Commissioning in water of HDR Valencia skin applicators

In surface brachytherapy, Valencia applicators are widely used for treating non-melanoma skin cancers. Typically, plastic phantoms are used for dosimetric measurements since the setup is simpler, unlike external beam radiation therapy, where water is the standard medium for dosimetry.

This study focuses on the commissioning in water of Valencia applicators using iridium-192 (Ir¹⁹²) Flexisource and Elekta Flexitron high-dose-rate brachytherapy (HDR-BT). Measurements of percentage depth dose and dose rate per unit kerma strength were performed with various detectors, including PTW microDiamond, microSilicon X, and Diode E for percentage depth dose (PDD) measurements. Roos, Semiflex 3D, and PinPoint 3D ionization chambers were used for dose rates dosimetry.By means of 3D printing, custom adapters were developed to integrate Valencia applicators with water phantom MP1, enabling precise dosimetric measurements in water.

Results showed that all detectors were suitable for in water PDD measurements, with minor differences attributed to setup geometry. Dose rates measured with the Semiflex 3D and Pinpoint 3D chambers revealed minimal discrepancies, while the Roos chamber exhibited a notable volume effect, producing measurements approximately 10% lower than expected. The study also shows that the source positioning within the applicator significantly influenced dose profiles, whereas PDD measurements' main influence is inverse square law, being more tolerant to positioning errors.

Overall, it is feasible to adapt external beam radiation therapy (EBRT) dosimetry equipment as ionization chambers and water phantoms for use in surface brachytherapy commissioning. Custom 3D-printed adapters facilitate this integration, allowing in water measurements, thus reducing uncertainties in clinical dose calculations.