A novel applicator for beta radionuclide brachytherapy of skin cancer using 188Re source

Background Brachytherapy (BT) is a useful modality for treating small, early-stage skin cancers. Beta-emitting sources have also been widely investigated due to their inherently steep dose fall-off, which helps spare deeper healthy tissues. Objective This study presents the design of fixed-geometry applicators for beta-emitting 188 Re-based BT, aimed at treating superficial skin cancers, developed using Monte Carlo simulations. Methods A cylindrical bio-ceramic 188 Re source was simulated and validated using the BT dose calculation formalism recommended in the American Association of Physicists in Medicine Task Group 60 (TG-60) Report. Subsequently, four applicator models (R10-R25) were designed, each equipped with flattening filters, to target tumors with 10, 15, 20 and 25 mm diameters. The dose rate, flatness ( F ), symmetry ( S ), and penumbra ( P ) of each applicator at the prescribed depth were evaluated using a soft-tissue phantom. Results The reference dose rate was calculated to be 7.25 ± 0.01 cGy/µCi/h, following the TG-60 formalism. At a treatment depth of 3 mm, dose rates for applicator models R10-R25 ranged from 274 ± 1–366 ± 1 cGy/min. The F ranged between 2.78 ± 0.25% and 5.94 ± 0.20%, while S varied from 1.00 ± 0.00–1.01 ± 0.01, and P ranged from 2.53 ± 0.01–2.92 ± 0.02 mm. The maximum radiation leakage, relative to the dose at the skin surface, was (5.79 ± 0.07) × 10 −4 and (1.69 ± 0.02) × 10 −4 at distances of 1 mm and 10 mm from the applicator body, respectively. Conclusions The proposed applicators show acceptable dosimetric characteristics in terms of F , S , and P . This performance enables accurate dose delivery with minimal irradiation to healthy tissues while reducing treatment time. Clinical application is currently limited to uniform skin surfaces and small superficial tumors (<25 mm in diameter).