Background: Acceptance and commitment therapy (ACT) is an evidence-based treatment to improve functioning and quality of life (QoL) for chronic pain patients, but outreach of this treatment is unsatisfactory. Internet-delivery has been shown to increase treatment access but there is limited evidence regarding feasibility and effectiveness of web-based ACT for chronic pain. The aim of the study was to evaluate and iterate a novel internet-delivered ACT program, iACT, in a clinical and a self-referred sample of chronic pain patients. The intervention was developed in close collaboration with patients. To enhance learning, content was organized in short episodes to promote daily engagement in treatment. In both the clinical and self-referred samples, three critical domains were evaluated: (I) feasibility (acceptability, practicality and usage); (II) preliminary efficacy on pain interference, psychological inflexibility, value orientation, QoL, pain intensity, anxiety, insomnia and depressive symptoms; and (III) potential treatment mechanisms. Methods: This was an open pilot study with two samples: 15 patients from a tertiary pain clinic and 24 selfreferred chronic pain participants, recruited from October 2015 until January 2017. Data were collected via an online platform in free text and self-report measures, as well as through individual oral feedback. Group differences were analyzed with Chi square-, Mann-Whitney U- or t-test. Preliminary efficacy and treatment mechanism data were collected via self-report and analyzed with multilevel linear modeling for repeated measures. Results: Feasibility: patient feedback guided modifications to refine the intervention and indicated that iACT was acceptable in both samples. User insights provided input for both immediate and future actions to improve feasibility. Comprehensiveness, workability and treatment credibility were adequate in both samples. Psychologists spent on average 13.5 minutes per week per clinical patient, and 8 minutes per selfreferred patient (P=0.004). Recruitment rate was 24 times faster in the self-referred sample (24 patients in 1 month, compared to 15 patients in 15 months, P<0.001) and the median distance to the clinic was 40 km in the clinical sample, and 426 km in the self-referred sample (P<0.001). Preliminary effects: post-assessments were completed by 26 participants (67%). Significant effects of time were seen from pre- to post-treatment across all outcome variables. Within group effect sizes (Cohen's d) at post-treatment ranged from small to large: pain interference (d=0.64, P<0.001), psychological inflexibility ( d=1.43, P<0.001), value progress (d=0.72, P<0.001), value obstruction (d=0.42, P<0.001), physical QoL (d=0.41, P=0.005), mental QoL (d=0.67, P=0.005), insomnia (d= 0.31, P< 0.001), depressive symptoms (d= 0.47, P< 0.001), pain intensity (d=0.78, P=0.001) and anxiety (d=0.46, P<0.001). Improvements were sustained at 1-year follow-up. Psychological inflexibility and value progress were found to be potential treatment mechanisms. Conclusions: The results from the present study suggests that iACT was feasible in both the clinical and the self-referred sample. Together with the positive preliminary results on all outcomes, the findings from this feasibility study pave the way for a subsequent large randomized efficacy trial.
