BACKGROUND: Implementing the thermoplastic mask as a treatment option in Gamma Knife radiosurgery (GKRS) has madethe discussion of the relative benefits of frame- or mask-based fixation for treatment a frequent occurence. Based on a case review, the authors discuss factors that need to be understood and considered by the treating team. OBSERVATIONS: The authors describe the case of an 81-year-old patient with pleomorphic dermal sarcoma that extended to and infiltrated the dura mater, who underwent extensive resection requiring a skin flap. Adjuvant GKRS was recommended. The fixation type was limited by the extent of the flap that would cause a suboptimal frame fixation (less than 3 points) and its compression by the lateral aspect of the mask. Creating a tailored mask with its lateral table-fixation cut out was required. To guarantee appropriate immobilization, an understanding of the primary stability points of the mask was needed, which was achieved by monitoring the intrafraction motion. The patient tolerated the treatment delivery well, with minimal movement and proper positioning maintenance. LESSONS: The option of a rigid frame or a mask allows for personalized treatment for each patient based on their unique needs. Understanding the advantages and limitations of each modality allowed a safe and precise treatment for the described case. https://thejns.org/doi/10.3171/CASE24852.