seconds; WBCT (bilateral), 207 seconds [46].

Radiation dose (RD)
RD per patient was calculated based on previous phantom measurements as part of obligatory standard periodic quality assurance protocols: R, 1.4 uSv; CT, 25 uSv; and WBCT 4.2 uSv [37].

Cost-effectiveness
For analysis of cost-effectiveness, device cost, working time cost of radiology technicians (similar to T), and reimbursement in the local setting were taken into consideration for the WBCT group. The total device cost was calculated at a 200,000 Euro acquisition cost with a 5-year asset depreciation range (40,000 Euro yearly) and an annual 5,000 Euro maintenance cost, i.e. 45,000 Euro yearly cost for the WBCT group. No device costs were included for the RCT group since the R and CT devices were already installed. Staff costs were calculated by multiplication of T with 20 Euro per hour (based on local practice fares). The only reimbursement that could be considered was the one generated by privately insured patients or self-payers which corresponded to 15.5/15.1% of WBCT/RCT groups at a rate of 30 Euro for each R series and 300 Euro for each CT/WBCT. Vice versa, no reimbursement was achieved and considered for the study for all other patients (with public insurance). The potential profit was then considered in total and per patient ( Table 2).

Data analysis / control group
All parameters were compared between WBCT and RCT group.

Statistics
Either a Student's T-test or Chi-square test were used for comparison between groups with normal distributed and binomial data, respectively. P-values were considered significant when lower than .05. IBM SPSS Statistics 25 (SPSS, Inc., Chicago, IL, USA) was used.
Despite these advantages, WBCT has yet to replace R and CT sequences in the standard assessment of foot and ankle patients. Arguments like higher RD in relation to R and device costs have hindered the broader distribution of WBCT [44,48]. Also, most institutions have already installed R and/or CT devices and are thus reluctant to additionally invest in a WBCT device [44]. To the best of our knowledge, this is the first study to investigate and compare RD as benefit for the patient and cost-effectiveness as benefit for the institution of WBCT use as standard of care in a large number of foot and ankle patients [44]. The study's setting was an institution with existing R and CT devices that installed a WBCT device in 2013 [44]. After using the device alongside R and CT for a comparative study, WBCT replaced R and CT as the standard imaging in this clinic a few months after installation [44,46]. Radiographs were limited to early postoperative (one to four days) imaging for patients without weightbearing, initial or better preoperative radiographs and CT were limited to trauma cases that comprised around 3% in the local setting [44]. Radiographs were indicated for initial assessment and CT when weightbearing was not possible and 3D-imaging was indicated (e.g. calcaneal fractures) [44]. In the control group (RCT) the imaging for early postoperative and trauma cases was the same [44]. As the indication for initial radiographs in trauma cases and early postoperative radiographs was similar in WBCT and RCT groups, this imaging was excluded from the comparative study [44]. Thus, the CT imaging in the WBCT group as described above was not excluded because it was also considered as 3Dimaging (as WBCT) [44]. However, with 10 CTs on average yearly, the effect of the CT in the WBCT group on the comparison is minimal [44]. In the RCT group, a high rate of CT (29% of all patients) was observed [44]. CT was indicated in addition to radiographs with weightbearing for (complex) deformities or other pathologies in the hindfoot, midfoot or in multiple locations [44]. The high rate for CT is consequently based on the high rate of pathologies in the hindfoot (10%), midfoot (9%) and multiple locations (49%) ( Table 1) [44]. This study was not focused on the type of pathology, type of treatment, or accuracy/sensitivity/specificity of the imaging. In this study, we found a substantial decrease in R and CT use for the WBCT group as expected [44]. The decrease of CT use from more than 250 per year (RCT group) to 10 per year (WBCT group) influenced the finding of decreased RD for the entire WBCT group [44]. RD for CT (25uSv) is more than 5 times higher than for WBCT (4.2uSv) which overcompensates for the 3 times higher RD of WBCT relative to R (1.4uSv) [44]. While the RD for WBCT is often argued to be greater, RD is definitively shown to decrease (10%) [21]. Other centres with low usage of CT might not decrease RD by substituting R alone with WBCT [44]. When analysing cost-effectiveness, the initial cost for device acquisition and the absence of specific reimbursement are usually taken into consideration as the main factors against WBCT device profitability [44]. While purchasing cost does not significantly differ between device types or countries, the reimbursement situation can vary drastically [44]. Our calculation is just one example in a special setting, and the numbers might differ in other countries with different insurance settings [44]. The special situation here was that only patients with private insurance or self-payers (around 15% of all patients in WBCT and RCT groups) were charged at all for the imaging [44]. Privately insured patients pay themselves and get reimbursement from their private insurance, whereas self-payers pay themselves without reimbursement [44]. So, this is a profit for the institution and cost for the private insurance. In the case of self-payers without private insurance, it is profit for the institution and cost for the patient. In all these considerations, the potential cost or profit of further treatment on the basis of 2D-or 3D-imaging is unclear and debateable [44]. A higher percentage of self-payers or privately insured would increase the reimbursement more in the WBCT group than in the RCT group, because the reimbursement is higher for WBCT/CT (300 Euros) than for radiographs (30 Euros) [44]. The situation has already evolved in many countries, such as the United States, UK, and Belgium, where authorities have recognized the general usefulness and benefits of WBCT for patients and institutions relative to the traditional RCT sequence [44]. We found the 77% decrease in image acquisition time for the WBCT group relative to the RCT group to be the main factor for increased profit [44]. This effect might also differ in other settings. However, cone beam technology (as in WBCT) is currently being developed to scan the entire body. This expanded application may possibly increase indications and usability of WBCT scans in institutions which are not specialized in foot and ankle surgery or with a more restricted flow of patients needing regular CT scans [44].

Shortcomings of the study
There are numerous shortcomings of the study [44]. Specific diagnosis for multiple foot and ankle pathologies was not analysed [44]. The indication for the imaging was not analysed and could differ in other institutions [44]. Preoperative and follow-up imaging were included in the analysis because this was found to reflect the local situation most appropriately [44]. For both groups, early postoperative radiographs without weightbearing were not registered and included in the further analysis [44]. This could be considered as a shortcoming because not all radiographs were included in the study [44]. However, the indication and frequency for these radiographs did not differ between RCT and WBCT groups and were therefore not included [44]. The same is true for initial radiographs in trauma patients as discussed above [44]. RD was not measured but projected with data from an earlier phantom measurement [37,44]. For this phantom study, the same WBCT device was used, but R and CT devices differed [37]. Consequently, the real RD might differ in our setting [44].. However, we are not aware of any other comparable study that measured RD in such a large patient series [44]. With later device generations (WBCT, CT and R), RD might differ [44]. To the best of our understanding, it would be more probable that newer WBCT technology would decrease RD more than the much longer available and further developed R and CT technology [44]. We expect the same for T that is influenced by the scanning time. We are aware all authors have a conflict of interest because all authors use WBCT in their institutions and some are consultants for one of the device manufacturers and board members of the International WBCT Society [44]. This might cause bias in the data interpretation [44]. However, we want to stress that this conflict of interest did not influence data collection (T, RD, cost/reimbursement) or statistical analysis [44].
In conclusion, 13,156 WBCT scans in 5,798 patients as substitution of R(+CT) over a 6.8 year period at a foot and ankle center resulted in 10% decreased RD (minus 0.5 uSV on average per patient). Yearly T decreased 380 hours (77%) in total (12.0 minutes per patient). Yearly financial income increased more than 54,000 Euro in total (58 Euro per patient). RD decreased despite higher radiation dose for WBCT than for R alone, based on substitution of a high number of CTs by WBCT. Other centers with low usage of CT might not decrease RD by substituting R alone by WBCT.