Positioning of Patients for Pelvic Radiation: Variability Across Treatment

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

Positioning of port films for radiation: variability is present

PURPOSE: Pelvic radiation treatment demands precision and consistency in patient setup for efficacy of therapy and to limit radiation dosage to normal tissue. Despite the use of immobilization devices and positioning techniques, there is still concern for variation in daily setup. The purpose of this retrospective study was to determine the presence and degree of variation in sacral slope in 20 subjects receiving radiation therapy for pelvic malignancies. METHODS: Each of the 20 subjects received between 20 and 25 fractions of external beam radiation treatment to the pelvis. The sacral slope was measured on each of the daily port films taken prior to treatment and compared to the sacral slope angle measured on the initial treatment planning simulation digitally reconstructed radiographic imaging. RESULTS: Compared to this initial imaging, the average sacral slope variation across all 20 subjects was 2.27 degrees (+/- 1.43 degrees ), and the average variation among patients ranged from 1.22 degrees to 5.09 degrees . Variation in sacral slope across all 20 subjects from one treatment day to the next was 2.05 degrees (+/- 1.47 degrees ), and ranged from 0.97 degrees to 3.21 degrees . CONCLUSIONS: This study demonstrates that despite the rigorous use of immobilization devices, there still exists day-to-day variation in sacral slope angle between treatment days and compared to initial baseline imaging off which the treatment plan is developed. There is an on-going study at our institution with an attempt to reduce this variation by offering exercises prior to radiation