1. Summary The STOP-CSAM Study is a two-armed randomized controlled trial of a non-pharmacological Therapy Chat Service for prevention of Child Sexual Abuse (CSA) and Child Sexual Abuse Materials (CSAM) in self-referred and self motivated patients with high frequent CSAM use and non-detected by the legal authorities.
2. Trial design This study is a prospective multicentred, stratified, parallel-group superiority study conducted in Germany, Czechia and Spain.
3. Background There has been a significant increase in child sexual abuse material (CSAM) on the internet in recent years. The use of CSAM is problematic especially because it creates a demand for and maintains contact child sexual abuse. Unfortunately, despite the significant increase in the number of CSAM users, limited resources are available for investigation and prosecution. Consequently, many users remain in the community, with neither intervention from the criminal justice system, nor the health system. The proposed study will examine whether a therapy chat service (TCS) intervention reduces the demand for, circulation and spread of CSAM in undetected offenders, as compared to a control group.
4. Methods The sample consists of individuals aged 18 years or older (expected N = 630), who have used CSAM in the prior two weeks and are seeking help voluntarily. Participants will be randomized to (1) a Therapy Chat Service (TCS) intervention or (2) a four-week waitlist (control group) followed by a TCS intervention. The TCS intervention group will receive four to six one-hour online therapy chat sessions over the period of four weeks, while the control group will remain on a waitlist for these four weeks before receiving the same TCS intervention. Assessments will be conducted at baseline (pre-intervention) and at 4-, 8-, 12- and 16-weeks post-intervention. The main objective of the study is to compare the effectiveness of TCS in the prevention of CSAM use within a sample of self-referred participants. The primary outcome is the significant decrease of CSAM consumption, which will be assessed by comparing self-reported severity and time spent using CSAM in the two weeks before the intervention and at four weeks following the intervention. Potential progress measures include time spent, severity and frequency of CSAM consumed. Psychological wellbeing and total sexual outlet will be also measured as secondary outcomes, other participant variables such as risk factors for CSAM consumption or sexual interests and therapeutic variables such as number of patient-therapist interactions, modules covered per session, common factors of psychotherapy, adverse effects of intervention and dropout rate will be also measured. Outcomes between groups will be compared following standard principles for RCTs.
5. Results The study will open for recruitment in October 2023, and data collection is expected to be completed by November 2024. The results for the primary outcomes are planned to be analysed by December 2024 and submitted for publication by the end of the project in March 2025.
6. Discussion The study will test whether the TCS intervention has a positive effect, not only in terms of reducing self-seeking potential sexual offenders' problematic sexual behaviours, but also on measures such as psychological wellbeing in CSAM users. Possible adverse effects of TCS intervention will also be assessed.

Recently, a similar trial called PRIOTAB-CBT, compared pre- and post-treatment outcome measures between a treatment group to a control group (Lätth et al., 2022). Results showed a significantly larger reduction in time spent using CSAM in the treatment group, in comparison to the control group. PRIOTAB-CBTh was a single-centre, single-blinded, psychological placebo-controlled RCT of an online cognitive behavioural psychotherapy. If the STOP-CSAM trial demonstrates that a TCS intervention reduces CSAM use, it could be an effective prevention strategy for sexual violence against children.

8. Funding European Commission - Internal Security Fund (ISF-2021).

Inclusion Criteria:

• Adult participant (≥18 years);
• use of CSAM in the previous 2 weeks;
• English, German, Czech, Spanish or Portuguese speaker;
• voluntary participation and agreement with the terms of the study.

Exclusion Criteria:

• Having severe neuropsychiatric comorbidities (unstable psychotic disorder, organic brain damage, diminished intellectual capabilities, untreated drug or alcohol addiction);
• current inpatient psychiatric stays and/or any other current treatment for CSAM behaviour;
• CSA perpetration history (past or present);
• currently under a criminal investigation, proceeding, punishment or probation status for committing online or offline CSA or CSAM use