[Impact of Source Position Error in Tandem-ovoid Applicator on Dose Distribution in Cervical Cancer Brachytherapy]

This study aimed to determine the discrepancy between planned and actual source positions in the Geneva applicator for cervical cancer brachy therapy and to evaluate its impact on dose distribution.

The Geneva applicator was placed on a computed tomography (CT) couch top, and CT images were acquired at each source dwell position to determine the actual source locations. The discrepancy between the actual source positions and the planned source positions reconstructed using the applicator modeling (AM) method was calculated. These discrepancies were then incorporated into the treatment plans of 13 patients who underwent brachytherapy for cervical cancer at our institution. Dose metrics, including D_90% for the high-risk clinical target volume (HR-CTV) and D_2cc for the bladder, rectum, small bowel, and large bowel, were evaluated between the original and the modified treatment plans.

The overall three-dimensional displacement of the source was 0.86±0.15 mm. Regarding dose metrics, the D_90% for the HR-CTV was significantly higher (mean increase, 1.38%) in the plans reflecting the actual source positions, while the D_2cc for the bladder and rectum was significantly lower (mean decrease, 2.29% and 2.57%, respectively) compared to the original plans.

The results suggest that incorporating actual source positions into treatment planning can improve the accuracy of applicator reconstruction in cervical cancer brachytherapy.