Source position evaluation using X-ray fluoroscopy of the Geneva and Venezia applicators for brachytherapy: An assessment of inter-applicator differences.

Purpose: This study aimed to evaluate the inter-applicator differences in source positions of the Geneva and Venezia applicators by using X-ray fluoroscopy to perform direct measurements of iridium-192 (¹⁹²Ir) source positions.

Materials and methods: Offset measurements of two to six sets of Geneva tandem and ovoid applicators and Venezia tandem applicators were performed. Each applicator was irradiated with ¹⁹²Ir at the most distal position and X-ray fluoroscopy images were acquired. The offset values were measured as the distance from the applicator tip to the center of ¹⁹²Ir source. For two sets of the Venezia ovoid applicators (set 1 and set 2), X-ray fluoroscopy images were acquired at a 2-mm step from the most distal position. The ¹⁹²Ir source positions were compared with the expected source positions using an applicator modeling module.

Results: The differences in offset values of the same types of applicators were up to 0.6 mm for Geneva tandem and ovoid applicators and 0.3 mm for Venezia tandem applicators. The mean standard deviation calculated for the same applicator types was 0.1 mm across all applicators. For Venezia ovoid applicators, the mean difference between ¹⁹²Ir source positions and expected source positions were 0.1 mm for the set 1 applicator (maximum: 0.6 mm) and -0.2 mm for the set 2 applicator (maximum: 0.6 mm).

Conclusion: This study demonstrated the feasibility of direct source position measurements using X-ray fluoroscopy. These results emphasize the need for commissioning all applicator, but individual characterization is unnecessary in clinical practice if differences fall within tolerance.