Comprehensive clinical dosimetry in contact skin interventional radiotherapy (modern brachytherapy): Practical tips and tricks.

Purpose: Contact interventional radiotherapy (cIRT) is an effective option for non-melanoma skin cancers, particularly in anatomically complex sites, where organ preservation, functional results, and cosmetic outcomes are relevant. This paper summarized practical dosimetric considerations in cIRT, focusing on the therapeutic window, surface curvature, boluses and air gaps, dose calculation algorithms, and 3D-printed devices. Material and methods: Key physical and clinical factors affecting dose distribution were analyzed from recent literature, including prescription depth, source-to-skin distance, applicator geometry, tissue interfaces, and patient-specific device design. Results: Therapeutic window is influenced by target thickness, source-to-skin distance, and surface curvature. Multilayer and intensity-modulated arrangements may improve target coverage while limiting superficial hotspots. Bolus and air gaps can modify local dose distribution, especially in irregular anatomical regions, while model-based algorithms better account for heterogeneities and interfaces than TG-43. 3D-printed applicators may further enhance conformity, reproducibility, and organs at risk sparing. Conclusions: Although clinically non-invasive, cIRT requires careful dosimetric optimization. Appropriate management of applicator geometry, dose calculation, bolus, air gaps, and patient-specific devices, may improve treatment accuracy, target coverage, and toxicity control.