Exploring the Dosimetric Impact of Applicator Rotations in HDR Brachytherapy for Cervical Cancer Treatment

Purpose: This study aims to improve the safety and accuracy of HDR (High-Dose-Rate) brachytherapy for cervical cancer by examining the effects of rotational movements of intracavitary applicators. It focuses on lateral (left-right), vertical (up-down), and axial (around the applicator axis) rotations to assess how these movements impact the dose to the high-risk clinical target volume (HR-CTV) and nearby organs at risk (OARs), such as the bladder and rectum. Material and Methods: A cohort of 13 cervical cancer patients treated with intracavitary HDR brachytherapy was analyzed using CT-based treatment planning on the Varian TPS. Rotational displacements of ±3°, ±5°, ±8°, and ±10° were simulated along each axis. Dosimetric metrics, such as HR-CTV D90% and OAR D2cc, were evaluated using dose-volume histograms (DVHs). Results: Vertical rotations caused the most significant dosimetric changes, with HR-CTV D90% decreasing by up to 10.16%, while bladder and rectum D2cc increased by 30.10% and 21.88%, respectively. Lateral rotations showed moderate variations, with HR-CTV D90% reductions up to 2.49% and OAR D2cc increases up to 2.99%. Axial rotations had minimal impact, with changes in all metrics below 1.45% Conclusions: It is crucial to note that rotational displacements, particularly those occurring along the vertical axis, can exert a substantial dosimetric influence in the context of HDR brachytherapy for cervical cancer. This underscores the necessity for adaptive planning, real-time imaging, and corrective strategies to address potential misalignments during treatment. Ensuring the stability of applicator positioning, particularly in the vertical direction, is paramount to optimize therapeutic outcomes and minimize organ at risk (OAR) toxicity.