Analysis of Target Coverage Variability and Compliance with Tolerant Doses Using a Fixed Dosimetric Plan for Intracavitary Radiation Therapy for Cervical Cancer. Tomsk City Oncology Center Experience

Abstract

Introduction. Radiation therapy is the treatment for locally advanced cervical cancer, typically involving a course of external beam chemoradiotherapy followed by a brachytherapy boost. The brachytherapy phase critically influences local control outcomes, making strict adherence to its technical requirements essential.

Aim. Clinical practice in some centers involves using a fixed brachytherapy plan, created during the first session, for the entire intracavitary treatment course. This study evaluates the clinical applicability of using a fixed brachytherapy treatment plan—developed during the first fraction—for subsequent fractions without replanning. The analysis focuses on two key dosimetric parameters: target volume coverage by the prescribed dose and adherence to organ-at-risk dose constraints.

Materials and Methods. We analyzed 42 brachytherapy fractions from 10 patients with locally advanced cervical cancer (stages IIB–IIIC).

Results. The first-fraction treatment plan proved applicable for subsequent fractions in 9 of 10 patients, maintaining adequate target coverage. One patient with extensive tumor infiltration of the uterine body required replanning due to target underdosage. The following dose constraint violations for organs at risk were observed: bladder dose exceeded limits in one patient (requiring replanning), sigmoid colon constraints were exceeded in four patients (requiring plan modification), and half of all patients showed minor intestinal dose exceedances.

Conclusion. Fixed-plan brachytherapy appears feasible for selected patients with small target volumes (<30–33 cm³), favorable distance between organs at risk and the radiation source, satisfactory patient compliance, and confidence in the patient's adherence to pretreatment preparation protocols.