Positioning of Patients for Pelvic Radiation: Variability Across Treatment

Abstract

Objectives: We aimed to determine the variability in position of the pelvis for patients while receiving daily radiation treatments for pelvic malignancies. Design: Therapeutic radiation targets lymph nodes that lie along the curvature of the sacrum. Any change in pelvic tilt could inadvertently move these targets in or out of the radiation field. This variability has clinical significance both to target cancerous lymph nodes and avoid healthy sacrum. To better understand this variability, we observed trends in the change in the sacral slope. This measurement was chosen because it is an objective radiographic finding, there is no significant difference between men and women, and joint replacement does not appear to change this measurement. Twenty subjects were identified from patients receiving whole pelvis radiation for at least four weeks. CT simulator images and lateral radiographs obtained as part of standard radiation care were reviewed. We manually calculated this measurement with sloping lines drawn with computer graphics on the same single lateral view daily for the course of radiation per subject. Results: Compared to the initial imaging, the average sacral slope variation across all 20 subjects was 2.27 degrees, with a standard deviation of 1.43, and average variation among patients ranged from 1.22-5.09 degrees. Variation in sacral slope across all 20 subjects from one treatment day to the next was 2.05 degrees, with a standard deviation of 1.47, and ranged from 0.97-3.21 degrees. Conclusions: Despite the best efforts of the provider, there may be some variability in the daily pelvic position of the patient between fractions. This is clinically important because presacral lymph nodes are part of the radiation target volume and sacral fractures are a potential adverse effect of radiation treatment. Exercises for pelvic relaxation could be explored to potentially reduce this variability.