Background: Neuroblastoma is the most common extracranial tumor in children. The mortality rate for patients with metastatic disease is over 50%. In the Netherlands, 30 new patients are diagnosed annually. Current clinical treatment guidelines are complex and include multiple treatment arms consisting of chemotherapy, surgery, radiotherapy, and immunotherapy (IT). Although poor patient health and complications are known to cause adaptations to the otherwise standardized treatment regimen, the extent to which these variations occur is unknown. This study aimed to validate the use of process mining, a data-driven technique, to retrospectively examine protocol adherence and variability within current clinical guidelines based upon the GPOH-DCOG NBL2009 neuroblastoma treatment protocol. Methods: Data was extracted from electronic health records, as well as laboratory, pathology, and pharmaceutical databases, to create individual event logs for each patient. Process mining was performed using a fuzzy mining algorithm. The treatment courses for all neuroblastoma patients were mapped. Commonalities and variations were highlighted, and the throughput time for key treatment phases was calculated. Subsequently, conformance with protocol was determined. Results: Analysis of 70 patients treated between 2018-2022 showed 62 distinct treatment processes, revealing significant variations in patient care. Patients with high-risk disease showed the least variation (n=47, 42 variants). Notably, 17 variants were identified among 18 patients who died, indicating a highly personalized approach in the advanced stages of the disease. Subgroup analysis of 17 high-risk patients who received IT consisting of alternating cycles of anti-GD2 antibody and retinoic acid showed 6 variants. 12/17 patients (70.6%) completed the full IT regimen. Other treatment adjustments included shortened anti-GD2 infusions for two patients (5 and 8 days versus the prescribed 10 days, respectively), potentially indicating treatment toxicity. One patient received a 15-day infusion, exceeding the prescribed limit of 11 days. The recorded interval between the administration of anti-GD2 and retinoic acid was a median 5.5 hours (range: 60 seconds – 6.4 days), deviating from the prescribed interval of 24 hours and warranting further investigation. Conclusions: Process mining is a valuable tool for analyzing protocol performance and adherence in neuroblastoma treatment. Despite standardized treatment protocols, significant heterogeneity was observed in the treatment of neuroblastoma patients, especially those with poor prognosis. Throughput time analysis revealed variabilities in the IT regimen that warrant further investigation. This study underscores the potential of data-driven approaches to optimize treatment protocols and support evidence-based practices in clinical oncology.