Abstract
Purpose: To evaluate clinical outcomes and toxicity of definitive interstitial or hybrid interventional radiotherapy (IRT; brachytherapy) using high-dose-rate (HDR) or pulsed-dose-rate (PDR) techniques for non-melanoma skin cancer (NMSC) unsuitable for standard superficial treatment. Materials and Methods: This retrospective single-center analysis included 49 patients with 50 histologically confirmed basal cell carcinoma or squamous cell carcinoma lesions treated between October 2020 and December 2023. Primary and recurrent lesions treated with definitive HDR- or PDR-based interstitial or hybrid IRT were included. Local control, acute reactions, late effects, and dosimetric parameters were assessed. Adverse events were graded according to Radiation Therapy Oncology Group criteria. Results: Basal cell carcinoma accounted for 37 lesions and squamous cell carcinoma for 13. Twenty-eight lesions were primary tumors and 22 were recurrences after surgery. Interstitial IRT alone was used in 35 lesions and hybrid IRT in 15; 30 lesions received HDR-IRT and 20 received PDR-IRT. Median follow-up was 21.2 months. Local control was achieved in 47 of 50 lesions (94%), and the estimated 2-year local control rate was 93.6%. Late grade 3 and 4 effects occurred in one and three lesions, respectively. Grade ≥ 2 late effects were associated with higher T stage ( p = 0.044), while no significant association was observed with HDR- versus PDR-based treatment modality. Conclusions: The findings of this study support definitive interstitial and hybrid IRT as a valuable treatment option for selected patients with recurrent or locally advanced NMSC.