Exploring the dosimetric impact of applicator rotations in HDR brachytherapy for cervical cancer treatment

This study aims to improve the safety and accuracy of HDR 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. A cohort of 20 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). 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 12.97% and 16.6%, respectively. Lateral rotations showed moderate variations, with HR-CTV D90% reductions up to 2.49% and OAR D2cc increases up to 2.13%. Axial rotations had minimal impact, with changes in all metrics below 1.02%. Applicator displacements especially vertical can cause significant dosimetric errors in HDR brachytherapy. These shifts may compromise tumor coverage and increase OAR toxicity. Integrating real-time imaging, adaptive planning, and motion correction strategies is essential to ensure treatment precision.