Impact of applicator curvature in contact interventional radiotherapy (brachytherapy) for skin cancer: exploring the “Nautilus Effect”

INTRODUCTION: Contact interventional radiotherapy (cIRT) is an effective technique for treating non-melanoma skin cancers (NMSC). The use of curved applicators may enhance dose distribution and optimize therapeutic outcomes. This study analyzes the impact of applicator curvature on dose distribution, introducing the concept of the "Nautilus Effect." MATERIALS AND METHODS: In silico simulations were performed on twelve different curvature configurations, in particular 12 ROIs were contoured in Oncentra Brachy treatment planning system (®Elekta) in the form of three-dimensional circular crowns with a uniform thickness t of 5 mm. Key dosimetric parameters were measured, including the therapeutic window (TW), defined as the distance between the 100% and 150% isodoses. RESULTS AND DISCUSSION: Results show a strong correlation between applicator curvature and dose distribution: as curvature increases, the concave TW decreases while the convex TW increases. The "Nautilus Effect" highlights the advantages of curved applicators in optimizing dose coverage in complex anatomical regions. CONCLUSIONS: Future works are needed to focus on clinical validation and creation of a personalized curvature applicator for complex anatomical regions to improve the treatment outcomes.