Our base case consists of a Swiss patient with an oropharyngeal squamous cell carcinoma (OPSCC), age 55, with operable T-category (T1 or T2) OPSCC and a probability of regional disease (N+) between 60–70%. Our analyses are performed from a Swiss hospital payer perspective and with a lifetime horizon.
We developed a two-stage model based on (i) a published model about the economic evaluation of TORS vs radiotherapy[13], (ii) additional literature[6] and (iii) authors’ expertise and statistics from the Centre Hospitalier XXX and University Hospital XXX.
The first-stage decision tree accounts for short-term outcomes of the surgery and its complications which are, in turn, carried forward as initial conditions for a second-stage model representing long-term outcomes through a Markov process.
The first-stage decision tree accounts for short-term outcomes of the surgery and its complications which are, in turn, carried forward as initial conditions for a second-stage model representing long-term outcomes through a Markov process.
The first-stage model is depicted in Fig. 1. The two surgical strategies constitute alternatives for the first decision node, after which a chance node distinguishes between cases undergoing surgery alone, and cases requiring adjuvant radiotherapy (RT) or chemoradiotherapy (CRT). Finally, potential complications of the surgical interventions and, where appropriate, associated adjuvant (ADJ) therapy are modeled.
The second-stage model deals with long-term outcomes and is constituted by a Markov model (Fig. 1b). It represents patients entering a state of remission after treatment and models their transitions through other possible health states until death. The Markov cycle has been set to 3 months and the time horizon is the entire patient life. Initial rewards of each Markov model are carried forward from the results of the first-stage model.
Model parameters representing estimates of probabilities of adjuvant treatment were derived from data published by Li et al. [6], which constitute the largest and most recent published database study with relevant outcome data. Other parameters modeling clinical events such as complication rates and recurrence rates were determined from systematic review of the literature[15]. The hospital admission rate for CRT was set at 75% of patients to be admitted once, and 25% twice. The proportion of patients needing hospital admission for RT was set at 25% only once. Regarding the need for a gastrostomy we considered a PEG-rate for CRT of 70% while 20% for RT as per institutional data from CHUV and USZ.
Transition probabilities between different health states of the Markov models were directly adopted from de Almeida et al. [13] and no relevant difference in survival is assumed between the TORS and TLM arms of the model, based on a recent retrospective analysis of the National Cancer Data Base (NCDB) [6]. Table 1, probabilities of events section, reports the specific value used for each parameter. Risk of death from non-cancer-specific causes is modeled following Swiss life tables, acquired through the Swiss office federal de la statistique. In order to perform probabilistic sensitivity analysis (PSA) all parameters were represented using probability distributions. Probabilities of event occurrence were represented as beta distributions, as indicated for variables ranging from 0 to 1 [16] (Table 1).
Costs were directly acquired from the “Centre hospitalier XXX” and “ University hospital XXX” administrative departments. Having adopted a hospital perspective, costs incurred by the patient are not considered in our analyses. All costs are represented as Gamma distributions, as suggested by Huinink et al [16] for values greater or equal than 0 (Table 1).
Utility coefficients (UCs) for the health states included in the model were collected with Standard Gamble method through our UceWeb [17, 18] platform from a set of 41 Swiss healthy volunteers. 17 different scenarios were evaluated by each participant [19]. Rating Scale method was also administered, to familiarize participants with the tool and as a consistency check of the obtained values. As for probabilities, UCs are represented as beta distributions (Table 1).
Table 1
Model parameters: Probabilities of occurrence of events, costs and utilities.
Variable name
|
Description
|
Mean
|
Standard deviation
|
Distribution type
|
Parameter 1 (alpha)
|
Parameter 2 (beta)
|
Probabilities of events
|
pes
|
Probability of esophageal stenosis
|
0.0476
|
0.0005
|
Beta
|
4
|
80
|
phem
|
Probability of hemorrhage
|
0.0243
|
0.0001
|
Beta
|
6
|
241
|
pho_adj
|
Probability of hospital readmission after adjuvant
|
0.1731
|
0.0027
|
Beta
|
9
|
43
|
pho_s
|
Probability of hospital readmission (TORS or TLM)
|
0.0333
|
0.0010
|
Beta
|
1
|
29
|
plg
|
Probability of long-term gastrostomy (1 year) after adjuvant treatment
|
0.0500
|
0.0003
|
Beta
|
9
|
171
|
plt
|
Probability of long-term tracheostomy (1 year)
|
0.0226
|
0.0001
|
Beta
|
4
|
173
|
psg
|
Probability of short-term (6 months) gastrostomy (TORS or TLM)
|
0.0144
|
0.0001
|
Beta
|
2
|
137
|
psg_adj
|
Probability of short-term (6 months) gastrostomy after adjuvant
|
0.2991
|
0.0019
|
Beta
|
32
|
75
|
por
|
Probability of osteoradionecrosis
|
0.0265
|
0.0002
|
Beta
|
4
|
147
|
ppf
|
Probability of pharyngocutaneous fistula
|
0.0253
|
0.0001
|
Beta
|
10
|
385
|
pTLMAlone
|
Probability of TLM alone
|
0.4085
|
0.0007
|
Beta
|
134
|
194
|
pTorsAlone
|
Probability of TORS alone
|
0.3740
|
0.0001
|
Beta
|
824
|
1379
|
pCRT_TLM
|
Probability of adjuvant CRT (TLM)
|
0.6289
|
0.0012
|
Beta
|
122
|
72
|
pCRT_tors
|
Probability of adjuvant CRT (TORS)
|
0.5272
|
0.0002
|
Beta
|
727
|
652
|
pRT_TLM
|
Probability of adjuvant RT (TLM)
|
0.3711
|
0.0012
|
Beta
|
72
|
122
|
pRT_tors
|
Probability of adjuvant RT (TORS)
|
0.4728
|
0.0002
|
Beta
|
652
|
727
|
plr*
|
Probability of local or regional recurrence (first 2 years)
|
0.0064
|
0.0000
|
Beta
|
11
|
1715
|
prr*
|
Probability of regional recurrence (first 2 years)
|
0.0064
|
0.0000
|
Beta
|
11
|
1715
|
pdr*
|
Probability of distant recurrence (first 2 years)
|
0.0038
|
0.0000
|
Beta
|
11
|
2900
|
Costs (CHF)
|
cTORS
|
Cost of TORS
|
14739
|
869.31
|
Gamma
|
287.4635
|
0.0195
|
cTLM
|
Cost of TLM
|
12671
|
516.23
|
Gamma
|
602.4698
|
0.0475
|
cCRT
|
Cost of adjuvant CRT
|
33911
|
2079.08
|
Gamma
|
266.0350
|
0.0078
|
cRT
|
Cost of adjuvant RT
|
27962
|
1714.35
|
Gamma
|
266.0342
|
0.0095
|
cES
|
Cost of esophageal stenosis
|
2362
|
410.65
|
Gamma
|
33.0832
|
0.0140
|
cGAST
|
Cost of gastrostomy
|
4332
|
410.65
|
Gamma
|
111.2820
|
0.0257
|
cHR_adj
|
Cost of hospital readmission (for adjuvant)
|
10097
|
619.05
|
Gamma
|
266.0342
|
0.0263
|
cHR_s
|
Cost of hospital readmission (TORS or TLM)
|
8203
|
803.41
|
Gamma
|
104.2498
|
0.0127
|
cORN
|
Cost of osteoradionecrosis
|
32111
|
1077.71
|
Gamma
|
887.7769
|
0.0276
|
cPF
|
Cost of pharyngocutaneous fistula
|
82892
|
333.96
|
Gamma
|
61609.3654
|
0.7432
|
cPH
|
Cost of hemorrhage (from surgical site)
|
4469
|
415.50
|
Gamma
|
115.6865
|
0.0259
|
cTRACH
|
Cost of tracheostomy
|
11688
|
612.67
|
Gamma
|
363.9366
|
0.0311
|
cREM
|
Cost of remission 0-2 y
|
168.5
|
9.68
|
Gamma
|
303.2588
|
1.7998
|
c2REM
|
Cost of remission 2-5 y
|
60
|
9.68
|
Gamma
|
38.4518
|
0.6409
|
cPC
|
Cost of palliative care
|
4137
|
367.86
|
Gamma
|
126.4754
|
0.0306
|
cRR
|
Cost of regional recurrence
|
7047
|
464.24
|
Gamma
|
230.4227
|
0.0327
|
cLR_chemorad
|
Cost of local recurrence (chemoradiation)
|
34041
|
2079.08
|
Gamma
|
268.0786
|
0.0079
|
cLR_s
|
Cost of local recurrence (surgical resection)
|
40513
|
2050.27
|
Gamma
|
390.4511
|
0.0096
|
cDM
|
Cost of distant metastasis
|
4137
|
367.86
|
Gamma
|
126.4754
|
0.0306
|
cPanendo
|
Cost of panendoscopy
|
388
|
23.79
|
Gamma
|
266.0337
|
0.6857
|
Utilities
|
uSURG
|
Utility coefficient of TORS or TLM
|
0.902
|
0.203
|
Beta
|
1.0328
|
0.1122
|
uRT
|
Utility coefficient of adjuvant RT
|
0.850
|
0.275
|
Beta
|
0.5831
|
0.1029
|
uCRT
|
Utility coefficient of adjuvant CRT
|
0.794
|
0.317
|
Beta
|
0.4984
|
0.1293
|
uHR
|
Utility coefficient of hospital readmission
|
0.954
|
0.140
|
Beta
|
1.1820
|
0.0570
|
uPF
|
Utility coefficient of pharyngocutaneous fistula
|
0.932
|
0.194
|
Beta
|
0.6374
|
0.0465
|
uPH
|
Utility coefficient of postoperative hemorrhage
|
0.910
|
0.203
|
Beta
|
0.8986
|
0.0889
|
Ug
|
Utility coefficient of gastrostomy
|
0.916
|
0.209
|
Beta
|
0.6975
|
0.0640
|
Ult
|
Utility coefficient of long-term tracheostomy
|
0.852
|
0.271
|
Beta
|
0.6109
|
0.1061
|
ues
|
Utility coefficient of esophageal stenosis
|
0.826
|
0.284
|
Beta
|
0.6459
|
0.1361
|
uORN
|
Utility coefficient of osteoradionecrosis
|
0.791
|
0.302
|
Beta
|
0.6428
|
0.1698
|
urem
|
Utility coefficient of remission after surgery and adjuvant
|
0.980
|
0.099
|
Beta
|
0.7702
|
0.0346
|
uremonlysurg
|
Utility coefficient of remission after TORS or TLM alone
|
0.957
|
0.151
|
Beta
|
0.9798
|
0.0200
|
ureg
|
Utility coefficient of regional recurrence
|
0.859
|
0.283
|
Beta
|
0.4401
|
0.0722
|
ulocxrt
|
Utility coefficient of local recurrence, RT
|
0.771
|
0.302
|
Beta
|
0.7216
|
0.2143
|
uloc
|
Utility coefficient of local recurrence, requiring surgery
|
0.755
|
0.316
|
Beta
|
0.6436
|
0.2088
|
udist
|
Utility coefficient of distant recurrence
|
0.213
|
0.336
|
Beta
|
0.2262
|
0.5106
|
upall
|
Utility coefficient of palliative care
|
0.307
|
0.350
|
Beta
|
0.1033
|
0.3816
|
*NOTE: for prr, plr and pdr 80% of recurrences were modeled in the first 2 years, and the remaining 20% between 2 and 5 years posttreatment (probabilities were adjusted accordingly, assuming 5% of patients have recurrences in the first 2 years6)
|
Willingness-to-pay was set to 4000 CHF/QALM (i.e. 48000 CHF/QALY [20, 21]. Incremental cost was computed from the difference in expected cost (CHF) between TORS and TLM. Similarly, incremental utility was computed from the difference in expected utility between TORS and TLM. The incremental cost-utility ratio was derived taking the quotient between incremental cost and incremental utility. All cost-utility analyses were performed using TreeAge Pro 2019 software (Williamstown, MA, 2019).
Key model parameters were varied using one-way and two-way deterministic sensitivity analysis in order to assess their impact on the results. In particular, we explored the key role of adjuvant therapy (RT or CRT) after surgery and costs of treatment. Furthermore, all parameters affected by uncertainty were varied in probabilistic sensitivity analysis (PSA). Probabilistic sampling was performed from the distributions described above for probabilities (Beta), costs (Gamma) and utilities (Beta). PSA was performed using second-order Monte-Carlo simulations using 1000 simulations. Incremental cost and effectiveness were plotted with 95% confidence ellipsoids.